[Jane]

I use PCB's (Printed Circuit Boards) which basicly
consist of 2 layers

1.The copper
2.The "FR-4"

or
3 layers
1.The copper
2.The "FR-4"
3.The copper



These PCBs can added together having  more l copper layers also. E.g. a 4-layer PCB can be something like

1.The copper
2.The "FR-4"
3.The copper
4.The "FR-4"
5.The copper
6.The "FR-4"
7.The copper


 FR-4 is a composite material composed of woven fiberglass cloth with an epoxy resin binder that is flame resistant (self-extinguishing).
Mostly( always)  only copper is removed ( according to a design) using a solution of Hydrochloric acid HCl  and Hydrogen Peroxide H2O2.
But now I need to remove  one FR-4  layer totally. Is it possible using some chemical? In other words what chemical can be used for an epoxy resin removal?
Thanks

[Arkcon]

This is going to to be difficult.  Epoxy resins, by their nature, are very hard to attack once polymerized, and the fiberglass actually protects the resin even further.  Epoxy resin, reinforced with powdered glass, is what laboratory bench tops are made of, and they last a very long time under very harsh conditions.  Since you want this to be a controlled attack, you've made it even harder.  You might just be asking too much for this to be possible.  Best of luck, anyway.

[Hunter2]

What do you want to do really. I work with this stuff every day.

Normally a process called "Desmear" which uses first an solvent and in second step alkaline  Permanganate solutions are used to clean the holes after drilling. The resin will be eaten. In the third step if necessary Hydroflourides are used to etch the glass during neutralization of Manganesedioxide..

But to remove a layer is unusual and in my opinion impossible.