Vapour phase soldering used for quality improvement of semiconductor thermogenerators (TEGs) assembly

The processing of harvested waste heat obtained from industrial or domestic installations directly converted into electrical energy using thermoelectric generators (TEG) is an interesting and future-proof solution. The TEG generator involves the serial connection of even tens of p–n thermocouples, through which a current of even a dozen amperes can flow. Its reliability strongly depends also on the quality of the solder joints, especially on the types of solder alloys, their quality, the soldering techniques applied and other factors. An additional difficulty is the functioning of thermogenerators and their solder joints at high temperature of up to several hundred degrees Celsius and with large temperature gradients between cold and hot plates. This paper presents the technical results of research investigation of semiconductor TEG model with particular reference to the technological aspects of the solder joint performances. Two types of solder pastes with different compositions and melting temperatures were examined. The main soldering method used was vapour phase soldering (VPS). VPS uses the latent heat of liquid vaporization to provide heat for soldering. A vacuum option during the soldering process was also applied. The results showed that the number of voids is strongly dependant on alloy composition and the presence of the vacuum.