Fatigue life models for SnAgCu and SnPb solder joints evaluated by experiments and simulation

In recent years, many solder fatigue models have been developed to predict the fatigue life of solder joints under thermal cycle conditions. While a variety of life prediction models have been proposed for near eutectic SnPb(Ag)-solder joints in the literature, not enough work has been reported in extending these models to lead-free soldered assemblies. The development of life prediction models, requires a deep insight into failure modes, constitutive models for the thermo-mechanical behavior of solders and an experimental reliability database. This is needed for the correlation of experimentally determined cycles-to-failure to simulation results by finite-element analysis. This paper describes in detail the life-prediction models of SnPb(Ag) and SnAgCu solder joints for thermal cycle conditions. To obtain reliable FEM input and to verify simulation results, a variety of material testing and experimental fatigue data is necessary. The accuracy of life-prediction tools has also become critically important, as the designs need to be evaluated and improved with a high degree of reliability, not through relative comparison but by providing absolute numbers. This work deals with the effect of different solder interconnect alloys (Sn59Pb40Ag1 and Sn95.5Ag3.8Cu0.7) and the effect of different package types (PBGAs, CSPs, Flip Chip on FR-4 with and without underfill) on the fatigue life. Different temperature cycling conditions are applied.