[SI-LIST] Re: regarding the stack up

  • From: "Benny Yan" <zyan@xxxxxxxxxx>
  • To: <wilson@xxxxxxxxxxxxxxxxxx>, <samynitt@xxxxxxxxx>
  • Date: Thu, 23 Aug 2007 22:39:30 +0800

Two solutions are acceptable, I prefer the first one for signals in four =
layers can GND reference.
As a 8 layers stackup, power layers will be splitted to several =
different voltage levels, hence resulting much smaller intact area.=20
This will bring little PWR/GND coupling effect.  To power noise or =
ripple, it depends on your decoupling solution and so on.

Benny Yan
IO Methodology Inc.=20

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On Behalf Of Ralph A Wilson III
Sent: Thursday, August 23, 2007 9:12 PM
To: samynitt@xxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: regarding the stack up

Personally,
I'd go with:

Top
Power-1
GND
Signal - vertical
Signal - horizontal
GND
Power-2
Bottom

This give you better power/ground coupling, isolates
the signal traces from power segmentation (reference
plane boundaries), good power/ground connections to
the ICs, and consistent reference plane for all signals.
Just make sure you have a good number of ground stitching
vias, in particular in the vicinity of signal vias changing
from horizontal to veritcal routing.

Ralph Wilson
Alcatel-Lucent

On 08/23/07 08:00, Govinda samy wrote:
> I am planning to have 8 layer stack up on my  board . The following is =
the structure=20
> =20
> --------- top
> --------- GND
> Signal
> =20
> PWR-1
> =20
> PWR -2
> =20
> Signal=20
> =20
> ----------- GND
> ---------- Bottom
> =20
> PWR - 1 and PWR-2 is spilit plane with multiple voltages . 1.2V , =
3.3V, 5 V, 2.5 V
> =20
> All the DDR related  voltages also included in that PWR-2 plane : =
1.25V, 2.5V
> =20
> My question is,  this Layer stack up is acceptable ? Because my =
concern is the high speed switching and transient current doesn't have =
any GND path underneath..
> =20
> is that will create any noise or ripples on the power rails ???=20
> =20
> Please let me know your point of views ..
> =20
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