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I have some electronics that are to be installed in a very damp location: an underground potable water pump station. This station is an underground concrete vault with some pumps and related electronics.

I currently have a PLC and cellular modem installed there and the PLC is showing fairly major corrosion and beginning to malfunction, after having been installed for approx 10 years. There is chlorine in the tap water, and quite a bit of water leaks out of the pump seals, thus increasing the corrosivity of the environment.

I want to replace the PLC with a new CLICK PLC from automation direct and also a raspberry pi type sbc. Before installing, I'm thinking of removing the plastic covers and spraying each pcb board with clear lacquer to protect from corrosion (obviously with connectors and terminals masked to prevent blocking). I also have some spray dielectric grease which can be applied to all connectors and terminals.

Does this sound like a reasonable way to inhibit corrosion? I can also disassemble the existing modem and coat its PCB likewise, although it's likely already got the beginning stages of corrosion, having been in this environment for about 3 years.

I'm not worried about voiding warranties by opening devices.

Per this article, standard krylon clear lacquer is a good choice.

Has anyone experience and recommendations in this area of protecting boards from corrosion?

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  • \$\begingroup\$ Protecting PCBs and connections piecemeal from corrosion sounds like a failure postponed. Can you submerge the entire assembly in a box of mineral oil? \$\endgroup\$
    – Neil_UK
    Commented Mar 12 at 10:31
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    \$\begingroup\$ I'm not writing this as an answer, because it comes from no experience with coating electronics whatsoever, but: It's unlikely to make things worse. However, I still wouldn't just go with an acrylic spray lacquer: in my experience, these are designed to be very runny liquids to creep very well, so that they probably get sucked into cavities between components, leads and board, not leading to a good coating on top; also, I think most lacquers will have some limited ability to transport water vapor, I guess, for wood conservation reasons, but I could be wrong. \$\endgroup\$
    – Marcus Müller
    Commented Mar 12 at 10:32
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    \$\begingroup\$ My first thought was a low melting point wax... But the mineral oil and/or an IP rated enclosure would likely be better \$\endgroup\$
    – Solar Mike
    Commented Mar 12 at 10:56
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    \$\begingroup\$ Why not just use acrylic conformal coating? I prefer silicone conformal though. \$\endgroup\$
    – DKNguyen
    Commented Mar 12 at 14:40
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    \$\begingroup\$ Why not just use acrylic conformal coating? I prefer silicone conformal though. You should note that an almost complete but imperfect coating can be worse than none since water can permeate through over long periods of time and then collect underneath. \$\endgroup\$
    – DKNguyen
    Commented Mar 12 at 14:51

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Real conformal coating is available in an aerosol can, so I don't see why you would do that except to save a couple dollars.

So, the short answer is no. For your application it does not make sense to use acrylic clear coat as a conformal coating.

I would add that I personally avoid the spray on products. I've had fabricators apply them in the past, and there was uncertainty for me as to whether the coating had sufficient thickness and coverage. I'm sure that can be solved with rigorous inspection under UV or something like that, but I prefer the certainty of a thick brushed on coating. It's also not much slower in most cases since you don't have to mask the connectors.

Last point. If you're seeing corrosion, you should try to improve the desiccant and waterproofing in your enclosure. That's the first line of defense.

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  • \$\begingroup\$ Thanks for this suggestion. Unfortunately there Is zero waterproofing or dessicants now. The devices are installed in a non sealed metal enclosure and are completely exposed to the moisture. I will look for brush on conformal coatings. \$\endgroup\$
    – Ryan Griggs
    Commented Mar 12 at 15:10
  • \$\begingroup\$ That's all well and good, but you should buy a new enclosure. Look on automation direct, they're not that expensive. Throw a couple big desiccant packs in there while you're at at. \$\endgroup\$
    – Drew
    Commented Mar 14 at 18:01
  • \$\begingroup\$ Yes I'm pushing the company to allow me to move this enclosure above ground, but we've been delayed getting approval. So I'm trying to solve it to the best of my ability in-place. \$\endgroup\$
    – Ryan Griggs
    Commented Mar 14 at 22:08
  • \$\begingroup\$ I'm thinking of just spraying everything down with a coat of dielectric grease, which would hopefully prevent corrosion from beginning until we can get this panel moved above ground. \$\endgroup\$
    – Ryan Griggs
    Commented Mar 14 at 22:09

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