ICT2014 Abstracts

Large temperature differences between two plates in thermoelectric modules (TEMs) intended for high temperature applications makes the TEM’s contacts vulnerable to the elevated thermal stress leading to possible mechanical failures.

Analytical and numerical modeling demonstrates that the maximum shear stress occurring at the contacts of the legs is supposedly responsible for the structural robustness of the TEM assembly. This maximum shear stress depends on the geometry, the boundary condition for the TEM assembly, and also the material properties, such as the coefficient of thermal expansion (CTE), and the Young’s modulus of various layers.

Previously, we have shown the maximum shear stress in a conventional TEM assembly occurs at the interface between the ceramic substrate and the copper metallization. This maximum shear stress can be reduced by decreasing the fill factor, i.e. fractional area coverage of legs. However, for high temperature applications, the analysis shows that localized CTE mismatch between these layers could play a significant role in creating the maximum shear stress in the other layers of assembly. Preliminary finite element modeling shows that decreasing the fill factor does not always reduce stresses due to CTE mismatch. In a design for high temperature application, a CTE mismatch between solder layer and SiGe thermoelectric leg leads to the maximum shear stress of the assembly at their interface. By engineering the material properties and by optimizing the solder thickness, the maximum shear stress is reduced and the trend followed analytical prediction. We will discuss sensitivity of the maximum shear stress to the material properties and the dimension of each layer, providing guidelines to design a mechanically robust TEM.