IMC consideration in FEA simulation for PB-free solder joint reliability

Thermal cycling reliability test and analysis for PBGA components with Sn-3.8Ag-0.7Cu Pb-free solder joints with Cu-OSP and ENIG surface finish were conducted. Failure mode after test was analyzed using cross section and optical microscope. From the test result, a two-parameter Weibull distribution failure model was used to determine the mean-time-to-failure (MTTF) for the PBGA solder joints. FEA simulation using quarter model and submodeling method was implemented to study stress strain behavior of Pb-free solder joints. In this study, finite element analysis modeling of solder joint reliability has been developed to model the effect of intermetallic compound (IMC) layer on solder joint fatigue behavior. Nano-indentation material properties for IMC layer and advanced material constitutive models such as viscoplastic model and the elastic-plastic-creep (EPC) model for lead-free solder are employed. Intermetallic compound (IMC) properties such as Cu₆Sn₅, CuNiSn and Ni₃Sn₄ were modeled with different IMC layer thicknesses in order to study the effect of IMC layer on fatigue life of the solder joint. It is shown that the IMC layer reduces the fatigue life of solder joints compared to the case without considering IMC layer. Thicker IMC layer leads to less fatigue life prediction than thinner IMC layer. The effect of Young´s modulus of IMC on stress strain behavior of solder was also carried out