Damage Mechanics-Based Failure Prediction of Wirebond in Power Electronic Module

A damage mechanics-based numerical approach for the prediction of the damage evolution in wirebond structures of the power electronic module (PEM) is presented. A simplistic damage evolution model is developed in an in-house finite element code, with a demonstration focused on the analysis of the wirebond damage evolution by thermally induced stresses in PEM subjected to varying thermal loads. The novelty of the proposed methodology is the damage evolution realized at the level of each discretised mesh element of the finite element model of the PEM structure in the numerical approach and the associated impact of damage on the mechanical material properties of that element. A simplified PEM structure is utilised as a case study to demonstrate the proposed damage evolution modelling. The thermal load of each discretised element of the PEM structure was imported from an external thermal code. From the thermally induced stresses, plastic strain rates were approximated and then, using these metrics a damage evolution metric was derived. The damage distribution plot of the wirebond structure for the applied load in the case study indicates that maximum damage accumulation at the heel structure reaches 2.4% of the total damage after 3 seconds. By extrapolating the trendline of damage evolution in wirebond, the time of the structural failure was also predicted. The maximum von Mises stress was observed on the busbar which reaches 64 MPa. The extreme stresses found at the busbar are attributed to the high value of the coefficient of thermal expansion of the busbar material.