Adsorption of Silicone Vapor on the Contact Surface and Its Effect on Contact Failure of Micro Relays

Terutaka TAMAI  

IEICE TRANSACTIONS on Electronics   Vol.E83-C   No.9   pp.1402-1408
Publication Date: 2000/09/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Current Electromechanical Devices and Their Materials with Recent Innovations)
silicone contamination,  contact resistance,  adsorbed silicone molecule,  switching rate,  SiO2,  

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Silicone contamination due to SiO2 caused by decomposition of silicone vapor is recognized as an undesirable phenomenon in electrical contact applications. The effects of silicone vapor adsorbed on the contact surface were examined by using micro relay contacts. The amount of SiO2 formed by the decomposition of silicone vapor is expected to depend on the amount of silicone vapor adsorbed on the contact surface. Hence, first of all, an increase in the thickness of the film from the adsorbed silicone vapor as a function of exposure time was clarified for the static state of the surface. The thickness of the film of adsorbed silicone vapor increased in proportion to exposure time and saturated at a thin monolayer. Moreover, in this exposure period, the thickness was affected by the concentration of the silicone vapor. After the thickness of the molecular layer saturated, the thickness of the layer was not influenced by the concentration of the silicone vapor. Next, from these results obtained by examination of exposure in the static state, the following is deducible. The silicone molecule adsorbs easily on the contact surface during the opening period of making and breaking contacts as well as in the static state. As the time the contacts are open determines the exposure time, the amount of adsorbed silicone molecules depends on the switching rate (operation per second). Contact failure due to increases in contact resistance might be affected by the switching rate in a silicone environment. Accordingly, contact resistance characteristic was examined over a wide range of switching rates. It was found that number of operations up to contact failure was affected markedly by the switching rate. Namely, the number of operations up to contact failure decreases as the switching rate increases. However, once a very thin layer such as the monolayer has formed, the film thickness ceases to grow. Accordingly, after the very thin layer is formed, the occurrence of contact failure does not depend on the concentration of silicone and the switching rate.