TEM observation of two-dimensional growth of lamellar gold electroplated on copper wires

Electroplating is an essential process to produce Cu–Au complex bonding wires. Therefore, mastering the general growth behaviour of gold film plated on copper substrate has an instructive effect on the subsequent processes of pinching-out and annealing in the processing of Cu–Au complex bonding wires. In this paper, plated gold film consisted of an intermediate layer and a gold layer, which were characterised in terms of transmission electron microscope (TEM) observations, especially the techniques of selected area electron diffraction (SAED) and displaced-aperture dark field (DADF). A thin intermediate layer with polycrystalline gold is observed adjacent to the ribbon-like copper substrate, which is due to the competing mechanism between chemical and electrochemical reactions. The gold layer is detected in the outer regions of the intermediate layer, and the formation of the gold layer is dominated by the electrochemical mechanism. Lamellar gold orients randomly in the gold layer, whose outer surface is mainly enclosed by the planes of {111}. The lamellar gold grows in only two dimensions, as the vertical direction is blocked by sulphite near the cathode.