Economical and robust PCB toner transfer paper

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Jul 20, 2000, 3:00:00 AM7/20/00
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I've recently tried many different paper types, and have found one or
two that give excellent results for making PCBs (printed circuit
boards) via a laser printer and the clothes iron toner transfer method.

I tried almost every glossy paper type that our local Staples office-
supply store carries, plus the "house glossy" from our local printer.
Most either had "pinholes" in the large black areas, or in the vertical
(to the print path) areas, or had removal problems after ironing. For
example, the HP Premium Photo Paper had perfect printing, no pinholes
at ALL. But, it was almost impossible to remove, even with long soaks
in soapy hot water, or in alcohol, and sometimes pulled the traces off
with it. Anyway, I finally found a good paper that's always free of
pinholes and still removes fairly easily. It also leaves extremely
strong toner/traces, which can be scrubbed fairly hard with a
toothbrush, or rubbed very hard by fingers, without being damaged.

It is the JetPrint "Graphic Image Paper, Gloss Finish", Heavy Photo
Paper. They also make a product called JetPrint "Multi-Project Paper,
Gloss Finish", Medium Weight, which almost falls off the board after
soaking for 10 minutes. Alas, it sometimes has pinholes. (I use an HP
LaserJet 4. Your mileage may vary...) However, the Multi-Project
paper IS PERFECT for doing the component sides of circuit boards, and
anything else where etching isn't required...

Here's my procedure, for those of you who have never done this before:

- Print the pattern, using the darkest printer settings. Cut the
pattern out, leaving at least 1/4-inch all around.

- Scrub the board with a Scotchbrite pad, equivalent to '0' steel wool,
usually in two orthogonal directions, with a lighter pass or '000'
equivalent at the end, so it's not TOO rough. I don't use real steel
wool, since it may cause rust after it's embedded in the copper.

- Wash the board with liquid dish detergent, then with acetone, then
with alcohol, drying with a new paper towel after each, and never
touching the board surface with fingers after the first wash.

- Lay the board on a paper towel, copper side up. Blow any dust off of
it, carefully, and off of the pattern paper, and lay the pattern face
down on it, lining it up just right.

- I use a regular clothes iron, set as hot as it will go ("Linen",
above "Cotton"), with no steam.

- Place the iron on the back of the pattern, for about one minute,
pressing very firmly, moving it by 180 degrees at the half-minute mark
(just in case the holes on the bottom might cause a problem). (Note
that if you try the HP paper, you better put a sheet of regular paper
between it and your iron, because it will stick to the iron!)

- After the board is heated (after the one minute), I place the rear of
the iron along an edge of the board (with the rest of the iron on the
board), and press hard near the rear of the iron. I move the iron 1/4
to 1/2 inch away from the edge and press hard again, for about a half-
second, and continue that way until I'm near the other side of the
board (with the rear of the iron), and it gets hard to keep the iron
flat against the board. When I reach the other edge, I go back the
other way, doing the same thing. If there are board-edges that are
wider than the iron's rear edge, I make overlapping passes with the
iron's side against the outer edge of the board, on both sides of the
wide edge. I usually do this starting from each of the four edges of
the board.

- Sometimes, at this point, I reheat the whole board for ten seconds or
so, or more, with moderate to heavy pressure on the iron.

- I usually go over the whole board with the tip of the iron, keeping
it flat but torquing the iron forward as I go, moving either side to
side, or by pulling the iron backwards, in lines about an inch apart,
across the whole board. But I'm careful to never let the tip gouge,
and never let any edge of the iron press against the board. I always
try to keep the bottom of the iron flat against the board, whatever
else I'm doing.

- At the end, I usually reheat the board (with pressure on the iron at
the same time, again). I also usually just press the iron flat against
the board, hanging almost halfway off one side, then in the middle,
then off the other side (still always keeping it flat against the
board), for good measure...

- The whole heating/ironing process takes between two and three minutes.

- Then, within five or ten seconds or so, I pick up the paper towel,
with the board on it, and hold it under cold running tap water for 15
to 30 seconds, to stabilize the toner. I turn it over and cool both
sides.

- Then I immediately place the board into a sinkful of hot water (about
130 deg F), for 10 to 20, or more, minutes.

- Peel off the paper, or at least the top layer. If the paper
underneath is still dryish, put the board back into the water, for
another ten minutes or so.

- Rub the remaining paper off with thumb pressure. It's OK to rub
hard. But your thumbs' skin may get sore. Usually, almost all of the
paper residue comes off, even off of the toner itself. So, you could
SEE if there were any pinholes, etc, in the toner. (I have yet to see
any, though, using this paper!)

- Use small circular motions with a toothbrush, to remove paper residue
from small or tight areas, and from hole marks. This may be the
hardest part. I will soon try leaving the residue IN the holes, to see
if the etchant can work through it.

- Rinse the board and wipe the board dry with a clean paper towel.

- Sometimes I wipe and rub the board with a paper towel and 70%
alcohol, especially if it needs correction-pen marks.

- Make any necessary corrections, using a Sharpie or other etch-
resistant marker. I sometimes have a couple of very small flakes of
toner fall off, on about one out of three or four boards, at the most,
especially if I scrub way too hard with the toothbrush.

- Etch. I use Ferric Chloride, in a tupperware plastic bread
container, in a sink of hot water, agitated by an old metal record-
player turntable turned on end, with a bolt an inch from the spindle
attached to a small piece of wood that is also attached to a bolt that
protrudes near the plastic container's top edge. I have a couple of
bricks in the sink, to keep the container in line side-to-side as it's
rocked front-to-back. I usually use either the 33 RPM or 45 RPM
setting. (Don't get the etchant on anything, especially a good
stainless-steel sink!) I keep the lid loosely on the container, to
catch any splashes.

If you use 1-ounce boards, instead of 2-ounce, etching is much faster,
and, correction-pen marks will last long-enough to work well. Plus,
over-etching isn't usually as much of a problem.

- When etching is almost complete, I usually remove the board and put
it in a small tub of half-strength etchant (diluted with water), and
lightly brush the areas that still have visible copper, until they have
been removed.

- Wash the board in laquer thinner, rubbing with a paper towel, to
remove the toner instantly. But be careful! I do it outside...

- Drill. Some people have suggested drilling BEFORE you etch. OK.
But I like the way the etched hole marks help guide my drill bit into
themselves, especially on small pads and when holes are very close
together. I use a regular floor-standing drill press. I have tried
the pure-carbide bits, about .035 inches, with the larger shanks. But
they are so strong they're too brittle, and they break too often, for
me. (Even getting 50 of them for $5 at a hamfest doesn't seem like a
good deal. That's how often I break them!) So, I usually just get
the "wire-gauge" high-speed steel bits, from the local hardware store.
I've been using the #60 (.04 inch), since they fit a large variety of
component lead sizes (all but the largest). I got 15 bits for about
$20. I change bits every few hundred holes, at least, or whenever I
notice the edges of the holes are getting pulled away from the board
too much. I guess the FR-4 board material doesn't transmit heat well
at all, and the steel bits get hot quickly, and consequently dull
quickly.

To hold the tiny bits in my large drill, I bought a small chuck that
fits into my larger chuck.

- If you're going to mark the component side, scrub it with the
Scothbrite pad, at this point, then wash the board in soap and water,
and then 70% (rubbing) alcohol. Make sure the holes are all dried
out. Hold the board and pattern up to a bright light, to align then
component marking with the holes' pattern. Then iron on the component-
side pattern, but using the other, more-easily-removed "Multi-Project"
paper, mentioned above. Soak for five or ten minutes in warm water,
then just peel it off. Rinse and rub the very minimal residue away,
dry the board, rub it with a paper towel with alcohol on it, dry it
again, and it's ready!

If anyone's interested, I can try placing the board on a scale, and see
how hard I'm actually pushing, with the iron.

The boards made this way come out nearly perfect, nearly every time.


Sent via Deja.com http://www.deja.com/
Before you buy.

to...@fullnet.com

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Jul 21, 2000, 3:00:00 AM7/21/00
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Well, I tried leaving the paper residue IN the holes and etching. But
the result was less than satisfactory. So, in order to minimize the
potential for damage to the traces from hard rubbing with the brush, I
tried letting a board soak overnight in water. Voila! The drill holes
were easily cleaned out with fairly light scrubbing with the
toothbrush. Of course, I usually can't wait overnight. Adding some
liquid dish detergent helps, if I'm in a hurry. Also, digging the
bristles on the tip of the brush straight into the holes, while making
tight circular motions, gets the residue out with minimal brush
pressure. It is still quite tedious, if there are lots of holes,
though.

Also, I DID put a bathroom scale under the iron, and simulated pressing
on a board. I was using at least 25-30 LBS of force. I don't know how
many PSI it is, because I use the same force on boards sizes of 4X6
inches and of 2.375X6 inches. Both seem to come out equally well. I
have, several times, used a lot more force on the iron, and it IS
possible to flatten out or blur pads or traces, if I press hard enough,
or if I accidentally scrape with the edge or tip of the iron instead of
keeping it flat.

Someone else suggested baking the boards in an oven, after the toner
has been applied and before etching. With my current paper and method,
I don't see why it would be necessary, since the toner seems so
strongly bonded to the board. However, back when I was using paper
that left pinholes in the toner, I wanted to try baking a board just to
see if the pinholes would close up. At the time, it also seemed like
heavier iron pressure might close them. But it never seemed to. Now
that I'm using the JetPrint Graphic Image Paper, I don't need to worry
about these things any more.

I will try to put this whole method on my website, at:
http://www.fullnet.com/u/tomg

Happy board-making, everyone!

Tom Gootee
Gootee Systems

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