I'm considering putting a circuit board in a ventilated NEMA 4 enclosure outdoors. I'm a little concerned about humidity and condensation inside the enclosure. Do I need to conformal coat my circuit boards, or take any other precautions?

  • $\begingroup$ Depending on the environment, you may also want to consider the next level, which is potting. That makes the electronics even more immune to humidity, liquid, dirt, bugs, etc, but also costs more and has other tradeoffs like decreased heat dissipation capability. $\endgroup$ Oct 10 '15 at 13:16

Requirements depend on environment,but, yes, conformal coating is, at a minimum, a really really good idea. Apart from condensation and misc stuff that manages to get in, ants can wreak havoc, depending on ventillation holes other denizens may also do their bit.

If you want a 'quick and easy' coating material that is a lot better than nothing at all then clear polyurethane "varnish:" spray is useful.

There are many commercial products offered for this purpose. Dow Corning make some good ones but there are many others as well. (My only association with Dow Corning is as a satisfied customer).

Here is a useful tutorial page from Dow Corning. While it obviously steers you towards their products it also provides good general advice.

  • $\begingroup$ I am under the impression that conformal coatings can do a great job of protecting circuits from liquids, but help very little if the PCB, or other components which are not hermetically sealed, are adversely affected by a long term exposure to high humidity. Is this correct? $\endgroup$ Oct 10 '15 at 15:04
  • $\begingroup$ @user5108_Dan I'd expect a CC to be better or equal in protective power for high humidity at a given temperature compared with a liquid. NOTHING is totally impervious to water. Very long life encapsulants such as the EVA or similar used in PV (Sol;ar) panels work by creating avoid free surface against the target material and have low dissol;ved water in the coating. So water reached the surface only as vapor so is ~~= 1000 x less concentrated than wityh liquid so corrosion rates are accordingly lower. $\endgroup$ Oct 11 '15 at 7:17

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