Abstract:The effects of Ag on the microstructure and corrosion behavior of pre-soldering Sn-xAg lead-free solders, and on the formation of intermetallic layer of the solders with Cu substrate were investigated. The Ag contents (x) were 0, 3.0, 3.5, 4.0, and 5.0 wt.%. The Ag content played a role in the morphology of Ag₃Sn phase in the solders. The microstructure analysis showed that the β-Sn phase was surrounded by eutectic networks in the 3.0Ag and 3.5Ag solders and large plate-like Ag₃Sn formed in the 4.0Ag and 5.0Ag solders. Nonetheless, the Ag content slightly impacted the corrosion behavior of the as-cast solders as characterized using potentiodynamic polarization test. After soldering, only a single layer of a Cu₆Sn₅ intermetallic compound formed at the Sn–xAg/Cu interface. By comparison, the Cu₆Sn₅ intermetallic layer of the Ag-doped solders was thinner than that of the 0Ag solder. The fine Ag₃Sn particles in the eutectic networks precipitating in the 3.0Ag and 3.5Ag solders effectively hindered the growth of Cu₆Sn₅ grains compared to large plate-like Ag₃Sn in the 4.0 and 5.0Ag solders.

Key words: Sn-Ag lead-free solders; microstructure; Ag₃Sn intermetallic phase; corrosion behavior; Cu₆Sn₅ intermetallic layer; wettability