Numerical analysis of ultrasonic wire bonding: Effects of bonding parameters on contact pressure and frictional energy

The elasto-plastic large deformation taking place in ultrasonic wire bonding is analysed by means of 2-D and 3-D finite element method. A special focus has been placed on how the important wire bonding parameters, such as bond force and power, affect the contact pressure along the wire-bond pad interface. It is shown that the contact interface had a long elliptical shape, and the maximum contact pressure occurred always at the periphery of the contact interface, which is consistent in the current 2-D and 3-D finite element analyses. The normalised real contact area as well as the maximum frictional energy intensity varied in a similar manner to the contact pressure, with the maximum values occurring at the periphery of contact interface, where weld is preferentially formed in practical wire bonding. A higher bond force does not result in a higher contact pressure, or higher frictional energy intensity, suggesting that a high bond force is not directly correlated to better wire bondability.