Corrosion behaviour assessment of lead-free Sn-Ag-M (M=In, Bi, Cu) solder alloys

The corrosion behaviour of lead-free Sn88.7Ag2.3In9.0, Sn86.6Ag3.0Bi10.4, Sn96.1Ag3.1Cu0.8 and Sn90.4Ag2.9Cu6.7 solder alloys was investigated in 0.1M NaCl solution and compared with that of the conventional eutectic Sn73.9Pb26.1 solder. Scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) were used to characterize the samples prior and after the electrochemical tests. Potentiodynamic polarization curves show that Sn88.7Ag2.3In9.0 and Sn86.6Ag3.0Bi10.4 solders exhibit poor corrosion behaviour compared to that of Sn73.9Pb26.1. On the contrary, copper addition enhances the corrosion resistance of Sn–Ag solder alloys which exhibit improved passivity behaviour compared to Sn73.9Pb26.1 solder. Moreover, increasing the copper content from 0.8 to 6.7 at% results in a significant improvement of the corrosion behaviour of Sn–Ag solders. The presence of tin oxychlorides were detected at the surface of all the alloys investigated after the electrochemical tests. In addition, indium oxychlorides were also observed in the Sn88.7Ag2.3In9.0 solder alloy.