The key element here is that copper and solder mask placements have extremely fine ... [Brian Benchoff] published a fabulous How to do PCB art in Eagle article. Of course, he’s gone deeper ...

Double-sided circuit boards might be able to pass through the process using a single stencil. This is known as an A/B flip ...

By cutting the solder mask layer into a business card with the laser cutter, it can be held on top of a PCB and then used as a stencil to add the solder paste more easily than could otherwise be done.