A damage parameter based on fracture surface for fatigue life prediction of CSP solder joints

FEM simulation for the fatigue life of CSP solder joints with various geometries and array types under thermal cycling condition is studied. Coffin-Manson law with inelastic strain range is used to estimate the fatigue life of CSP solder joints. Therefore, the two unknown material parameters in the fatigue life model need to be determined first. Actually, the two parameters are structure-dependent. In practice, they should be determined by comparing with experimental data of two typical structures so that they can characterize the fatigue behavior of other structures with common features. When determining the two structure parameters by comparing FEM results with experimental data, the problem of how to evaluate the inelastic strain range occurs. Some existing approaches include the maximum value, average values over an area or a volume around corner point. If the artificial factors and mesh-dependence are involved, it is found that these damage parameters don´t work well for the present purpose, i.e., the predicted fatigue lives cannot agree with experimental data. So a damage parameter based on fracture surface is proposed