Fracture mechanics analysis of solder joint intermetallic compounds in shear test

Solder joints in the electronics products are considered as critical reliability concerns. In this research, a quantitative evaluation of fracture mechanics parameters (such as Stress intensity factors (SIF, KI and KII) and kink angle, θ) in the IMC layer for SnPb and Pb-free solder joints has been carried out. Computation methods are based on finite element numerical modelling of stress analysis in a copper-IMC-solder-IMC-copper assembly under shearing condition. It is assumed that only one crack is present in one of the IMC layers. Linear Elastic Fracture Mechanics (LEFM) approach is used for the parametric study of SIFs and θ, at the predefined crack in the IMC layer of solder butt joint shear sample. different parameters studied in this research, the location of the crack from the solder interfaces has been found to be very sensitive. Crack near 1 micron distance from the interface has been found to be very prone to propagate. It is interesting to see that a thicker IMC layer reduces crack propagation propensity if there is only a single crack exists in the IMC layer and that crack is located at the middle of the IMC layer. Even if the whole solder layer is replaced by the IMC in the solder joint, the fracture propagation possibility is greatly reduced. Thickness of solder joints is also found to have a significant influence on the SIF values. It has been found that soft solder matrix generates non-uniform plastic deformation across the solder-IMC interface near the crack tip that is responsible to obtain a wide range of KI, KII and θ values.