[SI-LIST] Re: Effect of Pwr-Gnd plane pairing vs. non-paired planes on signal return currents
- From: "Yuming Tao" <YTAO@xxxxxxxxxx>
- To: <alexh1@xxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Thu, 16 Feb 2006 15:27:51 -0500
Hi, Alex
I agreed with you that there will be no quality difference (or possible =
better due to slightly less shunt capacitance) for the signal traversing =
from the top signal layer to the bottom layer in both stackups as long =
as the vertical via-transition is identical.
However, you lose the flexibility of power plane assignment if you are =
going to use power islands in your board design. Also plane capacitance =
will be reduced as you mentioned already.
Fuming
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Alex Horvath
Sent: Thursday, February 16, 2006 2:45 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Effect of Pwr-Gnd plane pairing vs. non-paired planes
on signal return currents
Normally, when I design a multi layer stackup I always try to alternate =
and pair Pwr-Gnd planes to maximize inter-plane capacitance. For =
example, a 16 layer stackup might look like-
=20
=20
Sig - - - - - - -=20
Gnd --------------
Pwr --------------
Sig - - - - - - - -=20
Sig - - - - - - - -
Gnd --------------
Pwr --------------
Sig - - - - - - - -=20
Sig - - - - - - - -
Gnd --------------
Pwr --------------
Sig - - - - - - - -=20
Sig - - - - - - - -
Gnd---------------
Pwr ---------------
Sig - - - - - - -=20
=20
For cost reasons I might be forced into a stackup with the same number =
of signal layers but with 2 power planes removed (14 layers, same =
dielectric thickness) -
=20
Sig - - - - - - -=20
Gnd --------------
Pwr --------------
Sig - - - - - - - -=20
Sig - - - - - - - -
Gnd --------------
Sig - - - - - - - -=20
Sig - - - - - - - -
Gnd --------------
Sig - - - - - - - -=20
Sig - - - - - - - -
Gnd---------------
Pwr ---------------
Sig - - - - - - -=20
=20
=20
Let's assume a signal traverses from the top signal layer to the =
bottom layer in both stackups. Let us also assume as a worst case that =
there are no nearby vias or decoup caps and the signal edge rate is =
approximately 10 times the via length (about 200 psec). Is there a =
significant difference in the expected signal quality when comparing =
these 2 stackups?
=20
My gut feel is that all else being equal the primary factor =
determining signal quality is the spacing of the planes. The DC =
assignment of the planes has (again ignoring effect of gnd or pwr vias) =
little effect and thus the signal quality in the above cases would be =
virtually identical.
=20
Since I hate to bet my designs on a gut feel hopefully someone can =
confirm or deny my assumptions.
=20
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at: =20
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
=20
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
