Influence of copper contamination on contact quality between gold wire and Nickel-Palladium bond pad through X-ray photoelectron spectroscopy

Wire bonding failures were observed on the copper bond pad with Nickel-Palladium (NiPd) surface. To understand the copper effect on the bondability of gold wire onto the NiPd pad, X-ray photoelectron spectroscopy (XPS) analysis was carried out. Results showed that significant presence of Cu 2p (in relative concentration) on the pad surface can potentially introduce adverse effect on wire bondability. Sputter depth profiles indicated that determining Cu 2p layer thickness on the bond pads is crucial in eliminating poor gold wire adhesion. It is also observed that the thickness of copper oxides at the surface of the bond pad may not attribute to the non-stick failures but the relative concentration of copper oxide at the respective surface depth may influence the contact quality between gold wire and the pad. Relative to well bonded pads, the sputtering rate for copper on the non-stick pads´ surface were lower. Copper impurities from plating process potentially adhere onto the surface of the bond pads and subsequently inhibit the attempt of wire bonding.