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, what’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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On Jul 5, 2016, at 1:31 PM, Grasso, Charles <Charles.Grasso@xxxxxxxxxxxx>
wrote:
Sorry - One last thing: I would refer you to Minimizing EMI Caused by
Radially Propagating Waves Inside High Speed Digital Logic PCBs - Franz Gisin
and Zorica Pantic Tanner.
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 than a
myth.
The following papers all show with laboratory testing that EMI does not "leak
out" the sides of a PCB to begin with. One of them even shows that with or
without these "grounding vias" the results are the same.
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
Electromagnetic Radiation From Printed Circuit Boards", UC Santa Cruz,
Publishing date unknown.
Chen, Huabo, et.al., "Effects of 20H Rule and Shielding Vias on EMI in PCBs",
UC Santa Cruz EE Department, May 2001.
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 have
a simulation tool or handy dandy formula to "guess" if there will be an
interference problem or not then a via fence is a good way to sleep at night!
(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 the
PCB.
There are parts and short traces on the outside layers, with ground pours.
The next layer in is ground on both top and bottom.
Will the ground fence always help with EMC?
- Or sometimes help because that energy has to go somewhere and will come out
any opening it can find?
- Or mostly help because those openings are small compared to the wavelength?
Curt
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