gEDA-user: wacky (or not?) solder stencil ideas

[Dave N6NZ <n6nz@xxxxxxxx>]

Yesterday while I was at the TechShop experimenting with the laser 
cutter and talking about solder stencils with other folks, this idea 
came up:

1) Take 3mil brass sheet, and paint both sides with "machinists' blue 
stuff" -- I'm not sure what it's properly called, but it's a blue paint 
that they put on metal so that they can scribe layout marks.

2) Slap it in the laser cutter, and print the paste layer on it with 
just enough laser power to blast away the blue paint.  (The CO2 laser is 
the wrong wavelength for cutting metal, it just reflects off.)

3) FeCl etch. The blue stuff is a resist. You now have a paste stencil.

Anyway, DJ, I've looked over your web site where you do basically this 
with the toner transfer method.  Got any comments?

Topic two: I've been trying to get a process that makes stencils in 3 
mil drafting mylar.  I've got a usable stencil with relatively fine-line 
parts, but it was more than a little tweaky.  There is a fine line 
between cutting through and getting goo because the material is so thin 
and prone to melt and stick to itself.  I ended up printing three the 
paste layers with 3 different bloat settings, converted all of them to 
dxf, and merged the drawings and cherry-picked the "best" image for each 
footprint.

I see where Grafix makes essentially the same material as drafting 
mylar, but coated with a "secret sauce" specifically designed to keep it 
from sticking to itself when laser cut.  I need to get hold of some 
samples of that.  It looks like they have a $100 minimum order on this 
material.  I'm guessing that Pololu and the other places that cut cheap 
plastic stencils for you are using this stuff.

Third wacky idea: TechShop has one of those PCB mils.  I suppose you 
might do a stencil in sheet brass with it, but I'm not sure it can cut a 
fine enough line.  I need to find out the specs.

Comments? Ideas?

-dave


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