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Ing. David Bušek, Ph.D.

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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.

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.

Modelling of thermocouple geometry variations for improved heat transfer monitoring in smart electronic manufacturing environment

  • DOI: 10.1016/j.csite.2022.102001
  • Odkaz: https://doi.org/10.1016/j.csite.2022.102001
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    In this paper, the effect of different thermocouple constructions on the hot spot temperature are investigated with a modelling approach to achieve more precise soldering profile acquisition and failure analysis at different reflow soldering heat transfer methods. The paper focuses on convection-based reflow and condensation based vapour phase soldering processes and related heat transfer coefficients. Different thermocouple constructions were investigated. The parameters include the ASTM-type (K, T, J), the length of uninsulated wire length, the insulation material (PFA, PVC, PTFE, woven glass-fibre), the insulation thickness and the diameter of the hot-spot. The physical dimensions were obtained with optical microscopy for validation. Finite element analysis was performed. After validation, the results show that most parameter and geometry changes - most significantly, the uninsulated wire end - can result in non-negligible timely differences in 100 ms range between different sensors, pointing to the requirement of sorting and pairing in a symmetric measurement environment. The results can be applied in a modern manufacturing environment and in future process modelling and evaluation tasks.

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/).

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.

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%.

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.

Modelling of thermocouple geometry variations for improved heat transfer monitoring in smart electronic manufacturing environment

  • DOI: 10.2139/ssrn.3972769
  • Odkaz: https://doi.org/10.2139/ssrn.3972769
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    In this paper, the effect of different thermocouple constructions are investigated from the aspect of reflow soldering, to achieve more precise soldering profile acquisition and failure analysis at different soldering heat transfer methods. The paper focuses on convection-based reflow and vapour phase soldering processes and related heat transfer coefficients. Different thermocouple constructions were investigated. The parameters involve ASTM-type (K, T, J), length of uninsulated wire length, insulation material (PFA, PVC, PTFE, woven glass-fibre), insulation thickness and dimensions of the hot-spot. The physical dimensions were obtained with optical microscopy for validation. Finite element analysis with multiphysics modelling (convection- and condensation-based heat transfer, and heat conduction in solids) was applied. After validation, the results show that most parameter and geometry changes – most significantly the uninsulated wire end – can result in non-negligible timely differences in 100 ms range between different sensors, pointing to the requirement of sorting and pairing in symmetric measurement environment. The results can be applied in modern manufacturing environment and in future process modelling and evaluation tasks.

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.

Validation of Heat-Level Vapor Phase Soldering Process and Workspace Leakage Detection with Applied Pressure Sensors

  • DOI: 10.3390/app11041755
  • Odkaz: https://doi.org/10.3390/app11041755
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The paper presents the application of pressure sensors and the obtained pressure/height profiles next to the generally used soldering temperature profiles for precise control of heat-level type vapour phase reflow soldering ovens in electronics manufacturing. Electronic manufacturing principles are continuously developing, further improving assembly quality and productivity. There is a continuous need to apply novel and improved methods of process monitoring to provide accurate measurement and control during assembling. In this paper, a new principle for monitoring filmwise condensation-based heat-level-vapour phase soldering (HL-VPS) is presented to improve the process control. The experiment is based on thermocouple sensors in fusion with a sensitive gauge type pressure sensor. The aim is to precisely identify the steps of condensation-based reflow heat transfer process with commercially available components and the mindset of possible retrofitting in the generally used HL-VPS soldering ovens. It was found that the gauge sensor can follow the state of the workspace more precisely as the thermocouples, by monitoring the hydrostatic state of the vapour. The pressure (time) function gives information about the build-up of the vapour column, highlighting four characteristic steps (phases) of the process, meaning: immersion of the sample to be soldered, condensation-based heat transfer, solder-break, and cooling. Combined application with thermocouples enables more precise control, improving soldering quality and can reduce idle time of the oven. In addition, it was showed that the gauge type sensors could highlight any failure in the oven sealing by a sensor signal threshold detection. The original concept of workspace identification also fits the present and future industry 4.0 directives.

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%.

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.

Dendritic Growth at Constant Voltage Between Electrodes Coated by SnBiAg, SAC, SnCu and SnPb Solder

  • Autoři: Ing. David Bušek, 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/ISSE49702.2020.9121013
  • Odkaz: https://doi.org/10.1109/ISSE49702.2020.9121013
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    In this work, dendritic growth between electrodes coated by Sn42Bi57Ag1, SAC 305, Sn99.3Cu0.7 and Sn63Pb37 Solder was studied. The water drop test method with a 0.02‰ concentration of NaCl dissolved in the deionized and purified water was used to support the growth of dendrites on the samples corresponding to the IPC-B-24 standard . The dendritic growth was induced under the constant low voltage DC bias (1.5V) between the electrodes and the results between different alloys were compared. The solder alloys electro-chemical migration resistance was compared with respect to their Tin content, however the low temperature solder paste with 42wt% tin content showed similar results as the solder alloy with 99.3wt% of Tin. The change of surface insulation resistance (SIR) in time during the dendritic growth was observed. The dendrites were subjected to an EDX analysis on the electron microscope and the fern dendrite structure material analysis was conducted.

Effect of different thermocouple constructions on heat-level vapour phase soldering profiles

  • DOI: 10.1108/SSMT-10-2019-0034
  • Odkaz: https://doi.org/10.1108/SSMT-10-2019-0034
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Purpose To improve productivity and reach better quality in assembling, measurements and proper process controlling are a necessary factor. This study aims to focus on the monitoring heat-level-based vapour phase reflow soldering (VPS), where - as it was found - different thermocouple constructions can affect the set parameters of the oven and resulting soldering profiles significantly. Design/methodology/approach The study experiments showed significant alteration of the heating profiles during the process of the reflowing using different construction of k-type thermocouples. In a heat-level-based VPS oven, polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA) gas and water-resistant, fibreglass, thin PFA and ultrathin PFA-covered thermocouples were tested with +/- 1 degrees C precision. The oven parameters were swept according to the heating power; the length of the introduced thermocouple cables was also taken into account. An FR4-based sample PCB was used for monitoring the temperature. Findings According to the results, due to the mass and volume of the thermocouples' wires, different transients were observed on the resulting soldering profiles on the same sample PCB. The thermocouples with lower thermal mass result in faster profiles and significantly different heating factor values compared to the thermocouples that have larger thermal mass. Consequently, the length of the thermocouple wires put in the oven has also considerable effect on the heat transfer of the PCB inside the oven as well. Originality/value The paper shows that the thermocouple construction must be taken into account when setting up a required soldering profile, while the thermal mass of the wires might cause a significant difference in the prediction of the actual and expected soldering temperatures.

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.

Heat transfer aspects of condensation during vapour phase soldering on aligned PCB-based surfaces

  • DOI: 10.1108/SSMT-11-2019-0038
  • Odkaz: https://doi.org/10.1108/SSMT-11-2019-0038
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Purpose: The paper aims to present an investigation on heat transfer in a vapour phase soldering (VPS) oven, focusing on the differences of horizontally and vertically aligned Printed Circuit Board (PCB) surfaces. The investigation can help develop a better understanding of the process and provide information for future modelling of the process. Design/methodology/approach: For the investigations, flame retardant grade 4 (FR4) PCB plates and sealed plate–based boxes were immersed into saturated vapour of an experimental oven. The temperature and resulting heat transfer coefficients were analysed according to the sample boxes and the surface orientations. In addition, the boxes’ vapour consumption was investigated with pressure measurements. Findings: The horizontal top- and bottom-side heating shows very similar results. In addition, the sides of a box were heated in a manner similar to the top and the bottom sides, but there was a slight increase in the heat transfer coefficient because of the vertical wall alignment. The pressure measurements reveal the dynamic changes in vapour after immersion of the boxes. Practical implications: The findings may help to show differences on different surface orientations, pointing to more precise, explicit and multiphysics simulation results. Originality/value: The experiments present an aspect of heat transfer coefficient differences in VPS ovens, also highlighting the effect of initial pressure drop inside the workspace of an oven.

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.

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.

Advances in Pressure Sensing for Vapour Phase Soldering Process Monitoring

  • DOI: 10.1108/SSMT-10-2018-0038
  • Odkaz: https://doi.org/10.1108/SSMT-10-2018-0038
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The purpose of the paper is to improve the control of vapour phase soldering (VPS). To enable better productivity and assembling quality, the industry needs to provide precise control and measurements during assembling. In the paper, a special monitoring method is presented for VPS to enable improved process control and oven state identification.

Advances on high current load effects on lead-free solder joints of SMD chip-size components and BGAs

  • Autoři: Straubinger, D., Geczy, A., Sipos, A., Kiss, A., Ing. David Bušek, Ph.D.,
  • Publikace: Circuit World. 2019, 45(1), 37-44. ISSN 0305-6120.
  • Rok: 2019
  • DOI: 10.1108/CW-11-2018-0088
  • Odkaz: https://doi.org/10.1108/CW-11-2018-0088
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Purpose This paper aims to present a novel approach on investigating critical current densities in the solder joints of chip-size surface-mounted components or device (SMD) components and ball grid array (BGA) lead-free solder joints with the focus of via-in-pad geometries. The investigation involves a numerical approach and a physical validation with selected geometry configurations and high current loads to reveal possible failure sources. The work is a continuation of a previous study. Design/methodology/approach Current density was investigated using finite element modeling on BGA joints. Dummy BGA components, 0402 and 0603 zero ohm jumper resistors, were used, both in daisy chain setups on standard FR4 printed circuit boards (PCBs). Respective physical loading experiments were set to find effects of elevated current density at hot zones of the joints. Cross-section analysis, scanning electron microscopy and shear force tests were used to analyze the joints. Findings The findings reveal alterations in the joints, while the current loading is not directly affecting the structure. The modeling reveals the current density map in the selected formations with increased current crowding zones. Overall, the degradation does not reach the level of electromigration (EM)-induced voiding due to the limiting factor of the FR4 substrate. Originality/value The experiments investigate current density from a novel aspect on frequently used BGA surface mounted components with modeling configurations focusing on possible effects of via-in-pad structure.

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.

Glass transition temperature of nanoparticle-enhanced and environmentally stressed conductive adhesive materials for electronics assembly

  • DOI: 10.1007/s10854-019-00784-5
  • Odkaz: https://doi.org/10.1007/s10854-019-00784-5
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The characterization of glass transition temperature (Tg) was performed for one- and two-component electrically conductive adhesive used in electronic joining technologies. Both adhesives were of the epoxy type with the silver filler. Dynamic mechanical analysis (DMA) was used to measure the Tg. The adhesives were modified with nanoparticles, namely, carbon nanotubes (concentration of 0.5 and 0.8% by weight) and silver nanoballs (2.5% by weight). The values of Tg were determined from the plot of the Tg δ parameter. Two types of environmental stresses were used for climatic aging: 125 °C/56% RH and 85 °C/85% RH. The aging of the samples at 125 °C and 56% RH caused increase Tg for all formulations.

Modelling of temperature distribution along PCB thickness in different substrates during reflow

  • DOI: 10.1108/CW-07-2019-0074
  • Odkaz: https://doi.org/10.1108/CW-07-2019-0074
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Purpose - In this paper, analytical modelling of heat distribution along the thickness of different printed circuit board (PCB) substrates is presented according to the 1 D heat transient conduction problem. This paper aims to reveal differences between the substrates and the geometry configurations and elaborate on further application of explicit modelling.

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.

Improved Contactless Method of IR Reflectance under Grazing Incidence for Measurement of Doping Profiles

  • Autoři: doc. Mgr. Jakub Holovský, Ph.D., Remeš, Z., Franta, D., Conrad, B., Ing. Lucie Landová, Ing. David Bušek, Ph.D., Poruba, A.
  • Publikace: Proceedings of the International Conference of 35th European Photovoltaic Solar Energy Conference and Exhibition. München: WIP Wirtschaft und Infrastruktur GmbH & Co Planungs KG, 2018. p. 278-280. ISSN 2196-100X. ISBN 978-3-936338-50-8.
  • Rok: 2018
  • DOI: 10.4229/35thEUPVSEC20182018-2AO.5.3
  • Odkaz: https://doi.org/10.4229/35thEUPVSEC20182018-2AO.5.3
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    We have elaborated contactless method of measurement and evaluation of doping profiles in silicon polished wafers based on infrared reflectance under high angle of incidence. We have found higher angle of incidence increases sensitivity, however approaching Brewster angle increases also experimental error, therefore 65 angle has been chosen. Moreover, to increase reproducibility we divide the measured spectra by reference spectra taken on an undoped sample, and further we rescale the spectra to fixed value in the region of 4000 cm-1–7000 cm-1. To reduce number of evaluated parameter, the carrier profile in boron-doped samples was parametrized by 3 parameters and that in phosphorous-doped samples was parametrized by 4 parameters, using additional empirically determined assumption that the first part of the profile is a constant plateau and that the following two exponential tails are joined at a value of 3x10^19 cm-3.

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.

Investigating the attack angle of squeegees with different geometries

  • DOI: 10.1108/SSMT-09-2017-0023
  • Odkaz: https://doi.org/10.1108/SSMT-09-2017-0023
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Purpose The attack angle of stencil printing squeegees with different geometries was analysed using finite element modelling. Design/methodology/approach A finite element model (FEM) was developed to determine the attack angle during the stencil printing. The material properties of the squeegee were included in the model according to the parameters of steel AISI 4340, and the model was validated by experimental measurements. Two geometric parameters were investigated; two different unloaded angles (45° and 60°) and four overhang sizes of the squeegee (6, 15, 20 and 25 mm). Findings It was found that the deflection of the blade is nearly homogenous along the length of the squeegee. This implies that the attack angle does not change significantly along the squeegee length. The results showed significant differences between the initial and the attack angle. For example, the angle of the squeegee with 15 mm overhang size and with 60° initial angle decreased by more than 5° for a specific squeegee force of 0.3 N/mm; resulting in an attack angle of 53.4°. Originality/value The attack angle during the printing is considerably lower than the initial angle as a result of the printing force. The papers, which were dealing with the numerical modelling of the stencil printing presumed that the squeegees were having their initial angle. This could have led to invalid numerical results. Therefore, we decided to investigate the attack angle during stencil printing for squeegees with different initial geometries to enhance the numerical modelling of stencil printing.

Measurement of doping profiles by a contactless method of IR reflectance under grazing incidence

  • DOI: 10.1063/1.5015988
  • Odkaz: https://doi.org/10.1063/1.5015988
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The grazing angle infrared reflectance method of the measurement and evaluation of charge carrier profiles in polished wafers was developed. Experimental errors were minimized by division by reference spectra taken on an undoped sample and further by normalization to a fixed value in the region of 4000/cm to 7000/cm. The carrier profile in boron-doped samples was parametrized by 3 parameters and that in phosphorous-doped samples was parametrized by 4 parameters, using additional empirically determined assumptions. As a physical model, the Drude equation is used with two parameters assumed to be concentration-dependent: relaxation time and contribution from band-to-band excitations. The model parameters were calibrated independently by infrared ellipsometry. The presented method gives results in satisfactory agreement with the profiles measured by the electrochemical capacitance-voltage method.

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.

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.

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.

Identification and caracterization of ß→α-Sn transition with electrical resistance measurements in SnCu1 bulk alloy inoculated with InSb

  • DOI: 10.1007/s10854-017-7539-5
  • Odkaz: https://doi.org/10.1007/s10854-017-7539-5
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    In this paper, the allotropic transition of ß to α-Sn (so called “tin pest”) was identified with electrical resistance measurements. Samples were prepared from SnCu1 alloy using mechanical treatment of two different sample sizes, artificially inoculated with InSb and stored at −18°C for 9 weeks. The electrical resistance measurement showed that in the case of SnCu1 solder alloy the α-Sn transition has three stages: nucleation, growth and the saturation phase, when the transition is almost stopped. It was proven by focused ion beam cross-sectioning and Mösbauer spectroscopy that the developed α-Sn phase can enclose the metastable non-transitioned ß-Sn preventing its further transition and resulting the saturation phase of the phenomenon. In addition, the results point out that the rate of vertical expansion of the α-Sn into the sample body can be equivalent or higher than the horizontal expansion.

Investigating the effect of large SMD components on heating during vapour phase soldering

  • Autoři: Geczy, A., Nagy, A., Illes, B., Gyorgy, Z., Ing. David Bušek, Ph.D.,
  • Publikace: IEEE 23rd International Symposium for Design and Technology in Electronic Packaging. Cavallioti, 2017. p. 44-49. ISSN 2641-287X. ISBN 978-1-5386-1626-0.
  • Rok: 2017
  • DOI: 10.1109/SIITME.2017.8259854
  • Odkaz: https://doi.org/10.1109/SIITME.2017.8259854
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The paper presents fundamental investigations into the field of vapour phase soldering, specially focusing on the effect of large surface mounted components (e.g. shadowing and possible consequent tombstoning). During the vapour phase reflow the heat transfer processes are based on condensation and the temperature distributions are affected by the geometry and thermal masses of the heated assemblies. The paper investigates the problem from the aspect of components with high thermal mass, which may affect the process of condensation, due to their increased thermal requirements. The experimental is based on FR4 type printed circuit boards, where large packages (SMD capacitors) are attached with SMD adhesives on the top surface of the board at specified locations. The thermocouples are fixed in bores inside the PCB at given locations to highlight any possibility of shadowing (caused by condensate flow blocking effect or vapour consumption) and inside the components where any significant transient effects serve information about the process itself. The measurements are logged with a custom data logger device, which was developed specifically for the investigations. The initial results show that shadowing might not be a problem even near large components, however the overall heating characteristics of the board and the components are affected by the relatively large thermal masses of the applied packages.

Numerical modelling of the heat and mass transport processes in a vacuum vapour phase soldering system

  • DOI: 10.1016/j.ijheatmasstransfer.2017.06.091
  • Odkaz: https://doi.org/10.1016/j.ijheatmasstransfer.2017.06.091
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The heat and mass transport processes were investigated with numerical simulations in a vacuum vapour phase soldering system during the vapour suctioning process. Low vapour pressure/concentration is applied during vacuum soldering to decrease the number of gas voids in the solder joints. Three-dimensional numerical flow model was developed which based on the Reynolds averaged Navier-Stokes equations with the standard k-ε turbulence method. The decrease of the vapour concentration and its effects on the solder joints were studied in the case of different oven settings. It was found that vapour suctioning has considerable effects on the heat transfer processes in the soldering chamber which might lead to early solidification of the solder joints and reduces the efficiency of the void removal. Different oven settings were simulated in order to decrease the heat loss of the soldering chamber during the vapour suctioning. It was shown that with appropriate setting of the vacuum vapour phase soldering technology, the efficiency of the void removal can be increased.

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.

Studying heat transfer on inclined printed circuit boards during vapour phase soldering

  • DOI: 10.1108/SSMT-11-2016-0029
  • Odkaz: https://doi.org/10.1108/SSMT-11-2016-0029
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Leider was the first to summarize the knowledge on VPS in recent years (Leider, 2002), covering the basic formulation of heat transfer during the process, which was based on the Nusselt theory of filmwise condensation. Leider also investigated different condensation media types, and the dependency of the PCB alignment, from the aspect of vertical and horizontal positioning in the work zone. It was clearly indicated that, with a vertical alignment, the heat transfer coefficient may rise by 25 to 50% depending on the condensation medium. More recently, it was found by Illés that the inclination of the board had a serious effect on the heating, and the heat distribution (Illés, 2016.); the results were obtained from verified modelling software. No actual practical investigation was published about the exact effect of inclination during VP soldering, so a deeper investigation was needed with novel measurement approaches.

Visualization of MEMS Structures for Education of Automobile Microsystems

  • Autoři: Kardoš, S., Ing. David Bušek, Ph.D.,
  • Publikace: Acta Electrotechnica et Informatica. 2017, 17(3), 17-21. ISSN 1335-8243.
  • Rok: 2017
  • DOI: 10.15546/aeei-2017-0021
  • Odkaz: https://doi.org/10.15546/aeei-2017-0021
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The work is aimed at visualization of working principles of microelectromechanical sensors which are used in automobile electronic systems. Attention is paid to accelerometric, inclinometric, pressure and MAF devices. These are used in systems for stability control, passive and active safety as well as comfort management. The visualizations were realized using modern animation techniques initiated by the creation of virtual materials, 2D and 3D objects, through scene exposure, pending their animation and final cutting.

Wetting balance test - Comparison of solder alloys wetting

  • DOI: 10.1109/ISSE.2017.8000923
  • Odkaz: https://doi.org/10.1109/ISSE.2017.8000923
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The article deals with wetting balance method comparison of solderability of the following materials combinations: two lead free solder alloys (Sn99Cu1, Sn95.5Ag3.8Cu0.7), one leaded solder alloy (Sn63Pb37), one soldering substrate type - copper wire (0.7 mm diameter) and four type of fluxes. The surface of tested samples was additionally evaluated by subjective optical analysis. The results confirm that the best results were achieved for Sn63Pb37 solder alloy - it has the fastest wetting speed (lowest zero cross time). Out of the lead free solder alloys, better results were achieved with Sn95.5Ag3.8Cu0.7 solder.

Effects of substrate thermal properties on the heat transfer coefficient of vapour phase soldering

  • Autoři: Illés, B., Geczy, A., Skwarek, A., Ing. David Bušek, Ph.D.,
  • Publikace: International Journal of Heat and Mass Transfer. 2016, 101 69-75. ISSN 0017-9310.
  • Rok: 2016
  • DOI: 10.1016/j.ijheatmasstransfer.2016.04.116
  • Odkaz: https://doi.org/10.1016/j.ijheatmasstransfer.2016.04.116
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    In this paper, dependence of heat transfer coefficient during vapour phase soldering on the substrate properties was investigated by numerical simulations. A three-dimensional model was developed to describe the phase change on the substrate and the transfer mechanisms in the condensate layer. Five different substrate materials were studied: FR4, polyimide, 94% alumina, LTCC glass–ceramic and insulated metal substrate. The effect of the substrate aspect ratio was also studied. The results present dynamic heat transfer coefficient values of the process for different substrate materials. It is shown that during vapour phase soldering – which is a transient-state condensation process – the heat transfer coefficient can be characterized with the thermal diffusivity of the substrate material together with the filmwise condensate layer thickness on the substrate. The formation of the condensate layer is determined by the thermal diffusivity of the substrate material. It was also found that the aspect ratio of the substrates influences the movement of the condensate on the surface of the substrate, ultimately leading to a substantial effect on the heat transfer coefficient.

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.

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 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.

Investigating the effect of solder paste viscosity change on the pressure during stencil printing

  • Autoři: Ing. David Bušek, Ph.D., KRAMMER, O., Varga, B.
  • Publikace: 2016 IEEE 22nd International Symposium for Design and Technology in Electronic Packaging (SIITME). New York: IEEE, 2016. pp. 36-39. ISBN 978-1-5090-4446-7.
  • Rok: 2016
  • DOI: 10.1109/SIITME.2016.7777238
  • Odkaz: https://doi.org/10.1109/SIITME.2016.7777238
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The purpose of this article is to present our experiments with Vapour Phase Soldering, where the temperature distribution and heat transfer mechanisms were investigated on four test-boards with different substrates. We developed a method to measure the temperature gradients on- board inside an experimental vapour phase soldering oven. VP soldering process is suitable for consistent and rapid heating on boards from small scale to large ones with power components showing considerable thermal capacities. The measurements were performed on FR4, ceramic, alumina composite and flexible substrates, where the results show significant differences between the different materials, and point to investigations with thermal diffusivity for future research.

Investigations on heat transfer with different PCB substrates during Vapour Phase Soldering

  • Autoři: Ing. David Bušek, Ph.D., Geczy, A., Fazekas, L., Nagy, D.
  • Publikace: 2016 IEEE 22nd International Symposium for Design and Technology in Electronic Packaging (SIITME). New York: IEEE, 2016. pp. 48-54. ISBN 978-1-5090-4446-7.
  • Rok: 2016
  • DOI: 10.1109/SIITME.2016.7777241
  • Odkaz: https://doi.org/10.1109/SIITME.2016.7777241
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The purpose of this article is to present our experiments with Vapour Phase Soldering, where the temperature distribution and heat transfer mechanisms were investigated on four test-boards with different substrates. We developed a method to measure the temperature gradients on- board inside an experimental vapour phase soldering oven. VP soldering process is suitable for consistent and rapid heating on boards from small scale to large ones with power components showing considerable thermal capacities. The measurements were performed on FR4, ceramic, alumina composite and flexible substrates, where the results show significant differences between the different materials, and point to investigations with thermal diffusivity for future research.

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.

Substrate influence on temperature distribution along the PCB during vapor phase soldering

  • Autoři: Ing. David Bušek, Ph.D., Fazekas, L., Geczy, A., Ing. Martin Plaček, Ph.D.,
  • Publikace: Proceedings of the International Spring Seminar on Electronics Technology. New York: IEEE Press, 2016. pp. 267-272. ISSN 2161-2536. ISBN 978-1-5090-1389-0.
  • Rok: 2016
  • DOI: 10.1109/ISSE.2016.7563203
  • Odkaz: https://doi.org/10.1109/ISSE.2016.7563203
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article is focused on measurement of temperature gradients in different locations on test-boards during Vapor Phase Soldering (VPS) with different materials as PCB substrates. VPS is usually applied in electronics assembly technologies due to its ability to heat the board fast and uniformly during reflow soldering. The heating rate differs significantly even on a moderate size PCB. The measurements were performed on different substrates, particularly on FR4, FR4 with aluminum core, ceramic, and polyimide flexible board samples. The temperature gradients were uniform with low heat capacity boards, contrary, the high heat capacity aluminum based PCB showed significant non-uniformity in heating, where observed temperature differences reached up to 20 °C.

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.

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.

Assembly method and its influence on electrically conductive adhesives and solder pastes joints durability

  • DOI: 10.1109/ISSE.2015.7248012
  • Odkaz: https://doi.org/10.1109/ISSE.2015.7248012
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article is focused on comparing of different assembly methods, particularly stencil printing and dispensing paste deposition and compares lead and lead-free solder pastes with one-component and two-component epoxy based electrically conductive adhesives. The evaluation method is based on resistance measurement after accelerated stress tests. The aging was conducted using automatic mechanical cyclic stress machine tester and joint resistance to environment was tested using long term temperature straining and combined humidity and temperature straining. Shear strength measurement was done in order to determine mechanical stability of the connection.

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.

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.

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 Thermomechanical Properties of One-and Two-Component Conductive Adhesives

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The goal of this work was to find if the numer of components in one- and two-component conductive adhesives influences their thermomechanical properties. All adhesive used in this study were of an epoxy type filled with silver flakes and all had isotropic electrical conductivity. It was also found that all adhesives were not optimally cured through curing was carried out in accordance with recomendation of a producer of adhesives.

Current Loading of Adhesive Joints Aged in Environment with High Humidity

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Electrically conductive adhesive with epoxy matrix and silver filler was used for forming of adhesive joints. The joints were at first aged at the humidity near 100 % for 300 hours. The joints were then loaded with the rectangular current pulses with the amplitude 10 A, 20 A and 50 A. The width of the pulses was 5 microseconds, the frequency 50 Hz. It was found that the pulses changed the joints resistance.

Diagnostic of Electrical Properties of Electrically Conductive Adhesives

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Electrical properties of electrically conductive adhesives are the DC resistance, the impedance, noise and nonlinearity od the current vs. voltage characteristic. The methods of measurement of these parameters are described - four termination and three termination measurement of the resistance, the impedance measurement, the current noise measurement and the odd and even nonlinearity measurement. Results of some basic types of the measurements are presented graphically.

Influence of nanoparticle additives on change of the glass transition temperature of electrically conductive adhesives

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    After elimination of lead from soft solders used for the electrical industry had to find new alternatives for creating electrically conductive connections. For some time no, one of the widespread options is using lead-free solders. Also another alternative comes to the fore. This alternative is using electrically conductive adhesives. The quality of their electrical and mechanical properties far does not reach the quality of lead-free solders. And therefore they are used only on places where is necessary.

Study of Glass Transition Temperature of Electrically Conductive Adhesives

  • DOI: 10.1109/SIITME.2012.6384364
  • Odkaz: https://doi.org/10.1109/SIITME.2012.6384364
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Electrically conductive adhesives with epoxy matrix and filled with silver flakes were modified with addition of multi-walled carbon nanotubes and with silver nanoparticles. Glass transition temperature was studied using dynamic thermomechanical analysis in penetration mode. It was found that the glass transition temperature increases after temperature ageing and decreases after humidity and temperature/humidity ageing.

Correlations between Mechanical and Electrical Parameters of Modified Electrically Conductive Adhesives

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Electrically conductive adhesive with isotropic electrical conductivity was modified with addition of silver nanoparticles. Contrast in electrical resistance and shear strength of adhesive joints formed of non-modified and modified adhesive was investigated.

Electrically Conductive Adhesives Modified Using Ions and Nanoparticles

  • Autoři: Ing. David Bušek, Ph.D., Pilarčíková, I., doc. Ing. Pavel Mach, CSc.,
  • Publikace: Nanocon 2011, Conference Proceedings. Ostrava: Technická universita Ostrava - Vysoká škola báňská, 2011. pp. 397-402. ISBN 978-80-87294-23-9.
  • Rok: 2011
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The general goal of this work is to improve electrical conductivity which is nowadays up to two orders worse when compared to lead or lead free solders. This work summarizes the results of experiments, where two basic adhesives AX20 and AX70MN are either additionally filled with silver nanoparticles, carbon nanotubes or AgNO3, or modified using nitric acid (HNO3), chloride acid (HCl), potassium cyanide (KCN) or treated with elevated temperature (200 °C) for the duration of 20 minutes (annealed).

Modification of Interfacial Properties Between Filler Particles in Electrically Conductive Adhesive

  • Autoři: doc. Ing. Pavel Mach, CSc., Ing. David Bušek, Ph.D.,
  • Publikace: 2011 IEEE 17th International Symposium for Design and Technology in Electronic Packaging. Timisoara: University Politehnica Timisoara, 2011. pp. 99-102. ISBN 978-1-4577-1275-3.
  • Rok: 2011
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Electrically conductive adhesives are materials filled with different types of conductive particles, with the silver flakes usually. Interfacital properties between particles influence quality of contacts between particles and electical properties of adhesive joints. Different ways of modification of interfacial properties were tested: rotary stiring of adhesive before application, addition of bi-carboxylic acid into adhesive before application and additional curing of the joints were tested. It was found that rotary stiring before application of adhesive is the most effective way for improvemet electrical conductivity of adhesive.

Properties of Modified Electrically Conductive Adhesives

  • Autoři: Ratislav, M., Pilarčíková, I., Ing. David Bušek, Ph.D., doc. Ing. Pavel Mach, CSc.,
  • Publikace: Nanocon 2011, Conference Proceedings. Ostrava: Technická universita Ostrava - Vysoká škola báňská, 2011. pp. P50/1-P50/5. ISBN 978-80-87294-23-9.
  • Rok: 2011
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This work deals with electrical properties of electrically conductive adhesives.The aim of this work is the measurement of electrical resistance and non-linearity of connections created with isotropic conductive adhesives and compare changes in these variables after adjusting adhesives by adding silver nitrate and its subsequent annealing.AX 20 and AX 70MN adhesives with similar composition were used, but AX 70MN is more pourable, which could take influence to results, especially in case of annealing and shouldering of PCB. Further aim was improvement of adhesive properties by adding not only silver nitrate but also dissolvent, which allows better dissociation.

Radio-frequency Solder Film Surface Resistance Measurement

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The paper deals with solder film measurement using high frequency resonator. Measurement of surface resistance of a conductor that consists of a layer of solder that is applied to the conductive material was done on high frequency, in the range of 500-5000 MHz.

Diagnostics of photovoltaic power plant operating

  • DOI: 10.1049/cp.2010.0929
  • Odkaz: https://doi.org/10.1049/cp.2010.0929
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article deals with solving problems of reliable function of photovoltaic power stations. Issues concerning monitoring photovoltaic power plant are real and ongoing. Guidelines for troublefree PV plant operation are discusssed in the paper. operation.

Modification of Adhesive Joints Resistance with Current Pulses

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Two groups of identical strip of electrically conductive adhesive were printed on a test PCB. The strip resistance was measured by the four-terminal method, the resistance of the contact between the strip and pads was measured in parallel with the temperature growth. It was found that the resistance at first falls down and then growths rapidly with the temperature growth.

Non-linearity measurement of low resistances

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    A method of non-linearity evaluation for low resistances by the use of determination of the level of intermodulation signals is described. The equipment can measure small resistances powered with current 2 A and an inherent signal to carriers ratio of 180 dB.

Thermal Ageing of Electrically Conductive Micro/Nano Adhesives

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Tempereture ageing of electrically conductive adhesives in dependence on the temperature and time of ageing was examined. Basic electrical parameters of adhesives were measured. Improvement and decrease of these parameters were found independence on the temperature curring of adhesives.

Thermal evaluation of the quality of electrically conductive adhesive joints

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The paper deals with electrically conductive adhesives and inovative quality estimation method based on thermal field evaluation. The resistance of joint heated by passing current can be roughly estimated by the used of temperature field picture.

Thermomechanical Analysis of a Bulk of Electrically Conductive Adhesive

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Mechanical properties of isotropically conductive adhesives depend not just on the internal structure and composition (amount and type of binder and filler) of the adhesive, but also on chemical processes that are influenced by curing. Thermomechanical analysis allows to distinguish the point when the adhesive is fully cured, it may reveal a difference in mechanical properties after different modifications of the adhesive, it may give a clue to better thermal processing of the adhesive while curing. Thermal analysis of totally nine types of adhesive modifications was performed, particularly the influence of carbon nanotubes addition, silver nanoparticles and colloidal silver was observed. In our tests, both one-component and two-component adhesives were used.

Thermomechanical Analysis of Electrically Conductive Adhesives

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Termomechanical analysis of elektrically conductive adhesives was carried out. Methods of static and dynamic thermomechanical alanyses as well as method of differential scanning calorimetry were used. It was found that adhesives vere not fully curred.

Usability of Electrically Conductive Adhesives for Power Components Assembly

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Sensitivity of resistance of adhesive joints formed of frequently used electrically conductive adhesives with isotropic electrical conductivity to loading with short current pulses of high amplitude was examined. It was found that that the resistance increases with the increase of pulses amplitude and with the temperature at which experiments are carried out.

Comparison of 13 Modifications of Electrically Conductive Adhesive (ECA), Possible Ways to Create Silver Ions and Nanoparticles in ECA

  • Autoři: Ing. David Bušek, Ph.D., Pilarčíková, I., Ratislav, M., doc. Ing. Pavel Mach, CSc.,
  • Publikace: Electronic Devices and Systems, IMAPS CS International Conference 2009 Proceedings. Brno: VUT v Brně, FEI, 2009. pp. 251-255. ISBN 978-80-214-3933-7.
  • Rok: 2009
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This work summarizes the result of experiments, where two basic adhesives AX20 and AX70MIN are either additionally filled with silver nanoparticles, carbon nanotubes or AgNO3, or modified using nitric acid (HNO3), chloride acid .

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.

Influence of Carbon Nanotubes Added to a Commercial Adhesive

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The paper describes the influence of carbon nanotubes onto electrical properties of electrically conductive adhesives.

Measurement of Conductive Connections and Joints Using Current Noise Evaluation

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The article describes a system with current noise evaluation for joints and contacts quality determination.

Electrical Connection Network Within an Electrically Conductive Adhesive

  • DOI: 10.1109/ISSE.2008.5276536
  • Odkaz: https://doi.org/10.1109/ISSE.2008.5276536
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article compares theoretical models with real measurement of the electrically conductive adhesive. The inner structure of the adhesive that is either formed by micro-sized particles, or micro-sized particles mixed with nano-sized particles, is described.

Electrically Conductive Adhesive Joints With Nanoparticles

  • Autoři: Ing. David Bušek, Ph.D.,
  • Publikace: Proceedings of Workshop 2008. Praha: Czech Technical University in Prague, 2008. pp. 248-249. ISBN 978-80-01-04016-4.
  • Rok: 2008
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The article discusses advantages and disadvantages of electrically conductive adhesives enriched with ball nanoparticles. The parameter evaluation is according to electrical parameters of the adhesives.

Equipment for Contactless Sheet Resistance Measurement

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Thin layer resistance measurement using the change of complex coil impedance .

Theoretical and Experimental Background of Resistance and Nonlinearity Measurement of Adhesive Conductive Joints

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The paper is focused on theoretical description of electrical resistance of the adhesive joints and on nonlinearity of current versus voltage characteristic of the resistance.

Can Conductive Adhesives With Nanoparticles Beat Commonly Used Electrically Conductive Adhesives Without Nanoparticles

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Nanoparticle addition into commonly used ECAs improves resistance to mechanical straining but lowers resistance to moisture.

Properties of Electrically Conductive Adhesive with Added ag Nanoparticlas

  • Autoři: Ing. David Bušek, Ph.D., Radev, R.
  • Publikace: SIITME 2007. Baia Mare: North University of Baia Mare, 2007. pp. 56-59. ISSN 1843-5122. ISBN 978-973-713-188-1.
  • Rok: 2007
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article deals with the use of electrically conductive nanoparticles in isotropically conductive adhesives. The advantages and possibilities achieved using surfactants for nanoparticles, the sintering effect and possible curing temperature is mentioned. Nanoparticles can improve resistance to mechanical straining while keeping the resistivity unchanged.

Quality Improvement in Electric Connection for Temperature Sensitive Devices Under Mechanical Stress

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Mechanical stress is is also very often presented for the completed device and therefore the quality and stability of such realized joint must be achieved.

Are Electrically Conductive Adhesives Suitable for Every Surface Finish?

  • Autoři: Ing. David Bušek, Ph.D., Duraj, A., doc. Ing. Pavel Mach, CSc.,
  • Publikace: SIITME 2006 - International Symposium for Design and Technology of Electronic Packaging. Iasi: Technical University, 2006. pp. 14-17. ISBN 978-973-8961-23-4.
  • Rok: 2006
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Electrical properties of adhesive joints created on different types of surfaces have been investigated. It has been found a strong dependence on the type of a surface

Correlations among Mechanical and Electrical Properties of Conductive Adhesive Joints

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The purpose of this research is investigation of correlations between mechanical and electrical properties of ECAs.Especially between electrical resistance, nonlinearity and mechanical strength. Also dependence on high climatic load has been evaluated.

Diagnostika vybraných elektrických vlastností ekologických spojovacích materiálů

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Jsou uvedeny techniky diagnostiky elektricky vodivých adhezních spojů. Z elektrických vlastností jsou sledovány odpor, nelinearita a šum.

Equipment for Measurement of Nonlinearity of Nominally Linear Components

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Nonlinearity of a nominally linear components is a significant parameter which informs about the difference of and investigated component from ideal one.Equipment is based on evaluation of intermodulation distortion.Experiment is focus on measurement of conductive adhesive joints.

Properties of Electrically Conductive Adhesive Added with Ag Nanoparticles

  • Autoři: doc. Ing. Pavel Mach, CSc., Ing. David Bušek, Ph.D., Duraj, A.
  • Publikace: SIITME 2006 - International Symposium for Design and Technology of Electronic Packaging. Iasi: Technical University, 2006. pp. 63-67. ISBN 978-973-8961-23-4.
  • Rok: 2006
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Properties of electrically conductive adhesives completed by Ag nanoparticles such as nonlinearity, resistance and noise have been investigated.

Influence of Interconnection Surface Finishes on Quality of Adhesive Joints

  • DOI: 10.1109/ISSE.2005.1491050
  • Odkaz: https://doi.org/10.1109/ISSE.2005.1491050
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Electrically conductive adhesives electrically connect and mechanically bond connected parts. Influence of types of surface finishes on quality of adhesive bonds has been Influence of types of surface finishes on quality of adhesive bonds has been examined.

Properties of Joint Made Using Electrically Conductive Adhesives

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    This article deals with the substrate quality influence on the electrical properties of joints prepared using electrically conductive adhesives. Significant dependence on surface quality was found.

Stability of Adhesive Joints Created on Pads with Different Types of Surface Finishes

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Stability of Adhesive Joints Created on Pads with Different Types of Surface Finishes was examined. It was found that highest stability is on gold surfaces.

Vliv materiálu kontaktních plošek DPS na mechanické vlastnosti lepených a pájených spojů

  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Cílem této práce je měření a vyhodnocování základních mechanických parametrů spojů (pevnost ve střihu a pevnost v odtrhu), realizovaných elektricky vodivými lepidly s izotropní vodivostí.

Za stránku zodpovídá: Ing. Mgr. Radovan Suk