Conformal coating PCBs to protect against moisture damage

[newtekuser]

I understand a layer of conformal coating such as acrylic, silicone or urethane can be used to protect PCBs and components against moisture damage. However, I'd like to know if connectors can also be protected.
Let's say I have a board that takes power from a USB port, can I spray the insides of the USB connector to protect it? What about coin cell battery sockets? In this case, the battery itself will be exposed to moisture, does the battery need to be coated as well?

I assume that if these are not coated I could see failures due to moisture causing a short either from the USB port side, or coin cell battery while the rest of the coated PCB will be fine.

[themadhippy]

can I spray the insides of the USB connector to protect it

you could,but conformal coatings tend to be insulators so getting it on contacts inside a connector might not be a good idea,well not if you want a  reliable  connection

[CaptDon]

DO NOT coat connectors or even get coating close to them. It will wick up inside and be the perfect insulator. We have fought this battle for years with our contract manufacturers!!! They use various methods of 'KEEP OUT' when dipping or spraying. Some methods work better than others. I can't begin to tell you how many coating contaminated connectors I have replaced!!

[newtekuser]

It makes sense not to coat them, but how does one prevent moisture from damaging the board through these ingress points? I'm thinking enclosing everything in a sealed case with the power cable coming out of it, but it's not a pretty solution.

[jpanhalt]

Gold plating with whatever intermediate metal is recommended will help.

[ataradov]

There are connectors with protective covers. But they cost a lot, bulky, and vendor-specific, making substitutions impossible.

The best approach is to make the product case be moisture proof and use regular connectors on the PCB. Sometimes simple rubber plugs are sufficient, but in some cases you may need screw covers.

It is almost impossible to make exposed connectors moisture proof. The interface between the plastic and the metal will always leak. It may not be an issue if you conformal coat everything inside, but be prepared to have condensation under worst conditions.

[Perkele]

Try to figure out what's the IP code that you need for that device.
https://en.wikipedia.org/wiki/IP_Code
A rough estimate would be good enough as a starting point.

[Bud]

For coin battery you can resort to not use battery holders, but batteries with welded tabs, just solder the battery in place and then you can coat it if you want. Other option is  batteries with heatshrink over it, factory available.
For USB there are IP rated screw over or bayonet type cover connectors but they are expensive.

[Solder_Junkie]

It makes sense not to coat them, but how does one prevent moisture from damaging the board through these ingress points? I'm thinking enclosing everything in a sealed case with the power cable coming out of it, but it's not a pretty solution.

Sealed enclosures are a problem, any moisture trapped inside will condense onto your board/components. Unless you are making something for immersion in water, it is better to have a tiny vent hole, or two, in the lower part of the enclosure, no bigger than 1/16th inch, which will let it breath and minimise the risk of insects setting up home in your box.

As per the other replies, think of soldered connections. Where plugs/sockets are unavoidabe, use gold plated contacts if possible, and lightly spray them with switch cleaner that includes lubricant to give the pins a protective coating. The common tin plated connectors can be a problem, even when used indoors in a dry atmosphere.

I have a few outdoor projects, the boards are sprayed with PCB lacquer, which seems to be similar to polyurethane varnish in a spray can. I also use liquid electrical tape (rubber dissolved in solvents) to protect any exposed coax braid, and to seal around any sockets, mounting screws, etc. You can also use non acidic silicone sealer (not the bathroom/kitchen stuff which gives off corrosive fumes when curing). One of my projects is a home made PA0RDT active HF receiving antenna, it has been outside for several years without any problems, it is powered via the coax.

SJ