LAUSR

The interfacial microstructures between Zn–Sn solder alloys and Cu substrate were investigated, and the effect of rare earth (RE) elements on the interfacial microstructures between Zn–Sn solder alloys and Cu substrate were also studied. The results showed that irregular shape, scallop-type ε-CuZn5 and flat γ-Cu5Zn8 and β′-CuZn IMC layers formed at the interface between Zn–Sn solders and Cu substrate. In solder part, dendritic ε-CuZn5 phase formed at the α-Zn phase during soldering process. Cu atoms are transported to the molten solder along the ε-CuZn5 grain boundaries during soldering process and result in columnar dendrite growth of ε-CuZn5 at the ε-CuZn5 grain boundaries. When small amount of RE element was added into solder alloy, the wettability of the solder alloys was significantly improved, while the thickness of the reaction layers at the interface of Zn–Sn solders/Cu was increased. At the same time, RE can promote the growth of columnar dendrite ε-CuZn5 phase.