"Feng Li" <[email protected]> wrote on 11/22/02 09:55 AM > the power and ground of various voltages and characteristics confused me a lot
I don't see why? Try some simplified 3D CEM type simulation and view the surface (or displacement) current patterns and the result of haphazard violation of the design rules would be understod better. This is doable nowadays. Else go for the old hit or miss method, if it aint broke don't fix it iterative routine for your layout follow by fabrication and testing, and soon the reason can be clear. > As a common guideline, it is necessary to check for power/ground > planes or shapes overlapping between adjacent layers in a PCB board? Yes, the rule is to avoid a situation that cause CM currents (or to put it in other words: to minimize ground potentials developing) developing from the lack of symmetry between any of the Power and Ground planes. This is especially true when the power plane extends outside the 'shadow' ground plane. There are some IEEE EMC Symp papers cir. 1999? on this but off the cuff I can only recall it is from some title that had to do with: Radiation from LCD display panels and PCBs ( Hold back your flaming arrows...) Older Design Rule: All power and ground plane must be gaped in the same places. Now: The 20H rule: The Ground plane must extends beyond the Power plane by at least 20 X the thickness of the board. It seems that it work quite well into the hundreds of MHz... In addition to this, no signal trace must cross a ground gap. If applied to a power trace that carries large amounts of charges slushing around, that is one of the design rules for controlling emission. If applied to a sensitive parts of your electronics, it is a countermeasure for immunity and ESD. Just my 2ยข worth... :-) cheerio Tim Foo for the other PCB design rules see: http://www.geocities.com/timfoo6143/Design_Rules.pdf OR if the site do not come on immediately navigate through http://www.geocities.com/timfoo6143 ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
