If you’ve ever made double-sided PCBs without professional equipment, you had to deal with connecting one side of the board to the other. You have a few obvious choices: 1) Rely on component leads to connect both sides (and solder both sides); 2) Create vias and solder wire to both sides of the board; or 3) Use through hole rivets. [Diyouware] had a different idea: use conductive ink. After a few false starts, they found a technique that seemed to work well.
This isn’t the first time we’ve heard of people trying conductive ink with varying degrees of success. The biggest problem, usually, is that the ink wants to run out of the hole. [Diyouware] has an interesting solution for this problem: Don’t drill the hole all the way thorough.
To do this reliably, [Diyouware] modified a drill press to get a signal when the bit makes contact with the bottom layer of copper. The result is a blind via that forms a well. It is a simple matter to fill that well with conductive ink later. Although you could fill the vias by hand, [Diyouware] used a dispenser robot and controlled it with output from an Eagle user program to convert the via pattern into machine instructions. You can see the creation of an experimental board in the video below.
It is worth noting that when you have a PCB made professionally, they often drill a blank board and then plate it, so the pins and vias conduct through with no difficulties. In addition to the plating, this also makes it challenging to get the artwork exactly lined up with the holes. There are other professional processes, too, that plate boards after drilling and the plating part is possible.
LPKF has a method for faking plated through vias, that also uses a conductive paste. Of course, one easy way to get nice plated through vias (and holes) is to just go ahead and have the boards made professionally.