I'm in the middle of designing a specialized communications device that uses an off-the-shelf radio module. This radio module is larger than desired and the PCB area that is not needed is easily cut away.
However, the module is built using a 10-layer PCB. Upon cutting away the undesired area, the internal conductor planes are visible and I need to make sure that the various layers do not have excess copper shards that can short to other layers.
I've used a fine-grit belt sander with the long cut edge of the PCB oriented in the direction of the sanding belt travel. In other words, the belt travel is such that it doesn't short across the various copper planes. This does clean the cut edge nicely but I still have copper smearing - the smeared copper from various internal layers is very close to the layers next to them.
I'm seeking advice on how to remove the unwanted copper from the edge of the cut PCB internal planes. My first thought was to use a high-speed down-cut router bit but, upon reflection, that will probably push the edges of the copper planes together and cause short circuits.
Another thought is to use a flat-bottomed vessel with a very shallow depth of PCB etchant, then stand the circuit board vertically with the edge of the cut PCB held just above the bottom of the vessel. I'd probably have to have some means of circulating the etchant so that the PCB edge is always exposed to fresh etchant.
Total quantity is quite small - perhaps 150 units or so.
The sections of PCB that I'm removing are away from the RF section. The area near the portion that I am removing contains power supply and accessory connector stuff.
One section is bare PCB with a number of test and factory-programming pads, the other section contains an accessory connector that isn't needed.
I've been very careful with my changes - remove a section, clean up the exposed layers at the PCB edge, test. Once I verified full functionality, I'd remove the next portion of circuit board and repeat the whole process.
I was fairly certain that the circuit board material did not contain important traces and my testing seems to confirm that. I have been able to remove all of the undesired board and the module appears to be completely functional.
The reason for doing the modifications in small steps was so that I would destroy at most only one module. As it is, I've lucked out and I appear to be able to remove all of the undesired circuit board and still have a fully functional module.
Now all I need to do is find an easy method of cleaning up the internal copper at the cut edges of the PCB.