Peroxy-Sulfuric Etchants and Etching

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Questions about:

1. I have made up a 5 liters of etchant solution. It takes me 10 min. to etch the board. After using the solution several times, it will no longer etch the board. So I have to replace the solution, right?

NO!
You NEVER throw away the etchant!!! Peroxy-sulfuric etchants based on our system will last for many years if properly maintained.

2. What chemical (and how much of it) do I need to add to my present etching bath to neutralize it for disposal?

Before neutralizing, and disposing of your etchant , read the entry above. If you are going to be etching more boards, there is no reason to dispose of a peroxy-sulfuric etching solution. Assuming that you do indeed, need to get rid of it, read on:

There is no easy way to remove the dissolved copper (which is classified as a toxic material) from the plating solution. If you have the capability, the copper can be plated out using an "electrowinning" cell. Then the acid can be neutralized and the solution disposed of.

The sulfuric acid can be neutralized with common baking soda. Be VERY CAREFUL when adding the baking soda!! The bath may foam up suddenly and flow out of it's container. Do not neutralize the solution in your plating tank. Decant into a holding tank first, and then proceed.

If you cannot remove the dissolved copper, neutralize the acid using baking soda as above and then evaporate off all of the liquid. The minor amount of solids that will be left should be acceptable to most disposal sites if it is properly labeled as "Copper Sulfate Pentahydrate Crystals".

3. My bath just isn't etching like it used to. What do I need to add to restore it's performance?

This will depend on the catalyst system that you are using, and how much use your bath has seen. If the bath is fairly fresh, you probably only need to add some hydrogen peroxide (with catalyst, if using FT-2 based system). As the bath etches more copper, the sulfuric acid is consumed to produce copper sulfate and an addition will be required. To determine how much of any one component that you will need to add, it will be necessary to analyze the solution and make additions as indicated by the results of your tests.