Abstract：Intermetallic compound (IMC) layers formed during soldering processes have a significant effect on the reliability of solder joints. The atomic diffusion effect during reflow and isothermal aging leads to growth and morphological evolution of IMC layers, and stress is developed in the IMC layers. The changed microstructure and the stress in the IMC layer result in degradation of mechanical performance of solder joints. Based on the mechanism of atomic diffusion-reaction, the diffusion-induced stress during the growth of the IMC layer is investigated. An analytic model with two interfaces(Cu/Cu6Sn5/Solder）at the early stages of IMC formation is proposed, and then the copper concentration distribution in the IMC layer is calculated by using the Laplace transformation method. Diffusion-induced stresses are obtained analytically by transforming atomic diffusion effects into bulk strain. The results show that the diffusion-induced stress is compressive, and it reaches its peak at the Cu/Cu6Sn5 interface. The diffusion-induced stress increases with the increase of the isothermal aging time, and finally it becomes stable and changes linearly along the thickness of the IMC layer.
2012, Vol. 33 
