Deformation characteristics of Au wire bonding

In wire bonding, the quality of the bonding between the Al film and the Au wire has an effect on productivity and reliability. It is required to reduce the bonding area to as small as possible without deteriorating the level of bondability to increase the level of integration. The effect of capillary tip shape on bonding was investigated by deformation analysis of the Au ball by the rigid-plastic finite element method and by experiments. The flow stress of Au wire for the numerical analysis was evaluated by conducting the tensile test of Au wire at an ambient temperature of 250 °C. The mean radii and the amount of sliding for the bonded areas were evaluated with respect to the radius of the compression-bonded ball as a parameter under three conditions of capillary tip angle θ: θ = 45°, 60° and 30°. Bonding can be achieved when the amount of sliding is 0.01–0.05 μm or greater. With decreasing the capillary tip angle θ, the amount of sliding tends to increase. The amount of sliding can be controlled by changing the tip shape of the capillary. The results of deformation analysis and experiments on Au ball deformation indicate that the evaluation of the relationship between the shape of the capillary and bondability can be carried out by rigid-plastic FEM. This method used here is effective for determining the optimum bonding conditions and the proper shape of capillaries.