Homebrew PCBs

A member of another mailing list I am a member of
found the following in a archive. Further, he tested
and it worked as advertised:

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.


Best

Marvin Dickens
Alpharetta, Georgia

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