Investigation of oxygen followed by argon plasma treatment on LED chip bond pad for wire bond application

Abstract

Purpose – The purpose of this paper is to investigate the efficiencies of argon (Ar), oxygen (O2) and O2 followed by Ar (O2→Ar) plasma treatments in terms of contaminant removal and wire bond interfacial adhesion improvement. The aim of this study is to resolve the “lifted ball bond” issue, which is one of the critical reliability checkpoints for light emitting diodes (LEDs) in automotive applications. Design/methodology/approach – Ar, O2 and O2→Ar plasma treatments were applied to LED chip bond pad prior to wire bonding process with different treatment durations. Various surface characterization methods and contact angle measurement were then used to characterize the surface properties of these chip bond pads. To validate the improvements of Ar, O2 and O2→Ar plasma treatments to the wire bond interfacial adhesion, the chip bond pads were wire bonded and examined with a ball shear test. Moreover, the contact resistance of the wire bond interfaces was also measured by using four-point probe electrical measurements to complement the interfacial adhesion validation. Findings – Surface characterization results show that O2→Ar plasma treatment was able to remove the contaminant while maintaining relatively low oxygen impurity content on the bond pad surface after the treatment and was more effective as compared with the O2 and Ar plasma treatments. However, O2→Ar plasma treatment also simultaneously reduced high-polarity bonds on the chip bond pad, leading to a lower surface free energy than that with the O2 plasma treatment. Ball shear test and contact resistance results showed that wire bond interfacial adhesion improvement after the O2→Ar plasma treatment is lower than that with the O2 plasma treatment, although it has the highest efficiency in surface contaminant removal. Originality/value – To resolve “lifted ball bond” issue, optimization of plasma gas composition ratios and parameters for respective Ar and O2 plasma treatments has been widely reported in many literatures; however, the O2→Ar plasma treatment is still rarely focused. Moreover, the observation that wire bond interfacial adhesion improvement after O2→Ar plasma treatment is lower than that with the O2 plasma treatment although it has the highest efficiency in surface contaminant removal also has not been reported on similar studies elsewhere.