Effects of intermetallic-forming element additions on microstructure and corrosion behavior of Sn-Zn solder alloys

The corrosion behavior of ternary Sn-9Zn-0.1X (X = Ni, Cr, Cu and Ag) solder alloys were investigated by electrochemical techniques and surface characterization, aiming to explore the effects of intermetallic-forming elements on the corrosion resistance. Zn-rich precipitates in the modified alloys were suppressed and refined by formation of Zn-containing intermetallic compounds. As a result, the corrosion resistance improved markedly with addition of these elements, and the potency to suppress anodic dissolution increased in the order of Ag < Cu < Cr < Ni. Such improvement was discussed in terms of refined Zn-rich precipitates and enhanced passive film stability.