How to make my circuit waterproof/moistureproof

[cocoadev]

I have a circuit i designed for some lights that are used in a night club, it uses one 18pin chip, and a few SMT transistors.

When instaled into the club, the lights started to go a bit mental from moisture.

Is there some kind of 'resin' I can smear over the PCB that is non conductive and waterproof I can use?

 

[zevon8]

Any of the conformal coatings designed for PCB use is what you need. Many are available in spray-can form. I use this one often:

https://www.mgchemicals.com/products/422a.html

 

[bloody-orc]

stick your board into molten parfine (molten candles) or cover it with silicone. this is much-much cheaper than use this proffessional coating.

 

[zevon8]

While I agree that Paraffin wax can be used as a sealant and reasonable dielectric, you need to be sure what you have is actually pure Paraffin. Paraffin is almost a generic term that covers a range of petroleum products from a liquid fuel to vaseline to hard wax. Many candles are definitely not pure paraffin, but could be animal or vegetable oils. Many also contain other chemicals to give the candle scent or or other properties. Not good for coating a circuit board.

Pure refined paraffin can be found as food grade blocks for sealing jars, etc, in a grocery store. This will work, but tends to be brittle. The melting point can often be too low ( 45C ) to make it suitable as a potting compound.

 

[mstechca]

dunk your circuit in thick, hot glue, and when the glue dries, your circuit is protected from water.

If you can't dunk it, then buy some glue sticks (meant for glue guns) and melt them with a soldering iron. Make sure the melted portion lands on the circuit.

 

[Oznog]

Silicone, like silicone caulk/adhesive, is corrosive to copper during curing. Turns it green fairly deep into it. Also being very thick it won't really flow and guarantee gaps are not left in there, which may actually mean moisture gets trapped inside it.

Paraffin will melt if the board warms up, or if your light is located anywhere near the board, or it just gets really hot like if the a/c is off or it's in the ceiling.

Basically, just use a spray coating intended for this purpose. It's NOT expensive and should have all these issues taken care of.

I'm kind of curious why your light bulb stuff is getting wet. Light bulb fixtures generally should not get wet. And shouldn't an enclosure prevent this too? Enclosures are good.

 

[zevon8]

As mentioned, a suitable enclosure would definitely be a good idea. An enclosure rated as NEMA 4 would be perfect. This is suitable for outdoor use, and there are plenty available, many shapes sizes and styles. Digikey carries a quite reasonable BUD line that has models with PCB mounts, clear lids, solid colours, etc. Even though I often use a NEMA 4 rated case for many items, I still protect the PCB with a conformal coating. This helps with condensation during temperature variations. the spray I listed will coat MANY PCbs, it goes a long way. It is easily repaired if changes to the circuit are required.

Most generic RTV silicone contains acetic acid for curing, this is what attacks the metals, especially copper. Some silicones designed for aquraiums, etc use other curing agents, and may not be as harmful to copper. This is still a very messy alternative though, and likely to be more expensive than just using a spray designed for the job.

 

[1st Mil-tech]

There are a number of compatible RTVs for electronics circuit boards. Dow Corning has a number of them. RTV 3145 adhesive is one and noncorrosive. They also carry 2 part epoxies. Just be sure that you consider the heat retention of coatings. Added to post GE also has some and others.

 

[drrogla]

Some people use a combination of pure parafin and pure bees wax to make it harder and not as brittle...

But I gotta say I`d go with the silicone... I guess you could spray the board with something like a hair spray to make a fine protective layer as to protect the copper from the silicone...