Etching faceplates, was RE: [sdiy] Plexiglass panels

[Robert Kent]

(I'm surprised with all this Plexiglass talk that nobody seems to have 
mentioned Lexan, a hard-but-flexible polycarbonate material that's supposed
to be much easier to drill, cut, etc. Somewhat more expensive and less 
available, but the local home improvement place sells sheets of it as
window-glass replacement.)

On Tue, 5 Jul 2005, Tim Parkhurst wrote:
> By the way, has anyone tried using standard PCB etching techniques to put
> legends/labeling on face panels? Does this work with aluminum? You wouldn't
> need (or want) to etch all the way through, just a little bit would work.
> How about etching a thin copper sheet, and then putting that on top of a
> thicker panel (and then protecting the copper from oxidation with a few
> shots of clear coat)?

Ferric Chloride works great for etching copper, brass or any ferrous 
metal. Here's a picture of a brass module faceplate I made using standard 
PCB etching techniques:

http://www.ccsi.com/~hanuman/modulator.jpg

This was done with some nasty, depleted etchant I had on hand. Total 
etching time was around an hour or so, which resulted in significant 
relief depth in the metal without undercutting the resist too badly.
Just for fun I tinplated the piece with a commercial PCB tinning 
solution before removing the resist, then polished the tinplate.
The results are striking.

Due to the weight of the brass I used a thin sheet of stock mounted over 
an aluminum L-channel for rigidity. The whole process seemed like a lot
of trouble, and I really wanted to etch aluminum instead. Ferric Chloride
is absolutely not recommended for use with aluminum, as others have noted.
I tried a few experiments with lye, but the violent reaction destroyed 
convential iron-on toner and permanent marker resists. Then I found out 
about a technique called galvanic or electrolytic etching, which works
with any conductive metal including aluminum.

Galvanic etching is done by suspending the workpiece in an electrolyte, 
along with a waste piece of the same material. A salt of the metal being 
etched is supposed to be the most effective electrolyte, but I used 
a few tablespoons of ordinary table salt dissolved in warm water. The 
workpiece (anode) is connected to the positive side of a low-voltage, 
high-current power supply (I used 13.8VDC at 5-10A, a car battery would
work as well). The waste sheet (cathode) is connected to the negative side 
and current is applied. After 15 minutes or so the bare areas of the anode 
are etched into sharp relief. I used toner-transfer etch resist which 
didn't transfer to the aluminum very well, requiring some touch-up with a
paint pen, but held up pretty well in the bath.

Below are the anode and cathode ready to etch:

http://www.ccsi.com/~hanuman/bass-preetch.jpg

And the results after cleaning, filling in the relief design with enamel,
brushing, and assembling the module:

http://www.ccsi.com/~hanuman/bass.jpg

Although moderately work-intensive, I am very happy with this process. The 
resulting front panel markings will never fade or wear away in the normal 
course of operation, and will probably outlast me.

Here's a site I found very helpful in explaining the chemistry and 
practice of galvanic etching:

http://greenart.info/galvetch/

--Robert