Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!uwm.edu!ogicse!milton!whit
From: whit@milton.u.washington.edu (John Whitmore)
Newsgroups: sci.electronics
Subject: Re: Etching PCBs ??
Message-ID: <18205@milton.u.washington.edu>
Date: 11 Mar 91 23:50:22 GMT
References: <1991Mar08.084952.7323@lynx.CS.ORST.EDU>
Organization: University of Washington, Seattle
Lines: 58

In article <1991Mar08.084952.7323@lynx.CS.ORST.EDU> vovut@prism.CS.ORST.EDU () writes:
>
>Does anybody etch their own PCBs?  If so,  would you mind describing how you
>do it and what kind of set up you need?

	I assume you want something quick-and-dirty.  We have made  
PCB's by various methods, and I will describe the do-it-yourself
approach (rather than the way you'd do it if you had all the
equipment in the world).
	First, prepare a negative of the printed circuit; two negatives,
with alignment bullseyes, if double-sided.  We use Kodalith 
transparency film (UV-exposure, alcohol (xylol) developed), available
at many art/graphic supply houses.  Touchup the negative as
necessary (keep the original artwork pristine).  This requires
a UV lamp (sun lamp is OK) with timer; typical exposure 1 minute
for a contact print.
	Then clean and coat a copper-clad board; we use steel wool
and soapy water, rinsing and blow-drying with compressed air.
Coat with photoresist (KPR type is available in aerosol cans);
we used to have an old 45 rpm turntable that we'd start up with
the PC board atop it, spraying while it spun.  The excess photoresist
went to the edges (and dripped off).  It is best to make a VERY
thin coat of photoresist.
	Bake for 15 minutes or air-dry for 3 hours (longer is better).
Then place the negative on the coated board and expose (same UV
lamp as before) for about a minute.
	Develop the photoresist (with KPR developer); we dip a cotton
ball in the developer and wipe, but you can also soak it.  Optionally,
here, you can dye the photoresist (after developing, it's VERY hard
to see) with any of several kinds of dye.  Rinse off the developer
and blow dry with compressed air.
	Then etch the board in a heated (120 F) agitated (we blew 
air into the bottom of the vat to stir it) vessel of ferric chloride
solution.  FeCl will cheerfully etch through copper, stainless
steel, you name it (and stains your hands and clothes a terrible
yellow-brown color); the only materials that should contact it
are glass, plastic, and titanium.  I believe the solution was
bought already mixed, though I think you can buy the chloride
dry and dissolve it in diluted hydrochloric acid.

	When the etching is complete, rinse the board and blow it
dry; scrub off the photoresist and (optionally) tin or silver
plate the board.  Tin-plating can be done by dipping in an electroless 
plating solution, silver plating by rubbing with 'Cool-Amp' powder with
a damp cloth (again, electroless plating).  Some people polish
the copper surface with Brasso...
	
	After inspection, drill the holes with a carbide drill
(typically #61 size).  Proper drill spindle speed is in the 10k-40kRPM
range.  A Dremel tool is the way to do this in small lots (and you
can use tool steel drill bits, but they'll wear down FAST going 
through fiberglass).

	If you're really serious about making PC boards, you should
at least browse through _Printed Circuits Handbook_, edited by 
C. F. Coombs, Jr.

	John Whitmore