From: david@moe.ece.utexas.edu (david lee)
Newsgroups: sci.electronics
Subject: Success! Resist Pen Works in HP Plotter!
Keywords: resist pens, pcb, etching
Date: 29 Aug 92 21:17:17 GMT
Article-I.D.: ut-emx.78655
Reply-To: david@moe.ece.utexas.edu (david lee)
Organization: The University of Texas at Austin

Netones:
 First off, thanks to everyone who replied to my posting
regarding resist pens in plotters. This is a preliminary,
but very promising progress report.

Act One, Scene 1:
David thinks of a neat idea for a circuit, but is too *@#$ lazy
to draw up a circuit pattern, make a mask, perform the usual
photolithography, and etch the board.
So, he says, "Why not just put a resist pen in my plotter, and
have the silly computer plot my patterns directly on the copper
clad pc board? Then I can plunk it in some ferric chloride and etch
it right away!"
Alas, there are two fundamental problems:

Problem 1: Mechanical Considerations or "Pass me the Duct Tape!"

 Just about any pen that you and I find that will protect copper
throughout the etching process "ain't gonna look like a plotter pen."
"No problem!", says Dave, "I'll just take an old HP plotter pen,
yank out the innards and run a drill (or a reamer) through it
so that my resist pen will slide inside it. I'll adjust the position
so that the tip of the pen will be held at just the proper level above the
writing surface."

But little does Dave realize that his HP plotter will not allow big ol'
pens to be loaded into the pen carousel. "No Problem!", says Dave,
"I'll use the old HP 7470A plotter. There is NO CAROUSEL anyway, just
two pen holding bays (one on the left, one on the right) which are
easily accessable; this plotter works with the cover raised, so there is
plenty of clearance for my new pen, and the pen holder has a circular
aperture which allows easy loading and removal of the pen into the
newly reamed out pen adapter."
Yes, but what happens when you download the drawing to the plotter,
and It tries to pick up a pen?! "Well, if you go ahead and fill both the
left bay and the right bay with pens, and then put our resist pen in the
plotter's "claw", this will lead to a momentary fit of "plotter spasm"
but have no fear, it works!

I admit that this is only a temporary solution, since not everyone has
an HP 7470A plotter. The goal is to fill a drafting pen (which is intended
for use with plotters) with a suitable resist ink. The following paragraph
addresses the ink issue.

Problem 2: The Ink Issue or "Pardon me, is that squid ink?"

 After the miserable failure of the Sanford Sharpie in the etching tank,
Dave heads for the campus bookstores, pockets full of clean copper clad
G-10 fiberglass!
 "Basically, I tried every pen in the University Co-Op Office supplies
section, every pen in the Art Store on MLK Blvd, and a couple from the
Campus Supply and Mail Store... Each time writing the name, tip size
and color of the pen on the freshly cleaned copper clad pcb. I made my way
back to the EE building and etched the board.....

And in the catagory of 'Best Pen to Withstand Etching of Copper Clad
Circuit Board Using Ferric Chloride' the winner is....

Manufacturer: Staedtler
Model: Lumocolor 313 AV
Ink color: Red

This Pen is available in several sizes; The S size has a 0.4mm tip
which is PERFECT for running traces *between* the 0.1 inch spacing
of DIPs. After Etching the boards in warm ferric chloride, every other ink
showed signs of pitting and undercutting. Only the Staedtler pen was
absolutely unchanged! So then I tried a longer etch in cool ferric chloride.
After 20 minutes, examination of the ink under a microscope revealed NO
pitting, and No dissolving of the ink. Prior to etching, I did gently heat the
boards with a heat gun to ensure that all the solvent was removed from the
inks, but I suspect (and will verify tonight) that I might omit this step:
this ink is awesome. (by the way, after discovering this, I checked my
e-mail and found a note from a guy at AT&T verifying the performance
of this pen!) By the way, I am using this pen now to draw boards for
100% surface mount. No Drilling! I can have a finished board in 30 min.
and I don't have to leave my lab!

The Future: The Best of Both Worlds or "Looks like a Borg vessel, Captain."

Several folks have written to me reccomending using drafting pens
that are designed for use in plotters. Perfect! Let's just get a bottle
of the Staedtler ink, and fill up such pens! Alas, I called Staedtler's
Customer Service number, and "no, we don't sell the ink."
(Insert picture here of David using a hydraulic press to squeeze the
ink out of a case of pens. :)
So I e-mailed to a buddy in Munich which is a short train trip from
Nurnberg, the birthplace of the Lumocolor Pen. He's going to see if
he can details/samples of the ink, and I'll post the results in
a (much shorter) letter.

Your Humble Servant,
David Lee (david@moe.ece.utexas.edu)

Zaphod: "What have you been doing in the car-park Marvin?"
Marvin: "Parking cars."
Newsgroups: sci.electronics