Prediction of thermo-mechanical fatigue for solder joints in power electronics modules under passive temperature cycling

A thermodynamically consistent cohesive zone model accounting for mixed-mode loadings suitable for analysis of thermo-mechanical fatigue is presented in this work. Fatigue effect on cracking is included using a damage evolution law which is dependent not only on the displacement jump, but also on the damage accumulation. The damage state is irreversible and evolves during loading, but not unloading. The stiffness of the cohesive zone is degraded with the increase of damage level. Temperature dependence of both stiffness and fracture energy is incorporated in the fatigue model due to the high operating temperature experienced by the solder material. Simulations are carried out in order to predict the number of cycles to failure of the solder joint in power electronics modules under passive temperature cycling conditions.