Effects of sulfur addition on the wettability and corrosion resistance of Sn-0.7Cu lead-free solder

The effects of sulfur on the wettability of Sn-0.7Cu on Cu and on the corrosion behavior of Sn-0.7Cu in 3.5 wt% NaCl solution were investigated. The results reveal that sulfur considerably improves the wettability of Sn-0.7Cu and the optimal sulfur content is 0.08 wt%. SnS and SnSO4 phases form on the surface of the sulfur containing Sn-0.7Cu solder alloy after soldering characterized by XPS and XRD analysis. The addition of sulfur decreases the dross formation of the solder melt and the formation of SnO2 is inhibited. The potentiodynamic polarization tests show that the corrosion resistance of Sn-0.7Cu solder alloy is obviously enhanced by sulfur element. Analyses by SEM and XRD indicate that sulfur promotes the formation of the corrosion product, Sn3O(OH)2Cl2, on the surface of sulfur containing Sn-0.7Cu solder and it keeps the solder alloy from further corrosion.