Electrodeposition of Sn-In Eutectic Alloy from Sulfosuccinate Bath for Flip-Chip Interconnection

Abstract

Electrodeposited tin-indium eutectic alloy promises to replace tin-lead solder coatings in LSI flip-chip interconnections thanks to its lower melting point and provide superior in thermal fatigue resistance. Eutectic tin-indium alloy film was deposited at 0.5-3A/dm² and at 25°C, in a sulfosuccinate bath using the additives 2, 2'-Dithiodianiline, polyoxyethylene-α-naphthol and polyethlene glycol 1000. The coexistence of these additives markedly inhibited preferencial deposition of tin. The eutectic tin-indium alloy film consists ofβ-Sn, In, InSn₄ and In₃Sn phases, and its solidus temperture was 117°C.