Reliability of lead-free solder in power module with stochastic uncertainty
Abstract The weak point for Insulated-Gate Bipolar Transistor (IGBT) modules in terms of reliability is thermal fatigue in solder joints due to the thermal stress induced by constitutive materials with different coefficients of thermal expansion (CTE). Now, many researches aimed to define accurate finite element simulation with constitutive equations of material behavior and fatigue failure relation connecting the inelastic strain and the number of cycles before failure. Even when these relations are clearly identified, the validation of the finite element model is difficult due to the scatter of input data. In fact, fatigue life of solder joints strongly depends on geometric shape, solders behavior (due to the process) and applied load. The aim of this article is to estimate the probability of failure of power module with structural reliability methods by considering geometric, material and loading variables as random variables. Since in a non-linear context, the finite element calls are expensive in terms of computer run time, an FE strategy is proposed here to replace conventional 3D mesh of layer by 3D-shell. To reduce computation time, response surface method, which approximates the output strain with respect to input random variable (RV) with the design of experiment (DOE) procedure, is used to perform reliability analysis. This reponse surface allows at the end to perform Monte Carlo random simulation process for fitting Weibull and fatigue life distribution on the output inelastic strain.