Copper and silver contamination of thick film gold surfaces

Abstract The surface composition of thick film gold fired onto alumina substrates was studied using Auger electron spectroscopy. Two configurations were evaluated: (1) isolated gold films and (2) gold films contacted by partially overlapping Pd Ag films. The necessary Auger calibration factors were developed so that compositions could be given in atomic per cent. Two principal results were obtained. (1) The “gold” surface contained copper oxide immediately after the gold firing step. The surface copper was believed to come from copper oxide which is added to the gold paste to promote adhesion of the gold to the Al 2 O 3 substrate. Auger surface analysis showed that the gold surface contained about 7 at.% Cu and depth profiling showed that the copper concentration decreased to less than 1 at.% after a depth of about 300A˚into the gold. (2) The gold surface also contained about 9 at.% Ag after firing the Pd Ag. The silver was thought to surface diffuse over the gold from the contacting Pd Ag. An effective surface diffusion coefficient at 850°C was estimated to be at least 2 × 10 −6 cm 2 s −1 .