Interfacial reactions during soldering with lead-tin eutectic and lead (Pb)-free, tin-rich solders

The use of lead (Pb)-containing solders for the interconnections of microelectronic subsystem assembly and packaging has become an environmental issue. Extensive research and development activities for replacing Pb-containing solders with environmentally safe Pb-free-solders are in progress in electronic industries, universities, and national laboratories. One key technical issue recognized with the Pb-free, Sn-rich solders is a need to develop a good barrier metallurgy to control the interfacial reactions, namely, dissolution of the base metal(s) and concurrent formation of intermetallics at the soldering interfaces. In this study, the interfacial reactions of Cu and Ni metallization with several Pb-free and Pb-containing solders are investigated. The dissolution kinetics of the base metal(s) as well as the growth kinetics of the intermetallics are discussed.