Effect of Mg doping on increase in the life with low contact resistance of Ag-Pd alloy switching contacts in silicone vapor environments

When silicone vapor adsorbed on contact surfaces is subjected to high temperature due to electric discharge in the atmosphere, SiO₂ is formed by chemical decomposition of the adsorbed silicone molecular. When SiO₂ is formed on contact surfaces and is caught in the interface of contacts, contact failure is caused by an insulation property of SiO₂. Newly developed contact material of Ag(40wt%)-Pd(60wt%) alloy with a small amount of dopant of Mg was applied experimentally to a microrelay. This material shows remarkable improvement of contact resistance property for contaminant oxide film in comparison with usual Ag-Pd contacts. In this study, the contact resistance property for the number of make-break switching operations of the Ag-Pd-Mg alloy was examined by wide range electrical conditions under saturated (1300 ppm) silicone vapor. Obtained contact resistance properties were compared with the Ag-Pd alloy itself and Ag-Pd overlaid with Au(90wt%)-Ag(10wt%) which is usually used. As a result, prolonged low contact resistance property of the Ag-Pd-Mg alloy for silicone environment was found. The mechanism of the low contact resistance property was clarified by cleaning effect based on removal of powder products formed from the contact traces. Moreover, activation of contact surfaces due to formation of MgO (magnesium oxide) on the surface of the Ag-Pd-Mg alloy was not observed by examination of arc duration. The arc duration of the Ag-Pd-Mg alloy was not as long as usual Ag-Pd alloy contact