Physics of Failure Based Lifetime Modelling of Double Side Cooled Power Electronics Modules of Electric Vehicles Under Power Cycling

Abstract:
The complex layout of double sided power modules of electric vehicles and the risk of damage initiation and propagation in different interconnection layers necessitate a full three-dimensional model capturing all the details related to joining layers, power dies, terminals, and substrates. However, reliability of power modules is often simulated using simple models including only one power semiconductor die and the surrounding mold compound. In this work, a full model of a double sided power module with eight SiC dies per switch and the associated silver sintered layers is created to perform a thermal-mechanical analysis, and estimate the damage and lifetime of silver layers. Each die and the spacer bonded to it includes three silver layers: the top silver layer between the spacer and the top ceramic substrate, the middle silver layer between the die and the spacer, and the bottom silver layer between the bottom ceramic layer and the spacer. In this study, we used Anand viscoplastic model to represent material behavior of sintered silver. The damage parameter used for lifetime prediction was accumulated equivalent inelastic strain. This detailed finite element model enables accurate calculation of damage distribution in different silver layers, and study of the effect of the manufacturing parameters such as heatsink mounting pressure, as well as the effect of the neighboring joints and terminals on lifetime and reliability.