Investigation on Interfacial Compound Growth Kinetics in Sn-0.7Cu/Cu Solder Joint and Mechanism Analysis: Experiments and Molecular Dynamics Simulations

Herein, the interfacial compound growth kinetics and corresponding mechanisms in Sn-0.7Cu/Cu solder joint at aging stage were investigated using both experiments and molecular dynamics simulations. The research results indicate that, the growth rates of interfacial IMCs (Cu6Sn5 6 Sn 5 IMC and Cu3Sn 3 Sn IMC) are affected by the aging temperature severely, the higher aging temperature leads to the larger growth kinetics for both Cu6Sn5 6 Sn 5 IMC and Cu3Sn 3 Sn IMC. At aging stage, Cu substrate continuously supplies Cu3Sn 3 Sn IMC with Cu atoms. Those Cu atoms diffuse across Cu3Sn 3 Sn IMC to the Cu3Sn/Cu6Sn5 3 Sn/Cu 6 Sn 5 interface and react with Sn atoms diffused from the Sn-based solder to form new Cu3Sn 3 Sn grains growing towards Cu6Sn5 6 Sn 5 IMC, and the main crystal orientations are (100), (42-1), and (3-10). As the grain boundary diffusion rate of Cu atoms in Cu3Sn 3 Sn IMC determines the Cu-Sn - Sn reaction rate (new Cu3Sn 3 Sn grains formation rate) on Cu3Sn/Cu6Sn5 3 Sn/Cu 6 Sn 5 interface, the growth of Cu3Sn 3 Sn IMC is driven by grain boundary diffusion, which is manifested by a growth index n near to 0.3. Meanwhile, the rod-like Cu6Sn5 6 Sn 5 IMC preferentially grows into Sn-based solder attributed to the large number of Cu atoms provided by Cu3Sn 3 Sn IMC, which can diffuse to the top of Cu6Sn5 6 Sn 5 IMC and reacts with Sn-based solder. While when Cu6Sn5 6 Sn 5 IMC is thick enough, Cu atoms cannot reach to the top of Cu6Sn5 6 Sn 5 IMC anymore, but diffuse laterally within the Cu6Sn5 6 Sn 5 grains, resulting in the widening of scallop-like Cu6Sn5 6 Sn 5 IMCs. As the thickening of Cu6Sn5 6 Sn 5 IMC is caused by the growth of the existing Cu6Sn5 6 Sn 5 grains, the diffusion of Cu and Sn atoms in Cu6Sn5 6 Sn 5 grains plays a decisive role. Therefore, the growth of Cu6Sn5 6 Sn 5 IMC is driven by bulk diffusion, which is manifested by a growth index n near to 0.5.