The interdiffusion of electrodeposited Ni, Pd and Pd-Fe with a Cu substrate was studied, at temperatures ranging from 300 to 900C, by using energy dispersive X-ray spectroscopy. Chemical interdiffusion coefficients were deduced by using the Boltzmann-Matano analysis. A difference in the interdiffusion coefficients, which was observed for Cu-Ni couples that were plated from differing Ni baths was attributed to differing initial grain sizes and microstructures. The grain-growth rate of the Cu/Ni couple at 500C, during the first 0.5h of heat treatment, was found to be higher than for the same couple after 48h of heat treatment; resulting in higher diffusivities. A transition at 700 to 750C was observed in the Arrhenius plot for the Cu/Ni system, thus indicating a change in the diffusion mechanism. The interdiffusion coefficients of the Pd/Cu system, as determined at 300 to 700C, were higher than those in the Cu/Ni system by more than an order of magnitude. Interdiffusion in Cu/Pd was reduced when the Fe was alloyed with Pd, as a Pd-25wt%Fe alloy, by electroplating. The apparent interdiffusion coefficients of the Cu/Pd/Fe system were higher than those of the Cu/Ni system for heat-treatment temperatures above 300C, but were comparable to those of Cu/Ni at 300C. Rapid interdiffusion in the Cu/Pd/Fe system at 500C was suggested to arise from vacancy formation.

Barrier Properties of Ni, Pd and Pd-Fe for Cu Diffusion. K.M.Chow, W.Y.Ng, L.K.Yeung: Surface and Coatings Technology, 1998, 105[1-2], 56-64