Early formation of Cu6Sn5 and (Ni,Cu) 6Sn5 during soldering was investigated. Sn 4.0Ag0.5Cu solder on Cu and electroless Ni-Au substrate was quenched in ice water after the initial stage of melting, and the solder-substrate interface was analyzed by transmission electron microscopy and energy-dispersive x-ray spectroscopy. At the contacting point, Cu3Sn and Cu6Sn5 were found at the solder-Cu substrate interface, while (Ni,Cu)6Sn5 and Ni2SnP were identified at the solder-electroless Ni interface. The contacting points were confirmed as the sites of heterogeneous nucleation. TEM analysis suggested that the nucleation of both intermetallic compounds can be attributed to diffusion-induced crystallization. Details of the early interfacial reactions are discussed.
- early melting process
- intermetallic alloys and compounds
- lead-free solder
- surface and interfaces