The Behavior of Surface Oxide Film on Ruthenium and Rhodium Plated Contacts

Although a surface oxide film on platinum-metal contacts is effective in preventing these contacts from polymerizing organic materials, it causes an increase in contact resistance. It is important to determine the thickness of surface oxide film which effectly prevents organic polymerization without causing a significant increase in contact resistance. Auger Electron Spectroscopy is used here to determine the thicknesses of the surface oxide films formed on Ru and Rh plated contacts at various temperatures in synthetic air. These are compared with results for untreated Ru and plated Rh contacts. Contact voltage versus contact resistance and contact force versus contact resistance characteristics of plated Ru and Ru oxidized after plating are measured by the crossed-rod method to study the relationship between contact resistance and thickness of a surface oxide film. The extent of organic polymerization on Ru and Rh plated contacts is determined by operating the contacts unloaded (dry) and monitoring the contact resistance after the treated and untreated contacts are exposed to benzene vapor. !t is found that, when the surface of the contacts is covered by a thin oxide film in either the case of plated Ru or plated Rh, the contact resistance can be low and stable, whereas contacts cleaned by Ar+ bombardment prior to sealing will be high in resistance. From these experimental results, it is determined that the thickness range of surface oxide film which prevents polymerizing without any measurable increase in contact resistance is approximately 5A ~25A.