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July 2009

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Subject:
From:
Kenneth Wood <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Kenneth Wood <[log in to unmask]>
Date:
Thu, 30 Jul 2009 09:55:28 -0400
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Pete,
That is part of the faraday cage model thinking.
I used to design handheld modules for Philips MRI equipment that needed to
be below -190dB emissions.
We tried that approach but the solid planes were far better.
Simply put, the model says that if the openings in the copper are smaller
than the wavelength (or some percentage of wavelength, I can't remember
right now)
that the signal would not escape the cage. That is why you see anechoic
chambers with copper mesh around them. I do not think the model says that
mesh works better than solid
it's just that you can use meshes instead of solids...
Ken



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Pete Houwen
Sent: Thursday, July 30, 2009 9:28 AM
To: [log in to unmask]
Subject: Re: [TN] Hashing-Out Hatching

We have one engineer, an analog kind of guy, who likes to insist hatching is

better for EMI.  He can't say why.  But most of our designs are RF, solid 
planes have turned out to be critical.  Trying make sure all those microvias
get 
a good solid connection, and don't split up the planes, means you need a
small 
enough hatch, you might as well make it solid and stop worrying.  

Gary brought me back to the days when, just for kicks, I would take other 
guy's designs and remove all of their vias, just to prove I could do it.
I've 
gotten help, I'm cured, a thousand vias is nothing anymore.  But that memory

made me feel old until Richard brought up soldering with iron sticks.

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