Abstract: Wetting balance method is used to evaluate the effects of Ga,Al,and Ag multi-additions on the wetting property of Sn-9Zn lead-free solders.Results show that the optimal loading of Ga,Al,and Ag is 0.2 wt.%,0.002 wt.%,and 0.25 wt.% respectively.The intermetallics formed at the interface of Sn-9Zn-0.2Ga-0.002Al-0.25Ag solder and Cu/Ni/Au substrate is investigated by scanning electron microscope(SEM)and energy dispersive spectroscopy(EDS)analysis.SEM images illustrate that two portions,a planar AuZn₃ layer and an additional continuous scallop-like AuAgZn₂ layer,formed in the intermetallics.Meanwhile,X-ray photoelectron spectroscopy(XPS)and Auger electron spectroscopy(AES)analysis on the surface components of Sn-9Zn-0.2Ga-0.002Al-0.25Ag solder indicate that Al aggregates at the surface of the solder in the form of Al₂O₃ protective film which prevents the solder from further oxidation and improves the wettability in consequence.