Bondability of gold wire to gold-plated electrodes

In order to clarify the dependence of wire-bondability on the thickness of plated gold film electrode and the plating method, samples with different film thicknesses were prepared by means of substitution plating, deoxidation plating, and electroplating. After the heat-treatment usually used for the integrated circuit (IC) assembling process, the samples were analyzed by means of Auger electron spectroscopy (AES) and then wire-bonded. Thin films were cut out by a microtome from the wire-bonded samples and observed by transmission electron microscopy (TEM). The effect of heat-treatment, plating method and film thickness on the bond strength were investigated by using a shear test for the samples with films plated by the three different methods. The results obtained are as follows. (1) Without heat-treatment the bond strength did not depend on either the film thickness or plating method. (2) The nickel (from the substrate) concentration at the film surface increased with increasing heating period, and as a result the bond shear strength decreased. (3) The strength of samples wire-bonded after heat-treatment recovered when a surface layer of the gold film was removed before wire-bonding. The effect of film thickness and plating method on the wire-bondability to gold plated electrodes is further discussed.