Wetting and interface microstructure between Sn–Zn binary alloys and Cu

Abstract

Sn–Zn binary alloys have been examined as a lead-free solder. Zn distributes in a Sn matrix as platelets. The hypoeutectic alloys show two endothermic peaks in DTA, which correspond to the eutectic and the liquidus temperatures. Three reaction layers are formed at the Sn–Zn/Cu interface without containing Sn: the thick γ–Cu5Zn8 adjacent to the solder, the thin β′–CuZn in the middle, and the thinnest layer adjacent to Cu. Although many nonwetting regions and voids are formed at the interface because of poor wetting, soldering at 290 °C can form a rigid interface, and tensile strength reaches about 40 MPa.