Effects of CO2 atmosphere on contact resistance characteristics of noble metal contacts

Mixed atmospheres of N₂ and an active gas such as H₂ or O₂ are used in sealed enclosures to assure stable contact resistance and to prevent failures due to adhesion in sealed contacts. The effects of a CO₂ atmosphere on contact resistance and adhesion characteristics are investigated to determine if CO₂ could be an alternative atmosphere, because it is considered to be stable and nonreactive with contact materials. The test contact materials are Ag, Au, Pd, Ag-Pd alloy, and Au-Pd alloy. For Ag, Au, Ag-Pd alloy, and Au-Pd alloy contacts, the contact resistance increases with the number of operations, but for Pd contacts it remains low and stable. The increase in contact resistance in Ag and Au contacts is caused by film formation on the contact areas. Most of the films are amorphous carbon, and the film formation is restricted to the contact area. These results indicate that the carbon films are formed by the reduction of CO₂ on the contact area and that this reaction is accelerated by the opening and closing contact operations