Ferric Chloride VS Muriatic Acid + Hydrogen Peroxide for etching

jpanhalt said:

I don't know where the rumors that ferric chloride is environmentally unfriendly and can 't be uses multiple times come from.

First, ferric chloride is widely used in waste water treatment because it is environmentally friendly. If there is any problem with discarding it after etching copper, it is from the copper it contains. Anything you use for etching will contain the same amount of copper, assuming the etched patterns are the same.

Second, ferric chloride can be re-used many times. Just calculate the amount of copper that can be removed given a certain concentration of ferric chloride. That calculation nevers need to be done in practice, as one can tell from behavior of the solution when it is getting weak. It should also be noted that re-oxidation of the reduced iron (mostly ferrous) is not only practical but prolongs the life of the solution. Letting it sit exposed to air is adequate. Bubbling air through it hastens the re-oxidation. If you add additional HCl, the etching solution eventually (after many PCB's) becomes mostly cupric chloride, which is also an excellent etchant. In other words, it is a mixture of ferric and cupric chlorides that is renewable effectively forever. Here is a link to an article by Adam Seychell that descrivbes the cupric chloride method:

https://jimlaurwilliams.org/projects/seychellePaper/

And from Chemcut on the same subject: **broken link removed**

In fact, Chemcut has several nice reference articles here: https://www.chemcut.net/technical-info/

Third, ferric chloride and cupric chloride give better definition and less undercutting than peroxide/HCl.

Finally, in my experience the peroxide/HCl etchant many affect the resist you are using. I use a photoresist, and it is pitted by that reagent.

John

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