Plasma chemical cleaning of chip carrier in a downstream hollow cathode discharge

Assembly & Packaging processes of semiconductor devices such as die attach, wire bonding, and molding can greatly benefit from Plasma Cleaning. The removal of surface contaminants prior to these process steps results in more reliable connections between the bonding surfaces. In this paper we present a new plasma process for die and chip carrier cleaning. Highly reactive radicals are generated in a hollow cathode discharge using different gas mixture; i.e. argon/hydrogen, argon/oxygen, and argon/ nitrogen. The radicals react with surface contaminants to form volatile compounds which subsequently degas from the substrate surface. The employment of a hollow cathode plasma source ensures a high degree of ionization and molecular fragmentation of the working gas. At the same time, the plasma potential was kept below 30 V. As a result, the cleaning process is purely chemical and not associated with surface erosion due to physical sputtering caused by energetic ions. Visual inspection, wire pull test, and contact angle measurements were used to confirm the cleaning efficiency.