Microstructural study of co-electroplated Au/Sn alloys

Gold-tin eutectic solder (20 wt% Sn), because of its excellent mechanical and thermal properties, is utilized for flip chip and laser bonding in optoelectronic applications. Coelectroplating of Au and Sn has been investigated as an alternative to conventional methods for depositing Au/Sn alloys. Pulse current (PC) and direct current (DC) plating tests have been performed and compared using a suitably stable plating solution. Plating conditions, including current density and ON and OFF times (for PC plating), have been varied to optimize the process. Reproducibility tests have also been performed. It is shown that a range of alloy compositions can be deposited, including eutectic and near-eutectic compositions, with compositional and microstructural uniformity potentially suitable for microelectronic and optoelectronic solder applications.