I have build several projects with the help of cheap pcb stripboard from china. These boards have very poor quality, the traces detach and break, which leads to very difficult to track down faults. Since i have this cnc milling machine, i thought it would be nice if we could mill a pcb. Some research on the internet brougt me to 2 programs that can help me realize this.
The 1st program is DesignSpark PCB. Here we can draw a pcb design and export this as a gerber file. This Gerber format is a vector format for printed circuit board (PCB) designs. It is the standard used by PCB industry software to describe the printed circuit board images: copper layers, solder mask, legend, drill data, etc.
The second program is flatcam. This can translate the board design into g-code for the cnc milling machine.
PRINCIPLE
I started of with a simple project: An Esp8266 that can switch a 12Volt load, such as high power leds, with a FET. This board has a powersupply of 12V dc, a regulator for the vcc of the esp, the esp itself and a FET. Furthermore it has connections for an signal LED and a tactile button.
Milling a pcb out of a copper clad board can be done in 2 different ways. We can mill away all of the unnecessary copper, this would be time consuming and inefficient. Or we can just isolate the traces from the rest of the copper. Which means that only around the traces we have to mill a trace of copper away. This is the preferred approach.
The milling can be done with a v-shaped chissel that clears a narrow trace of the copper around the traces. In case of low voltage this would be enough to isolate the traces from each other and the rest of the copper. Where there is grid voltage involved we need to clear much more copper because of the risk of shorts. Also we have to create a large copper clear area betweeen the high and low voltage parts.
Materials
What we need is copper clad board. Initial i bought some board from China with a thickness of 1,5 mm. The thickness of the copper layer was not specified. I turned out to be some 1.5mm. To clamp it on my machine i glued it on a piece of mdf board. Workung with v-bits mean that the surface of the board has to be completely flat.
DesignSpark
With this program we can create the schematic and the board lay-out of the circuit. I had a hard time to figure out how it works, the control is not very intuitive, at least for me. At last i drawed the schematic and than designed the board. The program can flag any discrepancies between them. The board lay-out can be exported as a gerber file. This file contains all the information regarding the traces. Another file that can be exported is in Excellon format. This contains the information regarding the holes in the board.
FlatCAM
This program will generate the toolpaths for the cnc machine in g-code. It took me several hours to fathom the working of this program. I want to mill different isolation widths for the high voltage part an the low voltage part.
With the help of the manual i could not figure out how to do that. Finally i discovered that i can define geometries that i can exclude when toolpaths are generated. This means that i end up with several g-codes, one for the milling of the low voltage part and one for the low voltage part. That should not be a problem.
For the drilling it is logical that we have 2 g-codes because the holes for the screwterminals are bigger.
CONCLUSION
After some experiments i produced a pcb that is not too bad at all. There are many settings to experiment with. The form, size and the angle of the tool, the depth of the cut, it all influences the result. I did not solder any parts on the board yet but. So there is still a chance that the fragile traces will detach. I am still looking for a way to clear some area's from copper. I don't like the high voltage part because it is poorly isolated. Now i have to clear the area's manually which is a monks work.
