Disclaimer: This is what I’ve found that works, but it could definitely use some streamlining. If you have anything to add/change, please let me know and/or post accordingly.
Big thanks to Scott Dixon from DB and Seamus from ADX for helping to make this happen!
Process:
1. You’ll need to slightly shrink the solder paste aperture sizes of your design to accommodate the kerf of the laser. In Eagle, the “cream” (solder paste) layer defaults to the same size as the SMD pads.
a. With your Eagle board design, open the DRC (Design Rule Check). Click on the Masks tab, and set the Cream Min and Max to 0.05 mm or 2 mil (depending on the units you are using). Click Apply. Your board's cream layers will be updated.
2. Open the Display dialog in Eagle and turn off all layers except the solder paste layer you want to make a stencil from. For top side use “tCream” and for bottom use “bCream”. Most designs use tCream.
3. Choose File, Export, Image and set 1200 DPI and full area. Click browse and select *.bmp and select a name/location for the BMP file. Click OK to export.
4. Using your favorite image editor, change the background color to white (RGB 255/255/255) and the foreground/cutout color to light yellow (255/255/155). Yes, color makes a difference, but I do not know how/why, sorry.
5. Put your modified BMP on a thumb drive and head down to ADX: http://www.adxportland.com/
6. At ADX, prep for the burn.
a. Stretch the Kapton out over the frame I left there and tape it down, be sure it’s tight/flat.
b. An ADX person will
i. Convert your file to an Inkscape SVG file (bonus points for doing the conversion ahead of time yourself, see improvements below).
ii. Raise the laser head to accommodate the frame.
iii. Use the Kapton printer driver already on their system (r=1200/rm=color/rs=50/rp=100 are the critical params)
iv. Burn your 2 mil stencil!
c. You’ll need to carefully brush/wash off any black char that remains. It flakes off easily.
Pricing: ADX will be chargin $1 per sq in when using their stock of material. That’s good for small designs. If you have larger/multiple designs, you may want to supply your own and pay the run time fee of $2(members) $2.50(non-members) per minute of laser time.
Material: ADX will be stocking 2 mil Kapton, that’s also what the print driver is tuned for. If you’d rather purchase our own, you can get it here: http://www.mcmaster.com/#kapton-polyimide-film/=e8g9jg
part number 2271K5
Improvements needed:
• It would be better to supply ADX with a PS or SVG file. I haven’t done that yet, but should be easy with InkScpape: http://inkscape.org/
• This process is specific to Eagle, would be better to use Gerbers directly so it can come from any tool. I just haven’t found a free tool that can do the conversion from Gerber format.
• The stencil openings come out slightly wider than specified in the Y direction. This is no big deal for larger parts, but cause some issues for small fine pitch stuff. Eagle doesn’t let you differentiate x/y, but it can be done from a Gerber.
References:
http://wiki.metrixcreatespace.com/laser-cutter