Abstract: The unified viscoplastic Anand model is employed to represent the inelastic deformation behavior of SnPb solders. Based on the experimental data and the elsto-plasto-creep model, the material parameters of Anand model for 92. 5Pb5Sn2.5Ag and 60Sn40Pb solders re determined.The linear viscoelstic Maxwell model is applied to describe the modulus and volume relaxation of a underfill material U8347-3 in flip chop package and the relaxation coefficients are obtained. In addition, the stress/strain responses of flip chip package under thermal cycling are simulated with finite element method. The viscoplastic strain and thermal fatiue lifetimes of SnPb solder joints are analyzed. The results show that the viscoplastic Anand and the linear viscoelastic Maxwell models can be used to represent the mechanical behaviors of SnPb solders and underfill material, respectively. The material models and underfill material, respectively. The material models can be applied to the reliability simulation and analysis of electronic packages.

Key words: Flip chip package, Material model, Reliability, SnPb solder, Underfill, CHF, Micro-structure surface, Spray cooling, Temperature non-uniformity