Reliability assessment of SiC power module stack based on thermo-structural analysis

摘要

Power semiconductor modules for power electronics converters are required to withstand significant temperature cycles in operation. Due to the availability of novel wide-bandgap semiconductors such as SiC, operation temperatures and corresponding temperature cycles of the power modules are intended to be increased. This can lead to severe lifetime limitation by fatigue failure mechanism induced by the CTE (coefficient of thermal expansion) mismatch of the material layers in the module. In this study a 3D finite element model (FEM) of an advanced power module concept was developed. The main material stack consists of a ceramic substrate, an Ag sintered SiC MOSFET and a sintered top plate that serves as a bond buffer to allow for Cu wire bonding. Stress simulations are performed for several thermal load cycles starting with an analysis of the initia bonding process during manufacture, and following a temperature cycling mission profile during operation. Plastic strain energy densities in the critical regions of the bond interfaces are computed and its development upon consecutives cycles are followed-up in the time domain. Based on these investigations, it is possible to propose design improvements that are effective in reducing thermo-mechanical stresses, and to increase fatigue life.