Electromigration Effect on Kinetics of Cu-Sn Intermetallic Compound Growth in Lead-Free Solder Joint

Intermetallic compounds (IMCs) growth is often accompanied by void and crack formation. It can reduce the mechanical properties and reliability of solder joints. In this paper, based on the Cu mass transport mechanisms, a theory model is established to analyze the IMC growth behaviors on Cu/Sn/Cu interconnection structures. The influence of IMC dissolution process is considered to investigate the polarity effect of electromigration (EM) on kinetics of IMC growth. Verified by reported experimental data, the model can accurately calculate the thickness of IMC growth under specific temperature and current stressing. The model reveals that during thermal aging, the thickness growth of IMC on Cu-Sn interfaces has a parabolic curve relationship with time. While under current stressing, EM Cu flux in Sn solder accelerates the anode's IMC growth and motivates the transition of its thickness growth from parabola-like curves to a linear-like relationship. The cathode's IMC will reach constant thickness with stressing time, which can be primarily determined by the dynamic equilibrium between Cu dissolution flux and chemical Cu flux. When the initial thickness of IMC is larger than this constant, the IMC on the cathode side follows a parabola-like curve to dissolve. Otherwise, it follows a parabola-like curve to increase.