Ing. Petr Veselý, Ph.D.

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.

Biodegradables are a promising path for the future of electronics in a greener mindset. The review study focuses on their applications and past and current research results. The paper also investigates the application of nanomaterials as fillers to control or increase the physical (electrical, mechanical, thermal) properties of biodegradable biopolymers. These biodegradables and nanocomposites are already effectively used in prototypes and advanced application areas with demanding requirements, such as flexible and wearable electronics, implantable or biomedical applications, and traditional commercial electronics. The nano-enhanced biopolymer substrates (e.g., with improved gas and water barrier functionalities) sometimes also with integrated, nano-enabled functionalities (such as electromagnetic shielding or plasmonic activity) can be beneficial in many electronics packaging and nanopackaging applications as well.

Due to the restrictions on lead solder alloy, there is an ongoing search for alternative lead-free alloys with the best possible solder properties similar to Pb-based solder alloys. Therefore, phosphorus and gallium are, for example, added to solder alloys, which could lead to an improvement in their solder properties (wettability, mechanical, lower melting point). These additives are usually used for the improvement of SAC alloys. This work focused on lead-free low-temperature solders based on tin and bismuth. The effect of added 1 wt.% gallium and traces of phosphorus on wettability and spreading was studied. These properties were observed on FR4 boards with three different surface materials: copper, copper with hot air solder leveling surface finish (HASL) and copper with electroless nickel-immersion gold surface finish (ENIG). Examined alloys were Bi58Sn42, Bi58Sn42P, Bi59Sn40Ga1 and Bi59Sn40Ga1P. The results showed that although the addition of Ga and P exhibited no significant improvement or even decrease in the wetting and spreading ability of the solder alloy on copper and ENIG surfaces, the wetting behavior of the doped alloys was better on HASL surface compared to the eutectic solder alloy.

This work aimed to analyze a reliability issue that occurred on printed circuit boards (PCB) primarily designed to study electrochemical migration (ECM) phenomena. The test boards were supplied directly from the PCB producer, and the copper traces were covered with a hot air solder leveling (HASL) surface finish. However, the solder layer was clearly inconsistent and poor, caused by contamination from improper solder mask application, as was confirmed by analysis using the scanning electron microscope. On these boards, a water drop test with distilled water (bias voltage of 10 V) and thermal humidity bias test (85 °C/90% R.H./25 V/168 h) was conducted to evaluate predisposition for electrochemical migration of boards with a such poorly fabricated solder mask. PCB without solder mask and with correctly applied solder mask was also included in this study for comparison. The results clearly showed that the test boards with the poorly fabricated solder mask were significantly more inclinable to electrochemical migration – in the case of the water drop test, the forming dendritic structures shorted the electrodes up to 6 times faster than on PCB without a solder mask, while the samples with correct solder mask exhibited the best resistance against ECM. During the thermal humidity bias test, the electrical short appeared after only 2 hours on PCB with the bad solder mask compared to PCB without the mask, where the dendrites grew after more than 27 hours. Energy dispersive spectroscopy confirmed that the migrating element was tin from the HASL cover layer.

The goal of this work was to evaluate changes in mechanical properties and microstructure of the lead-free bismuth-tin alloys when adding gallium and phosphorus. These elements were added originally on account of melting temperature decrease (Ga) and improvement of wetting (P). Six different solders were examined: the eutectic one Bi58Sn42 as a reference, then Bi59Sn40Ga1 and Bi57Sn40Ga3. In addition, the investigation was also performed on all the mentioned alloys with an added trace amount of phosphorus. Mechanical properties were measured by the shear test of a solder ball on a copper substrate with Organic Solderability Preservatives (OSP) surface finish. Furthermore, the small balls of solder alloys were reflowed on boards with three different surface finishes: copper-plated, Hot Air Solder Levelling (HASL), and Electroless Nickel Immersion Gold (ENIG). These coupons were left to aging in the climatic chamber for 500 and 1 000 hours at a temperature of 100 °C. The metallographic cross-sections were made, and the microstructure of the intermetallic layer (IML) was analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. The shear test showed a significant decrease in the shear force by adding gallium. It was also found that the addition of phosphorus has only a minor (but still statistically significant) impact on the shear force. The addition of gallium affected the IML thickness and caused a considerable decrease compared to alloys without Ga. The reason was the composition of the IML. IML of Bi-Sn solder joints consisted of Cu-Sn, whereas the gallium-containing alloys formed IML consisted of Cu-Ga.

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

New types of filaments were formed by adding various fillers into polymers during the fabrication. We designed two new composites in cooperation with a filament producer. Biodegradable thermoplastic polyester polylactic acid (PLA) was filled with carbon black. Carbon black (CB) formed 30 wt.% of in the final mixture. The second composite was made by compounding the polyethylene terephthalate glycol-modified (PET-G) with titanium dioxide. Two different contents of TiO2, namely 10 and 20 wt.%, were selected for filament preparation. The goal of the testing was to evaluate the change of mechanical and thermomechanical properties in contrast to pure filaments. The testing specimens were prepared by Fused Deposition Modeling (FDM), which belongs to 3D printings techniques. The printed samples were subjected to mechanical tensile testing and to microhardness measurement by the Vickers method. Thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA) were performed too. In particular, glass transition temperature, coefficient of thermal expansion (CTE), and storage modulus were analyzed. All composites showed a lower ultimate tensile strength than the neat polymer. Notable changes in thermomechanical behavior were also detected. The most significant difference was the drop in CTE above the glass transition in the case of filled PLA samples.

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

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.

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.

Abstract: The study attends to the evaluation of solder joints from a mechanical point of view. Two lead-free alloys Sn99.7Cu0.3 and Sn96.5Ag3Cu0.5 (SAC305) were selected for samples preparation. To compare the results of current alloys with the most utilized solder in the past, the study comprises eutectic lead solder paste Sn63Pb37, too. Solder joints intended for observation were created by assembling chip resistors. Assembled boards were reflowed employing a hot air convection oven. Mechanical properties were evaluated by performing shear tests and microhardness measurements. Microhardness of bulk solder and intermetallic compounds (IMC) was measured using the micro-indentation Vickers test. For this purpose, a metallographic cross-section of some samples was accomplished. Solder pads on testing boards were coated by Organic Solder Preservative (OSP) and Hot Air Solder Levelling (HASL). Depending on solder paste type, the results show more or less impact of surface finish on the solder hardness. Some difference in microhardness of IMC layers and shear strength was also detected but, in these tests, results are not in favour of one surface treatment.

Although stereolithography (SLA) is the oldest 3D printing method, only a few works have been published about the complex electrical properties of objects printed from unfilled photopolymerizable resins. In this paper, we describe how the dielectric constant, loss factor, dielectric strength, and volume resistivity of printed objects are influenced by the type of resin and the thickness of the sample. Two commercial resins were used - acrylate/epoxy "blue" resin and acrylate "orange" resin. The electrical properties were mostly dependent on the type of resin and thickness of the sample. Thicker blue samples showed the highest polarizability among all tested materials. Volume resistivity of orange samples was one order of magnitude higher than the one of blue samples. Dielectric strength was not dependent on the type of the resin but rather on the thickness of the samples. Our results contribute to the current knowledge about the electrical behavior of SLA-printed objects.

This work focuses on evaluating the anisotropy of the structures manufactured by two 3D printing technologies, Fused Filament Fabrication (FFF) and Stereolithography (SLA). According to the manufacturing process, printed structures are expected to have some level of anisotropy. It is essential to consider it while designing a model for 3D printing. Printed specimens were subjected to tensile testing, thermomechanical analysis (TMA), and dynamic mechanical analysis (DMA). Measurements were based on the ASTM D638, E1545 and D4065 standards. The specimens were printed in three different orientations for tensile tests and DMA, respectively in four orientations for TMA. The FFF specimens were prepared from poly-lactic acid (PLA) with different extruder temperatures, 210°C and 240°C. In the case of SLA specimens, photopolymer based on epoxy resin was used, the process differed in curing time (8 s and 16 s). The results clearly showed a higher level of anisotropy of the FFF specimens compared to SLA specimens. The FFF specimens show in the orientation XZ 1,5 times lower tensile strength than in the other two orientations, compared to SLA, where the tensile strength was similar. The anisotropy of the thermomechanical properties was high for FFF specimens; in contrast, the SLA specimens showed no difference in thermal expansion for different printing orientations.

This work aimed to evaluate the change of properties of joints based on bismuth-tin eutectic alloy soldered under various reflow conditions during long-term accelerated aging tests. Four temperature profiles were used for the reflow soldering of testing boards. The profiles differed in the reflow phase and the pre-heat phase when the soldering flux is activated. Subsequently, the first half of the testing boards was aged for 1000 hours in a climatic chamber at 85 °C and relative humidity 85 %. The second half was closed up in a temperature-shock chamber for 1000 cycles with the following settings: a hot temperature of 125 °C, a cold temperature of -40 °C, and a cycle time of 30 minutes. The solder joint properties - electrical resistance, shear strength, and thickness of intermetallic layers - were measured four times during the aging to observe trends. It turned out from the measurement results that the most stable during temperature-humidity aging were the joints soldered with higher temperature in the pre-heat phase and lower temperature in the reflow phase. On the contrary, the joints soldered with a lower temperature in the pre-heat phase and a higher temperature in the reflow phase were more resistant against the thermal shocks. The shear strength was even higher than before the start of the test. Overall, both pre-heat and reflow settings play an important role in solder joint reliability.

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

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%.

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

In this paper, we present results of long-term stability tests of a low-loss (<0.55 dB) hollow core fiber (HCF) to standard optical fiber interconnection prepared by modified gluing-based fiber-array technology. We measured insertion loss of three interconnected HCF samples over a period of 100 days at room temperature, observing a variation in insertion loss of less than 0.02 dB. Subsequently, we placed the HCF samples in a climatic chamber and heated to +85°C in four cycles. Maximum insertion loss variation of 0.10 dB was observed for HCF samples with angled 8° interconnections and only 0.02 dB for a HCF sample with a flat interconnection.

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.

The objective of this work is to examine the mechanical and thermal properties of novel lead-free bismuth-tin solder alloys with low melting temperature, each with a different percentage of added gallium and with phosphorus as a trace element. The motivation was to determine solder alloy with decreased melting point and maintain mechanical properties of eutectic bismuth-tin solder alloy at the same time. BiSn40, BiSn40P, BiSn40Ga1, BiSn40Ga1P, BiSn40Ga3, and BiSn40Ga3P were among the analyzed solder alloys. In addition, the same properties of BiSn42 were analyzed for comparison as a reference. The thermal properties were examined by differential thermal analysis, where the melting and solidification points were determined. The Vickers micro-hardness test was conducted for the observation of mechanical attributes. Moreover, the microstructure of the alloys was observed in a scanning electron microscope. The result of this study showed that the temperature of the melting point significantly decreased in the alloy BiSn40Ga3. Also, this alloy seems to have as sufficient mechanical properties as BiSn42. Therefore, it could possibly be used as a suitable substitution for the eutectic solder alloy.

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.

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.

This work aimed to evaluate a change of properties of Bi58Sn42 solder joints on different substrates during accelerated aging tests. Three different surface finishes of the copper soldering pads were chosen - Hot Air Solder Leveling (HASL), Galvanic Tin (GT), and Galvanic Nickel-Galvanic Gold (GNGG). Soldering pads without the surface finish were also used for comparison. The test boards with assembled chip resistors were aged in a climatic chamber at temperature 85 °C and relative humidity 85 % for 1512 hours. The measurement of electrical resistance and mechanical shear strength test was performed. Furthermore, metallographic cross-sections were made to evaluate the rate of intermetallic layer thickness growth. The intermetallic layers were also measured by Vickers hardness tester. The results showed that the growth of intermetallic layers and the increase of electrical resistance of the joints soldered on pads without surface protection, with HASL and GT, is similar; the resistance increased by up to 130%. On the contrary, joints on GNGG are more stable during aging. No significant difference was observed between resistance immediately after the soldering process and after the accelerated test. On the other hand, the hardness of Nickel-based intermetallic compounds, which grew between GNGG and the solder, pointed to greater fragility. The interpretation of the acquired results of such a comprehensive study leads to a better understanding of the solder joint reliability depending on the used surface finish of the printed circuit board.

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%.

This paper aims to study various physical properties of lithium silicate ceramics. The work starts with the synthesis followed by characterization of the compounds. The samples are synthesized by reaction between SiO2 and Li2CO3 powders, compacted by spark plasma sintering (SPS) and then characterized by XRD, SEM and other techniques. The electrical properties are studied by dielectric spectroscopy. Dielectric and conductive properties of lithium silicate depend on the composition and microstructure, which factors are interconnected with the processing parameters. Li2 SiO3 and Li2Si2O5 were the major components present in the SPS bulk. The best combination of dielectric parameters is relative permittivity 6.41 and loss tangent 0.001 at frequency 0.9 MHz for the sample sintered at 950 °C for 30 min. Relative permittivity as well as loss tangent was monitored to increase with temperature up to 250 °C.

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

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

The degradation of plastic materials induced by solar radiation can limit their use in outdoor applications. Therefore, we aimed to find a relationship between the photodegradation of 3D printed polylactic acid (PLA) and its electrical and thermomechanical properties. In the first stage, the printing settings were optimized with regard to the dielectric strength of samples. Afterward, the sets of printed specimens were exposed to UV light of different spectrum and duration. UV gas-discharge lamps with spectral peaks at 254 and 385 nm were used as intense UV light sources; the individual exposure times were chosen as 6, 12, 24, 48, and 96 hours. Subsequently, the dielectric strength of each set was evaluated, and thermomechanical analyses were performed. Although the irradiation at 254 nm caused substantial degradation of PLA, it did not remarkably affect its dielectric strength. Nonetheless, both sources of UV light caused a considerable brittleness that might be the limiting factor for the outdoor application of PLA.

Voids inside solder joints are empty spaces which can cause reliability issues. Solder joints with voids are weaker from a mechanical point of view. Additionally, the soled joints with voids are worse from the point of thermal and electrical properties. This article deals with voids inside solder joint prepared with Sn96,5Ag3Cu0,5 solder paste with different properties from the point of flux type and size of solder alloy powder. The aim of this work is to evaluate the influence of flux and particles size on the voids formation. Preparation of solder joints was done at the same process conditions for all samples. Solder joints were analysed via X-ray with following image analyses of voids. The results show that the less aggressive flux caused slightly higher voids formation from the point of the average surface area of voids at the soldering pad. Additionally, the results show that the slightly higher voids formation appears in case of solder paste with smaller solder alloy particles.

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

The aim of this work was to evaluate the use of FFF (Fused Filament Fabrication) technology in high and medium voltage applications. The research is based on previous work, where the dependence of dielectric strength of 3D printed objects on printing resolution (the thickness of one layer) was examined. Four polymer materials designated for FFF were chosen for the experiments - ABS (acrylonitrile butadiene styrene), PET-G (polyethylene terephthalate - glycol modified), ASA (acrilonitrile styren acrylate) and PP (polypropylene). The following tests of the printed samples from such materials were conducted - atmospheric impulse test with positive polarity, short-term AC and DC breakdown strength tests and measurement of partial discharges. Based on acquired results, the optimal material for unipolar stresses (DC and impulse) is PP, whereas for bipolar stresses it is a close match between ABS and PET-G. For systems in which all three types of stresses occur, ASA seems to be the best compromise. Although the dielectric strength of the examined 3D structures is sufficient, an improvement of these materials would be proper, for example by adding admixtures to the base materials or better printing quality.

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.

The intermetallic compounds growth at the interface between the eutectic solder Bi58Sn42 and the copper soldering pad was examined in dependence on the temperature profile selection that was expressed by a heating factor (combined influence of time and temperature above the melting point of the solder alloy). Eight temperature profiles were used for reflow soldering. In contrast to other studies, almost the identical value of the heating factor was achieved by the different shapes of the profiles in order to evaluate the effect of the whole profile shape. Consequently, the metallographic cross-sections of the solder joints were analyzed by scanning electron microscopy. Additionally, the shear strength test of solder joints and the transition resistance measurement were conducted. As expected, the intermetallic layer thickness increased with an increasing heating factor, but a different thickness was observed for the identical heating factor when the whole shape of temperature profile including the preheating phase was changed. On the other hand, the prediction of IMC growth based on heating factor can be used in situations, where only the melting phase varies and the preheating remains constant - but the influence of the heating factor on intermetallic layer thickness cannot be generally formulated for a specific solder alloy due to a strong dependence on the flux.

The paper describes the concept of solder paste dispensers with very low production costs.

This work was focused on the evaluation of the thermomechanical properties of 3D printed structures manufactured by FDM (Fused Deposition Modeling) method in dependence on the printing nozzle temperature. Two common materials designated for FDM were chosen for the experiments - poly-lactic acid (PLA) and acrylonitrile styrene acrylate (ASA). Measurement of thermomechanical properties was conducted by thermomechanical analysis (TMA). The results showed that PLA thermal properties strongly depended on the printing temperature - with increasing printing temperature, the dimensional deformation after the thermal cycle was decreasing. Also, the glass transition temperature decreased with increasing printing temperature. In the case of ASA, no significant dependence was noticed. Therefore, ASA seems to be a better choice, since the settings of the process do not influence the thermal behavior of the printed structure.

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.

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%.

Fused Deposition Modelling (FDM) is one of the most common methods of 3D printing used in many fields of industry, especially in development departments. Since plastics are fundamental materials for electronics industry, the aim of this work is to examine dielectric properties of objects printed from such materials. This work’s contribution is the evaluation of the dependency of the printed objects properties on printing quality and the use of 3D printed plastic components in electronics. For the experiment, three commonly used materials in FDM were chosen – PLA, ABS and PET-G. The materials were pure without any additional admixtures and the relevant test samples were printed with different printing resolution (height of one layer). The following properties were examined – permittivity, dissipation factor and dielectric strength. The results showed that permittivity slightly decreased with increasing height of one layer. Dissipation factor varied significantly in the measured range and there was no apparent dependency on the printing resolution. Rather, it was an indicator of the printing quality. Dielectric strength also slightly decreased with the decreasing resolution; however this parameter was governed primarily by the employed material. Generally, an improvement of the dielectric properties of these materials is required due to a relatively small dielectric strength, for example by adding admixtures to the base material or better printing quality.

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.

3D printing is an additive manufacturing process for building three-dimensional solid objects. This technology has use in many fields of industry, especially in rapid-prototyping. This project is focused on possibilities of use of 3D printing in electronics industry. 3D printed objects were investigated with a view to their electrical properties. The comparison of these properties for various common materials (PLA and ABS) was examined. The results showed that some of the properties of PLA are promising (relatively high dielectric strength, volume resistivity) compared to others (dielectric constant, loss tangent) that are not optimal for use in electronics industry and requires some improvements in form of additives. ABS has higher loss tangent than PLA, no significant difference in dielectric constant was found between ABS and PLA. Generally, an improvement of the electrical properties of these materials is required, for example by adding some additives to the base material.

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