Our Group has extensive expertise in interfacial reaction at metal-metal surfaces using electroless plating and has specifically studied the mechanism of electroless gold, nickel, and cobalt.
We employ a combination of surface, structural and morphological techniques to monitor the interfacial reactivity and plating rates, including electrochemical quartz crystal microbalance (EQCM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray photoelectron (XPS) analysis.
We have also developed EQCM based mass sensor arrays for correlating the bath chemistry with the overall plating quality on industrial wirebond samples.
We have shown that the mechanism of electroless gold deposition follows a multi-step electron transfer process during the oxidation of dimethylamine borane (DMAB) on gold in alkaline media.
According to this mechanism, the initial chemical step is the SN2 substitution reaction of DMAB with OH- leading to the formation of the active, reducing agent, trihydrohydroxy borate ion, BH3OH-, which depends on the pH of the solution. The resulting BH3OH- species undergoes a series of irreversible electrochemical oxidation producing the following intermediates BH2(OH)2-, BH(OH)3- and B(OH)4-, the latter of which is the final product.
The number of electrons transferred in each oxidation wave of DMAB in hydroxide was calculated and confirmed using the rotating disk electrode (RDE). When the KOH concentration is less than the dimethylamine-borane complex, the diffusion rate of hydroxide might be rate-limiting.
