Predictive Model Development for Life Prediction of PBGA Packages With SnAgCu Solder Joints

A fatigue model to predict the number of cycles for crack initiation and crack growth rate in Sn4.0Ag0.5Cu solder joints used in plastic ball grid array packages when subjected to accelerated thermal cycling has been developed. In addition to the conventionally used damage metrics such as accumulated strain and accumulated work, the normal strain in the solder joints has also been taken into consideration for fatigue model development. Unlike traditional fatigue models, which equate the life of the package to the life of the critical solder joint, the fatigue life of the package has been estimated by factoring in the reliability and hence the fatigue life of all the solder joints in the package. Good agreement was observed between the estimated package fatigue life from the fatigue model and the fatigue life as determined from experiments.