Abstract
This study investigates the evolution of interfacial microstructures in Cu/Sn–3.5Ag/Cu and Cu/Sn–3.5Ag/Cu–15Zn (wt%) microbumps. Due to the small size of microbumps, Cu–Sn intermetallic compounds (IMCs) rapidly form from the Cu pads. These brittle IMCs occupy the entire joint and weaken joint reliability. Moreover, Ag 3 Sn tends to precipitate inside the solder in large plates, which results in the accumulation of thermal stress due to a CTE mismatch between Ag 3 Sn and β-Sn. It is demonstrated that doping Zn into one of the Cu substrates effectively suppresses the growth of Cu–Sn and Ag 3 Sn IMCs. The mechanisms involved are explained in detail using thermodynamic theories and undercooling effects. Owing to the effective suppression of Cu–Sn and Ag–Sn IMCs, Cu/Sn–3.5Ag/Cu–15Zn microbumps are potentially useful in strengthening the interconnections of novel 3D-IC technologies.