Mechanism of stabilizer acceleration in electroless nickel at wirebond substrates

This paper examines the mechanism of stabilizer concentration at electroless nickel wirebond electrode. A one-step activation protocol was first achieved on copper substrates using acetic acid and dimethylamineborane. Thereafter nickel multilayers were grown onto the substrates using nickel sulfate heptahydrate as the source of nickel, sodium hypophosphite as the reducing agent, acetic acid as the complexing agent, and thiourea/lead acetate as the stabilizing agent. The morphology of the nickel layers and the effective concentration of the stabilizer were determined using quartz crystal microbalance, gravimetric techniques, and energy-dispersive X-ray analysis (EDX). The plating rate was obtained by measuring the thickness of the Ni-plated using X-ray fluorescence spectroscopy. It was found that lead acetate completely inhibited the plating, and a bimodal distribution was observed as the concentration of the thiourea was varied. We proposed a mechanism for the effect of stabilizer in electroless Ni baths. This mechanism was confirmed using Fourier Transform Infrared and EDX measurements.