Wetting properties and interfacial microstructures of Sn-Zn-xGa solders on Cu substrate

The wetting properties and interfacial microstructures of Sn-9Zn-xGa lead-free solders with Cu substrate were investigated. The wetting property is improved remarkably with the increase of Ga content in the Sn-9Zn lead-free solder. The lower surface tension, which results from the decrease of the oxidation of the Zn atoms owing to the formation of the Ga-rich protective film covered on the liquid solder, is the key reason for the better wettability. During soldering, the Cu5Zn8 compounds layer form at the interface of Sn-9Zn/Cu and the IMCs formed at the solder/Cu surface become much thicker when the Ga content is from 0.1 wt.% to 3 wt.%. However, neither Cu-Sn compounds nor Ga-rich phases are observed at the solder/Cu surface.