'PCB Methods: Iron On Transfers'
One method for making printed circuit boards is to use commercial
iron on transfer products, such as DynaArt Transfer Paper.
I have been using the DynaArt Transfer Paper for a couple of years.
When I first started I used an iron and got mixed results. Smaller
boards generally came out OK, but anything much larger than the
iron itself created a problem.
I finally stopped playing around with the iron and ordered the
SuperFuser, which is a laminator modified for a different temp range,
and much slower feed rate.
The advantages of the SuperFuser are:
1) consistency of results, and
2) once it is loaded you can do something else with your time.
The SuperFuser once properly adjusted for temperature, gives
me excellent boards. Note that different brands of toner require
slight changes in the temperature setting!
In the interest of helping others, here is a quick outline of
how I do my own PC Boards.
1) Clean the PCB blank vigorously with a Scotchbrite pad.
This mechanical cleaning is very important. The pcb blank should
be shiny, and when water is applied the water should cover the surface
2) When the mechanical cleaning is done I
then clean it with a little TSP solution(Tri Sodium Phosphate). This
helps remove fingerprints, grease, etc. Rinse thoroughly in running
water to remove all chemicals.
3)I then wipe dry with a CLEAN cotton wipe, making sure no lint
remains. Make sure *both* sides are completely dry.
4) I preheat the board with either a heat gun by waving it evenly
over the surface, or by placing it in a little oven I have that
was originally designed for drying glassware. This pre-heating
helps, because when a cold board is placed in the SuperFuser there
is a large temperature gradient, and the part of the board that goes
in first would otherwise not get as evenly heated as the last
part of the board.
5) When the board exits the SuperFuser I turn it around 90
degrees and run it through again immediately. If you do not do this,
then you will sometimes find that long runs that are parallel
to the board travel direction tend to lift off.
6) When the board comes out of the SuperFuser the second time,
I let it sit on a dry cloth for about three minutes. This allows
the board to cool slowly. Rapid cooling can cause the pattern to
pull away from the board.
7) Once the board is cool to the touch, then I place it in a pan
of room temperature water and let it sit for as long as it takes
for the paper to float loose. Avoid the temptation to speed the
process up by aggressively agitating the water, as this can cause
sections to lift.
You might also find it useful to preheat the transfer paper
that has the image on it. This preheating helps to cause any
tiny toner pinholes that may be present to disappear as the
toner melts slightly. You have to be careful not to overdo
this preheating. The idea is to allow pinholes to close up,
but not to allow any dimension changes in the toner image.
If you experience any problems with dimensional shrinkage of
the image, then you might want to preheat the transfer paper
*before* running it through the Laser Printer. That will cut
shrinkage down by at least half. I usually make smallish PCBs,
so I don't often have to resort to this.
As regards toner. I use an el-cheapo re-manufactured cartridge
to do my proofs, but the actual tranfer is done using an
original cartridge. I prefer the cartridges that have the
extra-fine toner. These are sometimes sold as 'extra black
graphics cartridges', or 'specially formulated for high
resolution graphics work' or something to that effect. I happen
to use a 1200 DPI (true resolution) Lasermaster Unity 1000
printer. I have found that the 300 dpi printers are not high res
enough. 600 DPI is useable. 1200 DPI is excellent. This goes
not only for direct tranfer PCB work, but also if you are
preparing your own 1:1 transparencies. When I do photographic
versions of my PCB designs I usually produce artwork that is
1.5:1 or 2:1 and then have it photographically reduced to
actual size. This allows for very fine lines, such as those that
go between IC pins.
And, it goes without saying, don't forget to make sure that the
image you PRINT is a mirror image. I have had my fair share of
times when I rushed a job only to discover that I had failed to
flip the image first. I always try to have some lettering on the
design that helps me know when I have made this mistake.
Better to mess up just a sheet of transfer paper than to actually
etch the board before you find the mistake!
I try not to waste the special transfer paper so as to save
money. I usually arrange my mirrored image so that it will
fall at the bottom corner of a sheet of paper. I first print
onto a regular sheet of paper, then I cut out the corner
that has the toner design on it, leaving a margin of between
1/4 and 1/2 inch. I then use Scotch Tape to hold on a section
of transfer paper that slightly overlaps the section cut out.
The shiny side of the transfer paper should be facing where
the toner will be applied. I then load this modified carrier
sheet and print the image again, with the exact same settings
as before. I adjust my printer so that the sheet comes straight
out the back of the printer, instead of turning around and coming
out the top. This helps to insure that the taped transfer
paper does not get stuck in the printer.
BTW, use 3M Scotch tape, and not some cheap imitation, as
some of the imitations cannot take the heat of the printer,
and they will melt inside and make a real mess.
I do my etching with Ammonium Persulphate that I purchase from
Mouser Electronics. My etcher is a slightly modified version
of the etcher sold by DynaArt. I made a few changes to enhance
the flow of etchant. Originally the pumps would give me
trouble. They were designed for pumping water, and the extra
densisty of the Ammonium Persulphate solution was just enough
to sometimes cause one or more of the pumps to stall. I
modified the pumps by cutting the rotor blades down a bit, and
now they pump reliably.
I can generally etch a board in 3 to 5 minutes with fresh
etchant that has been heated. Room temperature etchant takes
twice as long.
Hope this helps.
Fr. Tom McGahee
Where can the "SuperFuser" be found ??
Thanks for the information, it will be helpful !!
--- Thomas McGahee <SIGMAIS.COM> wrote: tom_mcgahee
Do You Yahoo!?
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> 5) When the board exits the SuperFuser I turn it around 90
> degrees and run it through again immediately. If you do not do this,
> then you will sometimes find that long runs that are parallel
> to the board travel direction tend to lift off.
> 6) When the board comes out of the SuperFuser the second time,
> I let it sit on a dry cloth for about three minutes. This allows
> the board to cool slowly. Rapid cooling can cause the pattern to
> pull away from the board.
Thanks for these tips, i think i may want to
try this before i retire my SuperFuser.
Having tried this method with the SuperFuser,
I personally prefer the Photoresist method in
terms of accuracy. However, the Toner-Transfer
method has great appeal, as it requires no
dark-room, or specially prepared PCB blanks.
Another tip that was given by a PIClister a while back,
and what prompted me to try this method in the first
place, is to use 'Epson Photo Paper' for Inkjet printers.
I think it works even better than the TTS stuff, because
it leaves a thicker coating on the copper (some of the
paper actually comes off with the toner). And it is much
cheaper to boot.
For those struggling with UV-resistant inks from their
printers, i have a possible solution: you might want to
try "Kodalith" film. It's black-white contrast film used
in the printing industry. You expose your image onto the
Kodalith, then from the Kodalith to the PCB. The drawback
is that it is somewhat costly. It only comes in a box of
100, at close to $200 for 8x11 size. I have not tried this
yet, only because I am still looking for someone to sell me
a few sheets to test the results.
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