Development of a stable non-cyanide gold-tin electroplating solution for optoelectronic applications

Abstract

A highly stable non-cyanide electroplating bath which can maintain clear at least one month was developed based on Au(III)-Sn(II) using 5,5-dimetheyl-hydantoin (DMH) and pyrophosphate as complexes. The combination of DMH and pyrophosphate can effectively minimize the difference of the deposition potentials between Au and Sn, making the codeposition of Au-Sn alloys possible. The cyclic voltammetry (CV) curve revealed that the codeposition of Au and Sn occurred at the potential of -790mV with a peak potential of -900mV. Pulsed plating was employed to optimize the morphology and composition of Au-Sn alloy films. The effects of pulse frequency, duty percentage and peak current density on the morphology and composition of the deposits were investigated. The compact Au-Sn eutectic alloy with Sn content controlled from 10 at.% to 50 at.% can be obtained. The Au-Sn deposits were characterized by the scanning electron microscopic (SEM) and energy-dispersive spectroscopic (EDS) analyses.