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

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 gamma-Cu5Zn8 adjacent to the solder, the thin beta'-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 degrees C can form a rigid interface, and tensile strength reaches about 40 MPa.