FreeLists / si-list / [SI-LIST] Re: stitching vias

[steve weir <weirsi@xxxxxxxxxx>]

Chris, a little dielectric loss can be a good thing.  In the dangerous 
realm of generalities, tighter stitching even on regular spacing is almost 
always better than looser stitching over a given planar area for the simple 
reason that it pushes the resonant frequency(s) up.

Regards,


Steve.
At 12:04 PM 7/5/2005 -0700, Chris Padilla (cpad) wrote:
>=20
>I would also say that it can cause problems and even resonances.  Most
>ground stitching vias are placed very, very uniformly...this can be
>very, very bad. :)  I would suggest an almost random placement of the
>stitching vias...definately don't make them uniform.
>
>Further, with stitching vias, when the energy hits the via, most of it
>reflects (and its sign changes) and is now available to couple again
>onto something.
>
>I guess it is a matter of where and how you want this energy to leak:
>out the edges of the board, out the top, coupling onto sensitive vias,
>etc.=20
>
>This is one area where a low-loss dielectric and stitching vias could
>get one into much trouble.
>
>For the record, I place stiching vias all around the periphery of my
>boards and they are all uniformly spaced.  However, I do think about the
>above situations and you should, too.
>
>
>Chris Padilla
>Cisco Systems
>408.525.4989
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>On Behalf Of Lynne D. Green
>Sent: Tuesday, July 05, 2005 11:48 AM
>To: naren@xxxxxxxxxx; si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: stitching vias
>
>Hello, Naren,
>
>This is a good question.  Designs have failed when stitching was not
>used.
>
>Here is one failure mechanism: Without stitching, a crosstalk aggressor
>signal can be coupled onto (and thus carried) by the "ground" (or
>"power") trace.  This can then cause crosstalk from that "ground" (or
>"power") net to another victim trace that is not physically close to the
>original crosstalk aggressor.
>
>Simulation can help you determine where and how much stitching is
>required for a design.
>
>- Lynne
>
>
>"IBIS training when you need it, where you need it."
>
>Dr. Lynne Green
>Green Streak Programs
>http://www.greenstreakprograms.com
>425-788-0412
>lgreen22@xxxxxxxxxxxxxx
>
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>On Behalf Of Naren
>Sent: Tuesday, July 05, 2005 6:59 AM
>To: 'si-list@xxxxxxxxxxxxx'
>Subject: [SI-LIST] stitching vias
>
>Hi gurus
>
>I want to know that why stitching vias are required?
>
>Please suggest me any web article, web portal etc (If Any)
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