Hi Lee,
It does not matter if the problem is made up. In this case, I want to
show that an open side of a PCB is much like an open wave guide, but
the the dimensions are so small that the interesting frequencies are
high enough as not to be a problem. This puts the argument about PCBs
into very simple language and that satisfies engineering curiosity.
Citing lots of data does not lead to an understanding of the overall
principle, which is what I am getting at.
So, I think the two cases are the same and was looking for your
insight. I have done the calculations, and making reasonable
assumptions on the dimensions, I get frequencies over 500 GHz where
edge radiation as from a waveguide would happen! Just wondering if I
did this correctly.
Doug
On Tue, 5 Jul 2016 13:56:08 -0700, Lee Ritchey
<leeritchey@xxxxxxxxxxxxx> wrote:
This seems to me to be another case of trying to solve an imaginary problem.
As a side comment on my posts and the responses to them, I often say
that I am from Missouri, and need to be shown that a problem actually
exists before I attempt to solve it.
In almost 50 years of engineering and participating in the design of
more than 3000 PCBs, I have not yet seen one of them fail EMI from
energy leaking out the edges and none of them have had via fences or
recessing to the 20h rule. So if the problem really exists, the
person making the claim owes an example of a failure due to the
absence of via fences.
There is a challenge for you! -----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Doug Smith
Sent: Tuesday, July 5, 2016 1:32 PM
To: Charles.Grasso@xxxxxxxxxxxx; curtmcn@xxxxxxxxx;
si-list@xxxxxxxxxxxxx; Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
Subject: [SI-LIST] Re: Via fence along board edge
Lee, a question. If the spacing between two planes was 1/2 wavelength
(at some very high
frequency) would not the edge of the board be a little like an open
waveguide? Probably not a practical case, at least not for another
few years. Doug
On Tue, 5 Jul 2016 11:39:53 -0700, Lee Ritchey
<leeritchey@xxxxxxxxxxxxx> wrote:
I think I have traced this myth to its origin. It is no more or less than a
myth. >shows that with or without these "grounding vias" the results are the
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 >
same.
Circuit > Design. January 1998
Brooks, Douglas. "90 Degree Corners, The Final Turn." Printed
Cruz, > Publishing date unknown.
Fang, Jiayuan, et.al., "Effects of 20-H Rule and Shielding Vias on
Electromagnetic Radiation From Printed Circuit Boards", UC Santa
in > PCBs", UC Santa Cruz EE Department, May 2001.
Chen, Huabo, et.al., "Effects of 20H Rule and Shielding Vias on EMI
[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Grasso, Charles
Hope this helps. >
Lee Ritchey
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx >
Sent: Tuesday, July 5, 2016 9:21 AMdon't have a simulation tool or handy dandy formula to "guess" if >
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 >
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)
[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Curt McNamara
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 >
Sent: Tuesday, July 05, 2016 6:51 AMinside the PCB.
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 >
There are parts and short traces on the outside layers, with groundpours. > The next layer in is ground on both top and bottom. >
Will the ground fence always help with EMC?will > come out any opening it can find?
- Or sometimes help because that energy has to go somewhere and
wavelength?
- Or mostly help because those openings are small compared to the >
Curt
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