Lidé

prof. Ing. Bc. Karel Dušek, Ph.D.

Všechny publikace

Analysis of solder mask roughness and stencil shape influence on void formation in solder joints

  • DOI: 10.1007/s40194-023-01505-7
  • Odkaz: https://doi.org/10.1007/s40194-023-01505-7
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Voids inside solder joints are empty spaces negatively affecting the mechanical, thermal, and electrical properties of the solder joint. This article deals with this problematics using two novel approaches to reduce voids’ occurrence. The first approach is the change of the roughness of the solder mask to influence the flux spreading around the solder pad. The second approach is the deposition of the same volume of the solder paste to the solder pads using a modified, thicker stencil with smaller apertures. The experiments were performed for solder pastes containing SAC305 alloy and two types of fluxes (ROL0/ROL1). Solder joints were inspected by X-ray imaging, and the shots were subsequently processed by image analysis. For determination of the spreading area of the flux around the solder pad during the reflow process, the tested boards were scanned by a confocal digital microscope. The results showed that more aggressive flux caused less voiding in terms of the average area of voids covering the soldering pad. Analysis of samples prepared with modified stencils showed a much lower proportion of voids than with the standard stencil. Furthermore, the results revealed that the selection of the solder mask type significantly influenced the voids’ formation within solder joints in the case of the unmodified stencil for solder paste deposition. On the other hand, when the modified stencils were used for sample preparation, the solder mask had no further impact on voiding. Therefore, modifying the stencil can be pointed out as a preferable and effective way.

Application of solid-phase microextraction arrows for characterizing volatile organic compounds from 3D printing of acrylonitrile-styrene-acrylate filament

  • DOI: 10.1016/j.chroma.2023.464180
  • Odkaz: https://doi.org/10.1016/j.chroma.2023.464180
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    3D printing is an extensively used manufacturing technique that can pose specific health concerns due to the emission of volatile organic compounds (VOC). Herein, a detailed characterization of 3D printing-related VOC using solid-phase microextraction-gas chromatography/mass spectrometry (SPME-GC/MS) is described for the first time. The VOC were extracted in dynamic mode during the printing from the acrylonitrile-styrene-acrylate filament in an environmental chamber. The effect of extraction time on the extraction efficiency of 16 main VOC was studied for four different commercial SPME arrows. The volatile and semivolatile compounds were the most effectively extracted by carbon wide range-containing and polydimethyl siloxane arrows, respectively. The differences in extraction efficiency between arrows were further correlated to the molecular volume, octanol-water partition coefficient, and vapour pressure of observed VOC. The repeatability of SPME arrows towards the main VOC was assessed from static mode measurements of filament in headspace vials. In addition, we performed a group analysis of 57 VOC clas-sified into 15 categories according to their chemical structure. Divinylbenzene-polydimethyl siloxane ar-row turned out to be a good compromise between the total extracted amount and its distribution among tested VOC. Thus, this arrow was used to demonstrate the usefulness of SPME for the qualification of VOC emitted during printing in a real-life environment. A presented methodology can serve as a fast and reliable method for the qualification and semi-quantification of 3D printing-related VOC.

Board Level Underfill – the Influence of Flux

  • Autoři: Plachý, Z., Hurtony, T., Géczy, A., prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: 2023 46th International Spring Seminar on Electronics Technology (ISSE). New York: IEEE Press, 2023. International Spring Seminar on Electronics Technology (ISSE). ISSN 2161-2536. ISBN 979-8-3503-3484-5.
  • Rok: 2023
  • DOI: 10.1109/ISSE57496.2023.10168355
  • Odkaz: https://doi.org/10.1109/ISSE57496.2023.10168355
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This work is devoted to investigating the effect of flux residues on the underfill. Prepared samples were made of copper sheets to eliminate the influence of multi-layered, inhomogeneous materials. Two sets of these samples were designed for this work; where one set was cleaned in an isopropyl alcohol bath in an ultrasonic cleaner, and the other was left uncleaned to highlight the presence of flux. Underfill was applied to both sets of samples, and the assemblies created in this way were subjected to several diagnostic methods. The work results showed that even when no-clean flux was used, its residues remained on the base substrates, contaminating the underfill or preventing it from completely filling the gap. The ultrasonic cleaner proved to be a suitable method for cleaning the samples, thus, eliminating the influence of flux residues or other impurities on the underfill. Furthermore, mechanical tests indicated that non-cleaned samples are characterized by a greater dispersion in mechanical properties than cleaned ones. Therefore, eliminating the influence of the flux will allow us to achieve more accurate results in the underfill's effect on the reliability of the assembly, which will allow a better potential comparison of different methods of underfill application and other materials.

Dielectric spectroscopy of PETG/TiO2 composite intended for 3D printing

  • DOI: 10.1080/17452759.2023.2170253
  • Odkaz: https://doi.org/10.1080/17452759.2023.2170253
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    3D-printed electronics belong to new approaches to how to build a complex object with multiple desired functions. For that purpose, materials with specific electric properties are needed: conductors, insulators, magnetics, or dielectrics with high permittivity. However, such materials are not commonly available in the form of filament for fused deposition modelling since the development is still ongoing. This paper describes the electrical properties of PETG-ceramic composite filaments. PETG (polyethylene terephthalate glycol-modified) was filled with titanium dioxide (10 and 20 wt.%) to increase the dielectric constant and, simultaneously, to preserve printing simplicity as the material key advantage. Dielectric spectroscopy and measurement of volume resistivity were performed on printed samples. Relative permittivity increased by 50% for a composite filled with 20 wt.% of ceramic particles (ϵr = 2.5÷4.4) against pure PETG. Permittivity and dielectric loss exhibited frequency and temperature independence. The prepared composite can be used for dielectric applications in electronics.

Effect of non-standard SnAg surface finishes on properties of solder joints

  • DOI: 10.1016/j.apsadv.2023.100483
  • Odkaz: https://doi.org/10.1016/j.apsadv.2023.100483
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    In this study, the effects of nonstandard near-eutectic SnAg surfaces on the wettability, intermetallic compound growth and mechanical properties of solder joints were investigated. Four types of surface finishes based on near eutectic SnAg alloys with different compositions and numbers of layers were analyzed. Design/methodology/approach: The effect of surface-finishes SnAg5NiP and SnAg7NiP, which were prepared with and without a Ni-P diffusion barrier, was tested. The Ni-P layer was produced either chemically or electrochemically. The effect of the SnAg surface finish on wettability, formation, and growth of intermetallic compound in the solder joint was analyzed. We further explored the impact of different PCB finishes on the quality of soldered joints. This investigation involved a comparative analysis of the behavior of SnAg finishes in comparison to pure copper, as well as the commonly employed HASL, ENIG, and ImSn finishes.Findings: It was found that SnAg surface finishes with a Ni-P diffusion barrier are wetted by molten solder faster than surface finishes without a diffusion barrier. The mechanical properties of the joints on both surfaces are comparable to those on ENIG. SnAg that include a chemically created Ni-P diffusion layer is characterized by the formation of more thermally stable ternary intermetallic compounds based on (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4. On the contrary, the electrochemically formed Ni layer supports the increase in the rate of intermetallic compound formation, which affects the properties of the soldered joints.Originality: Nonstandard near-eutectic SnAg finishes, which contains a Ni-P diffusion layer can be used as promising replacement of ENIG or other standard finishes.

Evaluation of Electrolytically Manufactured Copper Foils Properties

  • DOI: 10.1109/ISSE57496.2023.10168520
  • Odkaz: https://doi.org/10.1109/ISSE57496.2023.10168520
  • Pracoviště: Katedra elektrotechnologie, Katedra telekomunikační techniky
  • Anotace:
    This paper deals with electrolytically manufactured copper foils prepared under different manufacturing conditions. The main goal is to evaluate mechanical and electrical properties concerning the further use of foils for flexible applications in the electronics industry. Four samples of copper foil were prepared using an electrolytic manufacturing process, with different compositions of the electrolyte (Cu2+=50g/1, H2SO4=70g/1, Cadditives=0,5m1/1, and Cu2+=50g/1, H2SO4=70g/1, Cadditives=1m1/1) and different properties of cathodes (shiny stainless steel and roughened stainless steel, sanded with 1000 grit sandpaper). The current density was 1 A/dm2. The mechanical properties like elongation at break, modulus of elasticity in tension, tensile strength, and hardness were evaluated. The electrical conductivity of manufactured copper foils was also evaluated. The results show that the properties of copper foils were affected not only by changes in electrolyte composition (concentration of additives), but also by the roughness of cathodes (the higher roughness increased the effective surface of the cathode). The electrolytically prepared copper foils were compared with commercially available foil prepared by the metallurgical rolling process. The commercial sample exhibited similar electrical conductivity, lower hardness and higher modulus of elasticity in tension.

Filtering Efficiency of Sustainable Textile Materials Applied in Personal Protective Face Mask Production during Pandemic

  • DOI: 10.3390/ma16030903
  • Odkaz: https://doi.org/10.3390/ma16030903
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The COVID-19 outbreak increased demand for personal protective respirator masks. Tex- tile masks based on cloth materials appeared to be a sustainable, comfortable, and cost-effective alternative available in global communities. In this study, we used laser-based particle counting for mask material qualification to determine the concentration filtering efficiency in general, everyday community use. The efficiencies of eleven different commercially available textile materials were measured in single-, double-, and triple-layer configurations according to their grammage, mesh (XY), and inter-yarn gap. It was found that in the single-layer configurations, most materials were well below the acceptable standards, with a wide variation in filtering efficiency, which ranged from 5% to ~50%. However, when testing the fabrics in two or three layers, the efficiency increased significantly, exceeding or approaching the standard for medical masks. Three layers of natural silk was able to produce a level of filtration efficiency of 84.68%. Two-layered natural silk achieved 70.98%, cotton twill achieved 75.6%, and satin-weave viscose achieved 69.77%. Further options can also be considered in cases where lower filtration is acceptable It was statistically shown that applying a second layer was more significant in terms of overall filtering than increasing the layer count to three. However, layer stacking limited the breathability. The paper presents measurement-based qualitative and quantitative recommendations for future textile applications in face mask manufacturing.

Incorporation and corrosion protection mechanism of TiO2 nano-particles in SnAgCu composite alloys: Experimental and density functional theory study

  • DOI: 10.1016/j.ceramint.2023.04.216
  • Odkaz: https://doi.org/10.1016/j.ceramint.2023.04.216
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This work studied the incorporation mechanism of TiO2 nano-particles into SnAgCu solders and their effect on the corrosion behavior of the composite alloy. Composite solder alloys have been made from 99Sn0.3Ag0.7Cu solder alloy and TiO2 nano-particles between 0.25 and 1 wt%. The alloys in solder joints were exposed to 4000 h long 85 degrees C/85RH% thermal-humidity test, and their surface was observed by SEM and FIB techniques. Large localized corrosion spots and numerous Sn whiskers have been found on the samples, except for the samples with 0.25 wt% TiO2 content. The corrosion of the Sn grains resulted in a volumetric increase and mechanical stress, which was relaxed via whisker growth. TiO2 nano-particles in 0.25 wt% incorporated layer-like at the boundaries of the Sn grain. Density functional theory calculations proved that at soldering conditions, the Sn atoms of the solder alloy could bond to the TiO2 NPs through the O atoms of TiO2. The TiO2-Sn oxide layer at the grain boundaries could suppress the corrosion of the composite solder alloys and whisker growth. In the case of higher weight fractions TiO2, the nano-particles were agglomerated and could not perform corrosion protection effect.

Influence of No-Clean Flux on the Corrosivity of Various Surface Finishes After Reflow

  • Autoři: Sorokina, K., prof. Ing. Bc. Karel Dušek, Ph.D., Ing. David Bušek, Ph.D.,
  • Publikace: 2023 46th International Spring Seminar on Electronics Technology (ISSE). New York: IEEE Press, 2023. International Spring Seminar on Electronics Technology (ISSE). ISSN 2161-2536. ISBN 979-8-3503-3484-5.
  • Rok: 2023
  • DOI: 10.1109/ISSE57496.2023.10168358
  • Odkaz: https://doi.org/10.1109/ISSE57496.2023.10168358
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    High-quality soldered joint is necessary for the trouble-free operation of electronic equipment. The quality of the soldered joint is determined by several parameters. One of the parameters is the type of used flux. There are no-clean fluxes and fluxes that must be cleaned after the soldering process. Today, no-clean fluxes are widely used. This work is a continuation of the study [1] and it is focused on studying the effect of flux aggressiveness on commonly used PCB surfaces such as electroless nickel immersion gold (ENIG), immersion tin, and organic solderability preservative (OSP). Five fluxes with different classifications were investigated in the work: Weller Lötwasser, Topnik RF800, Topnik TE - 400, Topnik ESW 32, and Topnik LP-1. The most aggressive influence showed no-clean fluxes Topnik TE-410 and Topnik LP-1. These fluxes corroded the OSP surface by at least 0.5 μm. The results also showed the most resistant type of surface finish was ENIG and the most susceptible to no-clean flux aggressiveness was OSP.

Volatile compounds released from pvc wire coating

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Poly(vinyl chloride) is widely used in the field of electrical engineering as an insulating material. Its properties are significantly dependent on the content of the plasticisers. In this work we identify plasticisers in commercially available insulated electrical wire. We quantify and qualify released hydrogen chloride and qualify volatile organic compounds at enhanced temperatures by thermogravimetric analysis, potentiometric titration, and gas chromatography-mass spectrometry system. Changes in glass transition temperatures and mechanical properties caused by enhanced temperatures are measured by dynamic mechanical analysis. The data show a significant release of hydrogen chloride above 180 °C, which has a significant effect on the mechanical properties.

A Weakness of Wetting Balance Method during the Diagnostic of Connector Pins with Wetting Issue

  • DOI: 10.1109/ISSE54558.2022.9812772
  • Odkaz: https://doi.org/10.1109/ISSE54558.2022.9812772
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The wetting balance method is used for the precise classification of solderability of chosen substrates by solder alloys. This work deals with a weakness of the wetting balance method during the wettability measurement of connectors with the wetting issue. The wetting issues at examined pins connector appeared during the serial manufacturing production, and therefore, the connector pins were analysed using the wetting balance method. The wetting balance method showed a good wetting of the connector pins. The wetted pins were examined by scanning electron microscopy (SEM) to find the reason for the wetting issue. This analysis showed a non-wetted area at pins edges. Following investigation of pins microsections using confocal/optical microscopy showed the reason for the wetting issue, when the surface finish was much thinner or was missing on the edges of the pin. This was the reason for the wetting issue of the connector pins in serial manufacturing, even though the wetting balance test showed good wettability results because most parts of the pin surface had good wetting.

Behaviour of Moisture Sensitive Devices

  • Autoři: Plachý, Z., prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: 2022 45th International Spring Seminar on Electronics Technology (ISSE). New York: IEEE Press, 2022. International Spring Seminar on Electronics Technology (ISSE). ISSN 2161-2536. ISBN 978-1-6654-6589-2.
  • Rok: 2022
  • DOI: 10.1109/ISSE54558.2022.9812783
  • Odkaz: https://doi.org/10.1109/ISSE54558.2022.9812783
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Humidity is an essential and integral part of human life, of which electrical equipment and devices are already an integral part. The moisture problem is mainly associated with components in non-hermetic plastic packages. Understanding the behavior of these components is a basic prerequisite for proper handling during the manufacturing process. By proper handling of the components, various moisture-related defects can be avoided. For these reasons, moisture sensitive devices (MSD) are divided into different moisture sensitivity levels (MSL), which indicate their floor life. The main danger associated with moisture does not lie in its absorption itself, but in the mechanical stress caused by the rapid expansion of the evaporated water in a relatively short time during the reflow soldering process. Defects associated with delamination and cracks of the component packages are one of the most common defects in surface mounting technology. If the absorbed moisture does not cause mechanical defects during production within the Surface Mount Technology (SMT), it can further accelerate the degradation phenomena of the device. The results of this work clearly show that components exposed to environments with higher relative humidity (RH) absorb more moisture than the same components at lower RH. By reducing RH, the risk associated with defects caused by mishandling MSDs can also be reduced.

Influence of No-Clean Flux on The Corrosivity of Copper After Reflow

  • Autoři: Sorokina, K., prof. Ing. Bc. Karel Dušek, Ph.D., Ing. David Bušek, Ph.D.,
  • Publikace: 2022 45th International Spring Seminar on Electronics Technology (ISSE). New York: IEEE Press, 2022. p. 1-6. International Spring Seminar on Electronics Technology (ISSE). ISSN 2161-2536. ISBN 978-1-6654-6589-2.
  • Rok: 2022
  • DOI: 10.1109/ISSE54558.2022.9812708
  • Odkaz: https://doi.org/10.1109/ISSE54558.2022.9812708
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The use of flux when soldering is essential to obtain a reliable solder joint. No-clean fluxes are most often used in lead-free soldering. This raises the question of the need to clean the flux residues due to their aggressiveness. The purpose of this work is to understand the importance of the flux chemistry and impact of weak organic acids (WOAs) on the corrosivity of copper surface after reflow. During this investigation the aggressiveness of six different no-clean fluxes for lead-free soldering on toward copper surface was observed. The results showed the flux aggressiveness depended on the flux composition. Fluxes Weller Lötwasser and Topnik RF800 showed less aggressive effect toward copper surface after heat treatment. The results of the study also showed that one of more aggressive fluxes, such as Topnik LP-1, corroded the copper surface to a depth of about 50 μm.

Investigation of BGA underfill process based on multipositional computed tomography

  • DOI: 10.1088/1748-0221/17/06/P06037
  • Odkaz: https://doi.org/10.1088/1748-0221/17/06/P06037
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    In this paper, defect inspection related to an epoxy underfilling process between integrated circuits (ICs) and printed circuit boards (PCBs) is presented utilizing the data fusion of multipositional computed tomography (DFMCT). The work aims to verify the existence of underfilling epoxy which was not possible utilizing standard computed tomography due to strong metal artifacts created by ball grid array (BGA) packages. By interpreting the results obtained from the scanned samples, we were able to correlate the excess epoxy defects and the success of the underfilling process. We present the data fusion approach as an alternative method when traditional metal artifact reduction methods would be insufficient. The study was commenced by making a proper radiographic simulation using aRTist simulation software. The simulation enabled us to choose the right mounting positions which produce less metal artifacts for the experimental study. The DFMCT was achieved by acquiring multiple computed tomographic scans at different sample orientations. The reconstructed volumes were then aligned, and the fused volume was obtained by combining the corrected data and suppressing the disrupted data of the reconstructed volumes.

Latent heat induced deformation of PCB substrate: Measurement and simulation

  • DOI: 10.1016/j.csite.2022.102173
  • Odkaz: https://doi.org/10.1016/j.csite.2022.102173
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The work evaluates the impact of latent heat (LH) absorbed or released by a solder alloy during melting or solidification, respectively, on changes of dimensions of materials surrounding of the solder alloy. Our sample comprises a small printed circuit board (PCB) with a blind via filled with lead-free alloy SAC305. Differential scanning calorimetry (DSC) was employed to obtain the amount of LH per mass and a thermomechanical analyzer was used to measure the thermally induced deformation. A plateau during melting and a peak during solidification were detected during the course of dimension change. The peak height reached 1.6 mu m in the place of the heat source and 0.3 mu m in the distance of 3 mm from the source. The data measured during solidification was compared to a numerical model based on the finite element method. An excellent quantitative agreement was observed which confirms that the transient expansion of PCB during cooling can be explained by the release of LH from the solder alloy during solidification. Our results have important implications for the design of PCB assemblies where the contribution of recalescence to thermal stress can lead to solder joint failure.

Numerical simulation of electrochemical migration of Cu based on the Nernst-Plank equation

  • DOI: 10.1016/j.ijheatmasstransfer.2021.122268
  • Odkaz: https://doi.org/10.1016/j.ijheatmasstransfer.2021.122268
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Electrochemical Migration (ECM) is getting more attention in the microelectronics industry due to the continuing miniaturization, which increases the possibility of short circuit formation caused by the ECM induced dendrites. This work presents a 2D numerical model of the ECM based on the Nernst-Plank equation. The model contains the deterministic description of the metal dissolution, the changes of electrolyte properties, and the ion transport in the electrolyte. However, the reduction of the ions and the dendrite growth is described stochastically. The capability of the model was tested in the case of pure copper electrodes with a gap distance 200 mu m, 10 VDC bias, 20 degrees C temperature, and a contaminant-free electrolyte. The results of the model were validated by experimental water-drop tests. The results showed very good agreement between the experimental and the calculated mean time to failure values, dendrite morphologies, and the kinetics of the dendrite formation. The model showed that the developing dendrites consume most of the Cu2+ ions around them, which answers why only some dominant dendrites can develop in a given area. The model proved that not only the electric field but the diffusion of the ions is also dominant in given phases of the ECM process. Our model could be a useful tool for ECM failure prediction and for further ECM researches as the digital twin of the ECM process. Also the approach can be applied in various aspects of failure-prediction in modern reflow-soldering. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )

Overview of Various Failures of Luminaires Assembled with SMD LED Chips

  • Autoři: Ing. David Bušek, Ph.D., prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: 2022 45th International Spring Seminar on Electronics Technology (ISSE). New York: IEEE Press, 2022. International Spring Seminar on Electronics Technology (ISSE). ISSN 2161-2536. ISBN 978-1-6654-6589-2.
  • Rok: 2022
  • DOI: 10.1109/ISSE54558.2022.9812779
  • Odkaz: https://doi.org/10.1109/ISSE54558.2022.9812779
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This work describes common mistakes that are present in luminaires with light emitting diodes (LED) and suggests possible solutions or rather procedures and points that cannot be omitted during both luminaires manufacture and usage. LED packaging is designed to provide mechanical support, electrical connection, thermal management, spectral transformation, and optical control to the LED dies [1]. The LED chip package therefore brings a large variety of reliability issues that are described in the following work. The quality of wirebonds on an LED with soft chip encapsulant was negatively affected during placement. This is minimized when the setting of the machine is optimal, but further handling must also use softer approach when compared to LED chips with hard shell. Mismatch in coefficient of thermal expansion (CTE) also played a significant role in reliability due to fractures in solder joints as our measurement showed and the improper thermal design caused deterioration in the optics that further led to overheating. Several studies were conducted on the reliability calculations, taking into account theoretical or manufacturer declared properties of various LED chips or high power LED chip arrays [2], [3] or whole lighting system including the driver electronics (calculating with initial power consumption, efficiency of the optical system etc., trying to estimate remaining useful life of the entire system [4], [5]. However, real life situations bring into play other, usually unexpected factors such as improper handling.

Suppression of Sn whisker growth from SnAgCu solder alloy with TiO2 and ZnO reinforcement nano-particles by increasing the corrosion resistance of the composite alloy

  • DOI: 10.1016/j.jmrt.2022.08.172
  • Odkaz: https://doi.org/10.1016/j.jmrt.2022.08.172
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The main joining process of the electronic industry is still soldering with different alloys of Sn. This work studied the relationship between Sn whisker growth and corrosion resis-tance of 99Sn0.3Ag0.7Cu-TiO2/ZnO (0.25wt%) composite solder alloys in a corrosive envi-ronment via scanning electron microscopy and focused ion beam techniques. The corrosive environment test showed that the application of TiO2 and ZnO nano-particles almost totally suppressed the Sn whisker growth and improved the corrosion resistance of the composite solder alloys compared to the reference 99Sn0.3Ag0.7Cu alloy. The microstructural analysis of the reference 99Sn0.3Ag0.7Cu solder alloy showed that the volumetric increase of the corroded b-Sn grains resulted in local mechanical stress in the solder joints, which was released by Sn whisker development. However, in the composite solder joints, the increased grain boundary fraction and segregation of the TiO2 and ZnO nano-particles to the grain boundaries resulted in a relatively uniform and compact pro-tective oxide layer at the b-Sn grain boundaries. This suppressed the formation of SnOx, and via this, the corrosion-induced whisker growth.(c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Tepelné procesy a jejich vliv u pájení přetavením

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Tento příspěvek se zabývá vybranými vlivy teplených procesů se kterými se můžeme setkat při pájení přetavením. Teplotní profil a jeho nastavení může ovlivňovat některé negativní aspekty jako je například množství voidů v pájeném spoji, vznik náhrobního kamene (tombstoning), rozstřik tavidla do okolí, špatné vyvzlínání pájecí slitiny, průhyb součástí díky rozdílné tepelné roztažnosti, tloušťku intermetalické vrstvy apod.

Toward reducing no-clean flux spatter during reflow soldering: Investigating the effect of flux type, solder mask, and solder pad design

  • DOI: 10.1016/j.jmapro.2022.07.027
  • Odkaz: https://doi.org/10.1016/j.jmapro.2022.07.027
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This comprehensive study dealt with the reliability issue of no-clean flux spattering from the solder paste during the reflow soldering process. Several factors entering the process were investigated: the type of flux in the solder paste (ROL0/ROL1 according to the IPC J-STD-004B standard), the type of solder mask (liquid photo imageable/directly printed), and the type of solder pad design (copper-defined/solder mask-defined). A unique design of the test board was developed for a proper evaluation of flux spatter spots spattered from the solder paste. The testing board included real-sized soldering pads and a boron-silicate glass slide as a target area, ensuring the same evaluation process for all samples. The results showed a strong influence of flux chemistry on spattering. Changing the flux from ROL1 to ROL0 reduced the flux spot occurrence by 62 % on average. The type of solder pad design also slightly affected the flux spattering. No significant difference was found between the used solder masks; therefore, it is possible to use the novel, directly printed one without increasing the risk of flux spattering.

Understanding the Effect of Reflow Profile on the Metallurgical Properties of Tin–Bismuth Solders

  • DOI: 10.3390/met12010121
  • Odkaz: https://doi.org/10.3390/met12010121
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Sn–Bi alloys are desirable candidates for soldering components on printed circuit boards (PCBs) because of their low melting point and reduced cost. While certain tin–bismuth solders are well characterized many new alloys in this family have been developed which need proper characterization. The following study looks at the behavior of four different Sn–Bi alloys—traditional 42Sn58Bi and 42Sn57Bi1Ag and two new tin–bismuth alloys—in solder paste during the reflow soldering process. Each alloy was processed using different reflow profiles that had varying times above liquidus (TALs) and peak temperatures. The PCBs were then analyzed to see how the processing variables influenced wetting, voiding, microstructure, intermetallic layer composition, and thickness. After analysis, the PCBs were then subjected to thermal cycling experiments to see how reflow profile impacted microstructure evolution. The results demonstrated that reflow profile affects properties such as metal wetting and voiding. It does not however, greatly impact key metallurgical properties such as intermetallic layer thickness.

Analysis of a failure in a molded package caused by electrochemical migration

  • DOI: 10.1016/j.engfailanal.2020.105128
  • Odkaz: https://doi.org/10.1016/j.engfailanal.2020.105128
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Electrical components can fail during their function in an electrical circuit, especially in a harsh environment. One of the possible failure reasons is the electrochemical migration, which leads to a short circuit or change of electrical parameters of components. This paper focuses on electrochemical effects and explains mechanisms leading to the formation of a conductive path within a component molded in a plastic package. Appropriate diagnostic methods SEM/EDS and penetration tests have been chosen in order to find the root cause for short circuit creation. It was found that the conductive path appeared due to electrochemical migration of silver between the Electrically Conductive Adhesive (ECA) joints connecting the capacitor package. A tiny gap that was found between the molding compound and the leadframe of the package, showed to be the necessary condition for the electrochemical migration to appear. The main aim of this work was not just to identify the cause of an inadvertent conductive path creation, but also to identify the part of the manufacturing process, where similar problems can be prevented.

Comparison of Gold-Plated PCB Finishes after Thermal Stress

  • Autoři: Sorokina, K., Ing. David Bušek, Ph.D., prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: 2021 44th International Spring Seminar on Electronics Technology (ISSE). New York: IEEE Press, 2021. International Spring Seminar on Electronics Technology (ISSE). ISSN 2161-2528. ISBN 978-1-6654-1477-7.
  • Rok: 2021
  • DOI: 10.1109/ISSE51996.2021.9467593
  • Odkaz: https://doi.org/10.1109/ISSE51996.2021.9467593
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The article deals with thermal cycling influence on the electrical and mechanical properties of the soldered joint on various gold-plated surfaces. The purpose was to determine the effect of thermal aging on the properties of the soldered joint of Galvanic Gold and Electroless Nickel Immersion Gold (ENIG) surface finishes and two lead-free solder alloys SAC305 NC257-2 and SAC305 M8. Two different heating factors of limit values - minimum value of 218 s°C at which the solder is still possible to reflow and a maximum value of 2295 s°C which still fits to the manufacturer's specifications - were used for reflow process of used solders. Prepared samples were thermally cycled in a shock test chamber (-40°C, +125°C) or aged at 85°C and 85% RH (HH, Heat-Humidity chamber). The results show the influence of shock temperatures on the shear strength and resistance of soldered joints. The shear strength decreased after 1000 thermal cycles by 40% and soldered joints reflowed with a higher heating factor were stronger than the soldered joints reflowed with a lower heating factor. In contrast to shock temperatures, HH test did not have a significant effect on shear strength.

Electrical Properties of Photopolymers for 3D Printing

  • Autoři: Minář, J., Půlpán, J., Ing. Petr Veselý, Ph.D., Šefl, O., prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: 2021 44th International Spring Seminar on Electronics Technology (ISSE). New York: IEEE Press, 2021. p. 1-5. International Spring Seminar on Electronics Technology (ISSE). ISSN 2161-2528. ISBN 978-1-6654-1477-7.
  • Rok: 2021
  • DOI: 10.1109/ISSE51996.2021.9467515
  • Odkaz: https://doi.org/10.1109/ISSE51996.2021.9467515
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Although stereolithography (SLA) is the oldest 3D printing method, only a few works have been published about the complex electrical properties of objects printed from unfilled photopolymerizable resins. In this paper, we describe how the dielectric constant, loss factor, dielectric strength, and volume resistivity of printed objects are influenced by the type of resin and the thickness of the sample. Two commercial resins were used - acrylate/epoxy "blue" resin and acrylate "orange" resin. The electrical properties were mostly dependent on the type of resin and thickness of the sample. Thicker blue samples showed the highest polarizability among all tested materials. Volume resistivity of orange samples was one order of magnitude higher than the one of blue samples. Dielectric strength was not dependent on the type of the resin but rather on the thickness of the samples. Our results contribute to the current knowledge about the electrical behavior of SLA-printed objects.

Influence of Added Phosphorus and Gallium in Lead-free Bismuth-Tin Alloys on Wetting and Intermetallic Compounds

  • DOI: 10.1109/ISSE51996.2021.9467660
  • Odkaz: https://doi.org/10.1109/ISSE51996.2021.9467660
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The aim of this work is to evaluate a wettability improvement and microstructure changes by addition of gallium and trace elements of phosphorus to novel low-temperature lead-free Bi-Sn solder alloys. Four different alloys Bi59Sn40Ga1, Bi57Sn40Ga3, Bi60Sn40 and the eutectic alloy Bi58Sn42 were chosen. Furthermore, all these solders were investigated with an added small amount of phosphorus as well. For the wettability comparison, the wetting balance test in combination with three different fluxes was used. Moreover, these alloys were soldered to a copper plated test board and aged in a climatic chamber at the temperature of 80 °C for 24 days. Subsequently, metallographic cross-sections were made and analyzed by scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDX). The results of the wettability analysis showed the dominance of the chosen flux while soldering. However, it is still possible to draw the conclusion that phosphorus as an additive in Bi-Sn-Ga alloys supports the wetting, which is a crucial property of the solders. On the other hand, by the addition of gallium to the Bi60Sn40, the wetting force decreased. Regarding the microstructure, two different intermetallic compounds were identified. Namely, Cu6Sn5 at the interface between Cu board and alloys Bi60Sn40P and the eutectic one Bi58Sn42. The second detected IMC was CuGa2 between Cu and solder alloys with one and three weight percent of added gallium.

Influence of Flux and Related Factors on Intermetallic Layer Growth within SAC305 Solder Joints

  • DOI: 10.3390/ma14247909
  • Odkaz: https://doi.org/10.3390/ma14247909
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Flux contained in solder paste significantly affects the process of solder joint creation during reflow soldering, including the creation of an intermetallic layer (IML). This work investigates the dependence of intermetallic layer thickness on ROL0/ROL1 flux classification, glossy or matt solder mask, and OSP/HASL/ENIG soldering pad surface finish. Two original SAC305 solder pastes differing only in the used flux were chosen for the experiment. The influence of multiple reflows was also observed. The intermetallic layer thicknesses were obtained by the image analysis of micro-section images. The flux type proved to have a significant impact on the intermetallic layer thickness. The solder paste with ROL1 caused an increase in IML thickness by up to 40% in comparison to an identical paste with ROL0 flux. Furthermore, doubling the roughness of the solder mask has increased the resulting IML thickness by 37% at HASL surface finish and by an average of 22%.

Influence of Stress Factors on the Whiskers Growth on Sn-Cu Based Surfaces

  • Autoři: Kozák, M., prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: 2021 44th International Spring Seminar on Electronics Technology (ISSE). New York: IEEE Press, 2021. International Spring Seminar on Electronics Technology (ISSE). ISSN 2161-2528. ISBN 978-1-6654-1477-7.
  • Rok: 2021
  • DOI: 10.1109/ISSE51996.2021.9467629
  • Odkaz: https://doi.org/10.1109/ISSE51996.2021.9467629
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    One of the hardly predictable issuesin the case of solder joints are tin whiskers. Tin whiskers are electrically conductive crystals that spontaneously grow on a surface.This article deals with tin whiskers growth on the three types of metallization (pure tin, SnCu1 and SnCu3 solder alloy) of the copper substrate. Two stressing factors were considered in the experiment –temperature ageing (three temperature conditions were chosen: 20 °C, 50 °C and 80 °C) and mechanical stress via bend of wire before and after the soldering process. The incidence ofwhiskers on the surfaces was observed by confocal microscopy. The results show that the major influence on whiskers incidence has two factors, mechanical stress followed by the influence of temperature. Whereas the other factor –copper content in used materials showed a minor influence on whiskers incidence.

Investigation of Impacts on Printed Circuit Board Laminated Composites Caused by Surface Finish Application

  • DOI: 10.3390/polym13193203
  • Odkaz: https://doi.org/10.3390/polym13193203
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The purpose of this study was to compare the strength of the bond between resin and glass cloth for various composites (laminates) and its dependence on utilized soldering pad surface finishes. Moreover, the impact of surface finish application on the thermomechanical properties of the composites was evaluated. Three different laminates with various thermal endurances were included in the study. Soldering pads were covered with OSP and HASL surface finishes. The strength of the cohesion of the resin upper layer was examined utilizing a newly established method designed for pulling tests. Experiments studying the bond strength were performed at a selection of laminate temperatures. Changes in thermomechanical behavior were observed by thermomechanical and dynamic mechanical analyses. The results confirmed the influence of the type of laminate and used surface finish on bond strength. In particular, permanent polymer degradation caused by thermal shock during HASL application was observed in the least thermally resistant laminate. A response to thermal shock was detected in thermomechanical properties of other laminates as well, but it does not seem to be permanent.

Mathematical Modelling of Temperature Distribution in Selected Parts of FFF Printer during 3D Printing Process

  • DOI: 10.3390/polym13234213
  • Odkaz: https://doi.org/10.3390/polym13234213
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This work presented an FEM (finite element method) mathematical model that describes the temperature distribution in different parts of a 3D printer based on additive manufacturing process using filament extrusion during its operation. Variation in properties also originate from inconsistent choices of process parameters employed by individual manufacturers. Therefore, a mathematical model that calculates temperature changes in the filament (and the resulting print) during an FFF (fused filament fabrication) process was deemed useful, as it can estimate otherwise immeasurable properties (such as the internal temperature of the filament during the printing). Two variants of the model (both static and dynamic) were presented in this work. They can provide the user with the material’s thermal history during the print. Such knowledge may be used in further analyses of the resulting prints. Thanks to the dynamic model, the cooling of the material on the printing bed can be traced for various printing speeds. Both variants simulate the printing of a PLA (Polylactic acid) filament with the nozzle temperature of 220 °C, bed temperature of 60 °C, and printing speed of 5, 10, and 15 m/s, respectively.

Overview of Selected Issues Related to Soldering

  • DOI: 10.5772/intechopen.91023
  • Odkaz: https://doi.org/10.5772/intechopen.91023
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The formation of defects and imperfections in the soldering process can have many causes, which primarily include a poorly setup technological process, inappropriate or inappropriately used materials and their combinations, the effect of the surroundings and design errors. This chapter lists some examples of errors that can occur in soldering, while review is devoted to selected defects: non-wettability of the solder pads, dewetting, wrong solder mask design, warpage, head-in-pillow, cracks in the joints, pad cratering, black pad, solder beading, tombstoning, dendrites, voids, flux spattering from the solder paste, popcorning and whiskers.

Sn and Bi whisker growth from SAC0307-Mn07 and SAC0307-Bi1-Mn07 ultra-thin film layers

  • DOI: 10.1016/j.vacuum.2021.110121
  • Odkaz: https://doi.org/10.1016/j.vacuum.2021.110121
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    In the past years, the use of low silver content SAC0307 (99Sn0.3Ag0.7Cu wt%) solder alloy grew considerably due to its good soldering quality. In the latest version of this alloy, manganese, and bismuth are used to improve further its soldering parameters. In this study, a reliability issue, the whisker growth from SAC0307-Mn07 and SAC0307-Bi1-Mn07 solder alloys was investigated. Ultra-thin films (in 100-150 nm thickness) were vacuum evaporated from the investigated alloys onto Cu substrates. The samples were stored at laboratory conditions for 28 days. Whisker growth was followed by a scanning electron microscope, and the ultra-thin film layers structures were investigated in focused ion beam cuts. In the case of the SAC0307-Mn07, the mechanical stress due to the intermetallic layer growth resulted in whisker formation right after the layer deposition. However, Bi addition could increase the stress relaxation ability of the ultra-thin film layer; the whisker formation started only three days after the evaporation in the case of the SAC0307-Bi1-Mn07 layer. Besides, the SAC0307-Bi1-Mn07 alloy could entirely suppress the formation of filament-type whiskers that might cause reliability issues in microelectronics. Furthermore, a unique phenomenon was observed that the SAC0307-Bi1-Mn07 layer produced mostly Bi-Sn whisker couples.

Workplace for Demonstration of Electrochemical Migration Effect on Printed Circuit Boards

  • DOI: 10.1109/ISSE51996.2021.9467605
  • Odkaz: https://doi.org/10.1109/ISSE51996.2021.9467605
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Electrochemical migration is one of the issues that appears due to specific conditions when the electrolytic solution is present between two neighbouring conductors with different electrical potentials. This article deals with a student’s workplace, which demonstrates the electrochemical migration phenomena. The workplace can be included as a part of practical education in labs. The students can directly observe the electrochemical migration process, respectively, the growth of dendrites at prepared, printed circuit boards (PCB). The workplace is based on Peltier modules which enable to cool the sample (PCB) below dew point temperature. This ensures conditions for moisture condensation on the PCB with the following movement of metal ions in the presence of electric potential. The students obtain knowledge and experience from the field of electrochemical migration processes, moisture and its condensation. One of the advantages is that the workplace can be captured with a camera, and it can be used as a part of on-line education.

Analysis of no-clean flux spatter during the soldering process

  • DOI: 10.1016/j.jmatprotec.2019.116289
  • Odkaz: https://doi.org/10.1016/j.jmatprotec.2019.116289
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The investigation of the flux spattering in dependency on surface roughness of the substrate was conducted in order to decrease reliability issues during reflow soldering caused by insulating character of flux residues. Sample boards with matt and glossy solder mask, HASL and ENIG surface finish and two types of SAC305 lead-free solder paste with different flux chemistry (ROL1 and ROL0) were used in the experiment. The number of the flux residues, their area and the area of flux spreading around a soldering pad were evaluated by the image analysis. The dependency of the flux spattering on flux spread was found. The use of glossy solder mask instead of matt solder mask reduced the number of flux residues by approximately 50%.

Bond Strength Test of Soldering Pads with Various Surface Finishes Performed under Different Thermal Conditions

  • Autoři: Ing. Denis Froš, prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: 2020 43rd International Spring Seminar on Electronics Technology (ISSE). New York: IEEE Press, 2020. p. 1-5. International Spring Seminar on Electronics Technology (ISSE). ISSN 2161-2536. ISBN 978-1-7281-6773-2.
  • Rok: 2020
  • DOI: 10.1109/ISSE49702.2020.9121111
  • Odkaz: https://doi.org/10.1109/ISSE49702.2020.9121111
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The goal of this study is to evaluate the bond between the soldering pad and the substrate in dependence on the solder pad finish as well as on ambient temperature. Stated differently, measuring of pulling force necessary for detaching the pad from the substrate is a subject of submitted study. A conventional substrate (laminate) made of woven glass cloth and epoxy resin with glass transition temperature value of 135 °C was available. OSP and HASL were chosen as surface finishes for evaluating the impact on the studied concern. Bond strength test was performed in room temperature and at an elevated temperature around 60 °C. An influence of IMC layers on test performing and results is included. Achieved results suggest a difference in the rate of adhesion of soldering pad to the substrate considering surface finish. However, other testing variables don't affect the pad adhesion significantly.

Comparison of Gold-Plated PCB Finishes

  • Autoři: Sorokina, K., Ing. David Bušek, Ph.D., prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: 2020 43rd International Spring Seminar on Electronics Technology (ISSE). New York: IEEE Press, 2020. International Spring Seminar on Electronics Technology (ISSE). ISSN 2161-2536. ISBN 978-1-7281-6773-2.
  • Rok: 2020
  • DOI: 10.1109/ISSE49702.2020.9121062
  • Odkaz: https://doi.org/10.1109/ISSE49702.2020.9121062
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    In this work, two surface finishes - Electroless Nickel Immersion Gold (ENIG) and Galvanic Gold were compared. Solder joints were tested with respect to used materials (ENIG and Galvanic Gold finishes, lead-free solders SAC305 M8, SAC305 NC257-2), used technologies (heating factor of 218 s°C and 2295 s°C). The resistance of soldered joints was measured on prepared samples. The measurement results showed the influence of the heating factor on the resistance of soldered joints. With a heating factor of 218 s°C, the resistance of the joint is higher than that of a soldered joint realized using a higher heating factor, except for samples with a galvanic coating. A destructive shear strength test was also conducted. The results showed that heating factor may affect reliability of the soldered joint as the shear strength is influenced. In the case of SAC305 M8 solder, the shear strength values of the soldered joints with heating factor of 2295 s°C are approximately 21% higher, with the exception of the sample with half thickness of the standard thickness of ENIG surface finish. The SAC305 NC257-2 solder does not have big differences in shear strength at lower and higher heating factors during reflow.

Effect of Recrystallization on beta to alpha-Sn Allotropic Transition in 99.3Sn-0.7Cu wt. % Solder Alloy Inoculated with InSb

  • DOI: 10.3390/ma13040968
  • Odkaz: https://doi.org/10.3390/ma13040968
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The effect of recrystallization of 99.3Sn-0.7Cu wt. % solder alloy on the allotropic transition of beta to alpha-Sn (so-called tin pest phenomenon) was investigated. Bulk samples were prepared, and an InSb inoculator was mechanically applied to their surfaces to enhance the transition. Half of the samples were used as the reference material and the other half were annealed at 180 degrees C for 72 h, which caused the recrystallization of the alloy. The samples were stored at -10 and -20 degrees C. The beta-Sn to alpha-Sn transition was monitored using electrical resistance measurements. The expansion and separation of the tin grains during the beta-Sn to alpha-Sn transition process were studied using scanning electron microscopy. The recrystallization of the alloy suppressed the tin pest phenomenon considerably since it decreased the number of defects in the crystal structure where heterogeneous nucleation of beta-Sn to alpha-Sn transition could occur. In the case of InSb inoculation, the spreading of the transition towards the bulk was as fast as the spreading parallel to the surface of the sample.

Evaluation of Electrical Properties of Metalized Woven and Non-woven Polymer-Based Textiles

  • DOI: 10.1109/ISSE49702.2020.9120943
  • Odkaz: https://doi.org/10.1109/ISSE49702.2020.9120943
  • Pracoviště: Katedra elektrotechnologie, Katedra telekomunikační techniky
  • Anotace:
    The smart textiles seem to be a very interesting possibility in many industrial fields e.g. medicine, automotive, textile industry etc. These types of textile are mainly based on metalized threads. It is necessary to know the physical characteristics of smart textiles before their use for a specific application. This article deals with the preparation and characterization of three types of textiles - copper-coated non-woven polyamide fabric and copper and nickel coated woven polyester fabric. Characterization was based on the measurement of textiles properties like the thickness of metallization, electrical resistance. The measurements of thickness metallization were done at micro-section by electron microscopy. The electrical resistance was evaluated for further usage of these fabrics as a heating system in smart textiles, where a low resistance of the heating part is desirable. The sheet resistance was measured in different directions to obtain information about the isotropic or anisotropic character of samples. The highest electrical resistance had woven copper-coated polyamide fabrics. The anisotropic character of samples was more obvious for woven polyester fabrics.

Investigation of the Mechanical Properties of Mn-Alloyed Tin-Silver-Copper Solder Solidified with Different Cooling Rates

  • DOI: 10.3390/ma13225251
  • Odkaz: https://doi.org/10.3390/ma13225251
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Manganese can be an optimal alloying addition in lead-free SAC (SnAgCu) solder alloys because of its low price and harmless nature. In this research, the mechanical properties of the novel SAC0307 (Sn/Ag0.3/Cu0.7) alloyed with 0.7 wt.% Mn (designated as SAC0307-Mn07) and those of the traditionally used SAC305 (Sn96.5/Ag3/Cu0.5) solder alloys were investigated by analyzing the shear force and Vickers hardness of reflowed solder balls. During the preparation of the reflowed solder balls, different cooling rates were used in the range from 2.7 K/s to 14.7 K/s. After measuring the shear force and the Vickers hardness, the structures of the fracture surfaces and the intermetallic layer were investigated by SEM (Scanning Electron Microscopy). The mechanical property measurements showed lower shear force for the SAC0307-Mn07 alloy (20-25 N) compared with the SAC305 alloy (27-35 N), independent of the cooling rate. However, the SAC0307-Mn07 alloy was softer; its Vickers hardness was between 12 and 13 HV, whereas the Vickers hardness of the SAC305 alloy was between 19 and 20 HV. In addition, structural analyses revealed rougher intermetallic compound layers in the case of the SAC0307-Mn07 alloy, which can inhibit the propagation of cracks at the solder-substrate interface. These two properties of SAC0307-Mn07 alloy, the softer nature and the rougher intermetallic layer, might result in better thermomechanical behavior of the solder joints during the lifetime of electronic devices.

Kinetics of Sn whisker growth from Sn thin-films on Cu substrate

  • DOI: 10.1007/s10854-020-04180-2
  • Odkaz: https://doi.org/10.1007/s10854-020-04180-2
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The kinetics of Sn whisker growth was investigated on vacuum-evaporated Sn thin-films. Sn film layers were deposited on a Cu substrate with 0.5 and 1 mu m thicknesses. The samples were stored in room conditions (22 +/- 1 degrees C/50 +/- 5RH%) for 60 days. The Sn whiskers and the Cu-Sn layer structure underneath them were investigated with both scanning electron and ion microscopy. Fast Cu-Sn intermetallic formation resulted in considerable mechanical stress in the Sn layer, which initiated intensive whisker growth right after the layer deposition. The thinner Sn layer produced twice many whiskers compared to the thicker one. The lengths of the filament-type whiskers were similar, but the growth characteristics differed. The thinner Sn layer performed the highest whisker growth rates during the first 7 days, while the thicker Sn layer increased the growth rate only after 7 days. This phenomenon was explained by the cross-correlation of the stress relaxation ability of Sn layers and the amount of Sn atoms for whisker growth. The very high filament whisker growth rates might be caused by the interface flow mechanism, which could be initiated by the intermetallic layer growth itself. Furthermore, a correlation was found between the type of the whiskers and the morphology of the intermetallic layer underneath.

mu-CT investigation of tin whisker growth mechanisms

  • DOI: 10.1088/1748-0221/15/02/C02043
  • Odkaz: https://doi.org/10.1088/1748-0221/15/02/C02043
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The current paper considers the applicability of micro-tomographic methods for the investigation of growth mechanisms of metallic tin whiskers. Tin whiskers are metallic fibers that grow spontaneously from lead-free tin-coated surfaces, causing short circuit related issues in electronic devices, therefore making this phenomenon an interesting topic for in-depth analysis. In order to investigate such minuscule structures by X-rays, a tomographic setup employing a direct-converting pixel large area detector based on the Timepix readout ASIC is used. Featuring an extraordinary contrast and high dynamic range, these detectors have proven to be powerful tools in the analysis of samples containing fine features of low radiographic absorption.Initial tomographic results reveal fully 3D morphological information on tin whiskers, albeit at lower spatial resolution than by scanning electron microscope (SEM), which is the commonly used method to investigate this phenomenon. However, the additional morphological information obtained by micro-tomography gives additional means of analysis, likely to help understand the underlying growth mechanisms.

Novel Electrical Insulation Materials - Mechanical Performance of 3D Printed Polylactic Acid

  • DOI: 10.1109/Diagnostika49114.2020.9214627
  • Odkaz: https://doi.org/10.1109/Diagnostika49114.2020.9214627
  • Pracoviště: Fakulta elektrotechnická, Katedra elektrotechnologie
  • Anotace:
    The aim of this work was to evaluate the mechanical and thermomechanical properties of structures prepared by 3D printing from biodegradable thermoplastic polyester PLA (Polylactic Acid). PLA structures and their manufacture by 3D printing can be a cost-saving and ecological alternative to the current production of insulation systems, e.g. condenser bushings or substrates for printed circuit boards. For further practical application, the knowledge of the change of mechanical and thermal properties in dependence on process parameters is necessary. In this research, PLA test samples were first prepared at different printing speeds and nozzle temperatures. Then, they were characterized by thermomechanical analysis (TMA), dynamic mechanical analysis (DMA), and tensile tests. The data showed that the decrease of printing temperature remarkably increased the dimension change evaluated from TMA measurement of 3D printed structures. On the other hand, no significant differences were found between samples printed with different printing speeds. Our results should lead to a better understanding of how to set up the 3D printing process properly.

Novel Electrical Insulation Materials - Photodegradation Endurance of 3D Printed Polylactic Acid

  • Autoři: Šefl, O., Ing. Petr Veselý, Ph.D., Minář, J., prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: 2020 International Conference on Diagnostics in Electrical Engineering (Diagnostika). Institute of Electrical and Electronics Engineers, Inc., 2020. ISBN 978-1-7281-5879-2.
  • Rok: 2020
  • DOI: 10.1109/Diagnostika49114.2020.9214713
  • Odkaz: https://doi.org/10.1109/Diagnostika49114.2020.9214713
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The degradation of plastic materials induced by solar radiation can limit their use in outdoor applications. Therefore, we aimed to find a relationship between the photodegradation of 3D printed polylactic acid (PLA) and its electrical and thermomechanical properties. In the first stage, the printing settings were optimized with regard to the dielectric strength of samples. Afterward, the sets of printed specimens were exposed to UV light of different spectrum and duration. UV gas-discharge lamps with spectral peaks at 254 and 385 nm were used as intense UV light sources; the individual exposure times were chosen as 6, 12, 24, 48, and 96 hours. Subsequently, the dielectric strength of each set was evaluated, and thermomechanical analyses were performed. Although the irradiation at 254 nm caused substantial degradation of PLA, it did not remarkably affect its dielectric strength. Nonetheless, both sources of UV light caused a considerable brittleness that might be the limiting factor for the outdoor application of PLA.

Numerical investigation on the effect of solder paste rheological behaviour and printing speed on stencil printing

  • DOI: 10.1108/SSMT-11-2019-0037
  • Odkaz: https://doi.org/10.1108/SSMT-11-2019-0037
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Purpose The purpose of this paper is to investigate the effect of different viscosity models (Cross and Al-Ma'aiteh) and different printing speeds on the numerical results (e.g. pressure over stencil) of a numerical model regarding stencil printing. Design/methodology/approach A finite volume model was established for describing the printing process. Two types of viscosity models for non-Newtonian fluid properties were compared. The Cross model was fitted to the measurement results in the initial state of a lead-free solder paste, and the parameters of a Al-Ma'aiteh material model were fitted in the stabilised state of the same paste. Four different printing speeds were also investigated from 20 to 200 mm/s. Findings Noteworthy differences were found in the pressure between utilising the Cross model and the Al-Ma'aiteh viscosity model. The difference in pressure reached 33-34% for both printing speeds of 20 and 70 mm/s and reached 31% and 27% for the printing speed of 120 and 200 mm/s. The variation in the difference was explained by the increase in the rates of shear by increasing printing speeds. Originality/value Parameters of viscosity model should be determined for the stabilised state of the solder paste. Neglecting the thixotropic paste nature in the modelling of printing can cause a calculation error of even approximately 30%. By using the Al-Ma'aiteh viscosity model over the stabilised state of solder pastes can provide more accurate results in the modelling of printing, which is necessary for the effective optimisation of this process, and for eliminating soldering failures in highly integrated electronic devices.

Thermal Lifetime Calculation of Capacitor Insulation Using the Activation Energy Method

  • DOI: 10.1109/TCPMT.2020.3019275
  • Odkaz: https://doi.org/10.1109/TCPMT.2020.3019275
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    A rapid method based on activation energy values for the lifetime assessment of PP films used as dielectrics for capacitors is proposed. The activation energy is determined from a nonisothermal measurement made by differential scanning calorimetry and an aging test at a single elevated temperature. The use of the onset temperature of the exothermal peak is proposed to evaluate the activation energy of the degradation of the PP film. Four types of PP film capacitors were thermally aged at 100 degrees C for different aging times. For each aging time, the capacitance was measured at different frequencies. According to the standards, two end-of-life criteria (2% and 5%) were imposed for the reduction in the capacitance. The parameters of the lifetime line a and b were determined, and finally, the lifetime values were calculated. The novel proposed method is effective in terms of both energy and manpower costs compared with the current method, which uses three aging temperatures.

Development of Low-Cost Solder Paste Hand Dispenser

  • Pracoviště: Katedra elektrotechnologie, Katedra teorie obvodů
  • Anotace:
    In prototyping and piece-production, stencil printing of the solder paste is expensive, and with the use of the stencil, it is not possible to react fast on changes in the design. Therefore, automatic or manual dispensers are used. This work aimed to develop a low-cost dispensing system based on a simple principle that uses torsion springs and its plastic construction is printable by a 3D printer. Unlike other dispensing systems, the presented dispenser allows continuous deposition of the solder paste. As the performance test showed, the deposition can be as good as with a commercial dispenser. Furthermore, the cost of the dispenser does not exceed 1€. In comparison with other commercial solutions, it is a negligible amount.

Effect of Cu Substrate Roughness and Sn Layer Thickness on Whisker Development from Sn Thin-Films

  • DOI: 10.3390/ma12213609
  • Odkaz: https://doi.org/10.3390/ma12213609
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The effect of copper substrate roughness and tin layer thickness were investigated on whisker development in the case of Sn thin-films. Sn was vacuum-evaporated onto both unpolished and mechanically polished Cu substrates with 1 mu m and 2 mu m average layer thicknesses. The samples were stored in room conditions for 60 days. The considerable stress-developed by the rapid intermetallic layer formation-resulted in intensive whisker formation, even in some days after the layer deposition. The developed whiskers and the layer structure underneath them were investigated with both scanning electron microscopy and ion microscopy. The Sn thin-film deposited onto unpolished Cu substrate produced less but longer whiskers than that deposited onto polished Cu substrate. This phenomenon might be explained by the dependence of IML formation on the surface roughness of substrates. The formation of IML wedges is more likely on rougher Cu substrates than on polished ones. Furthermore, it was found that with the decrease of layer thickness, the development of nodule type whiskers increases due to the easier diffusion of other atoms into the whisker bodies.

Electrochemical migration of lead-free solders and Ag-based electrically conductive adhesives in NaCl solution

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    In this article, the electrochemical migration of lead-free solders and electrically conductive adhesives with an Ag content of more than 70% was studied by using a water drop test in NaCl solution. The results of solder pastes were compared with the results of electrically conductive adhesives. It was found that some solder pastes with a low Ag content have a lower susceptibility to electrochemical migration than, for example, solder paste Sn42Bi58. The highest resistance to corrosion has a conductive adhesive CRM-1033B with an Ag content of 75%. Resistance and voltage during the water drop test. From the measured values, it was determined that the values of resistance and voltage decrease with dendrite growing. X-ray spectroscopy was also performed to determine the chemical elemental composition of dendrites. It was found that the dominant element of the dendrite of solder pastes was Sn. In the case of electrically conductive adhesives, Ag was the main element of the dendrite.

Evaluation of Bismuth/Tin Solder Intermetallic Layers Based on Heating Factor

  • Autoři: Ing. Petr Veselý, Ph.D., prof. Ing. Bc. Karel Dušek, Ph.D., Staňková, A.
  • Publikace: 2019 42nd International Spring Seminar on Electronics Technology (ISSE). New York: IEEE Press, 2019. International Spring Seminar on Electronics Technology ISSE. ISSN 2161-2536. ISBN 978-1-7281-1874-1.
  • Rok: 2019
  • DOI: 10.1109/ISSE.2019.8810306
  • Odkaz: https://doi.org/10.1109/ISSE.2019.8810306
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The intermetallic compounds growth at the interface between the eutectic solder Bi58Sn42 and the copper soldering pad was examined in dependence on the temperature profile selection that was expressed by a heating factor (combined influence of time and temperature above the melting point of the solder alloy). Eight temperature profiles were used for reflow soldering. In contrast to other studies, almost the identical value of the heating factor was achieved by the different shapes of the profiles in order to evaluate the effect of the whole profile shape. Consequently, the metallographic cross-sections of the solder joints were analyzed by scanning electron microscopy. Additionally, the shear strength test of solder joints and the transition resistance measurement were conducted. As expected, the intermetallic layer thickness increased with an increasing heating factor, but a different thickness was observed for the identical heating factor when the whole shape of temperature profile including the preheating phase was changed. On the other hand, the prediction of IMC growth based on heating factor can be used in situations, where only the melting phase varies and the preheating remains constant - but the influence of the heating factor on intermetallic layer thickness cannot be generally formulated for a specific solder alloy due to a strong dependence on the flux.

Numerical investigation on the effect of the printing force and squeegee geometry on stencil printing

  • DOI: 10.1016/j.jmapro.2019.06.021
  • Odkaz: https://doi.org/10.1016/j.jmapro.2019.06.021
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The effects of printing force and different squeegee geometries on the process of stencil printing were investigated in this paper. Numerical models were established, which included squeegees with different geometries (different overhang sizes of 6, 15, 20, 25 mm) and took the printing force (specific value 0.3 N/mm) into account by using loaded squeegee angles instead of unloaded ones. The flow behaviour of the solder paste was captured by utilising non-Newtonian fluid parameters, which were determined by fitting a curve to the prior measurement results of a lead-free solder paste (particle size 20-38 mu m). The effect of different squeegee geometries was characterised by calculating the pressure distribution over the stencil. Results showed a significant difference in the pressure using the unloaded and the loaded squeegee geometries. In the case of unloaded squeegee angle of 60 degrees, the increase was (similar to)22%, (similar to)45% and (similar to)90% for overhang sizes of 15, 20, 25 mm respectively by applying loaded squeegees. In the case of unloaded squeegee angle of 45 degrees, the increase in pressure was even more noticeable; (similar to)45%, (similar to)102% and (similar to)250% for the overhang sizes of 15, 20, 25 mm respectively. This increase in pressure implies that neglecting the printing force and squeegee geometries in numerical investigation of the stencil printing process results in significant calculation errors.

Pájení - fenomén povrchového napětí

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Článek pojednává o povrchovém napětí a o jeho vlivu na pajecí proces.

Released of Latent Heat from Solder Joints to Surrounding during Solidification of Solder Alloy - Experimental Study

  • DOI: 10.1109/ISSE.2019.8810199
  • Odkaz: https://doi.org/10.1109/ISSE.2019.8810199
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The thermal behavior of solder alloys during melting and solidification is important from point of many aspects. It has influence on formation of joint structure together with intermetallic compounds, reliability issues like tombstoning effect or warpage effect, dimensional changes of components and printed circuit board etc. This article deals with influence of released latent heat from solder joints on the surrounding temperature. Printed circuit boards with soldering pads designed side by side in the matrix and solder paste based on SAC387 solder alloy particles was used in experimental study. The influence of increased number of solder joints in a defined area was examined. The temperature profiles were measured below soldering pads during reflow soldering to find the thermal influences. The results show that released latent heat from solder joint has influence on surrounding temperature and it can delay the solidification of neighbor joint.

Ruční dávkovač pájecí pasty s velmi nízkými výrobními náklady

The influence of the crystallographic structure of the intermetallic grains on tin whisker growth

  • DOI: 10.1016/j.jallcom.2019.01.247
  • Odkaz: https://doi.org/10.1016/j.jallcom.2019.01.247
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    In this paper, the relationship between the crystallographic structure of Cu-Sn intermetallic grains and Sn whisker growth was investigated. In order to prevent the influence of the elements in the alloy composition and the effect of the soldering process on the formation of the intermetallic layer, 99.99% pure Sn was vacuum evaporated onto Cu substrates. The Sn layer thickness was sub-micron region (~400 nm in average) to reach considerable and rapid compressive stress on the tin layer originated by the intermetallic formation. The samples were stored at room temperature for 1 month. Different types of whiskers (nodule and filament) and the layer structure underneath were studied with a scanning ion microscopy and transmission electron microscopy. It was found that not only the thickness of the intermetallic layer and shape of the intermetallic grains affects the whisker growth but the crystallo- graphic structure of the intermetallic grains as well. The susceptibility of the Sn layer to whisker development is higher in those regions where the intermetallic layer is composed of monocrystalline grains instead of those regions, where it is composed of polycrystalline grains. This effect can be explained by the higher compressive stress generated by the monocrystalline intermetallics compared to the polycrystalline ones.

Thermo-Mechanical Test of SnBi and SnCu Solder Joints on Different Surface Finishes

  • DOI: 10.1109/ISSE.2019.8810299
  • Odkaz: https://doi.org/10.1109/ISSE.2019.8810299
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The article deals with the heating factor influence on the solder joint reliability. A specific goal was to reveal the influence of the heating factor on the thickness of the Intermetallic Layer (IML) for Copper, Electroless Nickel Immersion Gold (ENIG) and Hot Air Solder Levelling (HASL) surface finishes and two lead free solders Sn42Bi58 and Sn99.3Cu0.7. Three different heating factors were used for hot air reflow of the Bismuth solder paste and another three for reflow of the SnCu solder paste. Micro-sections were prepared and the IMC (Inter-Metallic Compound) layer thickness was measured. The manufactured samples were subjected to destructive shear strength testing at laboratory temperature (20 degrees C) and at 65 degrees C. The results show an influence of intermetallic layer thickness on the shear strength and a minor decrease of the shear strength at elevated testing temperature for a low temperature Bismut based solder paste. When SnCu solder was used, the IMC layer was thicker and also the shear strength was lower, in an average (on all surface finishes) by 19%.

Dendritic Growth and its Dependence on Various Conditions

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Printed circuit board (PCB) as a basic supporting structure of electronic devices is a significant reliability factor in electronic manufacturing. The miniaturization in electronics leads to lower gaps between pads with different electrical potential and that increases the probability of fault caused by dendritic growth. Not just the ambient environment has influence on electrochemical migration, but the surface finish, the solder mask, used solder and the cleaning process influences the dendritic growth and its composition and thus the reliability of PCBs and the final product. The results indicate, that the use of suitable soldering mask without any doubt hinders, though not fully the dendritic growth. An unexpected result is that the dendritic growth was also hindered when the flux residues were present. The lowest resistance against dendritic growth was discovered with organic solderability preservatives (OSP) surface finish, the highest with electroless nickel immersion gold (ENIG). The element analysis showed that the dendrites do not grow directly from the soldering pads. The surface finish therefore does not have a direct influence on dendrites, but rather on the chemical compound that is formed between the surface finish and the solder. These compounds are then prone to electrochemical migration.

Effect of the vapour concentration decrease on the solder joints temperature in a vacuum vapour phase soldering system

  • DOI: 10.1108/SSMT-09-2017-0025
  • Odkaz: https://doi.org/10.1108/SSMT-09-2017-0025
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Purpose The vacuum vapour phase soldering method was investigated by numerical simulations. The purpose of this study was to examine the temperature changes of the solder joints during the vapour suctioning process. A low pressure is used to enhance the outgassing of the trapped gas within the solder joints, which otherwise could form voids. However, the system loses heat near the suction pipe during the suctioning process, and it can result in preliminary solidification of the solder joints before the gas could escape.

Influence of Manufacturing Mechanical and Thermal Histories on Dimensional Stabilities of FR4 Laminate and FR4/Cu-Plated Holes

  • DOI: 10.3390/ma11112114
  • Odkaz: https://doi.org/10.3390/ma11112114
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Irreversible dimension changes of an FR4 laminate board in the z-direction and FR4 laminate/Cu plated holes that depend on their manufacturing histories have been studied by thermal mechanical analysis in the temperature range from room temperature to 240 degrees C. It is found that the compression residual stresses generated in both materials due to manufacturing pressing are released during heating, leading to an elongation in the specified direction. This increase depends on the composition of the studied composite and number of pressing cycles. The second reason for the observed dimensional changes is insufficient curing during manufacture that causes post-curing after the first heating cycle and related board shrinkage in the z-direction. The temperature regions of these two processes are not the same. The post-curing process occurs in the transition temperature range (near the glass transition temperature), whereas the release of the compression residual stress is observed at higher temperatures. Both these processes are temperature-dependent and do not proceed to completion during one heating cycle. Moreover, the compression residual stress strongly influences the post-curing process.

Influence of vapor phase soldering fluid Galden on wetting forces (tombstone effect)

  • DOI: 10.1016/j.jmatprotec.2017.08.006
  • Odkaz: https://doi.org/10.1016/j.jmatprotec.2017.08.006
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Vapour phase soldering brings besides many advantages for reliability in electronic production an increased incidence of tombstoning errors. The imbalance of wetting forces has a decisive effect on the tombstoning phenomena, and the changes in wetting forces during the vapour phase soldering are therefore analyzed and evaluated. Two types of solders (leaded Sn63Pb and lead-free SAC387 alloy) and two types of heat transfer fluids (Galden LS 230 and Galden HS 240) were used. The use of soldering fluids changes the surface tension equilibrium vectors for both used solders and changes the measured wetting force by up to 20%. The measurement was performed by wetting balance method using non-wetting sample.

Nabídka expertní činnosti Katedry elektrotechnologie, ČVUT v Praze v oblasti povrchové montáže

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Příspěvek pojednává o expertní činnosti katedry elektrotechnologie v oblasti povrchové montáže.

Numerical investigation on the effect of condensate layer formation around large-size components during vapour phase soldering

  • DOI: 10.1016/j.ijheatmasstransfer.2018.04.079
  • Odkaz: https://doi.org/10.1016/j.ijheatmasstransfer.2018.04.079
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The reflow soldering process of large size components was always problematic in microelectronics manufacturing due to the possibility of component displacement failures after soldering; like tombstone formation or skewing, which can be traced back to the different heating of the opposite component sides. During vapour phase soldering, the efficiency of heat transfer highly depends on the thickness of the condensate layer. In this paper, the inhomogeneity of condensate layer formation and its effects were investigated at large size components during vapour phase soldering by numerical simulations. For this purpose, a 3D computational fluid dynamic model was established. According to the condensate layer formation in different cases, the onset differences in the melting of the solder alloy at the opposite leads of the component were calculated. By the results, the risk of the component displacement during reflow soldering was analysed. It was found, that the congestion of the condensate layer around the large size components can cause considerable differences in the onset of the solder alloy melting, which can yield in component displacement failures after soldering. The extent of difference in the onset of melting depends on the location of the component on the board and on the applied soak temperature. Keep-out zones on the board were suggested to reduce the possibility of the component displacement failures during the vapour phase soldering process.

Publication Techniques for Young Scientists in the Field of Microelectronics Engineering

  • DOI: 10.1109/SIITME.2018.8599245
  • Odkaz: https://doi.org/10.1109/SIITME.2018.8599245
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The authors' institutions are Partners in the VINMES network (Visegrad Network for Microelectronics Engineering Scientists), and they are conducting a Visegrad Fund project about “V4 Seminars for young scientists on publishing techniques in the field of engineering science”. The aims of the project are the enhancement and support the scientific publication of young scientists from V4 and the surrounding countries, with a knowledge transfer about presentation techniques at conferences, journal article writing, and publication practice. Furthermore, facilitate the publication possibilities on youth conferences and in special issues of scientific journals. Twelve hours long teaching system was developed about the basics of publication; best practices of the different types of publication (journal and conference paper, posters, oral presentation etc.); related topics like image preparation and statistical evaluation. Up to now, three pilot courses were organized at three Central European Universities. The feedback of the participating students was evaluated and the positive result of the pilot tests encourages us to consider developing our courses to e-Iearning materials. This may help to disseminate the information about our courses and attract more students to take the courses on-line. In this paper the conclusions of our work are summarized

Solder joint quality evaluation based on heating factor

  • DOI: 10.1108/CW-10-2017-0059
  • Odkaz: https://doi.org/10.1108/CW-10-2017-0059
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Purpose – The purpose of this paper is to increase the reliability of manufactured electronics and to reveal reliability significant factors. The experiments were focused especially on the influence of the reflow oven parameters presented by a heating factor. Design/methodology/approach – The shear strength of the surface mount device (SMD) resistors and their joint resistance were analyzed. The resistors were assembled with two Sn/Ag/Cu-based and one Bi-based solder pastes, and the analysis was done for several values of the heating factor and before and after isothermal aging. The measurement of thickness of intermetallic compounds was conducted on the micro-sections of the solder joints. Findings – The shear strength of solder joints based on the Sn/Ag/Cu-based solder alloy started to decline after the heating factor reached the value of 500 s · K, whereas the shear strength of the solder alloy based on the Bi alloy (in the measured range) always increased with an increase in the heating factor. Also, the Bi-based solder joints showed shear strength increase after isothermal aging in contrast to Sn/Ag/Cu-based solder joints, which showed shear strength decrease. Originality/value – The interpretation of the results of such a comprehensive measurement leads to a better understanding of the mutual relation between reliability and other technological parameters such as solder alloy type, surface finish and parameters of the soldering process.

Surface Area Evaluation of Electrically Conductive Polymer-Based Textiles

  • DOI: 10.3390/ma11101931
  • Odkaz: https://doi.org/10.3390/ma11101931
  • Pracoviště: Katedra elektrotechnologie, Katedra telekomunikační techniky
  • Anotace:
    In this paper, the surface area of coated polymer-based textiles, i.e., copper and nickel plated woven polyester fabric, copper and acrylic coated woven polyester fabric, and copper and acrylic coated non-woven polyamide fabric, is investigated. In order to evaluate the surface area of the woven fabrics, Peirce’s geometrical model of the interlacing point and measurement using an electron microscope are used. Non-woven fabrics are evaluated using an optical method, handmade method, and MATLAB functions. An electrochemical method, based on the measurement of the resistance between two electrodes, is used for relative comparison of the effective surface area of the coated woven and non-woven fabrics. The experimental results show that the measured and calculated warp lengths do not differ within the standard deviation. The model for the surface area evaluation of the Pierce’s geometrical model for monofilament (non-fibrous) yarns is extended to multifilament yarns and to a uniform sample size. The experimental results show the increasing trend of surface area evaluation using both modeling and electrochemical methods, i.e., the surface area of the copper and acrylic coated woven Polyester fabric (PES) is the smallest surface area of investigated samples, followed by the surface area of the copper and acrylic coated non-woven fabric, and by copper and nickel plated woven PES fabric. These methods can be used for surface area evaluation of coated polymer-based textiles in the development of supercapacitors, electrochemical cells, or electrochemical catalysts.

The effect of solder paste particle size on the thixotropic behaviour during stencil printing

  • DOI: 10.1016/j.jmatprotec.2018.07.027
  • Odkaz: https://doi.org/10.1016/j.jmatprotec.2018.07.027
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The thixotropic behaviour of different type lead-free solder pastes (Type 3: particle size: 20–45 μm; Type 4: 20–38 μm; Type 5: 10–25 μm) was investigated and compared. The viscosity decrease during the first stencil printing cycles is also described. The measurements were carried out with a rheometer using serrated parallel plates by sweeping the shear rate between 0.0015–100 s−1 with ten recordings per decade. Thixotropic behaviour of the solder pastes within the cycles of stencil printing was evaluated by including a “rest-period” between every rheological measurement to address the idle time between the printings. The “rest-period” was set to 15 s, 30 s and 60 s in this research The viscosity curve parameters η0 and η∞ were determined and were used to describe the viscosity change of solder pastes (from initial to stabilised state). Oscillatory stress sweep tests for different idle time periods were conducted in the stabilised state of the solder pastes. Significant difference was shown in the viscosity between the initial and the stabilised state of the solder paste; the η0 parameter decreased even to one thirds, and the η∞ decreased approximately to two thirds during the measurement cycles.

Thermal Cycle Testing of Printed Circuit Board Vias (Barrel Plates)

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Printed circuit board (PCB) reliability is a very important factor from the point of total quality of output products. The ambient environment has influence on the reliability of PCBs and various issues can appear during its lifetime, even if the PCB properly passes the quality control before and after its assembly. This article deals with reliability test-monitoring of resistance behavior of the printed circuit board vias (barrel plates) during thermal stress (shock test). Appropriate printed circuit boards have been designed for this purpose. PCB sample was double-sided, vias were connected serially and PCB design allowed the use of four wire measurement method for measuring of all vias at once. The temperature sensor Pt100 was attached onto the PCB for better temperature monitoring of PCB during shock test. The shock test cycle took 20 minutes, the temperature of hot zone was set to 160 degrees C and the temperature of cool zone was -60 degrees C. The experiments help in understanding the barrel plate behavior during thermal stress, when the thermal expansion of composite substrate (glass-epoxy laminate) cause force (Young's modules), which stretches the barrel plate from the middle outwards. The identification of faulty vias is not easy during ambient temperature, it is easier when a measurement is conducted during thermal cycling or when the PCB is heated.

Automatic characterisation method for statistical evaluation of tin whisker growth

  • DOI: 10.1016/j.microrel.2017.04.007
  • Odkaz: https://doi.org/10.1016/j.microrel.2017.04.007
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    In this paper, an automatic method was developed to characterise whisker growth quantitatively in SEM images. The key step of the automatic methods in this case is the determination of the optimal threshold value for image segmentation, i.e. separation of the objects (whiskers) from the background (substrate). A thresholding method was developed for this purpose and was compared to manual and to general purpose automatic methods as references. As it was proven in previous studies the vacuum deposited tin layers on copper substrates can produce numerous tin whiskers in various shapes and lengths in a short time. This layer deposition technology was therefore chosen for the comparison of the thresholding methods. Images of the produced whiskers were captured by a FEI Inspect S50 Scanning Electron Microscope. By executing the automatic methods in the captured images, the area density of the whiskers, and the maximum and the mean length of the whiskers were measured. Based on the results of area density, the automatic methods were compared to manual counting and the Mean Absolute Percentage Error (MAPE) was determined. Finally, the reference automatic methods were compared to the self-developed method from the maximum and mean length of whiskers point of view

Comparison of mechanical resistance of SnCu and SnBi of solder joints

  • DOI: 10.1109/ISSE.2017.8000924
  • Odkaz: https://doi.org/10.1109/ISSE.2017.8000924
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Mechanical stress act on solder joints during transport, function and storage of the electronic equipment. Therefore, the knowledge of solder joints resistance against it is very useful. This article deals with comparison of mechanical resistance of SnCu0,7 and Sn42Bi58 solder alloys. The experiments were based on two PCBs (smaller and larger one, with soldering pads designed according to commonly used chip package) which were soldered together. Surface finishes of soldering pads were OSP, ENIG and HASL. Mechanical test were based on sharp tip, which were driving between two PCBs. From overall point of view a slightly better results were achieved for Sn42Bi58 solder alloy. Additionally the thicknesses of intermetallic layers were compared and voids frequency inside solder joints were inspected.

Corrosion-induced tin whisker growth in electronic devices: a review

  • DOI: 10.1108/SSMT-10-2016-0023
  • Odkaz: https://doi.org/10.1108/SSMT-10-2016-0023
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Purpose - The aim of this paper is to present a review of the tin whisker growth phenomena. The study focuses mainly on whisker growth in a corrosive climate when the main inducing factor of the whisker growth is oxidation. The tin whisker phenomenon is still a big challenge in lead-free reflow soldering technology. Modern lead-free alloys and surface finishes with high tin content are considered to be possible sources of whisker development, also the evolution of electronic devices towards further complexity and miniaturization points to an escalation of the reliability risks. Design/methodology/approach - The present work was based on a worldwide literature review of the substantial previous works in the past decade, as well as on the results and experience of the authors in this field. Findings - The effect of corrosion on tin whisker growth has been under-represented in reports of mainstream research; however, in the past five years, significant results were obtained in the field which raised the corrosion phenomena from being a side effect category into one of the main inducing factors. This paper summarizes the most important findings of this field. Practical implications-This literature review provides engineers and researchers with a better understanding of the role of corrosion in tin whisker growth and the current challenges in tin whisker mitigation Originality/value - The unique challenges and future research directions about the tin whisker phenomenon were shown to highlight rarely discussed risks and problems in lead-free soldering reliability.

Influence of latent heat released from solder joints II: PCB deformation during reflow and pad cratering defects

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Rudajevová, A.
  • Publikace: Journal of Materials Science: Materials in Electronics. 2017, 28(1), 1070-1077. ISSN 0957-4522.
  • Rok: 2017
  • DOI: 10.1007/s10854-016-5630-y
  • Odkaz: https://doi.org/10.1007/s10854-016-5630-y
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This work is focused on the deformation of FR4 laminate, a material used to form many basic components of electronic assemblies, during the reflow process. The thermal expansion of FR4 was assessed from room temperature up to 250 °C. The dilatation characteristics of the laminate were found to be highly anisotropic in three directions. Special attention was paid to the irreversible changes in the laminate after the first thermal cycle, and the results were used to analyze the effects of latent heat on the deformation of FR4 during reflow. The latent heat released during solidification of a solder joint heats not only the joint but also its surrounding, leading to localized expansion of all materials around the joint and potentially causing pad cratering. Thermal expansion measurements demonstrated that the coefficient of thermal expansion (CTE) of the FR4 laminate in the z direction was at least 10 times that of the adjacent materials in the electronics assembly. This large difference in the CTE leads to residual strains in the assembly. An analysis of this problem is presented, and a model for the effect of latent heat on the FR4 deformation is proposed.

Investigating the thixotropic behaviour of Type 4 solder paste during stencil printing

  • DOI: 10.1108/SSMT-10-2016-0022
  • Odkaz: https://doi.org/10.1108/SSMT-10-2016-0022
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Purpose - A measurement method has been developed to reveal the viscosity change of solder pastes during stencil printing. This paper aimed to investigate thixotropic behaviour, the viscosity change of a lead-free solder paste (Type 4). Design/methodology/approach - The viscosity change of the solder paste during stencil printing cycles was characterised in such a way that the time-gap between the printing cycles was modelled with a rest period between every rheological measurement. This period was set as 15, 30 and 60 s during the research. The Cross model was fitted to the measurement results, and the eta(o) parameter was used to characterise the viscosity change. The number of printing cycles necessary for reaching a stationary state in viscosity was determined for various rest periods. Findings - It was found that the decrease in zero-shear viscosity is significant (25 per cent) in the first cycles, and it starts to become stationary at the sixth-seventh cycles. This means a printing process can provide the appropriate deposits only after the 7th cycle with the investigated Type 4 solder paste. Originality/value - Time-dependent rheological behaviour of solder pastes was studied in the literature, but only the viscosity change over continuous time at constant shear rates was examined. The time-gap between stencil printing cycles was not considered, and thixotropic behaviour of solder pastes was also neglected. Therefore, the authors developed a measurement set which is able to model the effect of time-gap between printing cycles on the viscosity change of solder pastes.

New method for determining correction factors for pin-in-paste solder volumes

  • DOI: 10.1108/SSMT-11-2016-0032
  • Odkaz: https://doi.org/10.1108/SSMT-11-2016-0032
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This paper aims to present a new method to calculate the appropriate volume of solder paste necessary for the pin-in-paste (PIP) technology. By the aid of this volume calculation, correction factors have been determined, which can be used to correct the solder fillet volume obtained by an explicit expression.

Pájení v elektrotechnice

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Pájení je nejpoužívanější metodou při elektronické montáži. Výraznou změnu pájení prodělalo při přechodu na a bezolovnaté pájecí slitiny. S touto změnou a se stále rostoucí miniaturizací elektrotechnických zařízení je spojena problematika vývoje vhodných slitin, výrobních technologií atd. Pájení se postupem doby stalo velmi komplexním procesem, do kterého vstupuje mnoho faktorů ovlivňujících výslednou kvalitu pájeného spoje, a tedy i výrobku. Tento článek se zabývá používanými materiály, pájením a vybranými problémy, které se mohu vyskytnout.

Problematika Iontové Migrace

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Článek pojednává o problematice iontové migrace na deskách plošných spojů a uvnitř pouzder součástek.

Residual Strain in PCBs with Cu-Plated Holes

  • DOI: 10.1007/s11664-017-5714-3
  • Odkaz: https://doi.org/10.1007/s11664-017-5714-3
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The residual strain in pure printed circuit boards (PCBs) and PCBs with Cu-plated holes has been obtained by measurement of the temperature dependence of their dilatational characteristics in the x, y, and z directions up to 240A degrees C. Shrinkage in all directions was observed for all samples of both materials in the first thermal cycle. No permanent length changes were observed in the second or subsequent thermal cycles. The residual strain was determined from the difference in relative elongation between the first and second thermal cycles. Relaxation of residual strain occurred only in the first thermal cycle, as a thermally activated process. The highest value of relaxed residual strain was found in the z direction for both materials. Relaxation of residual strain in the z direction of the pure PCB occurred only in the negative strain range, whereas relaxation of the PCB with Cu-plated holes occurred in both the positive and negative strain ranges. The relaxation of the positive strain in the PCB with Cu-plated holes in the z direction implies that this part of the PCB was under pressure during its preparation. This relaxation is a consequence of the high coefficient of thermal expansion of PCB laminate in this direction, which can also lead to cracks in Cu holes when the material is heated above the glass-transition temperature.

Study of temperature profile influence on intermetallic growth

  • DOI: 10.1109/ISSE.2017.8000922
  • Odkaz: https://doi.org/10.1109/ISSE.2017.8000922
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article deals with the study of influence of temperature profile on the intermetallic layer growth and its thickness. There are many studies that observed the IMC growth, but only few evaluate the IMC growth in dependence on the heating factor. The heating factor is defined as an amount of heat added after the moment when the solder alloy is already in the liquid state. Two solder pastes, SnBi and Sn96.5/Ag3.0/Cu0.5 were used for experiments. Copper with OSP surface finish was chosen as a soldering material for the pads. The results confirm that it is the heating factor that has a decisive influence on the thickness of intermetallic layer.

The evaluation of parameters of evaporated aluminium layers depending on initial conditions

  • DOI: 10.1109/ISSE.2017.8000954
  • Odkaz: https://doi.org/10.1109/ISSE.2017.8000954
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This paper focuses to the problematic of thin film metal layers. The samples prepared by vacuum evaporation of thin film meander-shaped aluminium layers were analysed. Electrical resistance and thickness of layer were included in the measured parameters. We evaluated these parameters in dependence of the volume of the source material, i.e., an aluminium wire. We observed a certain variance in measured values in a repeated experiment with a constant amount of the originating material. Sets of measured values were processed by statistical methods, namely histogram and Shapiro-Wilk normality test. We observe some interesting facts from the analysed data that can give us information about the influence of the evaporation process on the resulting properties of the layer.

Ultrasonic soldering, mechanical properties of solder joints

  • DOI: 10.1109/ISSE.2017.8000925
  • Odkaz: https://doi.org/10.1109/ISSE.2017.8000925
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Mechanical properties of solder joints have influence on reliability of electronic products. Therefore the knowledge of the mechanical behavior of solder joints is very important. This article deals with comparison of mechanical properties of solder joints prepared with conventional soldering methods and ultrasonic soldering methods. Material for samples preparation was based on two PCB (material FR4) with soldering pads which were soldered together. As solder alloy was used Sn965Ag3Cu0.5 for convention soldering method and active soldering alloy for ultrasound soldering. The mechanical resistance, changes according to used surface finishes the highest share strength, have been achieved for solder joints which ware prepared by ultrasonic soldering on pads with copper surface finish, worst results were achieved for pads with ENIG and HASL surface finishes.

Demontáž součástek se spodní výplní pomocí speciální frézky

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Članek pojednává o technologii opravy podlepených pouzder (nejčastěji BGA) na desce plošného spoje pomocí speciální, velmi jemné frezky.

Diagnostika residuí na testovacích ploškách desek plošných spojů

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Článek se zabývá diagnostikou residuí na testovacích ploškách desek plošných spojů pomocí elektronové mikroskopie.

Experimental and Numerical Analysis of Melting and Solidification of SnAgCu Joints

  • DOI: 10.1109/TCPMT.2016.2593709
  • Odkaz: https://doi.org/10.1109/TCPMT.2016.2593709
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    One of the most vulnerable components of electronic circuits is the solder joints. The most common technique of soldering used in electronics is the reflow soldering. During the soldering process, different issues may occur leading to the inception of some defects (tombstone effect, flux spattering, etc.). To avoid these defects, it is mandatory to follow the parameter values of the reflow process, especially temperature values. In this paper, the temperature distribution for three types of samples (two interconnected soldering pads–without solder, with solder on one pad, and with solder on both pads) during the reflow soldering process, calculated with Comsol Multiphysics software (heat transfer 3-D module) is presented. The calculated values are then compared to the ones obtained by experiments in order to verify the accuracy of the numerical model. To carry out the computations, the latent heat of melting/solidification and the variation with the temperature of the solder parameters were considered. The results show that there is a good correlation between the measured and calculated values, the differences (for all types of samples) being lower than ±3 °C.

Experimental study of the influence of the temperature profile on the BGA soldering

  • DOI: 10.1109/ISSE.2016.7563190
  • Odkaz: https://doi.org/10.1109/ISSE.2016.7563190
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    One of the most favour components, which are mounted on the printed circuit board (PCB), is Ball Grid Array (BGA) due to higher integration. On the other hand BGAs are components which are the most problematic from point of solder interconnection reliability. The aim of this work was to make experimental study of the influence of the temperature profile on the BGA soldering during its reworks on electronic equipments from point of observing the distance between the PCB and BGA package. Five temperature profiles were used with following maximum temperature in peak 239 °C, 246 °C, 253 °C, 255 °C and 259 °C. X-ray diagnostic of the distances between the BGA package and PCB were used with the inspection angle 45°. Three BGAs were soldered and inspected for each temperature profile. The issues were found only in case when was used the temperature profile with highest maximum temperature.

Flux effect on void quantity and size in soldered joints

  • DOI: 10.1016/j.microrel.2016.03.009
  • Odkaz: https://doi.org/10.1016/j.microrel.2016.03.009
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article is focused on both macro and microvoids in soldered joints and the use of additional flux to reduce their frequency and minimize their negative effect on the soldered joint reliability. In total five fluxes were used, three were gel based (NC559, MTV-125R, TSF-6516) and two of them were liquid based (Topnik G-5, JBC FL-15). They were used within two solder pastes, both lead and lead-free. The reflow process was identical for all of the combinations and was within the range of manufacturer recommended profiles. The amount of voids was evaluated using X-ray analysis. It was found that the use of increased amount of proper flux, specifically flux with higher activity, in the solder paste may significantly lower the void occurrence.

How to rework underfilled BGA

  • Pracoviště: Katedra elektrotechnologie, Katedra telekomunikační techniky
  • Anotace:
    A Ball Grid Array (BGA) component has become one of the most popular packaging alternatives for high density integrated electronics devices. BGA packages become smaller and electrical equipment has become lighter, therefore such equipment is more sensitive to mechanical stress. Therefore the underfill of the chips is used to improve the lifetime and reliability of electronic equipment. On the other hand there are issues with removing of the underfilled component from the printed circuit board (PCB) without damaging the PCB together with soldering pads. The goal of this article is to present the rework possibility of underfilled components, when a very fine milling machine was developed for the components rework purposes in LVR at CTU in Prague.

Influence of latent heat on the shape of temperature profile for different types of solder alloys

  • DOI: 10.1109/ISSE.2016.7563191
  • Odkaz: https://doi.org/10.1109/ISSE.2016.7563191
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Temperature profile is a very important parameter which has a high impact on reliability issues in electronic assembly manufacturing. The wrong shape of temperature profile (temperature/cooling gradients, maximum temperature, preheat together with flux activation) can lead to issues like flux/solder spattering, pad cratering, unwetting, excessive interrmetallic growth, tombstone effect shrinkage etc. This article deals with influence of latent heat on the shape of temperature profile, which starts to be more attractive due to higher integrity of electronics equipment. The experiments were based of two lead-free solder alloys (Sn96.5Ag3.5, Sn96.5Ag3Cu0.5), which were remelted on the copper pads in continual convection furnace. The temperature profile, were measured directly under the copper pads. Results shows, that the measured temperature profiles under soldering pads differs against the temperature profile which were measured on the PCB. Additionally the temperature profiles which were measured under soldering pads differ according to used solder alloys as well.

Influence of latent heat released from solder joints on the reflow temperature profile

  • DOI: 10.1007/s10854-015-3787-4
  • Odkaz: https://doi.org/10.1007/s10854-015-3787-4
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The reflow process of SAC305 solder paste was investigated by differential scanning calorimetry (DSC) and measurement of the temperature profiles in a real continual convection reflow furnace. Melting and solidification processes of two solder joints were investigated by both methods to determine the influence of latent heat on the surrounding temperature. While one peak was present during melting in DSC, two peaks were present during solidification of two joints connected by a resistor. The released latent heat from one joint increased the temperature of the surroundings and delayed the solidification process of the second joint. Analysis of the temperature profiles obtained during the reflow processes in a real furnace shows that latent heat influences the surrounding temperature not only during the phase transformation, but also during the whole following passage of the sample in the furnace. The maximum temperature increase of the joint is substantial: 25 mg of the solder paste increases the joint temperature by about 15 °C. When two joints are placed on the sample the temperature increase is close to 20 °C.

INFLUENCE OF REFLOW TEMPERETURE PROFILE ON THE MECHANICAL PROPERTIES OF SOLDER JOINTS

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    A temperature profile has an impact on the final quality of the solder joints. It is important from the perspective of proper reflow of the solder alloy, the correct activation of the flux and not exceeding the maximum recommended temperature resistance of the components and PCB. Additionally the temperature profile has a significant influence on the formation of intermetallic compounds. The thickness of intermetalic layers depends on the heating factor – amount of heat after the moment when the solder alloy is already in the liquid state. This article compares mechanical properties of two solder pastes based on SnCu and SnBi regarding to the different temperature profiles. The passivated copper and ENIG were used as surface finishes of soldering pads. Comparison of mechanical properties was based on the shear test respectively on the pull-off force. The results shows that the shape of temperature profile, respectively the heating factor has the influence on the mechanical maximum pull-off force and thus on the mechanical properties of solder joints.

Problem with no-clean flux spattering on in-circuit testing pads diagnosed by EDS analysis

  • DOI: 10.1016/j.microrel.2015.10.020
  • Odkaz: https://doi.org/10.1016/j.microrel.2015.10.020
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Surface Mount Technology (SMT) assembly often faces the issue of residues on In Circuit Testing (ICT) pads. These residues may have non-conductive character and therefore in-circuit test may mark tested product as failed though they would have worked normally. Since it is not possible to export such marked products, the total production quality decreases. In this work, we analyze the real manufacturing problem using Energy Dispersive Spectroscopy (EDS) analysis of the stains with the aim to find the possible source of residues that appear on the testing pads during the mass electronic assembly or during Printed Circuit Board (PCB) production. Analysis of potential source of residues together with its diagnostic and confirmation of its source is presented in this work.

Qualification processes during flux and solder paste evaluation

  • Autoři: Umlauf, J., prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: Proceedings of the International Spring Seminar on Electronics Technology. New York: IEEE Press, 2016. pp. 218-221. ISSN 2161-2536. ISBN 978-1-5090-1389-0.
  • Rok: 2016
  • DOI: 10.1109/ISSE.2016.7563192
  • Odkaz: https://doi.org/10.1109/ISSE.2016.7563192
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This paper deals with topic of testing the utmost important consumables at electronic industry that can be easily overlooked. The flux and solder paste has huge impact on final quality of electronic device and therefore picking the correct material and product from quality and price perspective is the key. For technical verification knowledge of process is critical in order to design best qualification matrix. Long list with every single possible testing and fail opportunity would give precise result, but would not be cost effective and also necessary time would be too long, making it reasonable only for big automotive industry. In this paper basic guideline will be given to the reader.

Temperature distribution during the phase change in the volume of the solder alloy

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Solder is usually an alloy of two and more metals. Very often is used tin, lead, copper, silver, bismuth, nickel, etc. for its production. If the alloy is exposed to a sufficiently high temperature, it is induced phase change from solid to liquid phase for it. Phase is changed again from liquid to solid during cooling substance. At this point, the substance generates a latent heat that is manifests differently for each alloy. Each component contributes its thermal and conductivity parameters into the overall properties of the alloy. The result determines quantity of the generated latent heat. And by final amount of the temperature acts on their surroundings. There have been several experimental measurements for determining of decomposition of temperature in a volume of electrically conductive solder joints during a phase change (from liquid to solidstate). Measurements were carried out on the reference alloy Sn-Pb (eutectic) and three lead-free solder alloys.

Teplotní profil - chyby při procesu pájení přetavením

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: SMT - info 10/16 Bulletin anotací, Pájení a tepelné procesy, čištění DPS, novinky v mikroelektronice, vady pájeného spoje. Brno: NOVPRESS, 2016. pp. 9-16. ISSN 1211-6947.
  • Rok: 2016
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Příspěvek se zabývá vybranými chybami (tombstone efekt, warpage efekt, pad cratering), které se mohou vyskytnout při pájení přetavením.

Whisker growth and its dependence on substrate type and applied stress

  • DOI: 10.1109/ISSE.2016.7563202
  • Odkaz: https://doi.org/10.1109/ISSE.2016.7563202
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article deals with influence of long term mechanical and temperature stress on whisker growth. The experiments were conducted on three different surfaces. FR4 substrate was having copper, gold and HAL surface finish. Copper and gold surface finish was provided with thin layer of solder. Altogether, three solders (Sn63%Pb37%, Sn99%Cu1% and Sn97%Cu3%) were used. The samples were exposed to long term stress. The aging lasted 6500 hours and the temperature was either laboratory for the first batch or elevated (50 °C) for the second batch. The whisker growth was not observed on samples where the solder alloy was deposited in a thick layer, not even after exposure to elevated temperature or bolt induced compressive stress. The highest amount of tin whiskers was observed on a sample with copper surface finish and solder with high tin content, specifically Sn99%Cu1% solder. The presence of lead in the solder hindered the whisker growth. The length of the whiskers varied from tens to hundreds of micrometers. The whisker observation and measurement was conducted using Olympus SZX8 microscope.

Comparison of shear strength of soldered SMD resistors for various solder alloys

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Ing. David Bušek, Ph.D., Beran, T., Rudajevová, A.
  • Publikace: 38th International Spring Seminar on Electronics Technology (ISSE 2015). New York: Institute of Electrical and Electronics Engineers, 2015. pp. 237-240. ISBN 978-1-4799-8860-0.
  • Rok: 2015
  • DOI: 10.1109/ISSE.2015.7247997
  • Odkaz: https://doi.org/10.1109/ISSE.2015.7247997
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Mechanical stability of solder joints has influence on total reliability of electronic products. Mechanical stress affect on properties of solder joints during function, transport and storage of the electronic products. A method which is commonly used in electronic industry to classify the mechanical properties and reliability of solder joints is shear test. This article deals with the comparison of mechanical stability of soldered joints from the point of shear strength of soldered SMD resistors. Three types of solder pastes, one lead Sn62Pb36Ag2 and two lead free Sn42Bi58 and Sn96.5Ag3Cu0.5, were used for solder joint preparation. In addition, influence of solder paste amount on shear strength of soldered SMD component, were compared. The type of solder paste and its applied amount together with the temperature profile are interesting parameters from point of economic aspects, especially in case of mass production, where it is possible to achieve considerable savings. The results shows, that the amount of solder paste has influence on the share strength of solder joins. The best results, highest share strength, have been achieved for Sn96.5Ag3Cu0.5 solder paste.

Determination of BGA solder joint detachment cause - warpage effect

  • DOI: 10.1109/ISSE.2015.7248011
  • Odkaz: https://doi.org/10.1109/ISSE.2015.7248011
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Many aspects such as different materials used during the electronic assembly, increasingly finer dimensions of components, different processes and their settings have an influence on reliability of electronics products. This article deals with BGA assembly, specifically the determination of BGA solder joint detachment cause - with a warpage effect. Samples for diagnostic were obtained from manufacturer, who already pointed to the probable problematic location (BGA component) by electric in-circuit test. Cross-section of BGA assembly was made and an open joint - thin longitudinal gap between BGA component and solder joints connection was observed. The task was to identify a cause that produced axial detachment of BGA solder ball from component pads. The use of Scanning Electron Microscopy (SEM) determined that detachment was caused by a warpage effect.

Influence fo Combined Ageing on Resistance and Noise of Electrically Conductive Adhesive Joints

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Four types of electrically conductive adhesives were used for adhsive assembly of resistors with "zero" resistance on the test PCB and the resistance and noise of adhesive joints were measured. Then the samples were aged at the 80 oC/80 % RH for 1000 hours and the electrical parameters were measured for 100, 300, 500, 750 and 1000 hours and their percentage changes were examined. It was found that the sensitivity of 1/f noise to changes of adhesive joints caused by climatic ageing is comparable with the sensitivity of joints resistances.

Surface finish influence on PCB contamination by flux spattering effect

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Ing. David Bušek, Ph.D., Slavata, M., Rudajevová, A.
  • Publikace: 38th International Spring Seminar on Electronics Technology (ISSE 2015). New York: Institute of Electrical and Electronics Engineers, 2015. p. 241-244. ISBN 978-1-4799-8860-0.
  • Rok: 2015
  • DOI: 10.1109/ISSE.2015.7247998
  • Odkaz: https://doi.org/10.1109/ISSE.2015.7247998
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Flux spattering effect can appear during the manufacturing assembly process, especially during reflow process, when the solder paste, which contains flux, is heated and the flux is spattered and contaminate surroundings. This effect mostly happened due to moisture absorption by the solder paste or due to improperly temperature profile settings during the reflow process. Spattered residues of flux have a non-conductive character and therefore it caused a problem in quality testing of the product, especially when a spot of flux reside appear on the PCB testing pad than the in-circuit test marked tested product as the bad one even though that it is a good one. This article deals with influence of surface finishes on flux spattering effect. Two solder pastes (Sn95.75Ag0.75Cu3.5 and Sn96.5Ag0.5Cu3 contains flux type ROL0) and four types of surface finishes (passivated cooper, hot air leveling, immersion tin, ENIG) were used in our experimental study.

Temperature distribution in solder joints during melting and solidification

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Stancu, C., Notingher, P.V., doc. Ing. Pavel Mach, CSc.,
  • Publikace: 2015 9th International Symposium on Advanced Topics in Electrical Engineering (ATEE 2015). New York: Institute of Electrical and Electronics Engineers, 2015. pp. 500-506. ISBN 978-1-4799-7514-3.
  • Rok: 2015
  • DOI: 10.1109/ATEE.2015.7133853
  • Odkaz: https://doi.org/10.1109/ATEE.2015.7133853
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The most vulnerable components of electronic circuits (PCA - Printed Circuit Assembly) are the solder joints. During the soldering process different anomalies may occur (changes in the reflow temperature profile, different cooling rates) leading to the inception of some defects, as excessive voids inside the solder, brittle phase formation, concentration gradients of elements or metallurgical composition etc. To avoid this, it is mandatory to follow the parameter values of the reflow process (speed, temperature values etc.). Temperature computing model for two PCA samples during the reflow soldering process, by using Comsol Multiphysics software (heat transfer 3 D module) is presented in this paper. PCA samples with and without resistor contains substrate with two soldering pads together with lead free solder. To carry out the computations, the latent heat of fusion/solidification and the variation with the temperature of the alloy parameters were considered. The results show that the presence of the resistor leads to the decrease of the temperature in the alloy during melting and its increase during solidification.

Vybrané defekty pájených spojů a možný způsob opravy čipů fixovaných lepením

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: Bulletin anotací - Pájení a tepelné procesy, čištění DPS, novinky v mikroelektronice, vady pájeného spoje. Brno: SMT Info, 2015. pp. 4-8. SMT info. ISSN 1211-6947.
  • Rok: 2015
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Příspěvek pojednává o vybraných vadách pájených spojů, jako například problém s nesmáčivou maskou, deformace kuliček u čipu BGA, deformacím díky rozdílnému koeficientu teplotní roztažnosti, head-in-pillow defektu a možnému způsobu opravy podlepených čipů na desce plošného spoje.

Aging Analysis of Metalized Film Capacitors

  • DOI: 10.1109/MECHATRONIKA.2014.7018336
  • Odkaz: https://doi.org/10.1109/MECHATRONIKA.2014.7018336
  • Pracoviště: Katedra elektrotechnologie, Katedra telekomunikační techniky
  • Anotace:
    This paper summarizes the results of metalized film capacitor analysis made on capacitors of different manufacturers and types. The capacitors were operated for about 12 years in a power supply and served as a reactance to reduce the supply voltage without losing active energy. The capacitors were long stressed by continuous presence of voltage and current pulses. The measured results are reviewed and the causes of excessive aging of capacitors, including photographs and X-ray analysis of defects are discussed.

Aspekty ultrazvukového pájení

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Starý, J.
  • Publikace: Bulletin anotací - Pájení a tepelné procesy, čištění DPS, novinky v mikroelektronice, vady pájeného spoje. Brno: SMT Info, 2014. pp. 41-42. ISSN 1211-6947.
  • Rok: 2014
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Příspěvek pojednáva o ultrazvukovém pájeni a jeho rozdílech oproti konvenčnímu pájení

Measurements of solder paste viscosity during its tempering and aging

  • DOI: 10.1109/ISSE.2014.6887590
  • Odkaz: https://doi.org/10.1109/ISSE.2014.6887590
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Solder paste printing is one of the most important steps in the surface mount technology, which has high influence on the resulting quality of solder joints. To achieve a good joint quality, the solder paste should have specific properties like adhesion, viscosity, size of the solder alloy particles, amount of flux etc. This paper is focused on the measurement of the solder paste viscosity during its tempering and aging with possibility of regeneration of solder paste properties by jelly flux. Three types of solder pastes were used in the experiment: Sn95.5Ag4Cu0.5, Sn96.5Ag3Cu0.5 and Sn62Pb36Ag2. Viscosity of solder paste is measured from storing temperature to the ambient temperature. Aging of solder pastes is made in ambient atmosphere. Regeneration of solder paste properties after aging was done by adding of jelly flux Amtech 4300/LF-4300-TF. The viscosity of pure solder paste before aging, pure solder paste after aging and solder paste after aging regenerated by jelly flux was measured by rotation viscometer Brookfield Synchroelectric Viscometer, model HBT. The article describes if the addition of jelly flux to the aged solder pastes regenerates their properties.

Study of influence of thermal capacity and flux activity on the solderability

  • DOI: 10.1109/ISSE.2014.6887589
  • Odkaz: https://doi.org/10.1109/ISSE.2014.6887589
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    During the surface mount technological process the assembled PCB is exposed to heat when molten solder alloy wets the surfaces and creates future solder joints. The PCB with all components should ideally be exposed to the same temperature profile during the soldering process. The temperatures differ throughout the PCB due to different thermal capacities of used materials and components even though the temperature profile is stable. The aim of the study was to assess the solderability of the copper material with different thermal capacity and to consider the effect of different types of fluxes. The measurement was done by wetting balance method, where the wetting force is measured as a function of time during which the test specimen is immersed into, remains immersed and then it is pulled out from the solder bath. In our experiments we used copper wire of four different diameters (0.7 mm, 1 mm, 1.5 mm), three types of solders - one lead (Sn63Pb37) and two lead free (Sn99Cu1, Sn97Cu3) solders and three types of fluxes.

Study of Undercooling and Recalescence During Solidification of Sn 62.5 Pb 36.5 Ag 1 and Sn 96.5 Ag 3 Cu 0.5 Solders in Real Electronic Joints

  • DOI: 10.1007/s11664-014-3121-6
  • Odkaz: https://doi.org/10.1007/s11664-014-3121-6
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Undercooling and recalescence were studied using the differential scanning calorimetry (DSC) method on real electronic systems. Two solder pastes, Sn62.5Pb36.5Ag1 a Sn96.5Ag3Cu0.5, were used for preparation of electronic joints. Various combinations of these solders and soldering pads with different surface finishes such as Cu, Cu-Ni-Au, Cu-Sn, and Cu-Sn99Cu1 were used.

Whiskers Growth on Thick Tin Layers and Various Types of Surfaces

  • DOI: 10.1109/ISSE.2014.6887591
  • Odkaz: https://doi.org/10.1109/ISSE.2014.6887591
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The transition from a highly widespread lead solders to lead-free solder alloy types meant many changes in the electrical industry. This transition has brought many technological phenomena that deserve our attention and they have to be still addressed in order to improve the quality and reliability of manufacturing printed circuit boards. One of them is the presence of small crystalline formations on the surfaces of tin and some tin alloys which are called whiskers. This article focuses on the influence of the used electrical materials and their surface treatments on the growth of tin whiskers. For our experiment were selected two lead-free solders with a high percentage representation of tin, by which are Sn95,5Ag3,8Cu0,7 (SAC 387) and Sn99Cu1. Solders were plated in a thick layer on the three types of metal substrates with various surface finishes. For this experiment was chosen copper, brass and phosphor bronze. The created samples were exposed to static mechanical stresses of compressive force under the action of permanent constant temperature at 50 degrees of Celsius.

Effect of reflow technology and surface finishes of PCB on solder spreading

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Vávra, J., Rudajevová, A.
  • Publikace: Proceedings of the International Spring Seminar on Electronic Technology. New York: IEEE, 2013. pp. 136-139. ISSN 2161-2528. ISBN 9781479900367.
  • Rok: 2013
  • DOI: 10.1109/ISSE.2013.6648230
  • Odkaz: https://doi.org/10.1109/ISSE.2013.6648230
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    A key process in surface mount technology is soldering, when a metallurgical joint is formed between the molten solder and metal surfaces. Solders in molten state have to show good spreading action together with good wetting of substrate. Each solder has a different degree of spreading on the metal surface. Degree of spreading mainly depends on combination of flux, solder alloy, soldered substrate. This study is focused to investigate effect of reflow technology and PCBs surface finishes on spreading of molten solders.

Influence of Humidity on Voids Formation inside the Solder Joint

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Vlach, J., Brejcha, M., Hájková, L., Žák, P., Pospíšil, L.
  • Publikace: Advanced Science, Engineering and Medicine. 2013,(5), 543-547. ISSN 2164-6627.
  • Rok: 2013
  • DOI: 10.1166/asem.2013.1321
  • Odkaz: https://doi.org/10.1166/asem.2013.1321
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Void is defined such as blow hole in the solder joint. Voids may degrade the mechanical and conductive properties of the solder joint and thus decrease the reliability. Article deals with influence of humidity on voids formation inside the solder joint structure. Experimental part was carried on testing samples, where we used three types of solder pastes (Sn62Pb36Ag2, Sn96.5Ag3Cu0.5 and Sn95.5Ag4Cu0.5), three types of reflow technology (hot air, vapor phase and infra radiation reflow technology) and three types of humidity environments. The inspection was made on X-ray and following diagnostic was made by image analysis with special software.

Influence of type of reflow technology and type of surface finish on tomb stone effect

  • DOI: 10.1109/ISSE.2013.6648229
  • Odkaz: https://doi.org/10.1109/ISSE.2013.6648229
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Surface mount technology has many problems during production. One of them is a problem called tombstone effect. Tombstone effect is a well known phenomenon, when one end of the component (commonly small passive devices such as resistor or capacitor), rises up out of the solder pad and breaks conductive contact. This article focus on the problem with tombstone effect, in concrete in this article we studied the influence of type of reflow technology and type of surface finish on tomb stone effect. In our experiments three types of reflow technologies, three sizes of SMD components, one type of solder paste and three types of surface finishes were used.

MEASUREMENT OF SOLDER ALLOYS SOLDERABILITY ON COPPER SAMPLES WITH DIFFERENT THERMAL CAPACITY

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Solderability is an essential characteristic of soldering system in electronics industry. Molten solder must show good solderability, on the substrate surface to ensure a good quality of solder joints. Solderability degree depends on many factors such as type of solder alloy together with type of flux and material substrate, type of atmosphere (ambient, inert – nitrogen), temperature of solder alloy etc. In our article we focus on dependence of solder alloys solderability on different thermal capacity. For measurement we used a wetting balance method. Wetting balance method is able to assess qualitatively the wetting of liquids (molten solders) on various substrates. Method measures wetting force during the test specimen is immersed into the liquid (into the molten solder bath). Material base of our experiments was carried on three types of solder alloys (Sn99Cu1, Sn95.5Ag3Cu0.7 and Sn63Pb37), three different thermal capacities of the samples. Different thermal capacity of the samples is given by different diameter of the samples, when we used copper wire with diameters 0.3 mm, 0.4 mm and 0.7 mm.

Možnosti využití RTG a CT diagnostiky (ne)jen v elektrotechnice - 4. část

Comparison of commonly used fluxes aggression on copper surface

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Náhlík, V.
  • Publikace: 35th International Spring Seminar on Electronics Technology. Wien: Technische Universität, 2012. pp. 193-196. ISSN 2161-2528. ISBN 978-1-4673-2240-9.
  • Rok: 2012
  • DOI: 10.1109/ISSE.2012.6273137
  • Odkaz: https://doi.org/10.1109/ISSE.2012.6273137
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article deals with observation of commonly used fluxes aggression on copper surface in electronics assembly during the reflow process. Ten types of fluxes were compared in our experiment. Measurement was carried on glass samples with copper vapor deposition. Determination of flux aggression on copper surface was based on the measurement of absorption of light on spectrophotometer.

Degradation of Soldered Joints Made of Lead Free Alloys and its Influence on Mechanical Properties

  • Autoři: Podzemský, J., Urbánek, J., prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: Proceedings of Electronic Devices and Systems EDS 2012. Brno: VUT v Brně, FEKT, 2012. pp. 196-201. ISBN 978-80-214-4539-0.
  • Rok: 2012
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The paper presents results of monitoring internal structure of soldered joints, its degradation during elevated temperature treatment (150 °C, up to 3000 hrs.) and influence of those factors on shear strength of the joints. Internal structure of solder joints made of new lead free alloys Sn-0,7Cu, Sn-3,5Ag and Sn-3,7Ag-0,7Cu was observed immediately after reflow using RT analysis. Changes of internal structures of the joints after the ageing were monitored. The main focus was on the presence of intermetallic compounds (IMC) and their genesis after reflow and temperature treatment. Shear strength of soldered joint was measured and the influence of internal structure was discussed.

Influence of Intermetallic Compounds on RF Resistance of Joints Soldered with Lead Free Alloys

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    During soldering process intermetallic compounds as a reaction between solder and substrate are created. Physical properties of those compounds are different to properties of solder and substrate. The influence of intermetallic compounds (IMC) on radio frequency resistance of soldered joint has been identified. Tested solders were lead free Sn-1Cu, Sn-4Ag and Sn-3.8Ag-0.7Cu and lead containing Sn-37Pb (all in weight percent). Samples were annealed up to 3000 hours at 150 °C to accelerated growing of IMC. Radio frequency measuring method has been developed and is described. Influence of IMC on resistance of joint is growing with growing frequency because IMC with slightly different resistivity to base solder is creating barrier to current. Resistance of joints has been measured up to 3 GHz.

Influence of the thermal history and composition on the melting/solidification process in Sn-Ag-Cu solders

  • DOI: 10.4149/km_2012_5_295
  • Odkaz: https://doi.org/10.4149/km_2012_5_295
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Presented work shows the results of DSC measurement for six Sn based solders. The alloys Sn96Ag4, Sn99Cu1, Sn97Cu3, Sn96.5Ag3Cu0.5, Sn95.5Ag3.8Cu0.7 and Sn63Pb37 were studied in the temperature range from room temperature up to 400 °C. The transformation temperatures for melting as well as for solidification were influenced by the composition and thermal history of the alloys.

Možnosti využití RTG a CT diagnostiky (ne)jen v elektrotechnice - 1. část

Možnosti využití RTG a CT diagnostiky (ne)jen v elektrotechnice - 2. část

  • Pracoviště: Katedra elektrotechnologie, Katedra telekomunikační techniky
  • Anotace:
    Článek navazuje na předchozí kapitolu, zaměřuje se na problematiku nedestruktivního testování pomocí 3D CT technologie. Zmiňuje princip rekonstrukce informací o sledovaném objekt a problematiku artefaktů.

Možnosti využití RTG a CT diagnostiky (ne)jen v elektrotechnice - 3. část

New types of lead-free solders and their properties

  • Autoři: Drápala, J., Petlák, D., Malcharcziková, J., Vodárek, V., Konečná, K., Smetana, B., Zlá, S., Kostiuková, G., Seidlerová, J., Lasek, S., Madaj, M., Kroupa, A., Urbánek, J., prof. Ing. Bc. Karel Dušek, Ph.D., Ing. Josef Sedláček, CSc., Sidorov, V.E.
  • Publikace: METAL 2012 Conference proceedings. Ostrava: Technická universita Ostrava - Vysoká škola báňská, 2012, pp. 1455-1466. ISBN 978-80-87294-31-4.
  • Rok: 2012
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The aim of this work is an experimental study of lead-free solders. Ternary and binary alloys with different ratios of individual elements Ag, Al, Bi, Cu, In, Mg, Sb, Sn and Zn were prepared experimentally. The study of low-fusing solder alloys was performed with the aspect of observing their selected physical, chemical, structural and technological properties. The following characteristics were studied: temperatures and enthalpies of phase transformations (DTA, TG, DSC) of individual solders at the rates of re-heating and cooling of specimens of about 4 °C/min, macro- and micro-structural analysis (optical metallography), micro-hardness, chemical analysis: ICP-AES, optical emission spectrometry (OES), X-ray micro-analysis of individual phases in the structure of solders (WDX, EDX), measurement of density and electrical resistivity of selected solders in dependence on the temperature, test of wettability with or without use of fluxes, measurement of corrosion properties.

NEW TYPES OF LEAD-FREE SOLDERS AND THEIR PROPERTIES

  • Autoři: Drápala, J, Malcharcziková, J, Konečná, K, Zlá, S, Seidlerová, J, Madaj, M, Urbánek, J., Ing. Josef Sedláček, CSc., Petlák, D, Vodárek, V, Smetana, B, Kostiuková, B, Lasek, S, Kroupa, A, prof. Ing. Bc. Karel Dušek, Ph.D., Sidorov, V
  • Publikace: NANOCON 2012. Ostrava: Tanger, 2012. ISBN 978-80-87294-32-1.
  • Rok: 2012
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The aim of this work is an experimental study of lead-free solders. Ternary and binary alloys with different ratios of individual elements Ag, Al, Bi, Cu, In, Mg, Sb, Sn and Zn were prepared experimentally. The study of low-fusing solder alloys was performed with the aspect of observing their selected physical, chemical, structural and technological properties.

Posouzení vhodnosti použití excimerového laseru k léčení onychomykózy

  • Autoři: Kymplová, J., Urzová, J., Mikšovský, J., prof. Ing. Bc. Karel Dušek, Ph.D., Bauerová, L.
  • Publikace: Lékař a technika. 2012, 2012(1), 16-21. ISSN 0301-5491.
  • Rok: 2012
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Posouzení vhodnosti použití excimerového laseru k léčení onychomykózy. Byly testovány účinky kratkých UV laserových pulzů na různé typy plísní a tkání.

Risk analysis of reflow technologies in electronics assembly

  • Autoři: Jirsa, J., prof. Ing. Bc. Karel Dušek, Ph.D., Černek, P.
  • Publikace: 35th International Spring Seminar on Electronics Technology. Wien: Technische Universität, 2012. pp. 178-182. ISSN 2161-2528. ISBN 978-1-4673-2240-9.
  • Rok: 2012
  • DOI: 10.1109/ISSE.2012.6273134
  • Odkaz: https://doi.org/10.1109/ISSE.2012.6273134
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The goal of this article is to present and remind some significant hazards of three basic reflow technologies - vapor phase soldering, hot air soldering and infrared technology. After all we try to highlight risks and we present concrete problems for each reflow technology.

Solderability and aggression comparison of commonly used fluxes

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article deals with solderability and aggression comparison of several types of fluxes. In our experiments we compare four fluxes (flux R, flux F 1, flux for nickel, and flux for aluminum). For solderability measurement we used wetting balance method. The flux aggression against copper layer was measured on spectrophotometer after the reflow process and it was determined by the measurement of light absorption on spectrophotometer.

Study of the components self-alignment in surface mount technology

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Novák, M., Rudajevová, A.
  • Publikace: 35th International Spring Seminar on Electronics Technology. Wien: Technische Universität, 2012. p. 197-200. ISSN 2161-2528. ISBN 978-1-4673-2240-9.
  • Rok: 2012
  • DOI: 10.1109/ISSE.2012.6273138
  • Odkaz: https://doi.org/10.1109/ISSE.2012.6273138
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article deals with study of SMD components self-alignment in surface mount technology. In this article, the component self-alignment with regard to different types of solders, different types of reflow technology, different solder paste volume and different component placement angles was observed.

Vliv mechanického namáhaní pájených spojů u elektrických zařízení

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Článek se zabývá problematikou vlivu mechanického stresu na pájené spoje, respektive sledováním změny elektrických parametrů pájených spojů z hlediska mechanického namáhání.

Bezolovnaté Pájky Teoretické a Experimentální Studium Fázových Rovnovah a Vlastností Nových Typů Pájek

  • Autoři: Drápala, J., Kursa, M., Kubíček, P., Vodárek, V., Seidlerová, J., Losertová, M., Lasek, S., Dudek, R., Morávková, Z., Vrbický, J., Malcharcziková, J., Burkovič, R., Smetana, B., Zlá, S., Konečná, K., Petlák, D., Kostiuková, G., Urbánek, J., Kroupa, A., Ing. Josef Sedláček, CSc., prof. Ing. Bc. Karel Dušek, Ph.D., Rudajevová, A., Sidorov, V. E.
  • Publikace: Ostrava: VŠB - Technická univerzita Ostrava, 2011. ISBN 978-80-248-2495-6.
  • Rok: 2011
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Monografie podává ucelený přehled o výsledcích studia fázových rovnovah materiálů pájek určených pro vysokoteplotní aplikace. Monografie rozšiřuje experimentální a teoretické poznatky o materiálech vhodných zejména pro bezolovnaté pájky pro aplikace za zvýšených teplot.

Device for Mechanical Bending of Assembled Printed Circuit Boards

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Gřunděl, J.
  • Publikace: Electronic Devices and Systems, IMAPS CS International Conference 2011 Proceedings. Brno: VUT v Brně, FEKT, 2011. pp. 25-28. ISBN 978-80-214-4303-7.
  • Rok: 2011
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Article deals with design, construction and usage of a device for mechanic bending of assembled printed circuits boards. Device is designed to test the mechanical reliability of SMD components connection on PCB. Device is specifically focused on mechanical tests of solder joints.

Diagnostické vybavení laboratoří LVR na FEL ČVUT v Praze

  • Pracoviště: Katedra elektrotechnologie, Katedra teorie obvodů
  • Anotace:
    Článek pojednáva o diagnostickém vybavení laboratoří LVR na FEL ČVUT. V článku je popsána vlastni technologie spolu s charakteristikou vlastniho diagnostického vybavení.

Image analysis of lead free solders

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Article deals with actual problem of lead free soldering and solves issue of image analysis of lead free solders and soldering process. For image analysis was used special software - NIS elements. In concrete article deals with image analysis of spread factor, observation of creation and growth of tin whiskers from surface finishes, analysis of manufacturing technologies (vapor soldering, hot air soldering) of soldered joints, cross sections of soldered and adhesive joints etc.

Influence of different surface finishes of PCB on the solder spread

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Novák, M., Rudajevová, A.
  • Publikace: 34th International Spring Seminar on Electronics Technology. Košice: Technical University of Košice, 2011. pp. 192-195. ISBN 978-1-4577-2111-3.
  • Rok: 2011
  • DOI: 10.1109/ISSE.2011.6053576
  • Odkaz: https://doi.org/10.1109/ISSE.2011.6053576
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Monitoring of the solder spread is one of the tools which should be used to solderability and wetability quantification. In this paper we focus on the different solder spread in correlation with different surface finishes of the PCB and different type of reflow process. In our experiment we used three types of solder pastes (one lead Sn62Pb32Ag2 and two lead free Sn95,5Ag4Cu0,5, Sn99,25Cu0,7Ni0,05 solders) and four types of surface finishes of PCB

Obrazová analýza povrchu bezolovnaté povrchové úpravy zaměřená na indikaci cínových whiskerů

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Práce se zabývá sledováním vzniku a růstu cínových whiskerů z bezolovnatých povrchových úprav pájkami Sn-3,8Ag-0,7Cu, Sn-4Ag, Sn-1Cu a olovnaté povrchové úpravě pájkou Sn-37Pb.

Shear Test of Joints Made of Lead-free Solder

  • Autoři: Podzemský, J., Urbánek, J., prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: 34th International Spring Seminar on Electronics Technology. Košice: Technical University of Košice, 2011. pp. 84-88. ISBN 978-1-4577-2111-3.
  • Rok: 2011
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This paper presents results of mechanical testing of soldered joints made of widely used lead free solder and most popular lead containing one. Measured parameter is shear strength. Tested solders were lead-free Sn-3,8Ag-0,7Cu and lead containing Sn-37Pb. With those solders set of SMD resistors was mounted on pads made of copper and copper electrolytic covered with nickel layer. As mechanical ruggedness of soldered joint strongly depends on presence of intermetallics compounds samples were treated to heat 150 °C 250 and 500 hours and shear strength was measured subsequently and values were compared to ones non thermal aged. Thickness of intermetallics compounds and its influence to shear strength was investigated.

Studies of surface mount technology and its risk analysis

  • Autoři: Jirsa, J., prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: 34th International Spring Seminar on Electronics Technology. Košice: Technical University of Košice, 2011. pp. 216-219. ISBN 978-1-4577-2111-3.
  • Rok: 2011
  • DOI: 10.1109/ISSE.2011.6053581
  • Odkaz: https://doi.org/10.1109/ISSE.2011.6053581
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Surface mount technology is commonly used technology in electronics assembly. It is a method where the components are mounted directly onto the surface of printed circuit board. This article deals with risk analysis of surface mount technology in electronics assembly. In this article we try to highlight several problems, which happen in the surface mount technology during the design of electronics circuits and which have the bad influence on the total product quality.

Studium metodiky měření povrchového napětí pájek

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, J.
  • Publikace: Proceedings of the 12th International Scientific Conference Electric Power Engineering 2011. Ostrava: Vysoká škola báňská - Technická univerzita Ostrava, 2011. pp. 1-4. ISBN 978-80-248-2393-5.
  • Rok: 2011
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Článek se zabývá studií měření povrchového napětí pájek. Ve článku jsme se zaměřili na metodu vyhodnocující pájitelnost, známou jako metoda smáčecích vah. Popsali jsem metodologii jak měřit povrchové napětí pájek na meniskografu.

Study of temperature profiles of the infrared continuous furnace

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Váňa, T.
  • Publikace: 34th International Spring Seminar on Electronics Technology. Košice: Technical University of Košice, 2011. pp. 188-191. ISBN 978-1-4577-2111-3.
  • Rok: 2011
  • DOI: 10.1109/ISSE.2011.6053575
  • Odkaz: https://doi.org/10.1109/ISSE.2011.6053575
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This paper deals with temperature profiles and temperature measurements on different experimental samples. Samples were made for illustrating problems that may occur in reflow-soldering technology that used IR emitter as a heat source.

Technologické vybavení laboratoří LVR na FEL ČVUT v Praze

  • Pracoviště: Katedra elektrotechnologie, Katedra teorie obvodů
  • Anotace:
    Článek pojednáva o technologickém vybavení laboratoří LVR na FEL ČVUT. V článku je popsána vlastni technologie spolu s charakteristikou vlastniho technologického vybavení.

Zajímavosti v oblasti osazovacích automatů

Assist Education Tool for Student's Preparation on Practical Laboratory Exercises

  • Autoři: Jirsa, J., prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: 33rd International Spring Seminar on Electronics Technology. New York: IEEE, 2010. pp. 515-517. ISBN 978-1-4244-7849-1.
  • Rok: 2010
  • DOI: 10.1109/ISSE.2010.5547337
  • Odkaz: https://doi.org/10.1109/ISSE.2010.5547337
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The common student's preparation for their practical laboratory exercises consists of reading something about it in literature or on the web page. In better cases some videos or animations about the themes on future laboratory exercises are provided for students. However students of our department can prepare on several subjects with practical laboratory exercises with the help of Adobe Flash animations enriched with real videos. In many animations there is necessary an interactive student assistance. By this way students can interactively simulate the real practical laboratory exercise on which they have to be prepared.

Comparison of Dynamic and Static Mechanical Stress Applied on Soldered Joints

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, M.
  • Publikace: 33rd International Spring Seminar on Electronics Technology. New York: IEEE, 2010. pp. 204-207. ISBN 978-1-4244-7849-1.
  • Rok: 2010
  • DOI: 10.1109/ISSE.2010.5547292
  • Odkaz: https://doi.org/10.1109/ISSE.2010.5547292
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article deals with the mechanical stress of lead and lead free soldered joints. During usage of electrical equipment are found structural changes of soldered joints, which can lead to cracks or failure of the solder joints. In this article, the changes of the electrical resistance of dynamic and static stressed soldered joints (lead Sn62Pb36Ag2 and lead free Sn95,5Ag4Cu0,5) are compared.

Electrically conductive adhesive junction usage for solar cells electrode system

  • Autoři: Macháček, Z., prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: IWTPV'10 Proceedings. Praha: Nakladatelství ČVUT, 2010. pp. 94-97. ISBN 978-80-01-04532-9.
  • Rok: 2010
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article deals with electrically conductive adhesive joints as alternative against soldered joints in the solar cells electrode system.

Evaluation of Tin Whisker Growth

  • Autoři: Podzemský, J., Čopjan, M., prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, J.
  • Publikace: 33rd International Spring Seminar on Electronics Technology. New York: IEEE, 2010. pp. 221-224. ISBN 978-1-4244-7849-1.
  • Rok: 2010

Měření smáčivosti desek plošných spojů s různou povrchovou úpravou

  • Autoři: Novák, M., prof. Ing. Bc. Karel Dušek, Ph.D., Váňa, T.
  • Publikace: Sborník konference ELEN 2010. Praha: ČVUT FEL, Katedra elektroenergetiky, 2010. pp. 1-4. ISBN 978-80-254-8089-2.
  • Rok: 2010
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Tento článek se zabýva měřením smáčivosti materiálů s různou povrchovou úpravou, která se běžně používá jako materiál pajecích plošek u DPS.

Solderability Measurement of Copper with Different Surface Finishes

  • DOI: 10.1109/ISSE.2010.5547267
  • Odkaz: https://doi.org/10.1109/ISSE.2010.5547267
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article deals with solders wettability measurement of materials with different surface finishes, which are commonly used as solder pads on printed circuit board. The measurement was carried out on two type of solders (Sn63Pb37, Sn95,5Ag3,8Cu0,7), two types of fluxes (94-RXZM (IPC-ANCI-J-STD-004 - REL0), 323-ITV (C-ANCI-J-STD-004 - REL1)) and as testing material we used one-side plating PCB (FR4) with four types of surface finishes (pasivated copper, H.A.L, immersion tin, chemical gold plating). For the measurement we have used one of the commonly used wettability evaluation methods - wetting balance (meniscograph) method. We marked the wettability, according to the shape of wetting curve, for each testing combination and sorted them into the table.

Vliv klimatických podmínek a mechanického namáhání na růst cínových whiskerů

  • Autoři: Čopjan, M., Podzemský, J., Urbánek, J., prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: Sborník konference ELEN 2010. Praha: ČVUT FEL, Katedra elektroenergetiky, 2010. pp. 1-5. ISBN 978-80-254-8089-2.
  • Rok: 2010
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Hlavním problém u cínového pokovení je tvorba elektricky vodivých, krystalických struktur cínu známých jako cínové whiskery. Tento článek se zabývá tvorbou whiskeru v závislosti na klimatických podmínkách, mechanickém namáhání a na typu použité pájky.

Electrical Parameters of the Solar Cells Soldered Joints in Comparison to Electrically Conductive Adhesive Joints

  • DOI: 10.4229/24thEUPVSEC2009-4AV.3.83
  • Odkaz: https://doi.org/10.4229/24thEUPVSEC2009-4AV.3.83
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article deals with possibility to use electrically conductive adhesive joints instead of soldered joints in the solar cells electrode system. One of the advantages of the using adhesive joints instead of soldered joints is less mechanical destruction of solar cells during the production. Like a next advantage we should notice on ecological point of view. Therefore in this article will be compared three different types of electrically conductive adhesives against solder. We prepared specific samples for four-point probe method measurement of the electrical resistance between conductive layer and tinned copper ribbon. The samples were temperature stressed and the change of the electrical resistance between the connection of the conductive layer and tinned copper ribbon was observed.

Electrically Conductive Adhesives - Study of Electrical and Mechanical Properties

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Basic characteristics of elekctrically conductive adhesives are presented. Dependence of the resistance of an adhesive joint on the temperature and dependence of nonlinearity on the temperature.

Image Analysis of Solder Spread Factor on Different Material Types

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The spread factor of the solders is one of the tools which should be used to solderability and wetability quantification. Two types of solders (Sn62Pb36Ag2, Sn95,5Ag4Cu0,5) four types of material (lead free H.A.L., passivated copper, immersion tin plating, chemical gold plating) ware used in experiment. The differences between the solder spread factor on the different types of material ware evaluated by image analysis of the spread factor surface.

Influence oh the Temperature Profile on the Mechanical Stressed Soldered Joints

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, M.
  • Publikace: Electronic Devices and Systems, IMAPS CS International Conference 2009 Proceedings. Brno: VUT v Brně, FEI, 2009. pp. 266-270. ISBN 978-80-214-3933-7.
  • Rok: 2009
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    In this article, the changes of the electrical resistance of mechanically stressed soldered joints (lead Sn62Pb36Ag2 and lead free Sn95.5Ag4Cu0.5) against reflow temperature profiles are compared.

New types of lead-free solders on the base of tin and their properties

  • Autoři: Drápala, J., Kozelková, R., Burkovič, R., Smetana, B., Dudek, R., Lasek, S., Urbánek, J., prof. Ing. Bc. Karel Dušek, Ph.D., Hájek, M.
  • Publikace: Kovové materiály. 2009, 47(5), 283-293. ISSN 0023-432X.
  • Rok: 2009
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The aim of the work is an experimental study of binary, trenary and quaternary systems on the base of tin alloys with diferent ratios of individual elements Ag, Cu, In, Sb, Bi, and Sn were prepared experimentally. In addition, 6 alloys of lead-free solders produced commercially (Kovohutě Příbram) were used and the Pb-Sn solder served as a comparative etalon.

Risk Management of Technology of Lead Free Soldering

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Risk management is complex of coordinated and repeating activities to control project with regard to risk. Risk management is concerned to reduce the probability of occurrence of particular risks or decrease its influence on project. This article is focused on possible risks of lead free technology in brief orientation to usability in automotive electronics.

Study of Wettability Measurement of Binary and Ternary Solder Alloys Based on Sn-Zn-Al

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Study of the wettability of the binary and ternary Sn-Zn-Al solder alloys is based on one of the commonly used wettability evaluation methods - wetting balance (meniscograph) method. We have measured a combination of different types of lead-free solders and different types of the testing materials. The measurement was carried out on eight different types of solders (69Sn28Zn3Al, 68Sn32Zn, 84Sn16Zn, 89Sn10Zn1Al, 76Sn21Zn3Al, 21Sn75Zn4Al, 61Sn35Zn4Al, 91Sn9Zn) [wt.%], two types of testing materials (copper, nickel) and two types of fluxes (390-RX-HT, 94-RXZ-M).

Cracks in Soldered Joints Subjected to Mechanical Stress

  • Autoři: Tučan, M., prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, J.
  • Publikace: Electronics Devices and Systems Proceedings. Brno: Vysoké učení technické v Brně, 2008. pp. 275-280. ISBN 978-80-214-3717-3.
  • Rok: 2008
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article delas with image analysis of the soldered joints. resulting Images sowed several differences concerning formation and propagation of cracks in joints that underwent thermal and mechanical stress.

Image analysis of soldered joints subjected to mechanical stress

  • Autoři: Tučan, M., prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, J.
  • Publikace: Applied Electronics 2008. Pilsen: University of West Bohemia, 2008. pp. 223-226. ISBN 978-80-7043-654-7.
  • Rok: 2008
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Image analysis of leadfree soldered joints subjected to mechanical stress and thermal aging.

Influence of Mechanical Stress and Temperature Aging on a Change of Electrical Connection Resistance

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Tučan, M.
  • Publikace: 31st International Spring Seminar on Electronics Technology. New York: IEEE, 2008. p. 41-44. ISBN 978-1-4244-3973-7.
  • Rok: 2008
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Article deals with the mechanical stress and the temperature aging of the lead and lead free soldered joints. Mechanical stress and temperature aging can change electrical properties of the soldered joints, e.g. electrical resistance. In this article, the changes of the electrical resistance of mechanically stressed and temperature aged soldered joints (lead Sn62Pb36Ag2 and lead free Sn95.5Ag4Cu0.5) are compared.

Junction Between Tinned Copper Ribbon and Conductive Layer on a Solar Cell and its Dependence on Interconnection Resistance

  • Autoři: Macháček, Z., prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: 4th International Workshop on Teaching in Photovoltaics. Praha: České vysoké učení technické v Praze, 2008. pp. 87-90. ISBN 978-80-01-04047-8.
  • Rok: 2008
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article discusses the temperature influence on such junction. Specific samples for four-point probe method measurement of the electrical resistance between conductive layer and tinned copper ribbon were prepared.

Methodology of the Lead and Lead Free Solders Surface Tension Measurement

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, J.
  • Publikace: Electronics Devices and Systems Proceedings. Brno: Vysoké učení technické v Brně, 2008. pp. 265-268. ISBN 978-80-214-3717-3.
  • Rok: 2008
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article deals with comparism of the special and common methodology of the lead and lead free solders surface tension measurement.

Surface Tension Measurement of the Solders by Non-wetting Specimen

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, J.
  • Publikace: 31st International Spring Seminar on Electronics Technology. New York: IEEE, 2008. p. 356-359. ISBN 978-1-4244-3973-7.
  • Rok: 2008
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article deals with the measurement of the surface tension of ninth different types of solders by non-wetting specimen.

Theory for Prediction of Electrical Contact Resistance of ACA Considering Electron Tunneling

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This paper describes few sample models for prediction of electrical contact resistance in ACA interconnects.

Utilization of Electrically Conductive Adhesives in Solar Cell Interconnections

  • Autoři: Duraj, A.D., prof. Ing. Bc. Karel Dušek, Ph.D., Macháček, Z.
  • Publikace: 31st International Spring Seminar on Electronics Technology. New York: IEEE, 2008. pp. 38-39. ISBN 978-1-4244-3973-7.
  • Rok: 2008
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This paper is focused on utilization of electrically conductive adhesives (ECAs) for solar cell intreconnections in place of soldering.

Influence of Inert Atmosphere on the Mechanical Stressed Soldered Joints

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Tučan, M., Urbánek, J.
  • Publikace: Electronic Devices and Systems - IMAPS CS International Conference 2007. Brno: Vysoké učení technické v Brně, 2007. pp. 280-283. ISBN 978-80-214-3470-7.
  • Rok: 2007
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    We compare the change of electical resistance of the mechanically stressed soldered joints which ware reflowed in ambient and inert atmosphere.

Influence of Mechanical Stress on Change of Electrical Resistance of Electronic Components Connection

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Tucan, M., Urbánek, J.
  • Publikace: Applied Electronics 2007. Plzeň: Západočeská univerzita v Plzni, 2007. pp. 45-48. ISBN 978-80-7043-537-3.
  • Rok: 2007
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The article compare changes of the electrical resistance mechanically stressed soldered joints lead Sn62Pb36Ag2 and lead free Sn95.5Ag4Cu0.5, Sn96.5Ag3Cu0.5.

Měkké pájení -pájky bez olova

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, J.
  • Publikace: Elektrotechnológia '07. Košice: TU Košice, FEI, 2007. pp. 128-129. ISBN 978-80-8073-834-1.
  • Rok: 2007
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Nalezení přijatelných bezolovnatých pájek namísto tradičních cín - olovnatých není jednoduchou záležitostí. Bezolovnaté slitiny mají vyšší teplotu přetavení a smáčí kovový povrch mnohem pomaleji, než cín - olovnaté pájky.

Měření pájitelnosti mědi, niklu pro různé druhy pájek a tavidel

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, J., Drápala, J.
  • Publikace: Diagnostika '07. Plzeň: Západočeská univerzita v Plzni, 2007. pp. 221-224. ISBN 978-80-7043-557-1.
  • Rok: 2007
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Pájitelnost definujeme jako schopnost povrchu být rychle a v daném čase na celé ploše smočen pájkou. V našem případě jsme měřili pájitelnost mědi, niklu a mosazi pro vybrané typy olovnatých a bezolovnatých pájek.

The Temperature Influence on the Interconnection Resistance between Conducitve Layer and Tinned Copper Ribbon

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article deals with temperature influence on the interconnection resistance between conductive layer and tinned copper ribbon, which is an important parameter for the efficiency of the solar cells.

Wetting Force Measurement of the Different Types of Solders and Testing Materials

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Wettability of diffeerent types of testing materials has been investigated using meniscograph. Measurement is focused on examination of surface tension of examined material and wettability of a sample under test.

Evaluation of the Surface Tension Values

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, J.
  • Publikace: Advanced Engineering Design AED 2006. Praha: České vysoké učení technické v Praze, 2006. ISBN 80-86059-44-8.
  • Rok: 2006
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The change of the surface tension is related to the change of the wetting force. For our measurement we used one of the solderability evaluation methods known as the wetting balance method, which is used to measure wetting force.

Influence of the Reduced Oxygen Concentration on the Wetting Force

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, J.
  • Publikace: 29th International Spring Seminar on Electronics Technology. New York: IEEE, 2006. pp. 61-64. ISBN 978-1-4244-0550-3.
  • Rok: 2006
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This work is focused on investigation of influence of oxygen concentration on wetting force of tin-lead (Sn63Pb37) and lead-free solders (Sn95,5Ag3,8Cu0,7). Concentration of oxygen is reduced with addition of nitrogen up to concentration 1000 ppm. Wetting force is measured with equipment Meniscograph - solderability tester Mk 6 and digital oscilloscope Agilent.

Measurement of the Solders Surface Tension Values

  • Autoři: Urbánek, J., prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: Thermal, Mechanical and Multi-Physics Simulation and Experiments in Micro-Electronics and Micro-Systems. Milano: IEEE, 2006. p. 337-340. ISBN 1-4244-0275-1.
  • Rok: 2006
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    One of the key parameter of the solderability is the known value of the solders surface tension. Values of surface tension are mainly caused on ambient conditions (solders temperature, ambient or inert atmosphere, different types of composition etc.).

Study of Influence of Working Conditions on Changes of the Surface Tension of a Solders

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Two types of solders, SnPb and SAC, have been investigated from the point of view of a surface tension. Different conditions, such as the solder temperature, contents of oxygen and type of surface have been applied, wettability of the solder has been measured.

Study of Influences on the Changes of the Surface Tension

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The knowledge of actual value of surface tension is important for the understanding to several soldering aspects, such as wetting, joint shape, fluxing action and, particularly, for the quantification of solderability testing.

The Temperature Influence on the Surface Tension of the Lead and Lead Free Solders

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, J.
  • Publikace: Radio-Electronics, Electrical and Power Engineering. Moscow: Moskovskij energeticeskij institut, 2006. pp. 31-32. ISBN 5-87789-022-0.
  • Rok: 2006
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    We have measured influence of the temperature on the wetting force. The change of the wetting force is related to the change of the surface tension.solder.

Contribution to Determination of Solders Surface Tension Values

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, J.
  • Publikace: Applied Electronics 2005 - International Conference Pilsen. Plzeň: Západočeská universita, 2005. pp. 97-100. ISBN 80-7043-369-8.
  • Rok: 2005
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The knowledge of actual value of surface tension is important for the understanding of several soldering aspects, such as wetting, joint shape, fluxing action and particulary, for the quantification of solderability testing.

Evaluation of the Mechanical Stressed Lead and Lead Free Soldered Joints

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Mechanical stress changes electrical properties of the soldered joints, such as electrical resistance. Mechanical stress could cause the occurrence of cracks on the surface of the soldered joints.

Hodnocení kvality pájených spojů pomocí obrazové analýzy

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, J.
  • Publikace: Diagnostika '05. Plzeň: Západočeská univerzita v Plzni, 2005. pp. 263-266. ISBN 80-7043-368-X.
  • Rok: 2005
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Tento članek se zabývá obrazovou analýzou pájených spojů. Obazová analýza pájených spoju je zpusob, kterým lze porovnávat vlastnosti pájených spojů.

Methodology Objective Evaluation of the Quality of Soldered Joints

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, J.
  • Publikace: Proceedings of Workshop 2005 - Part A,B. Praha: České vysoké učení technické v Praze, 2005. pp. 650-651. ISBN 80-01-03201-9.
  • Rok: 2005
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Currently pressure on limitation as well as exclusion of the lead from used materials means searching ecologically, technically and economically acceptable lead free solders.

Image Analysis of the Soldered Joints

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: Applied Electronics 2004. Plzeň: Západočeská univerzita v Plzni, 2004. pp. 36-39. ISBN 80-7043-274-8.
  • Rok: 2004
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Image analysis of the soldered joints is the way how to compare properties of the soldered joints

Influence of Mechanical Stress on Properties of Lead and Lead Free Soldered Joints

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Mechanical stress on solder joints (vibration, shock, cyclic bending, etc.) causes changes in the structure of the solder, which leads to a reduction in mechanical strength. Formed cracks can lead to destruction of joints. Changes on the electrical parameters of joints, mainly by increasing electrical resistance.

Influence of Mechanical Stress on Properties of Lead and Lead Free Soldered Joints

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, J.
  • Publikace: The 11th Electronic Devices and Systems Conference. Brno: VUT v Brně, 2004. pp. 381-384. ISBN 80-214-2701-9.
  • Rok: 2004
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Mechanical tests are mainly used for resistance evaluation of components, parts and whole products against mechanical stress, which is applied on objects during function, transport and storage.

Spoje pájené pájkami s olovem a bez olova

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, J.
  • Publikace: The 11th Electronic Devices and Systems Conference. Brno: VUT v Brně, 2004. pp. 381-384. ISBN 80-214-2701-9.
  • Rok: 2004
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Pájky s olovem a pájky bez olova se od sebe liší nejen složením, ale také svými mechanickými vlastnostmi a strukturou. Mechanické namáhání ovlivňuje elektrické parametry, hlavně elektrický odpor a nelinearitu.

Optimalizace nastavení teplotního profilu pece pro pájení přetavením

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D., Urbánek, J.
  • Publikace: Diagnostika 03. Plzeň: ZČU FE, Odd. elektrotechnologie katedry el. strojů, 2003. pp. 184-187. ISBN 80-7082-952-4.
  • Rok: 2003
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Pájení v průběžné peci vyžaduje správné nastavení časového průběhu teploty, na kterou je ohřátá pájená deska plošných spojů. Základní průběh udává výrobce pájecí pasty. Pájené součástky i deska svojí tepelnou kapacitou skutečný teplotní profil mění.

The Temperature Profile of Continuous Furnace

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Consequent quality soldered connection is given set-up correct temperature profile continuous furnace. The investigation influence using components on temperature profile of continuous furnace DIMA SMRO-0180 is the goal of this paper.

The Temperature Profile of Continuous Furnace Dima SMRO-0180

  • Autoři: prof. Ing. Bc. Karel Dušek, Ph.D.,
  • Publikace: Poster 2003. Praha: České vysoké učení technické v Praze, Fakulta elektrotechnická, 2003. p. PE6. ISSN 0277-786X. ISBN 0-8194-5368-4.
  • Rok: 2003
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The continuous furnace is used for hardening of conductive adhesives and for the recasting of soldering pastes, which are used for the planting of electrically components on the board with the printed wiring. The critical technological parameter for the preparation of the high-quality conductive joints is the temperature profile of the furnace. The exact shape of this temperature profile is given by the type of the applied conductive adhesive or soldering pastes and this profile is recomended by the producer of used connecting materials.

Za stránku zodpovídá: Ing. Mgr. Radovan Suk