ABSTRACT
One method that has been recommended for prevention of failures by silicone migration is to coat the area around the contact with a substance with lower surface energy than silicone that will impede silicone migration. Bernett and Zisman found that poly-IH IH-pentadecafluoro-octyl methacrylate, a polymer that can be put on substrates as a very thin film, was effective for impeding silicone migration (60). Figure 16.16 shows a comparison of relays tested with exposure to silicone migration with and without the above polymer as a barrier to migration (59). The silicone source was a silicone rubber seal with a high amount of extractable low-viscosity silicone fluid. The seal was put outside the relay and the barrier was coated onto all the plastic surfaces and terminals. The same relays tested with no silicone exposure are included as control for comparison. The control results are shown slightly off set with regard to the vertical axis for clarity purposes. The
No Si Si no barrier Si with Barrier
Switchi 13VDC, 12A, 1min off time, 25C 1
results show the control relay to much better than either test relay. It can be seen that the barrier produces some improvements but is far from being effective in stopping the migration of the silicone material. This testing was done at 25°C, and certainly the barrier would be much less effective for testing at higher temperatures where vapor transport of silicone would become more of a factor.
