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Author Topic: Protecting PCBs against tarnishing - on the cheap?  (Read 2042 times)
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Birmingham, UK
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As per subject...

I got complimented on my PCB construction in another thread (yay!) but there's one thing that I need to do to keep my projects looking nice, and that's stop the copper from getting tarnished.

I know the best way is to dunk the freshly etched/milled board in tinning solution, but it's stupidly expensive and the shelf life is really short. I bought a bottle a couple of years ago but I have very little time to play with electronics so it only ever gets used on a couple of projects before it stops working.

What methods do you all use to protect the copper on finished boards?

I'm wondering whether I could just use something like a clear spray wood varnish once the board is finished and cleaned. It'd be quick and cheap, at least. Don't want to accidentally spray my board with something that turns out to be conductive though...
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Depending on how cheap you mean, you can buy spray cans of circuit board lacquer
that you simply spray on the board after its finished.
Its non conductive and adhesive and protects the board.
Made by Servisol, and most electronic hobby stores sell something like it.
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Birmingham, UK
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Ahh... perfect, thanks. Found a can on eBay, much cheaper than tinning solution (and what can I say, I prefer that salmon pink copper look to silver)

smiley

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nail polish; polyurethane paint; ...
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Grand Blanc, MI, USA
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While I have used spray lacquer, etc., I also have to question the need. Below is a picture of a home-made PCB that is literally decades old. It was mounted inside an enclosure and resided in my basement for all that time. Solder flux (Kester 44) was not cleaned from the board either and there is no evidence of corrosion. If there are no contaminants introduced (including fingerprints from handling), things stay in amazingly good condition.


* oldPCB.jpg (359.32 KB, 1484x952 - viewed 48 times.)
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Use solder.  If you have a large tip for your iron, it's pretty easy to drag it all over the board. (It's also easy to clog up your through-holes, so don't get caries away with the solder.)

-j
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the land of sun+snow
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This entire approach sounds counterproductive. First off, I don't want lacquer
or any other coating covering the components on my pcbs, and especially
not on the copper surfaces of any headers or connectors that need to be
plugged and unplugged. How are you gonna plug something in if the connector
pins are coated?

Secondly, if you solder the components on soon enough, the copper won't
be discolored, so who cares what it looks like later on. What's important is
having good connections.

Thirdly, if your pcb is a year or two old, and the pads have discolored, you
can use steel wool to clean the tarnish off. Then they'll take solder with no
problem.

Fourthly, it's lots easier to buy professionally made pcbs and then the pads
are always pre-tinned in the first place.

All in all, coating sounds like more trouble than it's worth.
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Colorado
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oric, he's not referring to just the pads, but the entire board.  Not everyone get their boards professionally made.  Those who do it at home end up with bare boards with exposed copper traces just like Jack's picture.  Depending on the environment, the copper will tarnish over time.  While that doesn't affect the solder joints already made, it just makes for an ugly looking board over time.  This is where the coating comes in helpful.
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I haven't used them, but there are 'solder-through' urethane conformal coatings, which I take to mean you spray the PCB before placing/soldering components, so you aren't coating those.
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the land of sun+snow
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Quote
oric, he's not referring to just the pads, but the entire board.  Not everyone get their boards professionally made.  Those who do it at home end up with bare boards with exposed copper traces just like Jack's picture.  Depending on the environment, the copper will tarnish over time.  While that doesn't affect the solder joints already made, it just makes for an ugly looking board over time.  This is where the coating comes in helpful.

Yeah, I understand all that. Just the same, as I noted, it seems to me that
spraying any kind of lacquer on the pcb will cause more electrical problems
than any cosmetic issues it may solve.
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On the contrary a lacquer coating will protect against dirt and grime building up (which in humid conditions will conduct).

In normal conditions its not critical in the short term - avoiding fingerprints will prevent the most obvious tarnishing.

BTW tinning the board is not the best solution.  The reason is tin-whiskers.  This is one reason solder-resist is routinely used I believe.
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the land of sun+snow
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On the contrary a lacquer coating will protect against dirt and grime building up (which in humid conditions will conduct).

I wonder, how many of your pcbs have you actually lacquer-coated? :-)

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The most important thing I've found is to not get any fingerprints on the copper.  Oils and salt from your skin will corrode the copper quite quickly.

My favorite coating is a clear acrylic made by tamiya, with one drop of glycol added per ounce of coating, to give it long term flexibility.  I often use food coloring as the glycol source so I can keep tabs on what's been coated, and how thickly.  I apply it with a brush.
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Birmingham, UK
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How are you gonna plug something in if the connector
pins are coated?
[snip] .. so who cares what it looks like later on. What's important is
having good connections.
[snip] Fourthly, it's lots easier to buy professionally made pcbs and then the pads
are always pre-tinned in the first place.

Your points are, of course, valid in most situations but I'm after the aesthetic as well as the functional - I spent so damn long designing and milling this clock board that I want it on show when I'm done. Gonna mill out a nice clear acrylic case for it too. Otherwise I could just buy my wife a 99 pence clock (and it'd probably be more accurate, LOL). Can't afford to buy her something posh for Christmas this year so coming at it from the sentimental-value angle. Look babe, I didn't buy you jewellery, but I made you something you'll look at every day...  smiley-kiss

(note to self - must remember to etch her a message on the PCB somewhere too, chicks love that sorta thing)

Thanks for all the input guys smiley
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(note to self - must remember to etch her a message on the PCB somewhere too, chicks love that sorta thing)

Store a few messages in the mcu and display a rolling image of them from time to time (at the hour, on alarm, etc.)

You will score lots of points with her.
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