Effect of Organic Plating Additives Concentration on Carbon Content and Donor Density of Electroplated Tin

Pure tin is widely used as a replacement of Pb-Sn eutectic alloy as finish and solder material. This study aims to determine how the increasing concentration of organic plating additives affects the carbon content and donor density of electroplated Sn. Pure tin was electroplated on an Al sheet in a Hull cell using a commercial plating solution. Plating was performed in electrolyte baths with primary additive concentration from 100 mL/L to 600 mL/ L, and with secondary additive concentration from 8 mL/L to 48 mL/L. Current densities of 15, 8 and 3 A/dm(2) were considered. The increased concentration of organic plating additives caused an increase in carbon content of the deposit from 5 wt.% C to 8 wt.%C. Mott-Schottky measurements showed increasing electron donor density of up to four orders of magnitude as a function of current density and carbon content. A higher current density during deposition causes the tin oxide film to reach the donor density saturation value at lower concentrations of organic plating additives. This suggests that current plays a role in the decomposition of organic additives, which results in the incorporation of carbon in the deposit.