How to dissolve clear plastic coat from circuit boards?

R

Robbie Hatley

Guest
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
 
On Thu, 8 Jul 2010 15:26:10 -0700, "Robbie Hatley"
<see.my.sig@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?

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?
Click to expand...
Try Acetone.
 
In article <PtKdnWFfL-8fzavRRVn_vwA@giganews.com>,
Robbie Hatley <see.my.sig@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?
Click to expand...
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 <dplatt@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!
 
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
Click to expand...
to use it. :)
 
On Thu, 8 Jul 2010 19:24:02 -0700, dplatt@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.
Click to expand...
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.
Click to expand...
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
 
Robbie Hatley <see.my.sig@for.my.contact.info> wrote in message
news:ptKdnWFfL-8fzavRRVn_vwA@giganews.com...
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
Click to expand...
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.
 
"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".
Click to expand...
Ah, so that's what that coating is called. I was looking for "plastic clear coat".

MG chemicals makes one ...
Click to expand...
Brush-on gel. Don't think that's what I need.

Miller-Stephenson ... D0319B ...
Click to expand...
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...
Click to expand...
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
 
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.)
Click to expand...
Actually, you're mutating into a scorpion.
 
In article <PtKdnWFfL-8fzavRRVn_vwA@giganews.com>,
"Robbie Hatley" <see.my.sig@for.my.contact.info> wrote:

Are there better options?
Click to expand...
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
 
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