Lifetime prediction of a viscoplastic lead-free solder in power electronics modules under passive temperature cycling

Abstract : It is well established now that solder joint in power electronics undergoes a thermal-mechanical fatigue in service. In order to provide a predictive tool to assess fatigue lifetime of solder joint subjected to passive temperature cycling, a cohesive zone method (CZM) based fatigue model, accounting for mixed-mode loadings, is presented in this paper. A cohesive zone model with a specific fatigue traction-separation law is used in conjunction with the Anand viscoplastic behavior for the bulk solder for modelling the interfacial fatigue crack growth. Temperature dependence of both stiffness and fracture energy is incorporated in the CZM based fatigue model. The CZM based fatigue model as well as the Anand viscoplastic constitutive law is implemented in the Abaqus finite element code. Numerical simulations are carried out under passive temperature cycling. A particular attention is given to information in the region ahead of the crack tip such as stress concentration, process zone size, damage distribution. The evolution of the crack extension is used to estimate the number of cycles to failure at which the device becomes faulty