When making your own printed circuit boards, there's a definite learning curve. A simple single-layer board can be built quickly and easily through a variety of methods, ranging from chemical etching to computer numeric control (CNC) milling; dual-layer boards become more involved thanks to the need to line things up accurately and to drill 'vias' which connect traces on both sides. The drilling is only part of the problem, too: once drilled, each via must be filled with a conductive material - typically for the hobbyist solder, which can introduce issues with bubbling and poor connectivity - in order to electrically connect the two layers.
The makers over at Diyouware have been experimenting with a novel method for automating this process without overly expensive equipment, using a new tool head for its open-source TwinTeeth Plus multi-function CNC machine. As explained in the group's blog post, the technique works using two tool heads: the first uses an off-the-shelf rotary multitool combined with a clever carbon brush to detect when the bottom copper layer is reached to drill the vias; these are then filled using a separate tool head fitted with a conductive ink-filled syringe.
Rather than the traditional design of a hole drilled straight through both layers, the Diyouware technique creates wells with a small bump pressing into, but not through, the lower copper layer. This well is then filled with conductive ink, which is held in place by the lower copper layer until it dries out. The result is impressive: the automated creation of tiny, 0.8mm vias at a rate far faster than hand-assembly could manage. Combined with the TwinTeeth's other tool heads, it turns the machine into a single unit for the creation of dual-layer circuit boards: burning traces with an ultraviolet laser or milling them with a rotary multi-tool, drilling component holes and vias, filling vias, and dispensing solder paste for surface-mount devices - all in one open-hardware package.
If we want to make PCB wells we need to detect in some way when the drill-bit tip touches the bottom copper layer. Then withdraw it quickly before it could damage the copper sheet. In order to do it, we designed a “drilling interruptus device”. It is made with a carbon brush. We used a standard DC motor carbon brush and some bolts&nuts to attach it to the Dremel Toolhead.