How to dissolve clear plastic coat from circuit boards?

Robbie Hatley

unread,

Jul 8, 2010, 6:26:10 PM7/8/10

to

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

PeterD

unread,

Jul 8, 2010, 6:56:33 PM7/8/10

to

Try Acetone.

William Sommerwerck

unread,

Jul 8, 2010, 9:27:42 PM7/8/10

to

> Try acetone.

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

Dave Platt

unread,

Jul 8, 2010, 10:24:02 PM7/8/10

to

In article <PtKdnWFfL-8...@giganews.com>,
Robbie Hatley <see.m...@for.my.contact.info> wrote:

>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?

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 <dpl...@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Sjouke Burry

unread,

Jul 8, 2010, 11:09:00 PM7/8/10

to

William Sommerwerck wrote:
>> Try acetone.
>
> But with great caution. Acetone attacks a lot of plastics.
>
>

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

Jeff Liebermann

unread,

Jul 9, 2010, 1:13:15 AM7/9/10

to

On Thu, 8 Jul 2010 19:24:02 -0700, dpl...@radagast.org (Dave Platt)
wrote:

>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.

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.

>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.

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 je...@cruzio.com
# http://www.LearnByDestroying.com AE6KS

N_Cook

unread,

Jul 9, 2010, 3:41:18 AM7/9/10

to

Robbie Hatley <see.m...@for.my.contact.info> wrote in message
news:PtKdnWFfL-8...@giganews.com...

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.

Robbie Hatley

unread,

Jul 9, 2010, 5:20:58 PM7/9/10

to

"Dave Platt" wrote:

> Robbie Hatley wrote:
>
> > 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?
>
> Google "conformal coating stripper".

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

> MG chemicals makes one ...

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

> Miller-Stephenson ... D0319B ...

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!

> ... The pale-blue glow you observed is probably a UV-fluorescent tracer dye...

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

William Sommerwerck

unread,

Jul 9, 2010, 6:24:58 PM7/9/10

to

> 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.)

Actually, you're mutating into a scorpion.

Fred McKenzie

unread,

Jul 9, 2010, 8:27:30 PM7/9/10

to

In article <PtKdnWFfL-8...@giganews.com>,
"Robbie Hatley" <see.m...@for.my.contact.info> wrote:

> Are there better options?

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