what's the minimum trace distance from the pcb edge?

Hi experts,


What's the acceptable distance from the pcb edges for high-speed digital traces
from EMI point-of-view?



I once saw (don't remember where) the answer ro be 20H, where H is the trace
hight above the nearest plane, as far as I can recall. Can anyone confirm this?



Is there a relation to signal edge-rate or the cycle time (clock frequency) is
significant in this regard?



The question relates to Stripline as well as Microstrip traces.



Thanks

Itzhak Hirshtal
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ihirshtal 5 years 1 month 10 days

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Answered byOld_School 4 years 8 months 26 days
Hi Itzhak,

  Normally 5xH is sufficient for most applications to ensure that the impedance of the trace is what you expect and designed it for, ie: 50 ohms.  If you want to ensure that no energy gets out of the edge of your board you are better off to simply add 1 or 2 rows of thru GND vias, spaced approx 2 mm center to center all the way around the all edges of your board.

Cheers,
O.S.

Answered byleeritchey 5 years 1 month 10 days
As long as they are running over an intact plane, it won't matter from an
EMI point of view.

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