Epoxy Coated PCB Rework

[Roman2179]

As the title implies, I am trying to figure out how to approach doing a rework on a PCB that has a conformal coating, looks like about 2-3milimeters of epoxy on the entire PCB.

The PCB is the control board for a washing machine, problem is, it is on backorder for the next four months. The issue is actually simple enough, two of the capacitors are bulging and I guessing that's the reason the machine is having issues with spinning the drum. Capacitors are easy enough to replace but the entire PCB is coated with epoxy which makes things considerably more difficult.

I have never done any work on PCBs that had a conformal coating. So the question is, how does one remove the coating? Is it even possible without damaging the PCB?

This for more of a temporary solution until I can get a replacement PCB. Waiting four months isn't really a viable solution so I want to replace the components for now until I can source a replacement.

Thanks in advance!
Roman

 

[PottedMeat]

can you just rip off the old caps and peel off enough epoxy on the bottom to access the solder pads?

 

[Roman2179]

That's definitely on the list of things to try but it's farther towards the bottom. I'm hoping someone can give some ideas that have a smaller chance of damage. Last think I want do is damage the PCB while removing the caps. These are pretty large caps, btw.

This is the board. The caps in question are the two along the top of the board.

 

[sm625]

So the conformal coating is only on one side? Desolder the caps and rock them back and forth until they break the conformal coating and fall out. It's not like that's a multilayer board, the worst you can do is tear out a trace and have to run a jumper wire. Just dont crack the board.

 

[Roman2179]

The the PCB is coated on both sides with about 3mm of what looks like epoxy.

EDIT
From the pictures, it looks like only side is coated. It's actually two PCBs attached to plastic carrier. One contains all of the ICs, etc and the other just has the LEDs and the screen. The PCB that with the bad caps has coating on both sides. The second PCB that just has the buttons/LEDs is not coated but I don't have to do any work on that one.

 

[uclabachelor]

The the PCB is coated on both sides with about 3mm of what looks like epoxy.

EDIT
From the pictures, it looks like only side is coated. It's actually two PCBs attached to plastic carrier. One contains all of the ICs, etc and the other just has the LEDs and the screen. The PCB that with the bad caps has coating on both sides. The second PCB that just has the buttons/LEDs is not coated but I don't have to do any work on that one.

You need to get the conformal coating remover solution for the type of conformal coating the board is using, ie, silicon, epoxy, polyurethane, etc.

And after you're done repairing/modifying it, re-apply the coating. There's a reason why the manufacturer went through the extra expenses of adding conformal coating to the board - I suspect it would not last very long in the environment it was designed for if there was no coating.

 

[Roman2179]

Really I only need to last long enough for the parts to come back in stock but the estimate right now is March 2014.

Then again, I the fix actually works, then I really won't need to spend the money on the new part though I still probably would since they seem to be extremely rare.

 

[Slacker]

Check craigslist for a cheap parts donor.

 

[scoob8000]

Are the caps completely coated too? You might be able to rock the cap back and forth enough to break it off, leaving it's leads in the PCB. Then you could just solder the new cap to the stubs of the old leads.

 

[Soulkeeper]

can you take some pictures for us ?
or link us to the board that is on back order ?

 

[Mark R]

Some conformal coatings are reworkable; they melt off or burn off at soldering temperatures.

Worth giving it a go in a well ventilated area with a cheap iron tip. Use a scalpel to remove the caps from the other side. Then rework as normal.

 

[Roman2179]

The two capacitors in question are in the second picture along the top of the PCB towards the left side.

Unfortunately I am out of town until next Thursday on business, but once I am back I will be able to take some more detailed pictures. Right now I am planning on trying to dissolve the coating with acetone or paint thinner little by little with a qtip or something similar. Good/bad idea? Well see what happens with that.

Thank you for all of the replies so far!

 

[paul878]

That don't sound like regular conformal coating, more like glass epoxy.
Cut those capacitors off bit by bit. Use dermal tool to grin off just enough coating to get to the soldering points.

 

[bryanl]

Conformal Coating Removal Techniques:

http://www.paryleneengineering.com/pdf/conformal_coating_removal_techiques.pdf

I'd try scraping the coating off the solder joints and then simply melt and suck up/wick up the solder. Use 40-50 watts to get the job done quickly, before the copper traces are damaged.