How to coat protect PCB?

I was wondering (since I never did that before) how can I protect my hand-made PCBs?

I'm reading there's a silicone spray and other stuff that I can spray paint on the copper layer of my pcb (I make those once with the toner transfer method, awesome!) in order to prevent oxidation (that's my main concern, more than then mechanical protection againsts let's say scratches).

What would you suggest? I'm not looking for industrial-professional quality grade here, I'm a part-spare-free-time Arduino fan, I'll settle with a commercially available product that gives a reasonable protection of the copper and solderings over time against oxidation.

Nail varnish. Comes in a nice range of colours as well as clear! Oops did I just say that out loud?

There are a range of what is called conformal coatings you can spray on. The good ones allow you to solder through them if needed. Look at the electro chemical section of any large distributor.

mmcp42: Nail varnish. Comes in a nice range of colours as well as clear! Oops did I just say that out loud?

That stuff is quite useful. I keep a jar of fluorescent orange around to paint things such as indicator marks. I also found a color that matches the paint on my bicycle to touch up scratches. It will also function as thread lock.

Before my beard went grey, the orange kind of clashed with it though. :P

This is a link to the professional stuff:- http://uk.farnell.com/jsp/search/browse.jsp?N=2031+203113&Ntk=gensearch&Ntt=conformal+coating&Ntx=mode+matchallpartial

mmcp42:
Nail varnish. Comes in a nice range of colours as well as clear!
Oops did I just say that out loud?

You mean you paint the pcb over by hand with a brush?!? How’s that?

mmcp42: Nail varnish. Comes in a nice range of colours as well as clear! Oops did I just say that out loud?

Btw, is it going to be brittle as it cures?

I guess a silicone based coating would be more flexible (i.e. more adapting to changes in temperature).

At the refinery I worked at before I retired it was common practice to specific conformal coating on all electronic PCBs that were installed in the operating plants. The stuff most of our process control manufacturers used looked just like normal clear epoxy glue and they would coat the whole board components and all to almost a 1/16" thickness.

Seems that even trace amount of H2S gas that can occasionally escape into the plants atmosphere would turn copper and tin to a blueish color, very corrosive stuff. Anyway that epoxy conformal stuff would make component level troubleshooting and board repair a real pain in the rear, took very sharp meter leads to even pierce the coating to take voltage readings.

Lefty

robitabu:

mmcp42: Nail varnish. Comes in a nice range of colours as well as clear! Oops did I just say that out loud?

You mean you paint the pcb over by hand with a brush?!? How's that?

yup to be honest I usually use clear, but just brush it on it's not that brittle and PCBs don't flex that much and it's dead easy to remove using, you'd never guess, nail varnish remover!

There's also this stuff called Lquid Tin for protecting your traces. http://www.mgchemicals.com/products/421.html

Urethane Conformal Coat for the whole board when done. http://www.mgchemicals.com/products/4223.html

mmcp42: to be honest I usually use clear, but just brush it on it's not that brittle and PCBs don't flex that much and it's dead easy to remove using, you'd never guess, nail varnish remover!

Yup. Fignernails flex more than PCBs, I would think. I was thinking about cool effects you maybe could get using different colors, masking, and multiple applications. Too much trouble? And nail polish remover is ... acetone. (or at least, it used to be, but with some additives to make it nicer on the skin) No idea how it is for solder-through though. I did notice that purpose-type conformal coatings are a bit spendy -- ~$25/can, but then how much would you use in a year anyway? And, nail polish is designed to flat itself too, so brush marks shouldn't be visible once it dries.

I buy mine from the local chemists chain (drug-store to you foreign johnnies) remover 250 ml less than £1 as I recall clear nail varnish similar price, but you only get 50 ml as I recall

We also call it "nail polish" rather than "varnish" I think :-)

Speaking of which -- how about regular varnish stuff? You can get a spray can of polyurethane for a few bucks at Home Depot -- a store I feel more comfortable entering than, say, Sephora :-)

Or a can of Krylon? That stuff lasts pretty well, and also comes in colors. MANLY colors, like "hunter green" or "granite gray" or such :-)

Just cover up your connectors first and mask any IC sockets so you don't get the removable parts painted in place.

I have been known to use the el-cheapo 99 cent epoxy paint at walmart, it and it sticks to boards really well, I often spay perfboard with it but you would have to figure out how to mask off the parts you dont want covered as you cant really solder though it

I see people use whatever comes at hand to protect those PCBs. So I assume I could be less picky and simply cover my pcb copper side with anything that lasts to basic oxidation.

I think I'll have a go with a transparent synthetic (the one you dilute with acetone/nitro) rattle can I have at home. Anyone has "strong feelings" against it?

well something to keep in mind is that it really doest hurt copper to oxidise, its "rust" actually seals the metal under, which is why you can easily have a 100 year old roof...

For a copper roof (or a copper kettle) this is true. However, the copper on a PCB is thin enough that I would worry about the oxide actually going straight through thin traces, and significantly impairing the conductivity of the trace. If you plate up to 10 oz thickness, and use 100 mil traces, well, that's a different way of solving that problem :-)

Osgeld: well something to keep in mind is that it really doest hurt copper to oxidise, its "rust" actually seals the metal under, which is why you can easily have a 100 year old roof...

Sorry mate, no matter what you think, I would never think of a rusted pcb as a plus in my life ... :fearful:

The copper on the roof is quite thick, pcb traces are very thin - think 16oz per ft^2 vs. 0.5-2 oz. Some high-quality PCBs feature gold coatings to protect exposed pads but tin-like coatings are standard.

Just as important as the conformal coat though is what to do about leftover flux - it can eat your board contacts slowly over time if you don't remove it or use no-clean flux. I practice lots of scrubbing with 90%+ pure alcohol (nasty on the hands, wear gloves!) though some components also tolerate being washed with water.

Conformal coats can protect the board to some extent - but many parts have to be left uncoated so mask them - i.e. temperature and humidity sensors, connectors, test points that you still need to use, etc. Most heat sinks are at most partially coated so as not to lose performance.

Whether or not you coat, the takeaway is that the coating is but a small barrier. If the board is destined for a nasty environment, ensure that the enclosure can protect the thing. I would also plan in advance re: any uncoated parts that have to be exposed, i.e. make them removable/replaceable using sockets.