Re: [SI-LIST] : Effects of thieving on SI and EMC.....

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From: Scott McMorrow (scott@vasthorizons.com)
Date: Tue Aug 08 2000 - 14:27:46 PDT


Ravi,

If the thieving structures are spaced 20 times the dielectric thickness from
all signals in all directions x, y and z, then there will be no measurable
effects on characteristic impedance. It is the z-axis that is most easily
overlooked.

scott

Ravi Kiran wrote:

> Scott,
>
> When we stich this to Ground I agree that will reduce the resonance effects
> but what about the impedance of the traces. what will be the effect on the
> characteristic impedance?
>
> Ravi
>
> Scott McMorrow wrote:
>
> > Hey ... a good place to apply the 20H rule
> >
> > i.e. non signal related metalic structures should be
> > spaced a minimum of 20 times the height of the
> > trace to plane spacing away from all active
> > signaling lines to reduce parasitic coupling.
> >
> > As Pat has also pointed out, any large structure
> > should be stitched to ground to reduce resonance
> > effects. The distance between stitch vias should
> > be smaller than lambda/10 of the highest frequency
> > component that one wants to rid freespace of.
> > (Or keep from entering through freespace.)
> >
> > regards,
> >
> > scott
> >
> > --
> > Scott McMorrow
> > Principal Engineer
> > SiQual, Signal Quality Engineering
> > 18735 SW Boones Ferry Road
> > Tualatin, OR 97062-3090
> > (503) 885-1231
> > http://www.siqual.com
> >
> > Chris Padilla wrote:
> >
> > > Michael,
> > >
> > > From an EMI perspective, I have yet to notice any
> > > measurable difference between "thieved" and "non-
> > > thieved" boards.
> > >
> > > We tell our fab vendor to keep the pattern at least
> > > 400 mils away from any trace, via, pad, part, etc.
> > >
> > > As you point out, thieving increases manufacturability
> > > by minimizing warping of the board.
> > >
> > > ----->Chris
> > >
> > > >A thieving pattern is a bunch of very small shapes
> > > >added to a layer that helps equalize the plating
> > > >across a given layer (increases manufacturability).
> > > >An auto thieving utility or program uses a set of
> > > >criteria to determine how and where to put these
> > > >shapes. Unfortunately these programs are almost
> > > >exclusively focussed on mfg issues and not SI or
> > > >EMC issues.
> > > >
> > > >Usually if you see a bunch of 1/16" width diamonds
> > > >on an artwork layer, this is thieving.
> > > >
> > > >FYI
> > > >
> > > >MG
> > > >
> > > >-----Original Message-----
> > > >From: Ray Anderson [mailto:raymonda@radium.eng.sun.com]
> > > >Sent: Monday, July 31, 2000 11:12 AM
> > > >To: Greim, Michael
> > > >Cc: SI LIST
> > > >Subject: Re: [SI-LIST] : Effects of thieving on SI and EMC.....
> > > >
> > > >
> > > >OK, I'll bite. Educate me, what is a thieving pattern,
> > > >and an auto-thiever ????
> > > >
> > > >
> > > >-Ray
> > > >
> > > >
> > > > > Does anyone out there have a tool or reference
> > > > > that would allow one to calculate the effects of
> > > > > thieving patterns on signal integrity and EMC.
> > > > >
> > > > > I am trying to come up with appropriate rule sets
> > > > > for driving an auto-thiever utility.
> > > > >
> > > > > Thanks for the help.
> > > > >
> > > > > MG
> > > > >
> > > >
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> >
> > --
> > Scott McMorrow
> > Principal Engineer
> > SiQual, Signal Quality Engineering
> > 18735 SW Boones Ferry Road
> > Tualatin, OR 97062-3090
> > (503) 885-1231
> > http://www.siqual.com
> >
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>
> --
> Ravi Kiran 1-650-625-2225
> Sr. Hardware Engineer
> Nokia IP Routing Group
> 313 Fairchild Drive
> Mountain View, CA 94043

--
Scott McMorrow
Principal Engineer
SiQual, Signal Quality Engineering
18735 SW Boones Ferry Road
Tualatin, OR  97062-3090
(503) 885-1231
http://www.siqual.com

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