Growth behavior and morphology of sidewall intermetallic compounds in Cu/Ni/sn-Ag microbumps during multiple reflows

摘要

Sidewall intermetallic compounds (IMCs) grow rapidly by surface diffusion with the bump size shrinking. Cu/Ni/sn-Ag microbumps with thick Ni barrier have been fabricated and the inhibition effect of thick Ni barrier on sidewall IMCs growth during multiple reflows was investigated. Three kinds of sidewall IMCs were found: Ni3Sn4 (main product), Ni3Sn2 and Cu3Sn. The growth kinetics of sidewall Ni3Sn4 showed that the formation of Ni3Sn4 contained two stages: at first, sidewall Ni3Sn4 grew rapidly due to reactive wetting of molten solder; subsequently, the formation slowed down since the solder wetting was blocked by continuous Ni3Sn4 layer, and Ni3Sn2 and Cu3Sn formed by surface diffusion of Sn atoms.