Effects of Ga, Al, Ag, and Ce multi-additions on the properties of Sn-9Zn lead-free solder

Wetting balance method is used to evaluate the effects of Ga, Al, Ag, and Ce multi-additions on the solderability of Sn-9Zn lead-free solders, results show that the optimal addition amounts of Ga, Al, Ag, and Ce is 0.2, 0.002, 0.25, and 0.15 wt% respectively. The surface property of Sn-9Zn-0.2Ga-0.002Al-0.25Ag-0.15Ce solder is studied by X-ray photoelectron spectroscopy and auger electron spectroscopy analysis; results indicate that Al aggregates on the surface as a compact aluminum oxide film which prevents the further oxidation. The aggregation of Ce on the subsurface can reduce the surface tension of solder, and improve the solderability accordingly. Meanwhile, SEM and XRD analysis indicate that Cu5Zn8 and AgZn3 intermetallic compounds form at the interface between Sn-9Zn-0.2Ga-0.002Al-0.25Ag-0.15Ce solder and Cu substrate, while AuZn3 and AuAgZn2 form at the interface between solder and Cu/Ni/Au substrate. Moreover, results also indicate that the mechanical property of soldered joints is improved duo to the dispersion strengthening effects of AgZn3 in Sn-9Zn-0.2Ga-0.002Al-0.25Ag-0.15Ce solder.