Preparation of Sn–Ag–In Solder Bumps by Electroplating of Sn–Ag and Indium in Sequence and the Effect of Indium Addition on Microstructure and Shear Strength

This paper focused on the feasibility of preparing Sn-Ag-In ternary solder bumps with small size by two-step electroplating. The interfacial reaction and shear strength between three different solders (Sn2.2Ag, Sn1.8Ag9.4In, and Sn1.6Ag21.7In) and Cu under bump metallization (UBM) were investigated. After the reflow for 10 min, η Cu
₆
(Sn,In)
₅
and ε Cu
₃
(Sn,In) intermetallic compounds (IMC) were formed at the interface near the solder matrix and Cu UBM, respectively. Indium addition lowered the reflow temperature and improved the interface between solder and IMCs. The mean shear strength of Sn1.8Ag9.4In solder bump was higher than that of Sn2.2Ag and Sn1.6Ag21.7In solder bumps. After long time reflow, the mean shear strength increased.