Homebrew PCBs

no problem
I drill first with the cnc machine
then use the ink activation, then bake the board in a convention toaster
oven,
Then I plate the whole board in an alkaline "flash" copper. then dry in the
toaster oven, than a dip in hot tri sodium phosphate, a good scrub and
rinse, then I laminate on Negative resist, and expose a positive image and
develop, This results in everything but the traces and pads etc covered in
resist. I then plate the tin, This plates everything exposed (including the
holes), in very fine and solid detail, You can clearly see when everything
is fully plated, over plating is not a problem >you do need oversized holes
tho<. The next step is the resist stripper, then into the etch,  Sulfuric
Peroxy (which doesn't etch tin) and everything not plated with tin gets
removed. ... I'm actually using a 10% Lead content in the tin to keep the
tin from sprouting roots, and to "set" it, I have to reflow it, which means
back in the oven.   For boards, I plan on selling as kits (i.e.... not
immediately assembling), I also use a nickel undercoat (between the copper
and the tin, to prevent the anti-solderable intermetallic alloy forming)
There are other various pre dips and post dips and rinses between each step.
I've got it laid out in a nearly effluent free process. I can reclaim copper
sulfate from the etch to replenish the copper plating tank. The only things
I dispose of are the resist stripper (sodium carbonate) and the developer
(sodium bicarbonate) which are both very safe chemicals. www.thinktink.com
and www.caswellplating.com two US  links to more info. The only "odd thing I
had to source was the low lead tin anodes. I didn't feel 60/40 solder plate
was very Green considering how evil Lead is.   Pure tin grows metallic
fingers that will short circuit traces, and the intermetallic alloy
formation begins immediately, completely consuming the tin within 3 years
(in perfect storage)

JT


----- Original Message ----- 
From: "Markus Zingg" <m.zingg@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Wednesday, March 24, 2004 11:18 AM
Subject: [Homebrew_PCBs] plated tin as the etch resist


> On Wed, 24 Mar 2004 10:16:56 -0500,  Jeremy Taylor wrote:
>
> >I personally always dill before etch, but I use a completely different
> >process, which includes, plating the holes, and using plated tin as the
etch
> >resist.
>
> Intersting. I do the same thing, but I use photoresist laminate to
> avoid etching the just plated holes. Could you elaborate a bit on how
> you do your through hole plating? I'm just curious how others do it
> you know.
>
> Markus
>
>
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