Jim, from TechShop, has a nifty how-to on Instructables covering the sponge and Ferric Chloride method of quick n’ dirty PCB etching. He writes:
This weekend I tried this sponge and ferric chloride method to etch 3 Arduino shield boards I am prototyping for our RFID-enabled member access system at TechShop (TechShop is the 15,000 square foot membership-based DIY workshop with locations in Menlo Park CA, Portland OR and Durham NC). I was so impressed with the success of this technique that I decided to write it up as an Instructable.
The method I will now show you gives you the advantages of all the other methods, and none of the downsides. Specifically:
- You get a fast etch (much faster than either method I know of),
- You use a tablespoon of solution, so disposal problems are eliminated
- A small bottle of ferric chloride will last for hundreds of boards
- No tank or tub is needed, no heating or agitation
- Undercutting is practically non-existent, and the resist stays in place
- There is no need to try to reduce the amount of copper being etched
- The etch is so fast that it is actually exciting to watch and show your friends!