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Printed Circuit Board Design and Layout Questions

6. Does it matter if traces are routed along the edge of a PCB?

Power and signal traces can be routed near the edge of a board, but they should not be right up against the edge. The reason for this has nothing to do with radiation directly from the traces. Signal return currents flowing in the plane below the trace are partly constrained and concentrated on the edge when the trace is too close to the edge of the board. This increases the impedance of the return path (or more precisely, the mutual inductance between the signal path and potential antennas connected to the board). The space between a trace edge and board (ground plane) edge should be at least as high as the dielectric thickness [1].


[1] D. Berg, Y. Ji, X. Ye, J. Drewniak, T. Hubing, R. DuBroff, T. Van Doren and M. Tanaka, “FDTD and FEM/MOM modeling of EMI resulting from a trace near a PCB edge,” Proc. of the 2000 IEEE International Symposium on Electromagnetic Compatibility, Washington D.C., Aug. 2000, pp. 135-140.