[t_maggot]

I am an electronic engineer and have no chemical knowledge. But I use chemicals in the lab for prototyping PCB's (Printed Circuit Boards). I want to know the reactions take place there and what is produced from them to take care of safety and waste maintenance. Let me describe the process:

First, a prototype PCB consist of 3 layers:
1.The "FR4" (plastic οr something??)
2.The copper
3.The Photosensitive layer(??)

After exposure of the photosensitive layer (with a mask) the PCB is placed in sodium hydroxide NaOH (caustic soda) solution with water (about a small spoon of soda in ~300ml) and the exposed layer segment is "destroyed" revealing the cooper. I don't know to describe this reaction because I don't know of what is the photosensitive layer. But the "destroyed" layer takes a dark color before "disappeared".

Next, the PCB is placed in a solution of Hydrochloric acid HCl  and Hydrogen Peroxide H₂O₂ .The solution is 500ml of  15% HCl solution and ~50-80ml of 35%  H₂O₂ solution. In this phase the cooper is "destroyed" from the solution, the solution is heated producing some gas and in a few minutes (or seconds) the desired segments of cooper are disappeared, and the solution has take a blue-green color.

So I have the questions what is the gases produced in the reactions and what remain after the reactions. And if i mix in the end the remainders of sodium hydroxide solutions and Hydrochloric acid solutions what hapens? Is there a problem? In general I want to know if toxic products may released from all this process.

To summarize :

HCL + H₂O₂ + Cu -> X ?
X + NaOH  -> Y ?

Maybe the questions are trivial for chemical engineers but for me is essential for safety in my lab to know the products of reactions to handle with them.

[kevins]

As I know the copper removal process is by nitric acid (may be this process is out date).

In your chemical formula, the solution contains high concentration of H2O2 which give out oxygen gas during heating. So I think the gas evolved from the process may be oxygen. Please confirm with your Chemist.

If the gas is oxygen, then it will not affect the coming process but care should be taken the atmosphere is rich in oxygen.