EFFECT OF SILICONE VAPOR CONCENTRATION AND ITS POLYMERIZATION DEGREE ON ELECTRICAL CONTACT FAILURE

The effect of silicone vapour concentration on the contact failure was examined by using micro relays and motor brush-slip ring (commutator) contacts. [(CH3)(2)SiO](4): D-4 was used as a vapour source of silico ne contamination. Because the influence of the vapour of the silicone on the contact surface can not be avoided at all times due to its grad ual evaporation in the atmosphere. The contact failure caused by the s ilicone vapour was confirmed as formation of SiO2 on the contact surfa ce by analysis of EPMA and XPS. A minimum limiting concentration level which does not affect contact reliability was found. This limiting le vel was 10 ppm (0.13 mg/l). Validity of the limiting level was confirm ed by the relationships among concentration, temperature, SiO2 film th ickness and contact resistance. Furthermore, the effect of the degree of silicone polymerization on the limiting concentration was derived b y an empirical formula. This silicone is found to have polymerization degree larger than D-7: n=7. These results were confirmed by the conta ct failure data due to the silicone contamination.