Can a common 3D printer be used to print masks for PCBs which use SMD components?
In addition to the thermal issues Tormod raised, there is a conductivity issue. Present conductive filaments are much less conductive than copper. The power loss may be enough to affect functionality. Also, the lost power goes to heat, making the thermal problems worse.

For bulk materials, "volume resistivity" is measured in "Ohm-cm", which is the resistance of a 1 cm cube of the material, measured from one entire face to the opposite entire face (see https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity).

Copper has a volume resistivity of about 1.68 microOhm-cm. 

Proto-pasta conductive PLA filament claims 15 ohm-cm (http://www.proto-pasta.com/pages/conductive-pla). Functionalize F-Electic&trade; claims 0.75 ohm-cm (http://functionalize.com/about/functionalize-f-electric-highly-conductive-filament/).

Printing itself significantly raises resistivity. Proto-pasta claims 30 ohm-cm along X and Y, 115 along Z. More intuitively, each cm of length of a 2.5mm wide printed trace, 0.4mm thick, should add several hundred ohms with the Proto-pasta, or several tens of ohms with the F-electric. That may be enough to matter. 

It's probably worth mentioning that there's a specialized PCB printer (the "Voltera") that uses (pricey) conductive ink, and can also dispense solder paste: http://www.computerworld.com/article/2885188/3d-circuit-board-printer-a-smash-hit-on-kickstarter.html