Laser-cut solder stencil: water cool for 0.25-mm holes

[ChrisPhoenix]

I was having trouble cutting solder paste holes for a 0.5-mm SMD part... until I water-cooled the mylar.

It's simple: take a piece of laser printer paper, wet it, and put your mylar over it. I stack it on a scrap piece of acrylic. So you've got a thick plastic base, a wet piece of paper, and the mylar stencil. (This probably works for kapton as well, I haven't tried it.)

I find it works best to put a small puddle on the base, then put on the paper, drip more water on the paper, put on the mylar, and smooth it out with a paper towel. Work fairly quickly so the paper doesn't wrinkle. Dry off the top of the mylar. No need to tape the mylar down - the wetness holds it wherever you put it.

To cut, I use 10% power and 50-100% speed, 5000 Hz, air assist. The exact parameters really don't seem to matter. The laser will cut through the stencil, the paper, and etch the base... and the 0.25 mm lines between the pads will be left undamaged.

When you peel the stencil off the base, all the cut-out bits will be left stuck to the wet paper. When I used to cut dry mylar, some of the bits would stick to the stencil and have to be scraped off. This isn't a problem anymore.

Enjoy...

 

[3v0]

What laser cutter are you using ?

 

[ChrisPhoenix]

Epilog. I forget if it's 35 or 45 watt. As I say, the exact power/speed settings don't seem to matter much with this method.

I do reduce the pad size a bit, using a Gerber view package, because the laser has a non-zero cut width. But I think it would still work even if I didn't.