Effects of electroplating parameters on composition and morphology of Au-Sn alloy films

A non-cyanide Au-Sn alloy electroplating bath with high stability was developed. The bath used 5,5-dimethyl hydantoin (DMH) and K
4
P
2
O
7
as the major complexing agents for gold and tin ions. Na
2
SO
3
was a synergetic complexing agent for gold ion. Moreover, bath stabilizer and antioxidant were also added. Effects of the concentration ratio of gold ion and stannous ion and concentration of complexing agents and stabilizer on the composition and morphology of Au-Sn electrodeposits were studied. The concentration ratio of gold ion and stannous ion has a notable influence on the composition and morphology of Au-Sn electrodeposited alloy films. When the concentration ratio of gold to tin ion ranged from 1:2 to 1:4, the Sn content increased from 10 at.% to 48 at.% and the grains of Au-Sn alloys changed from needle-like to fine then to granular at the current density of 25 mA/cm
²
. When the molar ratios of Na
2
SO
3
to gold ion increased from 6:1 to 30:1, the Sn content decreased from 37at.% to 25at.% and the Au-Sn electrodeposits showed smooth morphology when the concentration ratio of Na
2
SO
3
to gold ion ranged from 6:1 to 24:1. The Sn content decreased with the increasing concentration ratio of ${{\text{P}}_2}{\text{O}}_7^{4 - }$ to Sn(II). Moreover, when the concentration ratio of ${{\text{P}}_2}{\text{O}}_7^{4 - }$ and Sn(II) ranged from 1:6 to 1:9, the grain size of Au-Sn alloy films were fine. Moreover, smooth surface morphologies were obtained. The Sn content decreased with the increasing stabilizer concentration and smooth surface morphologies were obtained with the stabilizer concentration varied from 0.01 mol/L to 0.02 mol/L.