PCB Boards are Cool, but the Holy Grail for robotics are the Kapton Flex Circuits which are both wire and circuit in one.
Using This Material, I was able to CNC a single-sided SMD circuit which is thin and flexible - though not quite Kapton :-(
For lightweight circuits that fit into odd shapes (like fuselages), etc, this is a process that can't be beat. You could probably use a chemical etch, but the CNC does the routing and cutout with the same tool.
First Design in Eagle then export in PCB-GCODE. I used 20mil spacing in eagle and a 16mil tool in gcode with a 3mil default (offset). I glued the scissor-cut material to a thicker PCB with spray glue, then held it down with clamps. It is critical to get the working surface flat (which took time and error).