Electrodeposition of Sn-Cu Alloy from Methanesulfonate Bath

Abstract

Electrodeposited tin-copper alloys show promise as lead-free alternatives to solder coatings. Eutectic tincopper alloy film was deposited at 0.5∼5A/dm² and 25°C in the following bath composition: 0.1974mol/L (CH₃SO₃)₂Sn, 0.0026mol/L CuSO₄, 2.0mol/L CH₃SO₃H, 0.01mol/L 2, 2'-dithiodianiline and 5g/L polyoxyethylene-α-naphthol. The coexistence of 2, 2'-dithiodianiline and polyoxyethylene-α-naphthol markedly inhibited preferencial deposition of copper over a noble potential range.
The eutectic tin-copper alloy film consists of β-Sn and η(Cu₆Sn₅) phases, and its solidus temperature was 227°C.
Tin and copper ions in the effluent were separated as hydroxide, and the residual concentration of tin and copper ions decreased to less than 0.01mg/L.