There have been a few recent techniques developed to 3d print circuitry. Most of them use a substances which was conductive which come out of an extruder. A man named Bas de Bruijn however, has come up with a different solutions. What he did was built a 3D printer which used FDM technology, but was able to add an extra little something to it. He added the ability for the printer to place copper wiring down a fraction of a second prior to the melted plastic. What you end up with is a 3D printer capable of printing copper wire coated in plastic. More details on the 3D Wire-Laying Machine can be found here: http://3dprint.com/4383/3d-additive-wire-laying-machine

Check out the video below of Bas de Bruijn's device. What do you think?