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, Ag3Sn tends to precipitate inside the solder in large plates, which results in the accumulation of thermal stress due to a CTE mismatch between Ag3Sn and β-Sn. It is demonstrated that doping Zn into one of the Cu substrates effectively suppresses the growth of Cu–Sn and Ag3Sn 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.
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