A parametric study of flip chip reliability based on solder fatigue modelling

A solder fatigue model for 63Sn/Pb solder has been developed by combining nonlinear finite element modelling with thermal fatigue data of assorted flip chip assemblies. The model characterizes the creep fatigue phenomena of the solder alloy by correlating the amount of creep strain energy dissipated per thermal cycle with the characteristic Weibull life of the critical solder joint. It has been validated for various die sizes, bump geometries, board materials and thermal profiles. Furthermore, the model has accurately predicted fatigue lives for flip chip assemblies with and without underfill. The solder fatigue model has been utilized to investigate the reliability of flip chip joints subjected to thermal cycling. In particular, a parametric study had been performed which shows how various flip chip design parameters will affect solder joint fatigue. Finite element models have been developed to analyze the effect of die size, die thickness, solder joint height, cap diameter and underfill properties on solder fatigue. For this investigation, all analyses have been carried out for parts on ceramic substrates. The results for underfilled parts show that while die size does not influence solder joint reliability, the effects of underfill CTE are very important. Non-underfilled parts are significantly influenced by die size, cap size and joint height.