[SI-LIST] Re: Stack up for EMI reduction, plane resonance and u-s trip radiation etc etc

From: "Istvan NOVAK" <istvan.novak@xxxxxxxxxxxxxxxx>
To: "Grasso, Charles" <Charles.Grasso@xxxxxxxxxxxx>,<Chris.Cheng@xxxxxxxxxxxx>, "steve weir" <weirsp@xxxxxxxxxx>
Date: Wed, 11 Feb 2004 22:31:46 -0500

Steve,

Something is not clear to me in this argument.  Via fence stitches planes
on the same DC voltage; mostly people stitch the ground planes.
Are you concerned about the cavity formed of GND-GND planes?
This might be a concern on boards where there are very few
components which would break the cavity with their vias.
On boards where you have many components, the necessary
ground vias will create probably sufficiently small sub cavities.

Regards,

Istvan


----- Original Message -----
From: "steve weir" <weirsp@xxxxxxxxxx>
To: "Grasso, Charles" <Charles.Grasso@xxxxxxxxxxxx>;
<Chris.Cheng@xxxxxxxxxxxx>; "'Istvan NOVAK'" <istvan.novak@xxxxxxxxxxxxxxxx>
Cc: <si-list@xxxxxxxxxxxxx>
Sent: Wednesday, February 11, 2004 12:13 PM
Subject: RE: [SI-LIST] Re: Stack up for EMI reduction, plane resonance and
u-s trip radiation etc etc


> Charles, sure.  First, because of the ESD issue, I also favor fences.
>
> The problem with fences comes back to plane resonance.  Fences do a really
> great job of setting up big standing waves on the planes as they make near
> perfect transmission line reflectors.  We can mitigate this somewhat by
> avoiding evenly spaced vias.  The advocates of 20H who know their stuff,
> rightly point out that 20H sets up a controlled leak, thereby effectively
> dissipating energy that would otherwise resonate in the planes.  20H is
> controversial, because that "dissipation" is release of energy outside the
> board.
>
> As I said before, if the planes were sealed tight, this would not be an
> issue.  But vias carry energy to the surface and features above the
surface
> then become radiators.  DET that Istvan has written about is one way to
> mitigate the problem.  There are some other interesting ideas around, but
> at least at this time, I don't have the resources to pursue them.
>
> Steve.


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Follow-Ups:
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  - From: steve weir

[SI-LIST] Re: Stack up for EMI reduction, plane resonance and u-s trip radiation etc etc

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