Safe levels of silicone contamination for electrical contact

The effect of silicone vapour concentration on the contact failure was examined by using micro relays and motor brush-slip ring (commutator) contacts. A minimum limiting concentration level which does not affect contact reliability was found. This limiting level was 10 ppm (0.13 mg/1). Validity of the limiting level was confirmed by the relationships among concentration, temperature, SiO/sub 2/ film thickness and contact resistance. Furthermore, the effect of the degree of silicone polymerization on the limiting concentration was derived by an empirical formula. These results were confirmed by the contact failure data due to the silicone contamination.