Thermal fatigue reliability analysis for PBGA with Sn-3.8Ag-0.7Cu solder joints

In this work, thermal cycling reliability test and analysis for PBGA components with Sn-3.8Ag-0.7Cu solder joints were investigated. Based on test results, a two-parameter Weibull distribution model was used to determine the mean time to failure (MTTF) of PBGA components. The MTTF was used for validation of finite element analysis (FEA) results. FEA analysis using quarter model and submodeling method was implemented to study stress strain behavior of Sn-3.8Ag-0.7Cu lead free solder joints considering three thermal cycles. In FEA analysis, two different solder joint material constitutive models, viscoplastic Anand´s model and elastic-plastic-creep model, and two different fatigue life prediction models, energy based and strain based fatigue life model, were used for comparison. Volume averaged method was used for extracting fatigue life prediction parameter. Traditional whole interface layer elements averaged method overestimates the fatigue life of solder joint due to lower energy or strain used in fatigue life model. In this paper, new averaging volume of outermost ring elements was proposed. It was shown that outermost ring elements averaging method gave better result compared to MTTF. Thermal cycling and thermal shock loads were simulated in FEA analysis to study the temperature ramp rate effects on fatigue life.