[throwa356262]

Cheap 3d printers are not terribly accurate, and the hot filament moves a bit (e.g. elephant foot). This method might not work well if your board is large or has very small components.

Also, even after ironing the surface will not be fully flat and some paste can end up in the space between the lines and go wasted.

A cheap low-power laser cutter is about the same price as a very cheap printer, which may be a better option if you can dial in the accuracy needed.