Finite-Element Simulation of Stress Intensity Factors in Solder Joint Intermetallic Compounds

The trend toward the miniaturization of electronic products leads to the need for very small sized solder joints, where the volume fraction of intermetallic compounds (IMCs) would be higher. In this paper, a fracture mechanics study of the IMC layer for SnPb and Pb-free solder joints has been carried out using a finite-element numerical computer modeling method. It is assumed that only one crack is present in the IMC layer. The linear elastic fracture mechanics approach is used for the parametric study of the stress intensity factors [(SIFs) K _I and K _II ] at the predefined crack in the IMC layer of the solder-butt-joint tensile sample. Contrary to intuition, it is revealed that a thicker IMC layer, in fact, increases the reliability of a solder joint for a cracked IMC-assuming that there is only a single crack that exists in 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. Values of K _I and K _II are found to decrease with the location of the crack farther away from the solder interfaces while other parameters are constant. Temperature and strain rate are also found to have a significant influence on the SIF values. It has been found that a soft solder matrix generates a nonuniform plastic deformation across the solder-IMC interface near the crack tip that is responsible for obtaining a wide range of K _I and K _II values.