Designs of Temperature Loads on the Fatigue Life Analysis of Lead-Free Solder in IC Packages

Firstly, finite element analysis software (ANSYS) is used to investigate the accumulated creep strain range and accumulated creep stain energy density properties of lead-free solder (95.5Sn-3.9Ag-0.6Cu) in IC packages under the temperature cyclic loading by the Garofalo-Arrhenius hyperbolic sine law. Then the Taguchi method is further used to analyze the effects of IC package models on the fatigue life subjected to the temperature cyclic loading. The five main factors are the high and low temperature dwells, the temperature ramp rate, and the dwell time of both high and low temperatures, respectively. Moreover, each factor has four levels. According to the L-16 orthogonal arrays of the Taguchi method, three different IC packages PBGA-256, PBGA-388 and CCGA-1657 are used as the noise factors. Furthermore, the Schubert's model is used in Taguchi method and ANOVA analysis is to find the main influence factors on the fatigue life and reliability of lead-free solders. It is thus expected to provide reference data for the setting lead-free solder temperature cycle testing criteria in the future. The results show that when applying accumulated creep strain range on fatigue life and reliability, the main influence factors are the temperature range. On the other hand, when applying accumulated creep strain energy density on fatigue life and reliability, the main influence factors are the low temperature dwell and temperature ramp rate. The main reason for this difference is that the accumulated creep strain energy density is obtained from calculating the surrounded area by the hysteresis loops of creep stress and creep strain.