The Effects of Microstructure and Ag3Sn and Cu6Sn5 Intermetallics on the Electrochemical Behavior of Sn-Ag and Sn-Cu Solder Alloys

The aim of this study is to evaluate the electrochemical corrosion behavior of Sn-2 wt.% Ag and Sn-2.8 wt.% Cu solder alloys in a 0.5 M NaCl solution at 25 degrees C as a function of microstructure features and Ag3Sn and Cu6Sn5 intermetallics. Both Sn-Ag and Sn-Cu alloys are becoming interesting lead-free solder alternatives. Microstructure morphologies obtained from a vertical water-cooled unidirectional solidification system under a cooling rate of about 15 degrees C/s are analyzed. Electrochemical impedance spectroscopy (EIS) diagrams, potentiodynamic polarization curves and an equivalent circuit analysis were used to evaluate the electrochemical parameters. It was found that although the relative cost 1.5 times higher for the Sn-2Ag alloy compared to that of the Sn-2.8Cu alloy, its corresponding electrochemical behavior is better in terms of polarization resistance, current density and pitting corrosion. This is shown to be intimately associated with the resulting fine and homogeneously distributed Ag3Sn intermetallic particles in the Sn-rich matrix.