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Some of the Worst EMC Design GuidelinesThese infamous design guidelines have become "urban legends" in the EMC world.
Circuit Board LayoutTraces should not make sharp right angle turns.Nobody seems to know for sure where this guideline originated. EMC engineers often say it's a manufacturing issue. Board manufacturers say it's an EMC issue. Chamfering the corner on a wide, impedance-controlled trace may be a good idea at Gbps data rates. However, there is generally no advantage to making two 45-degree turns as opposed to making one 90-degree turn. Power plane edges should not be flush with the edges of ground planes. They should be pulled in by a distance of 20 times the spacing between the planes (a.k.a., the 20-H Rule).While it is possible to conceive of situations where this might be a good idea (e.g. to prevent coupling of power bus noise to cables draped over the edge of a board), it is rarely necessary or desirable to do this. |