Electrochemical behaviors of the Sn-9Zn-xAg lead-free solders in a 3.5 wt % NaCl solution

The electrochemical behaviors, microstructures, and corroded products of Sn-9Zn-xAg lead-free solders were investigated in this study. The 63Sn-37Pb and Sn-3.5Ag solder alloys were also tested for comparison. The Sn-3.5Ag solder alloy had a higher equilibrium potential (-0.44 V-SCE) than the ones of 63Sn-37Pb (-1.10 V-SCE) and Sn-9Zn (-1.43 V-SCE). The Ag addition enhanced the corrosion resistance of the Sn-9Zn solder alloy. Passivation behavior occurred in the solder alloys used in this study except the 63Sn-37Pb one. X-ray diffraction patterns showed that the Zn segregated in the Sn-9Zn solder alloy as solidified, but it dissolved when 0.5 wt % Ag was added to the solder alloy. The AgZn3 and Ag5Zn8 were found in the Sn-9Zn-1.5Ag solder alloy but they were substituted by the Ag3Sn when the Ag content in the solder alloy was above 2.5 wt %. However, they were the initial sites for pits formation. The corroded product of SnCl2 was observed in all solder alloys tested. In addition, the ZnCl2, ZnO, and SnO were observed in the Sn-9Zn-xAg solder alloys. (C) 2004 The Electrochemical Society.