Phase identification of intermetallic compounds formed during In-48Sn/Cu soldering reactions

Transmission electron microscope observations and precise diffraction analyses were performed on the interfacial reaction between In-48Sn and Cu at the temperature range from 160degC to 250degC for up to 90 minutes. The results indicated that two different morphologies formed between In-48Sn and Cu at the temperature below 200degC: small-grain Cu₂(In,Sn) at the Cu side and large-grain Cu₂(In,Sn) at the solder side. If the soldering temperature is above 200degC, the Cu₆(In,Sn)₅ phase is the first phase formed at the solder/Cu interface. However, the subsequent solid-state diffusion of In and Sn atoms through the initial Cu₆(In,Sn)₅ layer drove the formation of Cu₉(In,Sn)₄ phase between Cu₆(In,Sn)₅ and Cu substrate.