Anodic dissolution characteristics and electrochemical migration lifetimes of Sn solder in NaCl and Na2SO4 solutions

In situ water drop tests and anodic polarization tests of pure Sn solder were carried out in deaerated 0.001% NaCl and Na2SO4 solutions to determine the correlation between anodic dissolution characteristics and the electrochemical migration lifetime. The electrochemical migration lifetime of pure Sn solder in NaCl solution (67.6 s) was longer than that in Na2SO4 solution (40.0 s). The pitting potential of Sn solder in NaCl solution (175 mV) was higher than that in Na2SO4 solution (−53 mV). The passive film (SnO2) formed on pure Sn during water drop tests in NaCl solution was more stable than that formed in Na2SO4 solution (SnO). Therefore, the longer electrochemical migration lifetime of pure Sn in NaCl than in Na2SO4 solution can be attributed to the higher pitting potential in NaCl than in Na2SO4 solution, which is ascribed to the formation of a more stable passive film in the former.