Reliability of hermetically sealed miniature relays in silicone-rich environments

Abstract

Organic Silicone materials such as Polydimethylsiloxanes (PDMS) are well-known for more than 60 years to affect the performance of devices with arcing contacts such as switches, relays or motors: liquid or volatile parts of the silicone materials can overcome long distances and penetrate through small gaps and are eventually transformed on contact surfaces within electrical arcs into inorganic silicon-dioxide which is an excellent electrical isolator. Even very small concentrations of silicone can be critical to the performance of the switching devices. Therefore the use of silicone materials is nowadays restricted in applications with switching contacts. Nevertheless silicone related failures of switchgear still occur since the relevance of these phenomena is often underestimated. The first part of this work gives therefore a detailed review of more than 60 years of silicone-related research. In the experimental part of this work relay housings with different sealing categories were investigated regarding their ability to act as reliable barriers: Silicone materials with high and low volatile contents were used within switching experiments in order to determine how reliable i) open, ii) sealed and iii) hermetically sealed relays can be operated within differently saturated silicone ambient. Contact resistance was evaluated as first criteria and after the tests contact surfaces were analyzed using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) in order to verify silicone contamination.