Dynamic Contact Resistance and Film Thickness of Relay Contacts Coated with Fluoropolymer Thin Films

Relay contacts were coated with two different fluoropolymer barrier solutions with 0.I wt% of the fluoropolymer poly-1H, 1Hpentadecafluoroctyl methacrylate (PFOMA) as the common solute. The solvent for the first solution (PFOMA-1) was 1,1,1-trichloro-l,2,2trifluoroethane (TCTFE), and the solvent for the second (PFOMA-2) was a mixture of 90 percent perfluorocyclic ether plus 10 percent TCTFE. Four modes of contact resistance behavior were observed when the dynamic closing contact resistance of these barrier-coated contacts was measured during their first 100 contact closures. These modes were 1) low stable resistance throughout (100-150 m
\Omega
) 2) low stable resistance except for a periodic high resistance (150-<200 m
\Omega
) 3) initial high resistance (>200 m
\Omega
) that stabilizes to low stable resistance after a certain number of operations (2-48); and 4) high resistance throughout (> 1
\Omega
). Ninety-five percent of the PFOMA-2 coated contacts had desirable contact resistance performance defined by behavior modes 1 and 2. Only 65 percent of the PFOMA-1 coated contacts were in modes 1 and 2 while 30 percent were in mode 3. The average thickness of the barrier coat film was 136 Å for 0.1 percent PFOMA-2 and 167 Å for 0.1 percent PFOMA-1 within a range of ± 15 Å.