The way that a circuit is laid out on a PC board is critical to its EMC performance. Although this is not made clear on the circuit schematic, each track acts as a component in its own right at high frequency - particularly its inductance and capacitance, and the mutual coupling between tracks that results, which become steadily more significant as frequency increases. It is dangerous to delegate this aspect of design to an auto-routing CAD package which is totally ignorant of high frequency layout aspects. For instance, auto-routers may treat the circuit 0V as a single node and must be specifically disabled (or worked around) in order to lay out the ground system properly.

Proper PCB layout should be regarded as an integral aspect of circuit design and should start with the ground return tracks (or ground plane). These tracks, or the definition and configuration of the plane(s), should be detailed first, continuing on to critical signal tracks such as those carrying high frequency clocks, data backplanes or especially sensitive circuit nodes. All of these tracks and their associated circuit components should be laid out to minimize their overall length and to minimize the area enclosed between them and their associated ground return path. Finally, the least sensitive or emissive circuits can be routed in the remaining available space.

Several distinct aspects of PCB layout need to be considered for EMC design. These are:

Proximity of signal and return

Power and ground planes in the x-y dimension

The layer stack (the z-dimension)

Layout of circuit functions

Connections to surrounding metalwork

Board level shielding