Advanced bonding interface inspection technique for process optimization in heavy wire bonding

This article focuses on the analysis of the interface formation of heavy wire bonding contacts. A test methodology is presented which combines the novel BAMFIT (Bondtec Accelerated Mechanical Fatigue Interface Testing) method, the 3D measurement of fracture patterns and the application of adapted evaluation algorithms. Unlike the shear test, which only measures resistance to mechanical deformation by the shear chisel, the test methodology used directly measures the connected area. Precisely knowing the percentage of bonded area allows the user to fine-tune bonding parameters to closely match the material system being used as well as to identify differences in the material behaviour. In order to work out these subtle differences, 4 wire types were investigated, which basically have very similar mechanical properties. Parameter studies using DoE (design-of-experiment) were performed for all wire materials used. In addition to the deformation of the bonding contacts, shear forces, shear strengths and the percentage of bonded interface area were determined. After analyzing the available data and modeling the process with DoE software, process windows were derived for the wire materials. Here, it was shown that accurate knowledge of the connected area – determined by the testing methodology presented in this publication – allows more accurate decision making regarding the wire material to be used. Furthermore, it could be shown where the heavy wire shear test reaches its limits in such investigations.