Electrochemical migration and electrochemical corrosion behaviors in 3wt.% NaCl solution of 64Sn-35Bi-1Ag solder with in doping for micro-nanoelectronic packagings

In this thesis, electrochemical corrosion and electrochemical migration characteristics of 64Sn-35Bi-1Ag (SBA) solder with In doping in 3wt.% NaCl solution are researched by potentiodynamic polarization measurement and a self-designed experiment, respectively. The surface morphology and elemental composition of corrosive products and dendrites during ECM process are determined by SEM, EDAX techniques. The results show that the corrosive current density (Icorr) decreased with In doping, which proves that anti-corrosion capacity increased with In increasing, the possible reason is relative to intermetallic compounds formation, such as β (In
₃
Sn) and γ (InSn
₄
), which consumes Sn content contained in solders and activated Sn-points decreasing is the directive induced reason of Icorr decreasing. From this point, In doping is benefit to improve anti-corrosive capacity of SBA solder. While, in ECM process, the dendrite growth rate is increased with In content increasing. The shapes of dendrites are completely different from each other, the former looks like as small feathers, the latter looks like tree leaves. The “bridge time” between 5mm fine pitch in DC=3V electric field is 200hrs without doping, while 100hrs with In doping in the same condition which is disadvantage to fine-pitch micro/nano-packaging. EDAX results showed that the contents on dendrites of 64Sn-35Bi-1Ag solder are mainly Sn, Bi, Cl, only little other elements. While the main contents of SBA solder with In doping are Sn, Cl, only little Ag. Therefore, it is benefit with In doping in SBA solder from point of corrosion, while, it is disadvantage to micro/nano-packaging from point of ECM process. Thus provides a good technical support to develop a new lead-free solder substituting for Sn-37Pb.