Thermal Equivalent Circuit Model of Multi-Die SiC Power Modules

The main aim of this work is to provide a straightforward tool to modelize the thermal behavior of power module packages. The proposed circuit-based modeling approach takes into consideration the mutual thermal interaction among the dies, which plays a key role in the estimation of their working temperature. Furthermore, this modeling method features a compact and modular structure that can be easily tailored for different package configurations, maintaining limited complexity and computational burden. Last but not least, this thermal model includes both heating and cooling effects, thus allowing to evaluate thermal stresses even under pulse width modulated power devices. The thermal model is obtained starting from the temperature profiles carried out through a finite element analysis (FEA), by applying a power loss step to each single die. Starting from these profiles, a fitting curve algorithm is used to identify the elements of the RC networks used to represent the auto and mutual thermal impedances. The thermal model is thus an algebraic linear system including the RC networks parameters, and it can be exploited to identify the thermal status of each die of the power module even operating at different load conditions. The method has been applied in a SiC 3 phase inverter power module in which the high side and low side switches are formed with four parallel connected 1200V 350A SiC MOSFET dies. The results outgoing from the proposed model are confirmed by that carried out from FEA.