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How to dissolve clear plastic coat from circuit boards?

Greetings, group. I've got a sticky issue here. I'm repairing a number of circuit boards from a manufacturer who coats their boards after assembly with some sort of plastic clear coat. (Polyurethane, maybe? Indoors it's clear and colorless, but outdoors under skylight, it glows a pale blue.) It makes probing and soldering/unsoldering quite difficult. What's the best way to remove it?

So far, I've tried:

91% isopropyl alcohol: Loosens bond between coat and board, but doesn't dissolve coat.

Unknown solvent in unmarked 55-gallon drum (possibly toluene-based): Dissolves coat, but very slowly, requiring a lot of scrubbing with a brush. Noxious fumes.

CRC Letra-Motive Electric Parts Cleaner: Dissolves coat, but slowly, requiring a lot of scrubbing with a brush. Turns coat into a thick goo that mucks-up brush and is hard to rinse out. Noxious fumes.

Are there better options?

--
Varnished,
Robbie Hatley
lonewolf [[at]] well [[dot]] com
Reply to
Robbie Hatley
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circuit

Try Acetone.

Reply to
PeterD

But with great caution. Acetone attacks a lot of plastics.

Reply to
William Sommerwerck

Google "conformal coating stripper".

MG chemicals makes one, which the MSDS says contains

1-methyl-2-pyrrolidinone Dibasic Ester (Mixture) Dimethyl Glutarate 55-65% Dimethyl Adipate 10-25% Dimethyl Succinate 15-25% D'Limonene Another source might be Miller-Stephenson (their D0319B or MS-115 strippers)... the former handles both urethane and epoxy coatings, the latter is optimized for epoxy.

Conformal coatings may be urethane, epoxy, acrylic, or silicone. I believe that the urethane types are the most common but I could well be wrong about taht. The pale-blue glow you observed is probably a UV-fluorescent tracer dye, added to the liquid coating so that boards can be checked during manufacture to ensure that they're properly coated.

--
Dave Platt                                    AE6EO
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Reply to
Dave Platt

I would try MEK(Methyl-ethyl-keton) if you are still allowed to use it. :)

Reply to
Sjouke Burry

I think acrylic is the most popular these days. If it's hard as a rock and clear, it's acrylic. If it's soft and yellowish, it's urathane. If it's hard and yellowish, it's epoxy.

Go unto thy local paint or hardware store and get some urethane and epoxy paint remover. Use it sparingly as it will attack G10 and FR4 PCB material, which is epoxy and fiberglass. Don't dunk the board into the stuff. Just paint some on the area where you're working and wipe it off when the coating gets soft. The rest of the way, use a scraper.

Yep. Get a UV lamp (black light) so you can see where the coating is missing.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com               jeffl@cruzio.com
# http://www.LearnByDestroying.com               AE6KS
Reply to
Jeff Liebermann

of circuit

probing

it?

brush.

brush.

out.

I've seen that purple-blue glow flourescence effect , in sunlight (UV?),with some formulations of hotmelt glue. Try a soldering iron somewhere on it. Makes as much sence using hot melt glue as a conformal coating as the paraffin wax covering a board I'm wrestling with recently. But other than for gluing down large lumps to pcbs I've never seen a covering with it but as the low temp formulation melts at 70 deg c or so a bath of it could make a conformal dip treatment.

Reply to
N_Cook

probing

Ah, so that's what that coating is called. I was looking for "plastic clear coat".

Brush-on gel. Don't think that's what I need.

Yep, I'm going to look into that, see if I can get a quart. (Have to order local, because it can't be shipped any way other than ground.)

Thanks for the tip on that!

Confirmed. Coworker put a UV light on it, and it glows crazily. (The cuticles of all the fingers of my left hand also glow extremely brightly under UV; seems I now have a poisonous muck of plastic resins, toxic solvents, and radioactive isotopes embedded under my fingernails. Great. Sigh. I'll have to remember to wear gloves before cleaning these boards from now on.)

--
Cheers,
RH
lonewolf [[at]] well [[dot]] com
Reply to
Robbie Hatley

Actually, you're mutating into a scorpion.

Reply to
William Sommerwerck

One thing I would try is fingernail polish remover. If it happens to work, it may be safer than many of the other suggestions.

I keep a bottle of cheap fingernail polish remover, along with a bottle of isopropyl alcohol (fuel-line antifreeze & water remover). The alcohol appears to be close to 100% isopropyl and is good for removing solder flux from PCBs. The nail polish remover is able to remove some paints, inks and magic marker from various surfaces with minimal damage.

Fred

Reply to
Fred McKenzie

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