Predicting solder joint reliability for thermal, power, and bend cycle within 25% accuracy

Solder joint reliability has received a renewed interest since the inception of BGA and CSP type packages. While traditionally board level reliability during thermal and power cycling is considered important for most applications, solder joint failures due to board bending have also become a major reliability concern for portable applications. 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. Although a number of life prediction models for solder joint under thermal cycle conditions have been proposed in the literature, not enough work has been reported in extending these models to power and bend cycle simulations. The accuracy of life prediction tool has also become critically important, as the designs need to be evaluated and improved with high degree of confidence not through relative comparison but by providing absolute numbers. This paper describes in detail the life prediction model for solder joints for thermal cycle conditions and its extension to power and bend, cycle conditions. The approach uses advance finite element modeling and analysis techniques such as constraint equations and sub-structuring and is based on mechanics of deformation. The model has been correlated with more than 60 data points and predicts life within 25% in most cases. The framework of modeling and prediction methodology described here is fully applicable for developing life prediction models for Pb free solder also, once the deformation mechanisms are identified.