Metastable pitting and its correlation with electronic properties of passive films on Sn-xZn solder alloys

The potentiostatically formed passive films on Sn-xZn solder alloys in NaCl solution was investigated by potentiostatic polarization and electrochemical impedance spectroscopy (EIS). Metastable pitting is quantitatively assessed in terms of pit size and frequency, which are found increase with Zn content. EIS results indicate the presence of transport behavior of charge species within the films. The Mott-Schottky analysis reveals that the passive films all behave as a highly disordered n-type semiconductor. The electronic properties of the passive films are greatly associated with metastable pitting susceptibility. The correlation between the stability and the electronic properties of the passive films is discussed.