Characteristic of Heat Affected Zone for Ultra Thin Gold Wire/Copper Wire and Advanced Finite Element Wirebonding Model

This paper demonstrates two major works, experimentally determines the material properties and accurately predicts the dynamic response of stressed region on the bond pad and beneath the contact area. The characteristic of heat affected zone (HAZ) on both Au wire and Cu wire have been carefully experimental evaluated. In addition, the dynamic response on Al-Cu pad and beneath the pad of Cu/low-k wafer during wire bonding process has been predicted by using finite element method. Material property for Cu wire from mechanical tensile test has shown much more rigid than Au wire. This would result in bond pad shoveling around the bottom of mashed ball during impact stage and the consequent thermosonic vibration stage. All the measured data serves as material inputs for the explicit commercial finite element software ANSYS/LS-DYNA. It is also demonstrated that the pad material for Cu/low K wafer can be replaced by Al-Cu pad or Cu pad to avoid large deformation on pad and cracking beneath the surface. A secondary electric flame-off (EFO) method has been conducted to reduce the strength of Cu wire and increase bondability and reliability. A series of comprehensive experimental works and FEA predictions have been performed in this study.