Numerical analysis of ultrasonic wire bonding: Part 2. Effects of bonding parameters on temperature rise

The thermo-structural analysis of ultrasonic wire bonding is performed by means of 3D finite element method. A special focus has been placed on monitoring the temperature rise during ultrasonic vibration. An equivalent method is used to simulate the wire and bond pad, where the large volumes of wire and bond pad are effectively reduced to small computational magnitudes. The history of temperature changes in the wire-bond pad-substrate interfaces influenced by varying bond forces and bond pad sizes is specifically studied. It is shown that the maximum bulk temperature obtained upon completion of ultrasonic vibration is far lower than the melting temperatures of the wire and bond pad materials, indicating that the bulk temperature rise due to ultrasonic vibration is not directly responsible for ultrasonic wire bonding. A large bond pad size usually leads to a lower temperature rise, and when the pad size reaches a certain value, the effect of bond pad size on temperature rise becomes insignificant. A higher bond force results in a marginally higher temperature rise than a lower bond force, which does not necessarily affect the wire bondability.