Numerical study of gold wire bonding process on Cu/low-k structures

A 2-D transient nonlinear finite-element (FE) analysis of thermo sonic wire bonding process on Al-capped Cu/low-k structure is carried out to understand the deformations of bond pad and the responses of structure under bond pad. An FE methodology is established that includes the ultrasonic vibration of the capillary and the analysis is studied at the impacting stage of the wire bonding process. The FE framework allowed for the detailed study of stress evolution in the Cu/low-k structure during the process in order to elucidate the evolved stresses due to the deformation behavior of the bond pad. A comparative study between bonding process on Al-capped and Au-capped low-k structures is also conducted. Effect of variation of frictional coefficients, low-k and undoped silicon glass (USG) modulus and bond pad thickness, on low-k layers and bond pad are investigated to observe their mechanical responses. The effect of implementation of porous low-k material is also highlighted and its presence is shown to increase the sinking of bond pad by a considerable amount. Analysis of the FE calculations together with experimental results suggested some optimal parameters for the bonding process.