Investigation of the pre-heating process during thermosonic wire bonding by FEM simulation

In this paper, the pre-heating process of the thermosonic wire bonding process was investigated. In the case of this method, the energy for the bonding process comes from three different sources: ultrasonic vibration, pressure (force) and elevated temperature. The pre-heating system contains a heating table and the sample is positioned on the top of it. In order to determine the exact temperature distribution, a numerical model was prepared, which takes into account the specific geometry of the arrangement and the heat transfer methods between the various surfaces. The heat transfer between the ceramic substrate and the heating plate depends on the surface roughness of the materials, and on the pressure which is exerted by the substrate to the heating table. In our investigation, we implemented a physical test setup with K-type thermocouples which can validate stationary numerical models. The temperature difference between the set temperature of the heating table and the measured temperature was 4–5 °C, while the difference between the set and modeled bond pad´s temperatures was only 2–3 °C, which information will help to set the temperature of the heating tables more accurate.