As a preperation for my next panel segment, the electric panel of the overhead, I wanted to find out if I'm able to produce my own pcbs here at home with the tools I have. I know that there are factories out there which can produce those pcbs on a much higher level but you have to give them shematics that lead to a working pcb. And in most cases you have to buy several units and have to wait for the delivery. And when I realize later during the tests that I have made a mistake, then I have wasted time and money. So the plan was to be able to produce working prototypes at home or maybe the final product.
I didn't want to work with too many chemicals that I have to dispose later. Especially when you are etching a pcb with a photo resistant surface and a laminated solder mask there are different components in use. So I wanted to use isolation routing on my homemade CNC and cover the copper with a thin layer of liquid solder mask that hardens under UV light. Before I start designing the final pcb for 15 7-segment displays I wanted to do the testing with a smaller project. And so I came out with this module for three 7-segment displays that even can come in handy in fact that I need such a component in one of my later panel projects.
To design the circuit diagram and the layout of the pcb I used the free tools KiCad and FlatCam. KiCad is used to draw all the diagrams and create the gerber files and FlatCam uses these files to create different program files for my CNC as well as a negative print out for the solder mask. By the way - if you are asking yourself if your CNC is accurate enough for such a project then you should test if it is able to isolate wires that are routed between two legs of an IC. Otherwise you can only design very simple pcbs.
After the isolation routing process I applied a thin coat of liquid solder mask and spreaded it unter a sheet of plastic. The negative mask print out is placed on top to cover the soldering pads from the UV light. Now I exposed it for 2 minutes. I think 90 seconds can also be enough. The light hardens the mask except for the solder pads. These can be wiped clean with a cloth and alcohol.
The download package contains all the gerber files that you need to create your own CNC programs as well as pictures from the shematics for a better unterstanding.