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|Packaging of High Temperature Thermoelectric Devices|
|Keywords: High Temperature, Thermoelectric, Reliability|
|A key issue with the thermoelectric devices today is the demand for increased operating temperature while maintaining high levels of reliability and low cost. While these requirements provide incentives to develop new materials which are able to operate at higher temperatures, and efficiently over wider temperatures ranges, it also creates challenges for the packaging of these devices. In a standard thermoelectric assembly, a large number of n-type and p-type semiconductor elements must be assembled in a regular manner and the thermal resistance between these elements and the heat exchangers is critical. While maintaining this optimal thermal path, the elements must also be electrically isolated from the heat exchangers and the entire array must be resistant to shock and vibration over the wide temperature range dictated by the ambient and operating conditions. The goal of this research efforts is to develop a commercially viable package assembly for thermoelectric generators that are suitable for high temperature operations such as in passenger vehicles. A potential brazing material was selected that can sustain extreme temperature and several brazing profiles were investigated to generate a strong bond with other materials such as direct bonded aluminum (DBA) substrate and Silicon Germanium (SiGe) die. Several test assemblies were fabricated in order to determine the compatibility of the braze materials with the DBA and SiGe. These test assemblies were subjected to shear testing followed by thermal shock from -40 C to +200 C to determine the strength of the brazing bond as a function of accelerated aging. High temperature storage (HTS) was also carried out for 1000 hours at 525 C to determine the bond strength as a function of hours. Thermo-mechanical and reliability analyses were conducted using finite element simulations to guide the design of the thermoelectric package assembly. Using FEA, critical locations in terms of larger stress, failure modes, and prediction of the fatigue life under thermal cycling was also investigated.|
|Shams Arifeen, Student
University of Idaho