for cleaning boards. Sure wished I could remember the name even though whatever it was is probably unubtanium now.

Yes. Ozone depleter because it has, "chlor" in it.
Replacements are available: http://www.relspec.com/solutions/trichloroethane.html?gclid=CO718MTzqsICFUQV7AodTmQAyQ

Still, that isn't what martinez needs.

 

... we used what was at the time a common degreaser.

Found it!!! ... this chemical resistance chart lists liquid ammonia (NH3 on page 9) as something that "diffuses through EPDM; attacks epoxy materials" (note 3 found in page 25)
If the encapsulating material used in my circuit is indeed epoxy, then this definitely is worth a try ... although ammonia seems to attack cooper too ... guess it will all come down to the total time of exposure, then...

 

Can't remember the name of the chemical, when I was working for Hughes Aircraft in the 60's we used what was at the time a common degreaser. We would just drop the potted module in a jar and in a few days the potting material would be laying on the bottom in small chunks. There was a big vat of the stuff in the circuit board fab shop for cleaning boards. Sure wished I could remember the name even though whatever it was is probably unubtanium now.

Found it Trichloroethane

Good stuff, used it for cleaning up military tube gear from years of cigarette smoke. I worked for Hughes Aircraft Naval & Maritime Systems out of Long Beach, Ca for a while in the early 80's mainly on weapon and comm systems. Still have the old jacket somewhere in the shed.

 

Good stuff, used it for cleaning up military tube gear from years of cigarette smoke. I worked for Hughes Aircraft Naval & Maritime Systems for a while in the early 80's mainly on weapons and comm systems. Still have the old jacket somewhere in the shed.

Wikipedia lists two definitions for:

Trichloroethane can refer to either of two isomeric chemical compounds:

• 1,1,1-Trichloroethane (methyl chloroform)
• 1,1,2-Trichloroethane (vinyl trichloride)

Which one is it?

 

The most common degreaser is ammonia... I doubt that would work in modern resins, though... I just remembered that diesel fuel attacks silicon compounds... melting them and making them rubbery after a while. Also, some oils eat through some plastics and epoxys ... I wonder if this could work for me, though... On the other hand, I have nothing to lose by submerging that thing in those fluids for a few days...

What you say is somewhat true, but not actually related to what you asked. For example, it is a rare silicone rubber that is also hard. It does no good for us to know that diesel fuel after a very long time will make it swell. Aliphatic sulfonic acids do the same and disrupt silicone bonds much quicker. But neither is related to your question. There is no general answer to, " Can something be removed?" Actually, I guess the answer is "yes." The devil is in the details.

If you seriously want to remove a potting compound chemically, you need to give more information.

John

 

Which one is it?

It was mainly methyl chloroform, we also used CFC-113 and carbon tetrachloride by the gallon. It's a miracle we didn't all die of liver cancer 30 years ago.

 

Ok,
The top three are...
Methylene chloride (also know as dichloromethane)
("super strength" paint stripper).
This is very toxic and should not be used indoors. Will cause nerve damage of skin surfaces - personal experience. It will dissolve many polymers. Also will give you a headache and, eventually, brain damage if repeatedly inhaled. Excellent degreaser too, will pull the oil out of your skin on contact - and the myelin off your nerves in an instant and permeate most gloves.

Trichloroethane (also known as TCE)
Getting difficult to find since it evaporates much more slowly than the above. This is the most common contaminat in ground water in the world - bad enough to make the water un-drinkable.

Was a common degreaser for automotive parts and machine tools. Also reacts (very slowly) with steel and leaves a polished look.

NMP (N-methylpyrrolidone)
Was considered a Safe solvent for years and recently became listed as a cancer suspect agent. One of few solvents that can dissolve urethane foam. It will also swell and soften some epoxy and silicones.

It was available in some paint stripper formulations. It will definitely clean hear-sink silicone from parts and sinks. Check labels for active ingredients or the Safety data Sheet - SDS (formerly known as MSDS).

THF (tetrahydrofuran)
Fairly safe by health standards for a "strong" solvent but Fairly flammable. Use outdoors.

Difficult to find in cans or pure form. Some brands of PVC pipe primer (purple) may be made up of THF if you can accept the purple dye. This is good with parylene - recommended to separate it from the pcb but you will still have to puts the coating apart to get it off components.
======

Good luck, be safe and you may be better off just buying new parts, the health and fire issues just aren't with it in most cases.

Also, if you are trying to un-pot an inductor (coil), you won't find anything interesting. The potting is usually there to prevent the coil from moving. Any movement changes frequency of an oscillator so they are often potted to connect the windings of an air-core in position relative to each adjacent turn and prevent movement vs the board.

 

If you seriously want to remove a potting compound chemically, you need to give more information.John

A valid request... but I don't even know what the exact compound is... not sure if it's epoxy or some other material, and I don't know how to test it to find out, either... what I was trying to say is that I'm not in a hurry, if two or three days (or even a week) will do the trick, then I'm willing to go for it. But before trying ammonia, I think I'll go for trichloroethane first, since BReeves mentioned that he's used it before for this purpose.
What I'm certainly going to do, though, is post my results in this forum after I'm done experimenting, so that others can benefit from this experience too.

 

A valid request... but I don't even know what the exact compound is... not sure if it's epoxy or some other material, and I don't know how to test it to find out, either... what I was trying to say is that I'm not in a hurry, if two or three days (or even a week) will do the trick, then I'm willing to go for it. But before trying ammonia, I think I'll go for trichloroethane first, since BReeves mentioned that he's used it before for this purpose.
What I'm certainly going to do, though, is post my results in this forum after I'm done experimenting, so that others can benefit from this experience too.

Don't use ammonia. It is a fairly strong aqueous base. It will corrode copper and will not do anything to most polymers. The solvents mentioned above will not do anything to the copper - the TCE and methylene chloride will give the copper a clean look but it will not corrode it and leave you with a malachite green mess.

 

Also, if you are trying to un-pot an inductor (coil), you won't find anything interesting

An excellent observation... what I'm trying to do is find out if the coil is the only thing inside the thing (I do know that it's actually an electromagnet). I've already had the part tested for inductance (will get the results tomorrow) and I know that it has a resistance of about 0.75Ω (will need to make a more accurate measurement than that, tough), and then I'll be able to estimate its wire gage and how many turns it has.
I've probably been getting ahead of myself with all this talk about chemically removing the compound. But that's also a subject I've been wanting to explore for a while now anyway, and now I know a lot more about the subject, thanks to all of you.
Thank you, Gopher, for taking the time to look this up and trying to help me out. My area of expertise is machine design, robotics, mechatronics, software and firmware programming, and digital electronics (MCU's, gates, oscillators, etc) ... my main weakness is analog electronics (and my wife... ha ha ha...)... Do let me know if you ever need something that I could help you with.
Thanks again.

 

Of course, an infrared spectrum of a Nujol mull or KBr glass of a few chips would tell us a lot, but I assume that is out of the question.

Still, a flame test can be useful. If you burn a small chip, does it smell olefinic, give a smokey flame, smell acrid, give a sustained flame, etc. Such flame tests were well known years ago. Today, you can still use them. If it is hard, I would be thinking of a polyurethane, polyester, or epoxy. If you have some known plastics, you can do such a test. By polyester, I mean like the resin used in autobody repairs. It has a characteristic "styrene" odor. With most of these polymers, you will not dissolve them, but you may denature them so they can be more easily removed.

Also remember that many components on a PCB may be made of the same resins. So in denaturing the potting compound, you may also affect components, such as connectors and optoelectronic devices (e.g., LED's, IR receivers).

I think the best you are likely to achieve will be a mechanical removal of the bulk of material plus a little clean up of specific areas.

John

 

Thank you, Gopher, for taking the time to look this up and trying to help me out.

I didn't look up anything, I'm a chemist.

 

I didn't look up anything, I'm a chemist.

Well.... that explains a lot!

 

...Sure wished I could remember the name even though whatever it was is probably unubtanium now.

Found it Trichloroethane

That was some nasty stuff! It's a known carcinogen and can lead to a host of respiratory, neurological and other illnesses. Trichloroethylene is a related substance and part of the legacy in Woburn MA, in the incident recreated in the movie "A Civil Affair".

 

I didn't look up anything, I'm a chemist.

You just got real valuable to me! Chemistry is one of those very wide fields that I did NOT accomplish much with.

 

You just got real valuable to me! Chemistry is one of those very wide fields that I did NOT accomplish much with.

So, DIY chemistry? Not as easy in the basement or garage as electronics or woodworking

 

You just got real valuable to me! Chemistry is one of those very wide fields that I did NOT accomplish much with.

My son has just decided to become a chemical engineer... (actually, a Nanotechnology and Chemical Sciences Engineer)... but I'm gonna have to wait at least 10 or more years before I can seriously consult anything with him... So for the time being (and I hope a LONG time) I'm going to rely on Gopher... if he doesn't mind, or course...

 

My son has just decided to become a chemical engineer... (actually, a Nanotechnology and Chemical Sciences Engineer)... but I'm gonna have to wait at least 10 or more years before I can seriously consult anything with him... So for the time being (and I hope a LONG time) I'm going to rely on Gopher... if he doesn't mind, or course...

We'll see how it goes. Electronics and Motorcycles were supposed to be a distraction from my day job - and an excuse why I don't have to help my wife with her projects.

Maybe a barter system. I give chemical advice and I get HVAC advice from Twelve.

 

We'll see how it goes. Electronics and Motorcycles were supposed to be a distraction from my day job - and an excuse why I don't have to help my wife with her projects.

Maybe a barter system. I give chemical advice and I get HVAC advice from Twelve.

An you can get MCU advice from me, if you ever need it...

 

Maybe a barter system. I give chemical advice and I get HVAC advice from Twelve.

No Problem. I have been the consultant/ go-to-guy for several companies, since somewhere in the 1970's and I have fixed air conditioners over the phone...I can't count that high. Let's just say, in at least 5 states.