Electrochemical corrosion behavior of Pb-free solders for die attachment

This study aimed to investigate the electrochemical corrosion behavior of the potential Pb-free solders, Bi-11 wt%Ag and Zn-40 wt%Sn, in 3.5% NaCl solution using the potentiodynamic polarization method with the scanning range from -2000 mV to +2000 mV. Pb-5 wt%Sn alloy was also examined for comparison. Experimental results show that the corrosion potential (E_corr) decreased in the decreasing order was Bi-11Ag, Pb-5Sn, and Zn-40Sn. Zn-40Sn exhibited the highest current density (I_corr), and that for Pb-5Sn was the lowest. The Pb-5Sn samples had a much extended passive region compared to Bi-11Ag, while the Zn-40Sn samples showed no passive behavior within the scanning range. According to the XPS and XRD data, the corrosion products were main PbCl₂ and PbO for Pb-5Sn, BiOCl, AgCl₂, and Bi₂O₃ for Bi-11Ag. Zn rich phases (ZnO and ZnCl₂) were found on the polarized surface of Zn-40Sn, and tin oxides were detected at the subsurface.