On the formation of the ordered phases CuAu and Cu3Au at a copper/gold planar interface

The formation of the ordered compounds, CusAu and CuAu, has been observed in a study primarily aimed at determining the rate of interdiffusion in the gold-copper system. In the planar diffusion couples aged at temperatures from 50°C to 400°C and for times to 4 years, the compounds were observed to form as layers at the goId/copper interface for temperatures under 400°C. The layers were visible in the scanning electron microscope backscattered image of polished cross-sections, and their compositions were determined by the corresponding plateaus observed in the electron microprobe X-ray intensity profiles. Kirkendall type porosity was also observed to form in the copper-rich zone adjacent to the ordered compound layers. These results are compared and contrasted to the findings of several other studies which have considered this reaction and its practical implications to device performance.