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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