Two-Side Growth of the Cu9Ga4 Phase during the Interfacial Reactions between Sn–Ag–Cu–Ga Solders and Copper Substrates

Abstract

Interfacial reactions between Sn–3.0Ag–0.5Cu–1.0Ga/1.5Ga in wt.% solders and Cu substrates have been investigated. The solder and substrate couples were annealed at 180°C for 6, 12, 18, and 24 days. Different layers of intermetallic compounds have been found to form, such as Cu₆Sn₅ and Cu₉Ga₄. Sn was also observed within the interfacial layer during the annealing. The Cu₆Sn₅ phase and the Cu₉Ga₄ phase were observed to form by turns from the substrate into the solder. The Cu₉Ga₄ phase grew from both the solder side and the intermetallics side. Growth of the Cu₉Ga₄ phase was found to depend on the Ga diffusion and the availability of the Cu₆Sn₅ phase.