Thermal resistance measurement and failure analysis of Multi-discrete SiC MOSFET System Module

At present, most of the power cycling tests only concentrate on researching the power device itself. However, in the actual electric vehicle inverters, connection layers are present between the power device and the heatsink, such as thermally conductive silicone grease. In addition to the internal packaging material for power device, the aging of external connection layer can also cause an increase in thermal resistance, resulting in the rise of junction temperature. As a result, the device aging can be accelerated. Thus, it is difficult to reflect the real failure mode and lifetime merely by evaluating the device internal reliability. In the current work, taking a multi-discrete system module in an electric vehicle inverter as a case study, a multiple structure function-based method for thermal resistance separation was proposed, which realizes the monitoring of the thermal resistance degradation for junction-to-case and two external layers of thermally conductive silicone grease. It was shown that the silicone grease aging was the main reason for the accelerated failure for the module. In addition, final simulation and experiment confirmed the accuracy of the proposed thermal resistance measuring method and failure analysis, also providing certain technical support for improving the reliability of system-level module devices..