Interdiffusion between Cu and Sn-rich solder: Dominant diffusion species

Extensive microstructural and kinetic studies on the formation and growth o f the intermetallics of Sn-rich solder/Cu couples have been reported. Howev er, experimental data on the dominant diffusing species are limited and in conflict. The dominant diffusing species for the soldering and aging of Sn- 3.5Ag alloy/Cu couples were investigated by using unsoldered or Cr-evaporat ed surface as a reference line. After soldering, the Sn-rich alloy on top o f the scallop-shaped Cu6Sn5 intermetallic compound was observed below the o riginal Cu surface. Sn was also observed to diffuse to Cu during the aging process. Therefore, Sn was suggested to be the dominant diffusing species f or both soldering and aging.