A printed circuit board or PCB, in general, is manufactured by using etching method or the wet method. However, the prototyping articles or prototype PCBs can be produced using the CNC engraving machines. This method is non-chemical copper removal process so PCB fabrication can be done in a lab environment without involving the hazardous chemicals. There are no hard and fast rules for this type of PCB manufacturing. However, some limitations do apply which are stricter than the conventional method. Most of the times this method suits to prototype PCBs such as university student educational projects, lab experiments, research labs, hobbyists, and proof of concept tests. The method is slightly costlier than the etching method because the engraving and drilling tools are costly. However, the machine installation cost is much more less than the large scale PCB production setups.
In Fig. 1, a CNC machine (of a renowned CNC machines manufacturing brand) is shown for PCB manufacturing. The input of the PCB is a gerber file generated after completing the PCB layout and checking the design rule check (DRC) of the PCB. The gerber files, which translate the gerber files into G-code or M-code, are the input of the machine for drilling and removing the extra copper from the lamination sheet. After removing the extra copper the remaining copper is the tracks, vias annular ring, ground/ supply planes and the pads. As the machine only removes copper by engraving method the vias are produced by conventional electroplating method or inserting the via barrels.
Fig 1. PCB fabrication using renowned CNC PCB fabrication machines producer
The PCB quality depends over the machine type used and its accuracy. However, this method specifically suits to the RF circuits and antenna design.
There are various advantage of PCB milling machines:
1.It does not require the hazardous chemicals
2.PCBs can be produced within the lab
3.PCB fabrication is instant
4.Tracks and land patterns can be produced very accurately such as for microwave and RF applications
5.A single machine can be used or milling, drilling and cutting the PCB
6.The gerber files can be directly linked to the CNC machine
7.Suitable for environments where PCBs are sufficient to be used without solder masking, through hole plated vias and pads and surface finishing
This method has also some disadvantages:
1.It is not suitable for large scale production
2.PCB cost is high due to tools breakage
3.Spindle cooling is required for high speed spindle machines
4.Minimum PCB tracks width, clearance, via size, annular ring and minimum hole size are the design side constraints
5.Separate machining setup is required for vias and through hole pads insertion
6.Any misalignment or deviation in drilling or milling tool causes inaccuracies in the fabricated PCBs. The PCB objects position precision is highly dependent over the machine spindle and tool.
In conclusion the large quantity precision PCBs production best suits by using the wet or etching method and very small scale prototype testing PCBs suit using the CNC fabrication method.
Fig. 2:- Final fabricated PCB using CNC engraving machine
Fig. 3:- Final fabricated PCB using CNC engraving machine