cmiyc wrote this Instructable: Polyimide (Kapton) PCB solder paste stencil
Creating a solder paste stencil for a toaster reflow oven or hot plate is simple when you have access to a laser cutter. I used the Laser Cutter at my local TechShop to create this and other PCB stencils.
This Instructable assumes you have created a PCB and are able to generate the Gerber Files for it. Specific directions will be given for EAGLE, but other PCB software can be used. The board used in this example is an Arduino RTC Shield based on the DS3231. Follow the link for the EAGLE design files if you want to follow along.
Via Electronic Lab.