High temperature Cu-Sn joints manufactured by a 250°C fluxless bonding process

A 250°C bonding process is developed to manufacture Cu-Sn joints that can withstand up to 415°C. This is made possible by solid-liquid interdiffusion in the mixture of Cu, Sn, and Sn liquid that contacts with Cu coated on a substrate. The mixture is produced by heating the Sn-Cu multilayer composite that is deposited on semiconductor in high vacuum to inhibit tin oxidation. Upon deposition, Cu interacts with Sn to become Sn-Cu₆Sn₅ composite where Cu₆Sn₅, prevents the Sn layer from oxidation in atmosphere. Thus no flux is needed. This is a fluxless, lead-free, low cost, low temperature process that provides high temperature joints