Vehicle ECU - dissolving PolyUrethane

[digsys]

A friends ECU recently died, and they want 2.5K$ and 1 month to replace it. Before we get all the standard replies :-) -
The ECU is filled with PolyEurethane and no-one wants to attempt to repair it.
I've searched 2nd hand parts, including o/seas - all repair joints etc etc. I've also researched ALL grades of PEU,
and ALL the solvents that can attack / dissolve it, plus "mechanics" experiences, so ALL that is done.
I have a short list of solutions that I will follow, but BEFORE I did, I just wanted to see if anyone here had PRACTICAL
experience with dissolving PEU (and leaving all electronics intact). I've done may ECUs, but never with PEU.

[jeremy]

Don't know, but keep us posted with your progress!

[eKretz]

I have de-potted a few boards with decent success. It takes take a good bit of time though. I use a tin to soak the board in acetone. A day or two then scrape off the softened layer, day or two more, scrape off the next softened layer, etc. If you're very careful it's possible to get to a clean board without losing any components. Anything like wire insulation or softer stuff like that will be destroyed though, so plan on replacing some stuff.  I sharpened a small flat blade screwdriver into a razor sharp chisel shape to aid in peeling/removing the softened layer and it works great.

[babysitter]

Try to get Tetrahydrofuran - I have quantities available at work, used to glue PVC. I actually have ready-made mixtures of THF and PU and also THF and MABS to coat stuff.

[peter.mitchell]

I use this stuff; http://www.mgchemicals.com/products/protective-coatings/conformal/conformal-coating-stripper-8310/
I also use the 8312 stuff, but its harder to find - infact, i can't find a link to it on their site.

[poorchava]

It depends on what has actually died in the ECU. I there's an obvious failure, like for example blown output stage I would use combination of acethone or nitro thinner and some sharp tool. If you need to clean entire board because point of failure is not obvious, then I'd use a proper urethane stripper. You need to watch out, because components may be damaged by stronger chemicals like acethone. As a matter of fact AEC-Q compliant devices are tested for resistance to IPA, turpentine and PGME not to mention, that older (like 5yr+) automotive electronics often contains a lot of industrial grade parts.

[digsys]

Thanks folks, I'll look into those suggestions. My plan now is - to use a dremmel chew out the bulk of PUE first !
The stuff has exactly the same consistency of jello. I was even thinking of using a sand blaster with very fine sand and low pressure.
I did a couple quick tests, seems to have pretty weak self-bonding.

[lewis]

I've successfully used Methyl Ethyl Ketone (MEK) to dissolve urethane resin, takes about a week of soaking in a sealed metal container and lots of poking with a screwdriver, but it doesn't damage certain plastics like acetone will. I've also used Dichloromethane to strip epoxy and urethane, it's very nasty stuff. There's an industrial chemicals supplier near me who sells it for graffiti removal applications. Again, takes about a week, but turns almost any encapsulant, even silicone, into a lovely foam.

I've used this company for replacement ECUs in the past, and they are very good: http://www.ecutesting.com/. UK based, but they trade globally.

[digsys]

I've used this company for replacement ECUs in the past, and they are very good: www.ecutesting.com

Thanks, but nothing there for Chrysler - especially Grand Voyager 2003 :-)  Trust my friend to own a rare van !!

[lewis]

They do do Chrysler stuff - http://www.ecutesting.com/catalogue/chrysler_eculist.html?category=4046&model=738, even if your ecu is not listed, might be worth giving them a try!

[digsys]

They do do Chrysler stuff -  even if your ecu is not listed, might be worth giving them a try! 

They say they can "rebuild them", so they must have found a way to dissolve / remove the PEU, and for that price all up,
it may not have been too difficult / messy? That's the part I'm interested in :-) Especially since the ones in OZ get thrown out.

[N2IXK]

Another vote for dichloromethane (aka methylene chloride). VERY nasty fumes and evaporates readily, so use only outdoors or under a proper fume hood.

Industrial plastics suppliers sell the stuff in quart and gallon cans for solvent welding acrylic and polycarb.

[vl400]

And another vote for MEK. Works a treat without damaging anything, this ECU I did awhile back still works fine .. http://yamahaecu.wikispaces.com/ECU+Hardware+Information

[digsys]

And another vote for MEK. Works a treat without damaging anything, this ECU I did awhile back still works

I've used MEK on many occasions for that hardened / black resin very successfully. This is the first time
I've seen something completely filled with a "jelly" PEU. That wouldn't normally bother me, but after
talking to several mechanics / electricians / ECU repair places, they ALL said it can't be done, and
none of them wanted to try. Not that I totally believe them, wouldn't be the first time, but I am being
very cautious.

[TerraHertz]

I've used MEK with some success for dissolving potting compound. (Not silicone based.) But that's only because you can buy MEK at hardware stores. It's in the paint stripper section.

One useful tip I can offer, is that the best tool for mechanically tearing out soft potting compound without damaging components, is a 'chisel' made of wood. Just cut pieces of wood to the best size for the bit you're working on, and whittle a fairly sharp flat edge on the piece. You can choose different hardness woods to suit the delicacy of components you don't want to damage. The end gets blunt fairly rapidly, so resharpen as required.

Bamboo cooking skewers and disposable wooden chopsticks are good cheap sources of suitable bits of wood, if you don't have a wood scrapbox. Also offcuts of hardwood timber floorboards for larger bits.

Edit: Btw, can anyone recommend a solvent for silicone-based compounds?

[vl400]

I've used MEK on many occasions for that hardened / black resin very successfully. This is the first time
I've seen something completely filled with a "jelly" PEU.

That ECU I linked was soft and flexible so likely PEU, it wasnt a hard potting compound like the pics make it look. The small bit missing to show the quartz was made using a plastic spudger.

[CaptnYellowShirt]

Edit: Btw, can anyone recommend a solvent for silicone-based compounds?

Brake Cleaner. None of that wussy non-chlorinated stuff, gotta go whole hog on this one.

I recently dissolved the silicone gel out of a pressure sensing IC with the stuff. Similar process to the ECU discussion: Soak and Scrape.

But in general silicone-based compounds (RTV's and the like) are non-resistant to fuels. So K-1 works well, plays well with most other compounds, and doesn't smell too bad.

[CaptnYellowShirt]

And another vote for MEK. Works a treat without damaging anything, this ECU I did awhile back still works fine .. http://yamahaecu.wikispaces.com/ECU+Hardware+Information

"Potting
The ECU is fully potted to become waterproof. It looks to be a mixture of a polyurethane and small fragments of quartz. The bulk of it can be carefully removed using a small screwdriver and sharp knife. The final stage is to chemically soften and then scrape away the remaining polyurethane using Methyl Ethyl Ketone (MEK), this can be purchased from good paint suppliers."

What in the world are those quartz chips doing in there?

[N2IXK]

Was wondering that myself. Maybe to prevent getting a good X-ray image of the thing?  Or to destroy cutting tools used to remove the potting? 

[nctnico]

Maybe a filler to enhance thermal conductivity? Or just to make the potting compound cheaper.

[peter.mitchell]

Quartz? Looks more like them little pebbles/gravel you get for your fish tank/aquarium...

[T3sl4co1l]

Probably saves cost and conducts heat slightly better, although x-ray is a good point too.

Beware with DCM, after long enough, it'll even swell epoxy, not to mention destroy....everything made of plastic, or coated in resin or whatever.

Tim

[440roadrunner]

I  do  realize this  answer  is not what you want to hear  and is  coming   completely  from left  field.  Have you considered    buying  a Megasquirt  and replacing the   OEM   computer?

[digsys]

I  do  realize this  answer  is not what you want to hear  and is  coming   completely  from left  field.  Have you considered    buying  a Megasquirt  and replacing the   OEM   computer? 

I'd never heard of them before, and just looked them up ... EEEEP I'd have to do some brain work :-) Trying to avoid that :-)

[insertcoolusername]

Hey all, I was searching an unrelated topic and stumbled upon this.  I realize its an old topic, but in case someone googles it, my response may be helpful.  Sorry if my reply is in violation of site guidelines as admittedly, I didn't read the rules.

In response to original poster or anyone in the same situation...

1) Absolutely ANYTHING that dissolves polyurethane will also eat electronic components.  So, to answer accurately, there is no such thing as a solvent that will dissolve polyurethane while leaving the board components intact  This is not debatable and anyone who claims otherwise  is either lying or misinformed.
 2) Practically, however, if you have a vintage ECU and don't mind the labor hours involved, you may use any reputable HVLP gun cleaner to dissolve the polyurethane hermetic seal/conformal coating.  Remove small quantities, avoiding contact with individual components.  Be aware that any damaged components must be replaced.  Once you have repaired the board, I recommend using a silicone conformal coating for future weather/shock proofing.

I hope this helps those of you in a similar situation.  However, I'm not available to answer any follow up questions, so please don't be offended or take it personally thinking I'm ignoring you.