A review of creep fatigue failure models in solder material - simplified use of a continuous damage mechanical approach

Abstract

Numerical methods have become a useful mean to predict the thermo-mechanical reliability of solder interconnects in electronics, at least comparatively. In principle, each calculation finally rests on a creep fatigue model or criterion. The article reviews some important failure models of solder found in literature, discusses their benefits and drawbacks, and finally compares them on the example of a semi-analytical assembly model. Cyclic fatigue criteria constitute the classical approach in creep fatigue modelling. Strain range, strain range partitioning, inelastic energy and energy partitioning, are all approaches which have lead to successful development of failure models for solder in electronics. Beside cyclic criteria, continuous damage mechanical models have been developed recently in different publications. They are basically extended sets of constitutive equations including a new variable called damage. In such approaches, damage may be integrated over any cyclic or non-cyclic solicitation. A semi-analytical model of a flip chip PBGA (plastic ball grid array) assembly has been developed in order to implement a continuous damage mechanical approach. Then it is used for comparisons with some cyclic fatigue criteria on the same thermal cycle. The assembly model is based on the theory of bi-material thermostats and on a continuous damage mechanical model found in a recent publication. Only the outline of the model is described. Easy parametrisation and short calculation delays allow to run the model over high number of thermal cycles and to study the damage evolution. Results have not been correlated with experimental data, but are in a correct order of magnitude, whatever failure criterion is applied.