I think part of the problem here is Lee works with PCB designs that are
generally well-grounded. That is, there are ground vias shorting the
planes all over the place. Those in themselves create a Faraday cage that
operates to contain internal resonances and energy that might be available
to radiate from the edge of the board. He also tends to have power systems
that are well-bypassed across the entire area of the planes.
If you are unfortunate enough to leave entire areas of planes without
bypass to suppress large rectangular cavity resonances, I'm sure it is
possible to radiate out the edge of a PCB with a half-wave resonant
frequency that rattles back and forth across the outer edges.
Scott McMorrow
R&D Consultant
Teraspeed Consulting - A Division of Samtec
16 Stormy Brook Rd
Falmouth, ME 04105
(401) 284-1827 Business
http://www.teraspeed.com
On Tue, Jul 5, 2016 at 4:37 PM, Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
wrote:
This has all the makings of solving an imaginary problem! Do we have time
for that?
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Ken Wyatt
Sent: Tuesday, July 5, 2016 1:23 PM
To: Charles Grasso <Charles.Grasso@xxxxxxxxxxxx>
Cc: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>; curtmcn@xxxxxxxxx;
si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Via fence along board edge
If EM waves indeed propagate through the dielectric, whatââ¬â¢s to stop
them
from radiating out the edges of a PC board? This assumes, of course, that
there are discontinuities or impedance mismatches that can cause
reflections.
Cheers, Ken
_______________________
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Wyatt Technical Services LLC
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Phone: (719) 310-5418
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On Jul 5, 2016, at 1:31 PM, Grasso, Charles <Charles.Grasso@xxxxxxxxxxxx>wrote:
Gisin and Zorica Pantic Tanner.
Sorry - One last thing: I would refer you to Minimizing EMI Caused by
Radially Propagating Waves Inside High Speed Digital Logic PCBs - Franz
than a myth.
Best Regards
Charles Grasso
Compliance Engineer
Echostar Communications
(w) 303-706-5467
(c) 303-204-2974
(t) 3032042974@xxxxxxxxx
(e) charles.grasso@xxxxxxxxxxxx
(e2) chasgrasso@xxxxxxxxx
-----Original Message-----
From: Lee Ritchey [mailto:leeritchey@xxxxxxxxxxxxx]
Sent: Tuesday, July 05, 2016 12:40 PM
To: Grasso, Charles; curtmcn@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] Re: Via fence along board edge
I think I have traced this myth to its origin. It is no more or less
"leak out" the sides of a PCB to begin with. One of them even shows that
The following papers all show with laboratory testing that EMI does not
with or without these "grounding vias" the results are the same.
Electromagnetic Radiation From Printed Circuit Boards", UC Santa Cruz,
Brooks, Douglas. "90 Degree Corners, The Final Turn." Printed Circuit
Design. January 1998
Fang, Jiayuan, et.al., "Effects of 20-H Rule and Shielding Vias on
Publishing date unknown.
PCBs", UC Santa Cruz EE Department, May 2001.
Chen, Huabo, et.al., "Effects of 20H Rule and Shielding Vias on EMI in
have a simulation tool or handy dandy formula to "guess" if there will be
Hope this helps.
Lee Ritchey
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Grasso, Charles
Sent: Tuesday, July 5, 2016 9:21 AM
To: curtmcn@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Via fence along board edge
If there is a concern about cavity resonances causing EMI and you don't
an interference problem or not then a via fence is a good way to sleep at
night!
the PCB.
(Just count vias instead of sheep ..one..two...three...zzzzzzz)
Best Regards
Charles Grasso
Compliance Engineer
Echostar Communications
(w) 303-706-5467
(c) 303-204-2974
(t) 3032042974@xxxxxxxxx
(e) charles.grasso@xxxxxxxxxxxx
(e2) chasgrasso@xxxxxxxxx
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Curt McNamara
Sent: Tuesday, July 05, 2016 6:51 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Via fence along board edge
I have seen this done, and understand the desire to trap EM waves inside
There are parts and short traces on the outside layers, with groundpours.
The next layer in is ground on both top and bottom.come out any opening it can find?
Will the ground fence always help with EMC?
- Or sometimes help because that energy has to go somewhere and will
wavelength?
- Or mostly help because those openings are small compared to the
Curt
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