Thermosonic ball bonding: friction model based on integrated microsensor measurements

A model of friction during thermosonic ball bonding is reported. The model is based on recent ultrasonic stress measurements during ball bonding using piezoresistive microsensors integrated below test bonding pads. At the bonding pad, the microsensor signal is a measure of the stress caused by periodic oscillation of the capillary and gold ball. The new model interprets the oscillation in terms of alternate periods of sticking and sliding during bond formation. The oscillation shape was examined using harmonic analysis and compared with electrical parameters from the ultrasound power supply. To further validate the model, test bonds were made on passivated test pads. The model was found to be consistent with the measurement data. Experiments were performed at temperatures between 35°C and 200°C