Effect of exposure to alkaline solution on Sn-9Zn solder joints

The microstructural, phase and mechanical behaviors of Sn-9Zn solder bulk and joint in 6 M potassium hydroxide solution were investigated by means of open circuit potential measurement. The anomalous eutectic structure of Sn-9Zn solder was completely replaced by sheet-like and flake-like corrosion products after immersion. Post-immersion phase analysis revealed that the mixture of Sn and Zn oxides dominated the surface. The preferential removal of Zn was determined to control the initial electrochemical reactions of the solder. Relatively poorer ultimate tensile strength than that of the as-prepared counterpart was obtained after immersion, revealing that the mechanical integrity of the Cu/Sn-9Zn/Cu solder joint was damaged by the preferential removal of Zn. The weak intermetallic compounds formed between the interfaces of the Sn-9Zn/Cu further reduced the interfacial strength of the Cu/Sn-9Zn/Cu solder joint.