Analytic Model Verification of the Interfacial Friction Power in Al us w/w Bonding on Au Pads

To close the gap between the development of wire bonding equipment and the knowledge about the welding process itself, a friction power model is presented. The model can be used to calculate the welding quality of a wedge in dependence to the bonding and material parameters. Based on theories for Au ball/wedge bonding, the model is enhanced for us wedge/wedge (us w/w) bonding with aluminum wire. Therefore, the deformation of the wire is described by the von Mises stress, and the geometry changes due to the decreasing wedge height during bonding are taken into consideration. Furthermore, the paper introduces the minimum friction amplitude needed for any frictional cleaning of the interface and takes the precleaning during touchdown into consideration. To prove the model, four equations are highlighted to theoretically predict the shear force, the tool tip and pad amplitude, and the characteristic of the deformation during the us stage of w/w bonding. These magnitudes are measured for different bonding parameters while bonding 25 μm AlSi-1 wire to Au metalized Si test structures. The model parameters were then fit to the experimental results for all bonding parameters.