Interfacial reactions in Sn–(Cu)/Cu6Sn5/Ni couples at 210 °C

Sn–(Cu)/Cu6Sn5/Ni couples with indentation markers are examined at 210 °C. The original thickness of Cu6Sn5 is 20 μm, and the Cu contents of the Sn–(Cu) solders are 0, 0.7 and 1.0 wt%. The Ni3Sn4 phase is formed in all Sn–(Cu)/Cu6Sn5/Ni couples. In the Sn–0.7 wt%Cu/Cu6Sn5/Ni, Ni3Sn4 is the dominant growing phase and the thickness of Cu6Sn5 remains almost unchanged with reaction. Both Cu6Sn5 and Ni3Sn4 grow thicker with longer reaction time in the Sn–1.0 wt%Cu/Cu6Sn5/Ni couple, while the growth rate of the Cu6Sn5 is much higher. In the Sn/Cu6Sn5/Ni couple, Ni3Sn4 grows at the expense of the Cu6Sn5 phase. Sn and Cu are more active diffusion species. The growth of Cu6Sn5 phase is at the Cu6Sn5/Ni3Sn4 interface, and that of the Ni3Sn4 phase occurs at both the Cu6Sn5/Ni3Sn4 and the Ni3Sn4/Ni interfaces.