Circuit board construction for the ATMer...?

["Sam Michael" <samm@idcomm.com>]

I have been dealing with a development effort for a circuit that my company
is developing.  In order to get fast turnaround of boards for testing, I
needed a way to make high quality circuit boards (multilayer) in under 8
hours.  Cost from commercial board houses for 24 hour turnaround was in the
range of $2000-$3000 per design.  In my case, I had to also develope plating
systems and through-hole activation, fast etching, and a hot 20 ton press
which I built by converting a shop press from harbor freight and adding a
temperature controller and heating elements.  etc.

For ATM purposes, 2 sided boards can be made for a minimal expense.

Because many on this list make their own circuit boards on occassion (for
stepper circuits and camera circuits), I thought I would share my experience
with the group.

I am currently producing 4, 6 and 8 layer circuit boards using equipment now
in my basement.  Granted my basement looks like a chamber of horrors, but I
suspect this is true for many on this list.  Eight mil traces and lands are
now easily doable and I am holding +/- 2 mil registration.

The greatest roadblock to producing good circuit boards was getting good
artwork on a transparency.  In that regard, I have made several discoveries
which are not immediately intuitive.

First, getting really good artwork for the spec above is not possible with a
laser printer.  Phase error creeps in and even for printers claiming 1200
DPI the accuracy just isn't there.  I tested this with several models of HP
printers including the 2000 series and the 4000 series.

In addition, the toner is just not dark enough.  You end up having to
underexpose the photoresist in order to get good removal and then you have a
problem with undercured photoresist that will not tent over holes and whose
sides are weak.  Further the developing process just trashes the
underexposed resist.

I finally decided to try an inkjet printer.  After some research looking for
a printer that supported high resolution in black, I purchased a Canon.
Initially, I purchased the S300 but it turned out that clever marketing made
is sound like it supported high res black.  In reality, the black was only
600 DPI like every other printer...  Not enough resolution.  I then tried
the S800, which did support 2400 x 1200 DPI in color and in Black - the only
printer that supported high resolution black printing.  Experiments with
this printer unfortunately revealed the problem that most people have with
bubble jets.  The black is simply not dark enough in UV.  This despite the
fact that it was a pigment based ink.

I did have moderate success stacking tranparenies.  This allowed me to
increase the exposure time, but because only the first transparency was ink
down (the second had to have a full 5 mil separation for the thickness of
the first transparency, the edges were not very clean.

I then had a brainstorm, I realized that my UV filters for my flourescent
lighting were amber.  I decided to try other colors...  I quickly discovered
that yellow was just as dark (in UV) as black.  Disappointed that it was not
darker, I began thinking about ways I could change the formulation of the
ink to include a coreactive UV blocking chemical.  I started searching the
net when I discovered that ink fading as a result of UV is a real problem
for photography.  To my surprise, my printer already contained an ink that
was UV blocking.  All I had to do was tell the printer that it was printing
on high resolution photopaper.  This automatically switched cartridges to
the PC (Photo Cyan) and PM (Photomagenta).  Yellow remains the same because
yellow only fades to yellow.

In any case, once I did that, I was able to fully expose the Photoresist.
In comparing a foil blocked section and a photo ink exposed section there
was little difference.  Moreover, in testing artwork created by a real
photoplotter (costing $200,000).  There was no difference.  The only
difference was that I settled on "GREEN" as being the color that was best.
This selected the darkness of yellow in UV and the chemical UV blocking in
Photo Cyan to produce a very dark black in UV and a pretty green in
visible... :-)

Perfect exposures!  That along with unbelievable resolution of these
printers make for a killer combination for producing your own artwork and
consequently your own circuit boards.

The bottom line is this.  You DON'T want a printer with a dark black!
Forget whether it is pigment based ink or dye based ink.  That is all
irrelavent, none of them are going to be dark enough.

You want a PHOTO printer with PHOTO ink.  Further ALL photoprinters have
high resolution in color!  Even the cheap ones ($100)!  Just make sure a
photo ink is available either from the manufacturer or for an ink refiller.
All photo ink is, is ink with UV blocking added so the photos you print
don't fade.

What will the photoplotter companies do???

Armed with this information, there is no reason everyone on this list does
not do steves killer mod for the Philips Vesta camera or the many circuits
for telescope motorization and tracking.

Good Luck.

Sam.