Investigation of IMC layer effect on PBGA solder joint thermal fatigue reliability

Thermal cycling reliability test and analysis for PBGA with Sn-3.8Ag-0.7Cu lead free solder joints with Ni/Au surface finish were investigated. Failure mode of PBGA component exhibits solders fatigue failure with failure site close to solder/IMC interface. The MTTF was determined by Weibull model and used to calibrate the finite element analysis (FEA) results. Intermetallic compound (IMC) layers of CuNiSn are formed when SnAgCu solder is reflowed on PCB board with Ni/Au finish. The reliability of electronic assembly is affected by IMC during thermal cycling. In this paper, finite element analysis of solder joint reliability has been developed to model the effect of IMC layer on solder joint fatigue behavior. It is shown that the IMC layer reduces the solder joint fatigue life. In this study, the elastic modulus for CuNiSn IMC was measured by nanoindentation using a continuous stiffness measurement technique. The IMC elastic modulus effect on solder fatigue was also investigated by FEA modeling.