Surface- and microanalysis as a tool for studying the corrosion of aluminium

Corrosion phenomena of Al-1 % Si bond wires, observed after life testing of certain transistors, are studied. The following information is derived from laboratory simulation tests: the kinetics of the corrosion process, information about the corrosion mechanism and critical parameters, especially the influence of the environmental gas and Si content and finally the identification of the corrosion products and their comparison with those found for the transistor. It is demonstrated, using a combination of several surface analytical techniques, that the A1 pitting corrosion is induced and enhanced by the presence of water as a transport medium and surface electrolyte in an oxygen-rich atmosphere, with chloride ions as a stimulating and activating species. The effect of 1 % Si in the wire consists in acceleration of the corrosion rate, and is probably due to grain boundary effects. All critical corrosion parameters could be traced in the transistor system by electron microscopy, laser microprobe mass analysis and residual gas (and moisture) analysis by mass spectrometry.