--- In
Homebrew_PCBs@yahoogroups.com, brane2 <brankob@...> wrote:
>
> Dne 20. 07. 2013 21:53, piše brane2:
> > How about using thin aluminuim plates for printing machines ? They
> > come cheap.
> >
> > Bonus is that they already come presensitised with photosensitive
> > layer...
> >
> >
>
> And how about etching them instead of machining BTW ?
>
I've been using .003" brass shim stock for several years to make
paste stencils. I already had a laser photoplotter I built for
making master artwork for PCBs, and a dry film laminator. So,
I make two mirror-image artwork films with black for the pads,
and glue them together in alignment on a light table. I put
a scrap of film between them as a spacer to equal the shim.
First, I wet-sand both sides of the shim stock to remove
what seems to be some kind of anti-corrosion film they apply
to it. I use 400 grit sandpaper. I laminate the dry film resist onto both sides of the shim stock with the heated-roll laminator.
I have to put a paper shim on the other side of the brass shim
as the machine is calibrated for proper pressure on a .062" thick PCB.
I expose to UV, develop the dry film resist and then etch, just like a PCB, in Ferric Chloride. It takes no more than 2 minutes to etch through from both sides in a heated spray etcher.
This works great, and I routinely do boards with 0.65mm lead pitch,
and have done them down to 0.4mm pitch. I do reduce the aperture
size to less than the actual pad size on the board.
Jon