I have been thinking about adding conductive traces a-la PCB to 3D prints in a DIY setting for a while. Obviously, conductive filaments exist - but they are not remotely in the same category as copper.

My initial hope was that doping PLA, PETG or some other material with a conductor and then applying strong variable magnetic field near the print head to force creation of conductive domains while the filament is amorphous and hot. This turned out to be not feasible, as O3 explained to me repeatedly, over hours of chats.

A simpler and surprisingly workable solution appears to be adding a second printing head loaded with tin. Tin is not as good as copper - but it's still leagues ahead of conductive filaments. To offset the poor conductivity you can use thin, but very broad traces.

A speculative approach would work like this:

1. Print PETG layers using a regular filament, but leave "baths" for tin traces. A bath should be an opening at least 2-3 millimeters tall, to account for the surface tension.

2. After N layers, fill the baths from the tin head. Tin melting point is near PETG, but it would cool rapidly and, hopefully, weld to the plastic.

This way you could probably integrate a pcb into a print. I haven't tried that, but i recall people actually trying to print with tin - so that part is at least not a complete fantasy.