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Validated simulation of the ultrasonic wire bonding process

Ultrasonic wire bonding is an indispensable process in the manufacturing of power semiconductor devices. These devices consist of one or more semiconductors in a common housing with integrated connectors. To interconnect individual components, wire bonds are used. Bonding machines form a joint between bond wire and components using ultrasonic vibration. In high power applications, such as electric vehicles, wind turbines and solar power systems, the thermal and mechanical limits of aluminum interconnects are nearing. The limits could be overcome using copper wire bonds, but their manufacturing poses challenges due to the harder material, which leads to increased wear of the bond tools and to less reliable production. Parameter values for which a stable process can be maintained can only be changed within a small range, making it necessary to compute suitable parameters beforehand. To this end, and to gain insights into the process itself and allow automated process parameter adaptation at runtime, the ultrasonic bonding process is modeled. The process model is composed of several partial models, which were introduced before. This paper focuses on the validation of a coupled point contact model which is used to calculate the friction and bond formation in a discretized bonding area. By doing this, new insights into the bonding process can be shown. For example, the growth of the welded area in the interface of wire and substrate during the bonding can be shown for different points in time. At the end, an experimental validation of the process model reveals a high model quality. This is one major step towards truly understanding the parameter influences on bond quality.