Effects of bonding force on contact pressure and frictional energy in wire bonding

A numerical study is made of the elasto-plastic deformation taking place in ultrasonic wire bonding based on the 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 2D and 3D 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.