Purpose – The main advantages of vapour phase soldering are a non-oxygen environment, the elimination of overheating and the possibility of the vacuum application, which can guarantee undeniably higher quality of solder joints, especially as regards void formation. These features are less affected by the alloy composition. The paper aims to discuss these issues. Design/methodology/approach – The quality of solder joints made in two VPS options (with and without vacuum) was investigated in terms of voids formation. Solder alloys of 37%Pb63%Sn (PbSn) and 96%Sn3.5%Ag0.5%Cu (SAC 305) were applied to an etched Cu layer on a glass-epoxy substrate using the screen-printing method. 1206 SMD resistors were placed on the solder pads with a Quadra pick-and place machine. For the inspection of joint structure and void identification, 3D X-ray images of samples were taken using a computed tomography system with a 180 kV/15 W nanofocus. For comparison, traditional cross-sections of the samples were performed using a metallographic polisher. The cross-section analysis was done in a scanning electron microscope (SEM). To confirm the relevance of these data, a statistical analysis was carried out. Findings – The paper shows that alloy composition has less impact on the quality of joints as regards void formation. The tendency for a different arrangement of voids in a junction depending on the distance SMD element and the thickness of the solder layer was investigated using X-ray computed tomography. Originality/value – The use of 3D computed tomography for void investigation gives full information about the internal structure of the joint and allows for precise void identification. Vacuum application during the soldering allows significant voids elimination.

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Purpose – The purpose of this paper is to assess the reliability of thermoelectric generators after ageing at elevated temperature and to determine the influence of the technology used (i.e. type of thermoelectric material, type of substrate and soldering technology) for thermogenerator (TGE) assembly. Design/methodology/approach – In this paper, the Seebeck coefficient and the current voltage were measured for lead telluride doped with either manganese (PMT), germanium (PGT) or sulfur (PST) TGEs. The Seebeck coefficient measurements were taken at temperatures between 230 and 630 K. Findings – The Seebeck coefficient determined for PMT, PGT and PST TGEs increases approximately linearly with increasing temperature and is greater by about 40 per cent for PST and about 30 per cent for PMT than in commercially available PbTe TGEs. The best outcome in terms of stability after long-term ageing was that of PMT material. Originality/value – The choice of proper technology (i.e. thermoelectric materials, type of substrate and soldering technology) for the TGE assembly is essential for their functioning overtime and reliability.

PurposeThe purpose of this paper is to investigate tin pest formation in lead‐free alloys.Design/methodology/approachSamples of Sn99.5Ag3.0Cu0.5, Sn99Cu1 and Sn98Cu2 alloys were prepared in four different forms. The first group was prepared using traditional PCB technology and a hand soldering method. The next group of samples was composed of as‐received ingots of these alloys. To check the impact of mechanical treatment on the transformation process, additional cold‐worked and cold‐rolled samples were prepared (30 kN). All samples were placed initially either at −18°C or at −65°C for low temperature storage testing. Visual observations, scanning electron microscopy observations and X‐ray diffraction analysis were performed to identify the transformation process. Additional samples were prepared using a force of 75 kN and placed in a chamber at a temperature of −30°C for long‐term testing.FindingsThe detectable symptoms of tin pest in samples subjected to mechanical processing with 1 and 2 wt.% of Cu addition stored at −18°C were observed at the edges of the samples after 17 months of storage. Further aging at −18°C showed the progress of α/β transformation with time under low‐temperature stress, but only in these specimens. With the application of greater force to the pressing process (75 kN instead of 30 kN) and at a temperature of storage close to the maximal transformation rate (−30°C), there was a significant acceleration of the α/β transformation, and this dependence can be used in predicting the risk of tin pest occurrence in various lead‐free alloys.Originality/valueThe paper shows that the degree of mechanical processing had a great influence on the α/β transformation rate. Based on these observations, it is proposed that such mechanically processed samples can be used for accelerated testing of tin‐rich lead‐free alloys at low temperatures. Such tests would be appropriate for a practical estimation of the tin pest risk when the design life of some electronic equipment ranges from 15 to 25 years.