Homebrew PCBs

Simon Gornall wrote:



> 
> (BTW: What on earth does 'quimical' mean ?)
> 
It should be a typo for 'chemical' since in both Portuguese and Spanish
chemistry is spelled as 'qu�mica' (quimica for non-utf8 users), and
Vicent seems Spanish name. I am Portuguese and didn't even realize the
typo until you did ;)


So about chemical vias (and skipping all mechanical methods) the ones
that can be 'homebrewed' are palladium and carbon black. But is more
difficult the copper plating bath itself. There is a really great method
found by a great mind of homebrew PTH but he never shared it here. That
Chinese machine Simon posted seems to be built around the same trick, it
will take 75 to 90 min to plate a pcb but is fair simple to build. I
really am the 'flag-boy' for palladium since it's much simpler to use
than carbon black (all wet vs 2 times drying), and super trustful (i
made thousands of boards with palladium without missing a hole) and
longer bath life (years vs months). Posting recipes will be bad faith
since i haven't homebrew experience in either. Both are fair simple,
both have a similar to industrial degreaser conditioner, a ionic
suspension for one or in surfactant in other for activation and a ion
remover with copper as accelerator for palladium or a common simple
micro etch for carbon black. Of course that during last year i tried to
get everything needed for the palladium chemistry and still miss some
stuff (sh*t really happens...).

I moved and am living away from where i have all my tools and stuff and
so not much progress on this, but for construct it the acrylic glass
with solvent is amazing, even if you cut the acrylic with 1 mm breaches,
multiple passes of solvent fill the holes. I tried both store expensive
solvent (it says dichloromethane and nitroethane) and pure
dichloromethane cheap from eBay. With 100eur for a 3 sq meter 5mm thick
sheet is fair cheap to build (there is two types and only one works with
the solvent). 


THE SIMPLEST method i know about (and wish to try one day) is the good
simple plating setup from one person with also his sharing from 12 years
ago about drilling holes above graphite powder. There is some reference
from IPC about this but never disclose what can be used under the pcb.
Graphite chemistry is just like carbon black but almost 1000 times more
conductive per hole with one pass only, but can last one day only if
additives are used. Using it on a CNC is dumb but a simple drill press
with a deep pool for powder seems to worth the money to try it.

> 
> Apart from the chemistry, you're still looking at the high-hundreds for a reverse-pulse-plating machine if you DIY it.

Simon, i looked into your descriptions. Reverse pulse can be really good
but neither do you seem to full understand it either is a
simple/complete answer. I am also building my driver, also with a avr,
but with very low RDSon FETs (and fet drivers), using 4 psu's and 8 fets
(multiple anodes and cathodes) for a tricky chemistry (big expectations
in it). But for example i never figure out which voltage is appropriate
for the reverse pulse. You don't seem to realize it but it all goes
around current densities on surface vesus hole. And the magic number is
3 (or higher) - 3 times shorter reverse pulse, 3 times much current. For
_SLAPPING_ copper from surface and leave holes without touch, using same
values for both is wasting energy. You need at least 3V for plate pcb's
nicely, but since the common setup uses additives to require voltage
increase as current increases (without them current goes exponential
above ~0.7V) there isn't document proof on which voltage to use (or
known which psu to buy). Commercial systems say 12-20V capable but thats
crazy it will electrolise water. Ohh and i am having big trouble on this
so the avr changes voltage and current limits at cheap switched mode
psu's. 

And thats all for quimical vias :D
Simao

> 
> 
> > 
> > Anyway, some of this "inventions" can work with more o less result, but I'm
> > convinced the way is to go to a quimical or electrolytical plated process.
> > Is there anything affordable for the hobbyier?
> > 
> > 2010/12/15 Donald H Locker <dhlocker@...>
> > 
> > >
> > >
> > > I have no personal experience. I think a plated-through-holes (PTH) process
> > > is usually a bit beyond the hobbyist level, but is the only way of achieving
> > > no-bulge vias. All other methods (eyelets, fine-gauge wire) leave
> > > protrusions on the surface that prevent flat mounting of components.
> > >
> > > It _might_ be possible to put down a pad with a slot in the copper
> > > (extending radially from the hole) just wide enough to lay a fine gauge wire
> > > in and bridge the pad's slot and the wire with solder, producing a
> > > nearly-flat surface, but I wouldn't want to do many of those. Never mind.
> > > 1oz copper is about 0.0013 inches thick, while 30AWG wire is 0.010 inch
> > > diameter - that's about a 0.009 inch ridge on the board.
> > >
> > > Donald.
> > > --
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> > >
> > >
> > 
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> > 
> > 
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