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MEK to Remove Solder Mask from PCB

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wraper:

--- Quote from: magic on January 02, 2020, 06:12:05 pm ---If soldermask is made of epoxy like FR4 than things may be tricky indeed.

Although the truth is that there is actually no such thing as "the epoxy resin". Epoxy is not a particular chemical like polyethylene or PTFE but really a process for polymerizing various kinds of molecules into heavily cross-linked networks, named after the epoxide group which is involved in curing of the resin and then is gone from the final product.

So the constituents determine what the "epoxy" really is and its chemical properties. If you are lucky, you may find some solvent which will remove one epoxy resin from another. Case in point, DCM (supposedly) will eat PCBs but will (certainly) leave transistors and ICs which are "epoxy" too.

--- End quote ---
Normally solder mask is negative photoresist. Either liquid or dry film. After exposure to UV and baking at high temperature it becomes very durable.

magic:
I found this PCI article too a few weeks ago but now it's showing me a paywall :wtf:

Anyway, the most important takeaway I remember is that ICs are typically packaged in novolak based epoxies. Novolak is apparently a phenol-based polymer akin to bakelite. A quick search for chemical attacks on the latter brought me to the Science Madness forum where the general response was "no way" and "you have to be nuts", but somebody linked lecture slides by one dr. Hazizan which suggest that phenol resins may be vulnerable to 1-naphthol, formic acid and strong oxidizing acids. The latter of course is no-shit-Sherlock for anyone interested in decapsulation :)

But I'm digressing. No idea what soldermasks are made of, but perhaps you could find articles similar to the above about ICs.

I'm not sure if you will want to play with all those organic solvents once you read the safety datasheets, but formic or acetic acid seems safe enough to try. Even the mineral acids don't look too bad in comparison, at least not carcinogenic. They do nothing at room temperature BTW, so if you are lucky perhaps one polymer will give up before the other on heating. Maybe.

T3sl4co1l:
I mean... acetic acid has a complex for copper, it might dissolve that faster. :P  And it looks formic does as well.

Tim

Yansi:
Neither does MEK dissolve a common soldermask types, nor does it dissolve the PCB binder. Certainly not within a short application time. Bathing the pcb in MEK for extended periods of time may make a difference.

Yansi:

--- Quote from: graybeard on January 02, 2020, 12:19:48 am ---MEK attacks almost anything organic.  I would worry about it attacking the binder in the PCB. 
I have used it to clean deposits in antique motorcycle engines, but never on a PCB.

--- End quote ---

Not true. MEK is a bastard, but certainly not "attacks almost anything organic".

Sure, your fingers and ABS plastic it eats for breakfast, but a common polypropylene? Maybe even polyethylene? PTFE? Likely doesn't touch it with a long stick.

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