Abstract
Sn-In alloys are promising low-melting-point Pb-free solders. Cu and Ni are common substrates in the electronic products. This study examines the interfacial reactions in the Sn-20 at.% In(γ-InSn 4 ) /Cu and Sn-20 at.% In/Ni couples at 160°C. Only the η-Cu 6 Sn 5 phase layer is formed in the Sn-20 at.% In/Cu couple, and the layer grows thicker with longer reaction time. The reaction path is γ-InSn 4 /η- Cu 6 Sn 5 /Cu. A peculiar phenomenon with the bulging of the couple near the Ni substrate is found in the Sn-20 at.% In/Ni couple. A liquid phase is formed by interfacial reaction in the solid/solid Sn-20 at.% In/Ni couple at 160°C, and the reaction path is γ-InSn 4 /liquid/δ-Ni 3 Sn 4 + liquid/(δ-Ni 3 Sn 4 )/Ni. Usually Ni has a slower reaction rate with solders; however, the consumption rates of Ni substrate are much higher than those of Cu substrate in this study when they are in contact with the Sn-20 at.% In alloy at 160°C due to the formation of the liquid phase in the Sn-20 at.% In/Ni couple. © 2006 Materials Research Society.