Finite element analysis of copper wire bonding in integrated circuit devices

Axisymmetric finite element models of copper wire-bond-pad structure for an integrated circuit device were developed to investigate the effects of bonding force, initial bonding temperature, Aluminum metallization thickness, bond pad thickness and free air ball (FAB) diameter on induced stresses in the wire-bond structure. The results show that an increase in bonding force greatly increased the induced stresses in the copper FAB and bond pad (aluminum and silicon). However, a change in bonding temperature while keeping the bonding force constant does not result in an appreciable change in the stress. Similarly an increase in aluminium metallization thickness does not yield appreciable variation in the stress and strain in the bond pad. Over the range of FAB diameters studied it is found that bigger FAB yields smaller stress in the overall structure.