Accumulated creep strain and energy density based thermal fatigue life prediction models for SnAgCu solder joints

Pb free solder is fast becoming a reality in electronic manufacturing due to marketing and legislative pressures. The industry has pretty much concluded that various versions of SnAgCu solder alloy offer the best alternative for eutectic Sn/Pb solder currently in use. With the current trend of cheaper, faster, and better electronic equipment, it has become increasingly important to evaluate the package and system performance very early in the design cycle using simulation tools. This requires life prediction models for new solder alloy systems so that the package-to-board interconnect reliability can be predicted for various environmental and field conditions. This paper describes in detail the life prediction models for SnAgCu solder joints. The models are based on published constitutive equations for this alloy and thermal cycle fatigue data on actual components. The approach uses advanced finite element modeling and analysis techniques and is based on mechanics of deformation. Both accumulated creep strain and creep strain energy density based models are developed. The model has been correlated with a number of data points and predicts life within 25% in most cases. The framework of modeling and prediction methodology described here is fully compatible with the framework used for SnPb solder previously.