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Cleaning vintage PCB - Damaged by isopropyl?

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xfd1001:
Hello,

I recently bought some vintage instruments that needed some cleaning.
Since I don't have expertise with cleaning vintage PCB's; I did some extensive searching on the web to make sure I don't use any cleaning substances that might damage the (bakelite?) PCB material.
Every single post that I read said it's fine to clean with isopropyl alcohol and some some people suggested using dishwasher soap.

So after I had the guarantee it was fine; I carefully started cleaning with a Q-tip & isopropyl alcohol. And within minutes the spots that got in contact with the alcohol started to look damaged. 😓

Can anyone tell me if it's actually damaged and if yes; why it got damaged? How to repair the damaged surface & how to proceed without further damage?

Attached you find a picture of the damaged surface.


Thanks

AndyBeez:
Looks like the IPA lifted a conformal coating. A coating that may have used IPA as the thinner - some 40/50 year's ago. From the vintage, maybe a resin or a wax based coat? It's possible the coating had not keyed onto the SRBP surface. So far, just cosmetic/no harm. Try diluting your IPA 1 with 3 part water - so it's not so agressive.

Gyro:
The board itself is of course not damaged, but whatever the coating is, it is clearly soluble in IPA.

As the traces are not tinned, it was common that some form of coating would have been applied to the surface to prevent them from corroding. This was often something as simple as a layer of flux or a an IPA soluble laquer of some type.


P.S. Do you actually need to clean the board surface?

jpanhalt:
Shellac apparently has been used as a conformal coating -- at least early on.  It is not surprising IPA damaged it.  If you want to remove it completely, the more common solvent for shellac is absolute ethanol (not denatured "alcohol" for fuel).  Woodworking suppliers may be one source.

xfd1001:
Thank you all for the help! I wish I had read this before damaging the coating & hope others who search on vintage isopropyl cleaning will find this thread.
I guess it would be okay to just leave it like this and just refrain from further cleaning?

@jpanhalt Aside from that it looks ugly damaged now; I guess it's better to leave the Shellac on? Or would it be better to get rid of it completely and apply a new coating?
If it doesn't matter I will leave it on. Preferably restore the coating to it's original state but I guess that will be too difficult?

@AndyBeez
Yup, a bit older actually; it's an analog multimeter from 1969 that I'm trying to repair & preserve.

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