Packaging of thin film thermoelectric generators for autonomous sensor nodes

This paper focuses on packaging of thin film thermoelectric generators (TEG) for energy harvesting applications in sensor nodes for the internet of things (IoT). The TEGs have to be robust against mechanical stress caused by the assembly and packaging process steps and the mismatch of the coefficients of thermal expansion of the used materials. In this work, the mechanical stability of TEGs was evaluated by using a shear force test apparatus and a four line bending test. Furthermore the influence of underfill and stress decoupling thermal adhesives on the mechanical performance was investigated. It could be shown that underfill between the two substrates improves the shear force stability of the investigated thermoelectric generators. During mechanical tests the internal electrical resistance of the modules was monitored. It was observed, that the electrical shutdown coincides with the mechanical shutdown of the generator. By using selected thermal adhesives with and without underfill a sufficient robustness of the thermoelectric generator against typical warpage as known from a standard molded land grid array (LGA) sensor package was achieved.