Homebrew PCBs

nedtron@... wrote:
> Greetings,
> 
...
> Ferric chloride is also useful for etching copper and brass thin sheet 
> metal parts.
> 
> Railroad model hobbyist etch out very detailed and intricate railroad car 
> shells from thin sheets of brass. After etching, the brass sheets are 
> folded up and brazed to create the body of the model railroad cars. The 
> detail down to the individual rivets is amazing.
> 
> We have used ferric chloride to etch out precision shim washers that were 
> 1mm in thickness for the laser optics industry. We resorted to ferric 
> chloride etching when die punch efforts failed.
> 
> Temperature controlled ferric chloride provides reliable, repeatable 
> results with less toxicity than the alternatives. Ammonium persulfate is a 
> suitable and reasonable alternative to ferric chloride.

I've tried etching thin (0.2mm) brass and copper sheet in FeCl and the action
took *hours* and didn't give a clean finish. Solution was 1:1 dilution with
water at room-temp in a bubble etcher. A was told by a pcb fabricator that
the ease of pcb etching might have something to do with phosphorous in the
copper that modifies the crystal grains. I tried cleaning and degreasing
the shim, but it was still a reluctant etch.