From: "Barry L. Ornitz" <ornitz@tricon.net>
Subject: Etching Panels
Date: May 13 1997
Newsgroups: rec.radio.amateur.homebrew

Geoffrey Schecht <geoffs@onr.com> replied to an original post by Bob 
Duckworth, WB4MNF, about panel engraving:

> Save your money; photoengraving is a lot simpler. You'll go broke 
> stocking all of the bits that one of those CNC engravers uses and  the 
> hold-down jigs required for the various panels you'll be doing  is 
> gonna run into a lot of money, too.

He then wrote some useful, but very outdated, information about 
photoengraving and photoresists.

Most "photoengraving" of electronic panels today is really a photo-
anodizing process.  Either the colored anodizing on an aluminum panel 
is dissolved away, or in high-production runs is applied to a blank 
panel.  The deep engraving of the past has almost disappeared in 
today's modern world.

The idea of using a CAD program to generate an original panel layout 
is certainly a good one.  A Gerber file is rarely necessary as today's 
inkjet and laser printers usually have quite adequate resolution for 
most panels.  Negatives can be shot directly from your original on 
paper, and you can often print directly on transparencies.

Using printed-circuit photoresists is possible IF you know what you
are doing.  Not all photoresists are capable of withstanding both acid
and caustic baths.  The modern dry-film photoresists typically develop
in mild caustic and dissolve in strong caustic baths.

KPR (originally Kodak photoresist) has not been made by Kodak for 
years.  I believe they may have sold the rights to Shipley.  It seems 
to keep extremely well as I have three bottles of the concentrate from 
back in the days when Eastman Chemical was part of Kodak.  KPR can 
achieve really fine details but I STRONGLY suggest the amateur stay 
away from it.  The material is extremely toxic and it contains known 
carcinogens both in the resist itself and in the developer (mainly 
monochlorobenzene).  Unless you have the proper safety equipment 
including respiratory protection - stay away from it.

If you have access to a laminator, the dry-film resist is easy to work 
with.  The developer is safe and relatively mild.  I suspect some of 
the "iron-on" resists for home use would work well too.  I have used 
the dry-film resist and mild hydrochloric acid to etch lettering into 
a brass plate successfully.  I used an acetate transparency in a laser 
printer to expose the dry-film photoresist.  You often need to play 
with the font styles and sizes as the etching can undercut the resist.

Remember when etching metal to not use the same etchant as you do for 
copper circuit boards.  Also remember that acid etching releases 
extremely flammable hydrogen gas.  Strong caustic etching of aluminum 
is possible but you have to have a resist that can handle the caustic.
Agitation of the bath during etching is important.

  73, Barry L. Ornitz  WA4VZQ  ornitz@tricon.net, ornitz@eastman.com