Peculiar Patterns of SiO2 Contamination on the Contact Surface of a Micro Relay Operated in a Silicone Vapor Environment

Terutaka TAMAI  

IEICE TRANSACTIONS on Electronics   Vol.E82-C    No.1    pp.81-85
Publication Date: 1999/01/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section LETTER (Special Issue on Electromechanical Devices and Their Materials)
electric contact,  silicone contamination,  SiO2,  contact failure,  contamination pattern,  

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Peculiar patterns of SiO2 contamination around the periphery of the contact trace caused by silicone vapor under switching at the boundary of 1.6 W were confirmed. For micro relays, the electrical power conditions are restricted to lower level. Therefore, it is important to ascertain the upper limit of the electrical power conditions for normal operation. The peculiar pattern is important as it is recognized as the first stage of the origination of contact failure. Causes of this pattern were discussed from the viewpoints of temperature distribution in the contact trace, molten metallic bridge, micro arc discharge, and supply of silicone vapor with oxygen. It is proposed that during the closing contacts, as maximum Joule heating occurs at the periphery of the true contact area and silicone vapor with oxygen is easily supplied at the periphery, SiO2 grows around the contact trace. For the opening contacts, as the bridge or micro arc appears, silicone vapor with oxygen is supplied only outside of the contacts. Thus SiO2 is formed mainly around the periphery of the trace. Moreover, SiO2 was scattered radially depending on the sputtering of molten metal under rupture of the bridge. Therefore, the peculiar pattern forms as a result.