The effectiveness of a variety of 1 to 2-μm-thick barriers in preventing the interdiffusion of copper substrates with gold overplates was investigated. These studies were carried out at both elevated (400 and 500°C) and low temperatures (100 and 175°C). In the high temperature range, of the materials studied, only the cobalt and cobalt-5 weight percent phosphorous were found to be effective barriers. Their effectiveness was comparable to that of the nickel-8 weight percent phosphorous barrier reported by Turn.

The low temperature results were anomalous in that the specimens annealed at 100°C show greater penetration than those annealed at 175°C. It is proposed that this temperature effect is related to the concurrent recrystallization of the gold overplate taking place to a larger degree during the higher temperature diffusion anneal. Thus, at the lower temperature the high density of grain boundaries characteristic of asplated structures is better preserved and leads to a larger overall (grain-boundary) diffusive flux.