Thermosonic bonding is used for bonding gold wire with less heat, less pressure and less time, when compared to the thermocompression technique. This bonding process allows reduced temperatures during the bonding process.
The addition of ultrasonic energy is what allows all of the reductions in heat and pressure. The lower heat is still supplied by a heated workholder, which holds the part being bonded. The bonding wedge is usually unheated. The bonding machine supplies the lower pressure as it pushes down the wedge onto the wire. The time or duration is how long the bonding wedge sits on the wire and this time requirement is typically reduced as well.
The ultrasonic energy results from a mechanical vibration of the wedge at a standard frequency of 63khz. New high frequency systems offer frequencies of 110-120Khz. The ultrasonic vibration of the wedge is what allows all the reduction in forces and temperatures, and scrubs the bonding wire into the metal interface.