I've tried making my own solder paste stencil using 4 mil polyester (for overhead projection slides) on a 45W Epilog laser cutter at the local TechShop maker space.
I could not "cut" the stencil cleanly, because the edges charred and became uneven.
I had some more success with "etching" the stencil, but the solder paste application still had a lot of slop around a 0.5mm TQFP footprint (generating several solder bridges.)
Meanwhile, when I used a stainless steel stencil from Advanced Circuits, for the same footprint and paste/applicator, the imprint was super crisp and no solder bridges.
I know that others are successfully applying solder paste with polyester/mylar based stencils from places like Pololu or OSH Stencils. Given that I have access to a laser cutter, I'm thinking there's got to be a way to make them on my own, and probably the problem I had was that I used an inappropriate film/material.
However, researching online, I can't find any material specifically billed as being good for this kind of work — so, does anyone have experience to share on particular materials for laser-cut stencils? Part numbers or at least specific brand/model names would be great!
EDIT in October 2016: OSH Stencils now offers affordable steel stencils, so making my own is much less desirable. I highly recommend steel over plastic!
Best Answer
As you noted, at Pololu, we use Mylar for our Laser-Cut Mylar SMT Stencil service. It's not that hard to find Mylar films: McMaster has a bunch of them. Take a look at McMaster part number 8567K32. (Sorry for not linking, McMaster is hard to link to.) The main trick is carefully tuning the cutting settings and design to account for the quirks of your cutting process. We use internal computer programs we've written to modify the designs to make the cuts turn out well in our process.