Hello everybody, just a theoretical question.

When you apply a toner to a copper board, and you start etching it with your acids, why does it not dissolve all the copper ? As in, the toner is applied, it keeps the acid from dissolving through the toner, but would it not at some point start going UNDER the toner ? Ilustartions in mspaint

 

Hello everybody, just a theoretical question.

When you apply a toner to a copper board, and you start etching it with your acids, why does it not dissolve all the copper ? As in, the toner is applied, it keeps the acid from dissolving through the toner, but would it not at some point start going UNDER the toner ? Ilustartions in mspaint

Yes, that happens. The term is "undercutting," and that can be a problem. Some etchants produce less undercutting than others. Ferric chloride is said to produce about the least amount of undercutting. A major cause regardless of the etchant is leaving the board in the solution too long.

Edit: Here's a link to Chemcut that discusses that subject: http://www.chemcut.net/wp-content/uploads/2015/03/Chemcut_Thoughts_on_Undercut.pdf

NB: The Chemcut link has changed since 2014.

John