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.