Ion Motion in Silicone and Polyimide Polymers.

Upper limit estimates of the permeability of sodium through silicone and polyimide films (obtained by radiotracer techniques) and of the rate of copper ion motion in polyimide films (from current measurements) have been made. These upper limit estimates are compared with previously reported permeabilities for other polymer and paint films and are shown to be much lower. A model for device failure related to ion motion through RTV is discussed and compared to these experiments. While a direct comparison is not possible, the permeability estimates suggest that failures by ion motion through the silicone or polyimide are unlikely.