DJ Delorie wrote: > What's a good thing to coat my built boards with, to protect them from > the environment? I've got a temperature/humidity sensor outdoors on a > small pcb, but I just got done cleaning some corrosion off it. Epoxy? > Spray paint?
The product term I've heard is called "conformal coating". Don't know precisely what the fundamental stuff is, but there are lots of different kinds based on what you need protection from. As I understand things, you have to be careful what you use because some potentially useful materials don't expand/contract with the board and components, so over time you get cracks, the coating pulls the components off the board, and so forth. Others are electrically conductive, corrosive, etc. The material selection it isn't intuitive, unless you're a chem-e. Things like dissimilar metals being in contact with each other, and other blah blah that I hear makes me want to leave the problem to someone else. :) I am aware of a few situations where they put the board into an enclosure and then flushed the inside with nitrogen before sealing it up (have a valve on either end of the box, not unlike what you might see on an air-inflated bicycle tire). That's a pretty safe bet, works particularly well in very cold temperatures at least until you lose the seals on the box. And unless you maintain a positive pressure over temperature, Schrader-type valves will actually promote moisture intrusion as the environment warms back up. If you have a board or two to spare, I've always wanted to "brick" something in the clear epoxy you often find at arts/crafts stores for preserving insects, stones, and such. That would definitely keep stuff out, especially if you put a pliable grommet around the wires and/or the goo would bond to the insulation. Let me know how it turns out. :) :) As long as we're experimenting with disposable hardware, you might consider silicone bathroom caulk, too. Petroleum jelly? I've seen the former used in a pool installation, but there was no expectation that the thing would live because of all the chlorine (which is extremely corrosive to metals, not just lungs). Don't know if the latter would dissolve packages, or not. I once asked an auto mechanic about putting distilled water into a radiator (we live in an area with very hard water). He said that as long as you aren't continuously adding water, the minerals themselves aren't a concern--- they build up, then redissolve and move on. Based on that logic, maybe just putting the board into an enclosure that does a reasonably good job of not facilitating air movement would be good enough--- if you were careful not to seal it up on a really humid day! b.g. -- Bill Gatliff b...@billgatliff.com _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user