I had a chance to play around with some CuCl2 (Cupric Chloride)
etching last Friday and performed a test etch with a small segment of
PCB created using the "cheap paper laser toner-transfer method".
The traces are 10 mil in width.
You can see check out some pics at
http://www.techfreakz.org/~rolan/mypics/cucl2/The neat thing about using CuCl2 is that the byproduct
of the etching process generates more CuCl2. And because of
this, the etchant solution can be used over and over.
I can't imagine why people are still using Ferric Chloride.
~Rolan