Ground plane layout for noise suppression/immunity
Generally gapping the ground plane is universally bad for EMI. Here is why:

If you fail to contain the generated energy at its source due to bad layout, it will spread throughout the board regardless of GND split or not. Use good layout, cabling and io-filtering. Minimize all loops.

the GND split will amplify radiated emission and pickup (slot antenna).

instead of gapping the plane, place your components in functional groups that are far from each other to isolate them mutually from common impedance noise. Within the group, cluster components as tight as possible to minimize loops. For a motor drive, all the components surrounding the driver circuit are one group though. But things like MCU and oscillators should be a bit off

there are countless more subtle rules to follow (but gapping GND is not one of them). In your case I think having connectors on one side of the board will help with cable radiation.


If you have something really bad that does not need a ground plane (like a motor), then don't gap the GND plane around it but pull the GND plane back and connect it with traces. That way at least you won't get slot antennas