Remove Potting Compound for Repairs

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...

Steam slightly above boiling can turn epoxy to soft putty

NT

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:

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.

- 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:

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.

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.

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. See "consider the cure" section.

"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".

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

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

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

Simply boil it == long and hard.