Growth mechanism and kinetics of Cu3Sn in the interfacial reaction between liquid Sn and diversely oriented Cu substrates

In this study, the effects of reflow temperature, reflow time, and substrates (polycrystalline and (001/110/111) monocrystalline Cu substrates) on the growth of Cu3Sn at the Cu/Sn3Ag interface were investigated. Results show that the growth of Cu3Sn on the interface shows grain boundary diffusion regardless of the orientation of Cu substrates. The formation of Cu3Sn is considered as the reaction between Cu atoms and Cu6Sn5 at Cu6Sn5/Cu3Sn interface due to the similar interfacial outline to Cu substrate. In addition, the growth of interfacial Cu3Sn is positively correlated with reflow temperature and time. And the preferred plane orientation of Cu substrate has a significant effect on the growth rate of Cu3Sn during reflowing. In this experiment, the growth of Cu3Sn shows grain boundary diffusion. The growth of Cu3Sn on polycrystalline Cu substrate is faster because it has a lot grain boundaries. And the growth rate on (110)Cu single crystals is the fastest among single-crystal Cu substrates because the high surface free energy of single-crystal oriented (110)Cu substrates promotes the growth of Cu3Sn and the diffusion distance of Cu atoms is the shortest in this direction.