Remove Potting Compound for Repairs

[Bob Griffin]

Someone brought in a small device for me to repair that is potted in
what appears to be black epoxy. I told them to simply buy another, but
it cannot be replaced.

Can someone with success in this please advise what procedure they
used?

So far, I have heard of solvent being used to dissolve the whole block
(into a sticky mess), or a heat gun to pick off the bottom layer.

Thnaks,

Bob Griffin

[DecadentLinuxUserNumeroUno]

It depends on exactly what the epoxy is.

If it is "Stycast", you *could* presumably heat it to the point at which
it softens enough to pry it off in chunks.

The thing with epoxy is that it tends to like having been polymerized/
vulcanized and doesn't like to "go back".

If it is rubbery like an RTV type, then you have to pry it off in
chunks, but at least it is easier than doing it hot, like most epoxies
would need.

[Don Y]

This depends entirely on the material used to pot it.

What are you likely to encounter *inside* the device? I.e., if it was
some sort of "air-wired contraption" (i.e., where components exist in
"random" x,y,z locations within the blob) then your approach has to
consider "accidentally" encountering a component "along the way".

If the device is simple/obvious enough (that being a function of your
own capabilities), you might consider just *redesigning* it, instead.
And, if form factor is important, just "hull" the existing device and
fit your new guts to it.

If it is sufficiently precious, you could consider Xray to take a peek
before you poke (we used to do this to "protect" designs in the 80's...
pot things with "invisible" conductors so Xray wouldn't reveal critical
connections, etc.).

I suspect you're going to regret the undertaking...

[meow...@care2.com]

Steam slightly above boiling can turn epoxy to soft putty


NT

[Jeff Liebermann]

On Mon, 05 Jan 2015 08:31:27 -0800, Bob Griffin

<bgri...@cybernode.com> wrote:

>Someone brought in a small device for me to repair that is potted in
>what appears to be black epoxy.

Are you sure it's epoxy and not some kind of silicon rubber or
urethane compound? Epoxy is hard as a rock and quite brittle. Rubber
and urethane compounds will bend and are not as brittle.

Different solvents for different epoxies:
<http://www.dynaloy.com/products/epoxy>

Over the years, I've used various concoctions to remove potting
compounds. In order of most effective to lots-of-luck are:
- Acetone or nail polish remover.
- Goof Off or xylene.

<http://www.goofoffproducts.com/http://goofoff.barradmin.com/product/pro-strength-remover>
- Deet (diethyltoluamide) or just toluene.
- Glacial acetic acid. Soften, scrape, soften, scrape, soften,
scrape, soften, scrape, ad nauseam.
- Various hot chlorinated hydrocarbon solvents in an ultrasonic
cleaner (Trichlorethane, MEK, methyl chloride, etc).
- Picric Acid (yes, it's an explosive so be very careful).

Gross generality (probably wrong): If the epoxy was from a 2 part
mix, it can be dissolved. If single part mix, forget it.

The problem with most of these is that while they will soften the
epoxy potting compound, they will also attack some of the molded epoxy
cases used for transistors, plastic IC's, Kemet epoxy caps, etc. It
will also dissolve the epoxy used to hold G10/FR4 printed circuit
boards leaving you with a rather useless fiberglass matting. In other
words, anything strong enough to attack the potting compound, will
also be strong enough to destroy what you're trying to repair.

Another method is to check a list of chemical compounds that epoxy can
tolerate. Use the chemicals that are "not adviseable" as epoxy
solvents:
<http://www.engineeringtoolbox.com/chemical-resistance-epoxy-d_786.html>

Standard warning: Most of the compounds listed are toxic,
carcinogenic, volatile, explosive, shock sensitive, and/or will
penetrate through the skin. Some will attack just about everything
within a few feet. Adequate protection and due caution are highly
advisable.


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

[Bob Griffin]

On Sun, 04 Jan 2015 18:00:07 -0800, Jeff Liebermann <je...@cruzio.com>
wrote:

>Over the years, I've used various concoctions to remove potting
>compounds. In order of most effective to lots-of-luck are:

>- Acetone or nail polish remover. (snip)
>

Acetone is probably the easiest for me to get.

Soak the potted circuit in a sealed glass jar or metal tray overnight
... sounds promising. Then pick away at the glop.

I am assuming it is two-part epoxy.

Bob Griffin

[Jeff Liebermann]

On Mon, 05 Jan 2015 13:36:33 -0800, Bob Griffin
<bgri...@cybernode.com> wrote:

>On Sun, 04 Jan 2015 18:00:07 -0800, Jeff Liebermann <je...@cruzio.com>
>wrote:
>
>>Over the years, I've used various concoctions to remove potting
>>compounds. In order of most effective to lots-of-luck are:
>>- Acetone or nail polish remover. (snip)

>Acetone is probably the easiest for me to get.
>
> Soak the potted circuit in a sealed glass jar or metal tray overnight
>... sounds promising. Then pick away at the glop.

Nope. If left in a metal tray, the acetone will rapidly evaporate.
You'll need some kind of air tight container, like a jar. Do it
outside as the vapors are rather noxious.
<http://www.msdsonline.com/blog/2013/06/18/acetone-the-hidden-hazard>
<http://www.ccohs.ca/oshanswers/chemicals/chem_profiles/acetone.html>

>I am assuming it is two-part epoxy.

Assumption, the mother of all screwups.

If it was done on a production line, it is almost certainly one-part
epoxy. The stuff is easy to handle, easy to apply, and requires only
a heat cure to harden. By comparison, two-part eliminates the heat
cure, but can harden in the syringe making handling a mess.
<http://www.ecnmag.com/articles/2012/05/get-most-out-epoxy-potting-and-encapsulation-compounds>
See "consider the cure" section.

[DecadentLinuxUserNumeroUno]

On Sun, 04 Jan 2015 20:08:50 -0800, Jeff Liebermann wrote:

>>I am assuming it is two-part epoxy.
>
> Assumption, the mother of all screwups.

"Epoxy" is the finished product of a chemical resin mix.

"Epoxies" are typically a two part mixed type polymer.

Is is a perfectly valid assumption as those which have more than two
parts are expensive and rare and usually "special use".

[Mac Decman]

Having done this a few times also...

I agree with the post below that assuming it is two-part epoxy is
crazy, there are all sorts of common potting compounds.

The reality is, at this point, it doesn't really matter what it is.
Once polymerized or cross linked or what ever the ochem guys call the
thing, you are preseneted with a big problem.

You can try attacking it with acid/base type compounds or you can try
very strong solvents. I have seen on the net before a document made
by the USN at Keyport,WA which outlines what they used to de-pot
unreplaceable components. You might find it. It has a list of
solvents, and test results for them, which you can order from a
chemical house.

If it is a polyurathane type potting compound like mine tured out to
be, I can get the name from work of what I ended up ordering. They
had it in stock at a local place in Tacoma for cleaning Polyurathane
guns.

Of course as other posters said, soak and scape is the method. For my
polyurathane, it was soak in the solvent, put in an aluminum debur
machine with soap water which would dry the polyurathane of the
solvent and make it like foam, and then remove the foamy part.

Good luck,

Mark

[Mac Decman]

On Mon, 05 Jan 2015 12:52:35 -0800, Mac Decman
<dearma...@gmail.com> wrote:

<snip>

>Having done this a few times also...
>
>I agree with the post below that assuming it is two-part epoxy is
>crazy, there are all sorts of common potting compounds.
>
>The reality is, at this point, it doesn't really matter what it is.
>Once polymerized or cross linked or what ever the ochem guys call the
>thing, you are preseneted with a big problem.
>
>You can try attacking it with acid/base type compounds or you can try
>very strong solvents. I have seen on the net before a document made
>by the USN at Keyport,WA which outlines what they used to de-pot
>unreplaceable components. You might find it. It has a list of
>solvents, and test results for them, which you can order from a
>chemical house.
>
>If it is a polyurathane type potting compound like mine tured out to
>be, I can get the name from work of what I ended up ordering. They
>had it in stock at a local place in Tacoma for cleaning Polyurathane
>guns.
>
>Of course as other posters said, soak and scape is the method. For my
>polyurathane, it was soak in the solvent, put in an aluminum debur
>machine with soap water which would dry the polyurathane of the
>solvent and make it like foam, and then remove the foamy part.
>
>Good luck,
>
>Mark

PS. I talked with someone from Keyport a few years ago and their new
method for de-poting was an optical system on a milling machine which
would remove 1mil layers and take high res photos. Then a program
would reconstruct the image stackup into something useful. ;-)

Mark

[daku...@gmail.com]

Simply boil it == long and hard.