Clear coating PCB's solder side ?

[drolo]

While visiting my parents, I just stumbled upon some old PCB's I had done in school (about 20 years ago) and noticed they were clear coated on the solder side. Then I remembered we used to brush the soldered PCB's with a fine metal brush and ... I guess alcohol or something. Then applied clear coat to seal it.

Since I have started making pedals I have never bothered doing this. I have not noticed any particular alteration on the solder joints, even in older pedals.

Was that cleaning and sealing we did in school overkill? Or do I have dozens of pedals at home waiting to crap out on me?

[deadastronaut]

when i make my own pcbs i clearcoat them once built..(car spray laquer)

and can still be soldered/modded after too..

[CodeMonk]

I spent many years in the electronics manufacturing industry and many companies I worked for used clear coat (Referred to as Conformal Coating) on completed PCB's.
They also coated both sides of the PCB.
This was done primarily to protect against the environment (moisture, dust/dirt and other nasty things).
Many of those companies I worked for were military contractors/sub-contractors making thing that when into stuff like planes, aircraft carriers, subs, etc so moisture was a concern.
It would probably be just as protective if you were playing a gig and someone spilled a beer or puked on your super duper overdrive

[karbomusic]

and can still be soldered/modded after too..

Really? That would be wonderful because I've been thinking of doing this forever and was afraid it would be a mess if I had to change something later.

[Mark Hammer]

I like to tin my PCBs with actual solder, as opposed to tinning solution.  I wouldn't expect anything to happen to the solder joints themselves over time, if I left all the traces untinned, but I like to monkey around with boards, post-build, and often you can't fit that different-value cap from your parts bin in the spot set out for the original value, and you have to pop a hole somewhere else on the board to accommodate it.  And when that happens, I like to know that I have a nicely tinned spot to solder leads to everywhere on the board.  It's my quirk, and no "recommended best practice".

But I mention this just as a caveat regarding the clear-coating of boards.  If you know you're not going to tinker/mod, post-build, coat away.  I would just recommend that a) you take steps to clean off all flux from the board, b) once clean, you check for any and all possible cracks and solder bridges, and c) not apply too thick a coating.  You CAN always clean off the coating with a Q-tip, dabbed in the appropriate solvent, if you need to access a solder joint and don't want to stink the place up with putrid smoke.  But since the optimal way to coat the board is before the components are installed, you'll need to be certain the board itself poses no challenges to the circuit working.  And for that, the board needs to be clean, unshiny, and easy to inspect (which is why the advice to clean off the flux).

[davent]

I spray the copper side, after cleaning off the etch resist, with whatever 'lacquer' i'll be using for the enclosure clearcoat. Flashes off wih the touch of the hot soldering iron, just prevents the copper from oxidizing. Returned this week to some pcb's done a few years ago, can solder to the protected pads like they were freshly cleaned. With Liquid Tin i found that if the pcb's been left for any length of time it's just as hard to solder to as if the copper had beeen left bare and oxidized.

Testors sell transparent candy colours of lacquer which if you can spray well and i can't, can look convincingly like commercial solder mask.
dave

[Mark Hammer]

With Liquid Tin i found that if the pcb's been left for any length of time it's just as hard to solder to as if the copper had been left bare and oxidized.

That's why I prefer to tin with actual solder.  Much easier to come back to after an extended period.

[mykaitch]

Yes but a word of warning.If later you decide to wash the board in IPA and any ICs have sockets you are in deep s***
The coating will leech through the IC holder and quite often insulate the IC pin. It also does this to any other sockets etc.
I've made this mistake a few times!!! Don't get me wrong- con coat is perfectly good to use-- just be careful if you use a solvent later.
Twice I gave up and built a whole new board because of the trouble I caused.

[CodeMonk]

I like to tin my PCBs with actual solder, as opposed to tinning solution.  I wouldn't expect anything to happen to the solder joints themselves over time, if I left all the traces untinned, but I like to monkey around with boards, post-build, and often you can't fit that different-value cap from your parts bin in the spot set out for the original value, and you have to pop a hole somewhere else on the board to accommodate it.  And when that happens, I like to know that I have a nicely tinned spot to solder leads to everywhere on the board.  It's my quirk, and no "recommended best practice".

But I mention this just as a caveat regarding the clear-coating of boards.  If you know you're not going to tinker/mod, post-build, coat away.  I would just recommend that a) you take steps to clean off all flux from the board, b) once clean, you check for any and all possible cracks and solder bridges, and c) not apply too thick a coating.  You CAN always clean off the coating with a Q-tip, dabbed in the appropriate solvent, if you need to access a solder joint and don't want to stink the place up with putrid smoke.  But since the optimal way to coat the board is before the components are installed, you'll need to be certain the board itself poses no challenges to the circuit working.  And for that, the board needs to be clean, unshiny, and easy to inspect (which is why the advice to clean off the flux).

Agree on the doing a thin coat.
Most of the companies I worked for used a spray.
Except NASA, we brushed it on, about 1/8 thick, then put them in a vacuum chamber to remove the air bubbles.

And while conformal coating can come in various colors, ALWAYS use clear.

[amptramp]

We used to find that circuit boards that were given a bright tin coating for the traces were difficult to solder whereas the duller solder coating soldered very well.

If you use conformal coating, it will create difficulties if you have to repair or modify something later.  Use something that has an associated solvent so you can remove it at a later date.  I have seen some people use silicone-based conformal coating.  Nothing dissolves it that wouldn't damage board components and it is resistant to heat.  Some conformal coating materials are designed to vapourize if they are subjected to soldering heat.  These are a bit more useful.

[Keppy]

I spray the copper side, after cleaning off the etch resist, with whatever 'lacquer' i'll be using for the enclosure clearcoat. Flashes off wih the touch of the hot soldering iron, just prevents the copper from oxidizing. Returned this week to some pcb's done a few years ago, can solder to the protected pads like they were freshly cleaned.

This is what I do as well. A thin coat of lacquer is easy to solder through, and doesn't make any noticeable fumes compared to the solder itself. I run a desk fan on my bench and an exhaust fan vented outdoors to make sure I don't breathe any solder/lacquer fumes too directly, and I don't do high volume.

I don't worry about the joints as much as the thin copper traces, so coating before populating is my preferred method. One small downside is that getting the iron anywhere it shouldn't be will cloud the laquer, making the board appear flawed when it's perfectly fine.

[duck_arse]

(before the days of fab houses and solder-masking for the masses,) there used to be "pcb laquer" that we were supposed to spray onto our freshly etched pcb's before soldering, just to protect the copper. it was meant to be soldered through. I had one can, never bought a second one.

my impression of conformal coating has always been that it was a thick, plastic, protective coating, applied/dipped last thing after final test. it was not meant to be worked-through, as it was then not-conformal. if you wanted to work on a board, it had to be stripped, then recoated when finished. we used to be "threatened" with it back doing navy contracts.

[drolo]

Would you say that with a fabricated PCB with soldermask, no coating would be needed?

[R.G.]

Would you say that with a fabricated PCB with soldermask, no coating would be needed?

Yes, emphatically.

[R.G.]

Here's some reading material on what exists and is possible.
http://www.peters.de/us/products/conformal-coatings