> It is quite surprising that coating a PCA in silicone would not provide > a water proof seal. But based on what I have recently read, you are > right that conformal coatings are permeable to water.
It is a mater of how long it takes. > What about potting the circuit rather than applying a conformal coating? > Could that provide a true water proof hermetic seal? For instance, > suppose I wanted to immerse a temperature measurement circuit in a > container of water for extended periods. Could it be potted in > silicone or some other commonly available substance to protect it from > water? Nothing beats a welded box with gasketed connectors. I've seen water wik up cables fifty feet in the air, got a shower from one when I disconnected the connector. I've seen potting wik as well. Water always wins, it is just a question of how long it takes. The other thing to watch for is pressure differentials from inside to outside the box. Changes in pressure cause flexing that act like a pump to suck water in. I've seen membrane switches turned into balloons, when being transported from a mile below ground to a mile above ground. Gortex can help with that problem. Like all things in this line of work it is all trade offs. _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user