How to age or remove color from circuit board fiberglass?

[belloq]

Is there any way to gently remove color from a PCB (printed circuit board) made of FR4 fiberglass that is a bit too bright a yellow? Hot water, bleach, peroxide, acetone, sunlight...?

 

[TazMan2000]

https://www.seeedstudio.com/blog/20...d-circuit-boards-are-usually-green-in-colour/

You will need some sort of solvent to remove the mask. Really nothing gentle about that though. I would assume that you just want the proper colour, not to be able to use the board again?

TazMan2000

 

[Darth Lars]

Solder mask can be dissolved in a boiling hot solution of sodium hydroxide (also known as lye, caustic soda). Acetone has little or no effect.

The actual fibreglass substrate... I dunno. The resin in FR4 should be an epoxy.
Maybe submerging in a warm solution of hydrogen peroxide for a few hours, like when "retr0brighting" yellowed ABS plastic.

Edit: I googled a little. The epoxy in FR4 should not be harmed by hydrogen peroxide but there might be microscopic gaps in the substrate where it may enter and later when h2o2 decomposes into oxygen and hydrogen those bubbles could cause delamination under stress. source.

 

[belloq]

Thanks all. Yes, the board is not functional and I do not need to touch the mask- just want to make paler the yellow color of the FR4 itself. I read online today that acetone may whiten the FR4 a bit as it degrades the epoxy. Will try a test of dipping a sample for various lengths of time.

 

[Monkeyboi69]

Stick it out in the sun for a few days?