Surface and Grain-Boundary Diffusion of Gold-Copper

Abstract

The diffusion of gold into copper grain boundaries from thin sources has been studied from 760° to 625°C. The activation energy for the grain‐boundary diffusion of gold into copper is 25 kcal/mole. At the lower temperature, there was observed surface depletion of gold at the grain boundary in accordance with theoretical solutions. The surface diffusion of gold on copper (100) surface was studied from 705° to 580°C under 10⁻⁹ Torr. The activation energy for surface diffusion was about 25 kcal/mole. The rates of surface diffusion were found to be less than those for grain‐boundary diffusion at the same temperature. Gold‐copper whiskers were generated adjacent to the grain boundaries for diffusion at or below 660°C. The growth of such whiskers is diffusion‐controlled and is attributed to the stress resulting from volume increase due to gold diffusion into the grain boundary.