Diffusion-induced stresses in the intermetallic compound layer of solder joints

Atomic diffusion in soldering process leads to growth and stress developed in the intermetallic compound layer in solder joints. The stress and morphological evolution of the intermetallic compound layer, which is driven by the stress, result in degradation of mechanical performance of solder joints. Microstructure of the intermetallic compound layer in solder joints is modeled. The model consists of the Cu6Sn5 layer. The Cu atom concentration distribution in the intermetallic compound layer is derived based on the Fick´s second law. Then the diffusion-induced stress is obtained analytically by transforming atomic diffusion effects into bulk strain. The results show that the diffusion-induced stress is compressive. When the diffusion time is long enough, the diffusion-induced stress has a linear distribution along the thickness of the intermetallic compound layer.