Electrodeposition of Sn-Ag Eutectic Alloy from Methanesulfonate Bath

Electrodeposited tin-silver eutectic alloy is a promising candidate to replace tin-lead solder coatings and provide superior thermal fatigue resistance. Eutectic tin-silver alloy film was deposited at 0.2∼5A/dm2 and at 25°C in a methane-sulfonate bath using the additives L-cysteine, 2, 2′-dithiodianiline, and polyoxyethylene-α-naphthol. The coexistence of these additives markedly inhibited preferencial deposition of silver over a range of low current densities.Tin and silver ions in the effluent were separated as hydroxide, and the residual concentration of tin and silver ions decreased to less than 0.01mg/L.Eutectic tin-silver alloy film consists of β-Sn and e (Ag3Sn) phases, and its solidus temperature was 221°C. Whisker were not observed on the alloy film of the copper substrate after one year of aging at 50°C.