Effects of thiourea and gelatin on the electrodeposition of Sn-Ag solder alloy

Sulfuric acid based Sn-Ag plating baths were developed to study the individual as well as synergistic effects of thiourea (TU) and gelatin on the characteristics of Sn-Ag deposits. Electrochemical behavior of each bath was investigated by cathodic polarization studies. Results showed that the deposition potential gap of both elements was reduced by both additives, hence allowing co-deposition of Sn-Ag to occur. In this study, TU increases Ag composition and changes deposits microstructure. Low content of gelatin inhibits Ag deposition but high content of gelatin results in enhanced Ag deposition. Microstructure of deposits has been improved by the synergistic effects of these two additives. Near-eutectic composition of Sn-4.0 wt.% Ag is achieved with the aid of 2g/L of TU and 1g/L of gelatin at a current density of 10mA cm^-2.