Strain based approach for predicting the solder joint fatigue life with the addition of intermetallic compound using finite element modeling

Finite element analysis is extensively used for simulating the effect of accelerated temperature cycling in electronic packages. There are number of issues that need to be addressed to improve the current FEM models. One of the limitations for the models presently available is excluding the effect of intermetallic compounds (IMC) (Cu₆Sn₅, Cu₃Sn) formation and growth between solder joint and Cu pad. The mechanical reliability of these IMC clearly influences the mechanical integrity of the interconnection. The brittle failures of solder balls have been identified with the growth of a number of IMC both at the interfaces between metallic layers and in the bulk solder balls. Previous study on intermetallics modeling discussed the energy based approach for predicting the fatigue life. The results show contradictory trends of life, not consistent with experimental data. This paper focuses the fatigue life prediction of the solder joint incorporating the effect of IMC using plastic and creep strain approach in finite element modeling. As a typical application, 3D Quarter model of a CSP is chosen to do the FE analysis. Accelerated temperature cycling is performed to obtain the plastic work due to thermal expansion mismatch between the various materials. Accumulated plastic strains were incorporated to predict the fatigue life. The model incorporates time dependent and time independent plasticity (i.e. creep) for the solder materials. The results are compared with conventional models that do not include intermetallic effects. It is shown that the strain based approach gives results that are consistent with general trends.