Warm liquid goo phase... or, is unpotting possible?

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Steve Jones

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Jun 4, 2004
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506
Location
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Need to get some potted modules open, and while I have had success opening lots of ARP submodules to repair them, they are usually only hard epoxy on top, with silicon cheese underneath that can be picked out.

I guess there are many epoxy compounds, but I am curious to hear if anyone has found any solvents that may get some of them dissolved. Probably the kind of chemicals that would stop you from ever being able to have children after one sniff, but what the hell, no kids means more spare money for gear.
 
Chortle.... :green:

This is a subject close to my heart, but I'm yet to succeed in my quest to get a 2520 apart in one piece.
I've had some success with 'ACETONE', but it's a laborious task and takes weeks.
During research the name 'Dynasolve 165' came up, it's not available in the UK, but it's main constituent appears to be 'Dichloromethane', so if you search for some of that stuff, you may have some joy.

Keep us up to date.

peter
 
Thanks for that lead, it looks like it could be nasty enough to do the trick, probably take all the bands off the resistors too, but if I can find some here I'll give it a shot and post the result.
 
Some of the solvents you can get into to dissolve epoxides are pretty nasty... Dichloromethane is an excellent solvent (although I'm not sure it will dissolve epoxides, and will likely dissolve the varnish on resistors and other components) but it is quite carcinogenic and toxic. Also, it's highly volatile, which means you either need to work with it in a laboratory fume hood, or assuming you don't have one of those, outside.

Dimethylformamide or aniline may work better but I have no idea where you'd get it, either in the US or abroad. They are both toxic and hazardous, read the MSDS (Material safety data sheets) online before you purchase or attempt to use them.

Epoxides are so hard and durable because they are highly cross-linked. They have an extremely high molecular weight and they are bulky molecules because of the degree of cross-linking that goes on. (you know, "bridges" that form between adjacent long strands of carbon molecules!) The problem in dissolving them is that you need to use a good quantity of solvent and you may need to do a fair amount of careful physical work as well. Bulky molecules have a huge surface area, which means that the solvent has to do a lot more work to pull it into solution. (and a lot of solvents may not have the energy to put forth!)

There are two ways to attack the problem though: If you have nerves of steel, you can obtain some nitric or sulfuric acid (doesn't have to be fuming - and WARNING!! THESE ARE VERY DANGEROUS!) and carefully break down the epoxy by applying them drop by drop. Keep some water on hand to flush the acid off the surface in case you hit something, and again, definitely do that outside.

The acid thing of course has a downside which is that you can dissolve the components quite readily, and your fingers/clothes/house/floor too. So if you do work with any of these chemicals, PLEASE do it outside, wear latex gloves, and have a large bucket of water handy so if you spill any on yourself you can flush the area before you get severely burned.
 
I have had good results with dimethyl formamide. Take all safety precaution seriously with this stuff. I just put the potted module into a sealer jar and submerge with the dimeth. After a day or two the epoxy starts falling off in flakes. I understand heating the solution speeds up the process, but I have never done this. The dimethyl formamide doesn't seem to affect plastic like transistor cases, but it will remove the coating off resistors. The resistors however, can still be measured afterwards, as well as caps and transistors.
 
I remember a substitute for Keytone, MEK or methyl ethyl Keytone how ever you know it as. It was a biodegradable Graffiti remover, broke down all types of solvent type paints and adhesives. I'll check on the potting compound solvent the was used in the Electrical labs. Can't remember. Solvents work but they shure don't keep you smart. :? I'll try and get the Graffiti remover part number and company name, it worked very well on MEK based Adhesives. Bondfast etc. 3M stuff as well.

Later
 
Holy crap there is a flood of new biodegradable products on the market. Type in MEK or trichloroethane substitute. Tons of companies world wide. Should be easy enough to get a 1/2 gallon shipped anywhere. The graffiti remover was used on the MEK based adhesives and worked as well as or better than MEK. The trichloroethane substitute was OK, used on Locktite products at least I saved my brain cell(s). Check it out for yourself, there are a ton of Citrus based cleaners and don't kock em because they don't smell bad and make you cry. There also easier to get hold of since they are not considered Dangerous Goods

Later
 
You can also dilute hydrochloric acid (now it becomes mecuric acid I believe, used in swimming pools and stuff)
The weaker acid will melt the epoxy but hopefully quicker that the metal parts.
Never tried it but my boss says it works.
cj
 
Feed me some bad moules (Mussels) and I'll come and get rid of that potting compound for you...Just ask a French campsite shower block near Vannes... :green:

chef
 
:green: :green: :green:

Yeah, I think I remember hearing something about that on "A Current Affair"... So that was you eh? Duck eggs and Pernod could be effective too.
 
I will never be able to look Ray Martin in the face again :shock:
Duck eggs and Pernod could be effective too.
Actually any eggs for me! They don't like me :green:
Especially French ones... :oops:

chef
 
No adequate human studies of the relationship between exposure to dichloromethane and human cancer were found (IARC 1979, 1982, 1999), though there is evidence of cancer in tests conducted in laboratory animals... the metabolic pathway for degradation may be different in animals than humans so it may or may not be relevant. Handle it carefully as if there a positive link... with that said, the best epoxy remover is a combination of dichloromethane (methylene chloride) and methanol.

PCB with epoxy covering...
fuzz33.jpg


PCB with no epoxy...
fuzz35.jpg


:grin: :grin: :grin: :grin:
regards, Jack
 
Thanks Jack, I am off to try and find some dichloromethane locally, if I have any luck I will give it a try. Can you let us know the proportions of dichloromethane and methanol to use?
 
The proportions are not critical... seems like I used about 3 parts dichloromethane to 1 part methanol, though you could also use isopropanol as it is easier to find. Keep the vent fan running! :grin:

regards, Jack
 

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