[SI-LIST] Re: 10 Layer Board Stack up

Mike,
     Can you recommend the stackup when the routing density dictates at
least 6 signal layers?. I have employed successfully the following stackup
for a 100MHz board:
 1 TOP
 2 GND
 3 SIG1
 4 PWR (corresponding to the mostly used Logic Supply Voltage by the digital
circuits)
 5 SIG2
 6 SIG3
 7 SPLIT POWER PLANE (Corresponding to the less frequently used supply
voltages)
 8 SIG4
 9 GND
10 BOTTOM

While routing I keep the high-speed signals confined to Layer 1&3 or Layer
8&10. Low speed signals having less stringent crosstalk requirements are
confined to Layer 5&6. Can someone recommend me a better layout than the
afore-mentioned one with 6 signal layers and 4 power planes ?
Also I am curious to know what difference it makes by interchanging the
order of Single Power Plane and Split Power Plane, i.e, interchanging Layer
4 and Layer 7.

ADEEL MALIK,
Avaz Networks

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Mike Brown
Sent: Tuesday, December 03, 2002 7:20 AM
To: nagaraj@xxxxxxxxxxxxxxxxxxxx
Cc: vasudevan.duraiswamy@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: 10 Layer Board Stack up



Nagaraj,

Symmetry is important - so is shielding.  A modified stackup with cap
(pad-only) layers top and bottom, with stripline construction, might be

 1 pad
 2 Gnd
 3 Voltage
 4 Sig
 5 Gnd
 6 Voltage
 7 Sig
 8 Gnd
 9 Voltage
10 Pad

Given your voltage requirements, you could make layer 9 into a ground,
but it would be beneficial to make it a voltage plane to lower the
impedance on one of your voltages.  Or you could use it to distribute
miscellaneous voltages.

This construction gives you good shielding of the internal wiring, and a
relatively constant impedance environment wherein you can switch layers
to achieve routing with a minimum of impedance discontinuity. The
stackup is immune to inter-layer crosstalk, and provides good HF
decoupling of the power distribution system.  It also gives you room on
the board surface to embed EC changes or to avoid seriously congested
areas.  This use should be avoided if at all possible.

Multiple ground (or power) planes are necessary because you have
multiple signal layers and multiple voltage layers. Planes are needed
adjacent to each signal layer to carry the return currents associated
with fast risetimes.  Without the planes, the return currents find their
way onto nearby wires and you become the victim of crosstalk.  If you
have two signal lines between planes, they need to be routed at right
angles to each other to minimize this problem. Ground planes are needed
next to the voltage layers to provide low-impedance distribution of the
voltages.

 Symmetry and shielding aren't everything.  There are probably thickness
constraints dictated by the enclosure into which the board must plug,
and by manufacturing component lead protrusion requirements.  There are
6 dielectric layers (those between signal and adjacent plane) that must
be relatively thick to give you a workable signal impedance, and 3
(those between power and adjacent ground) that should be as thin as
possible to provide low Z power distribution.

I can't assess what this stackup would do to your manufacturability
requirements.  I have used similar construction successfully, but the
board thickness was always a nagging concern.

Regards

Mike

Nagaraj wrote:

>Hi,
>
>We cann't Provide more GND Plane ( 4 ) as you specified and There is no
>Provision for
>
>Splitting VCC2.5 in VCC3.3 Plane as There are 12V and 5 Volts are Already
>Shared the VCC3.3 and 2.5 Plane
>
>Is there any Other Layer Stack up Can you Suggest.
>
>My Question is Why Multiple Ground are Very much Needed?
>
>
>
>Thanks in Advance
>
>Regards
>
>Nagaraj
>
>
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx
>[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of
>vasudevan.duraiswamy@xxxxxxxxxxx
>Sent: Monday, December 02, 2002 5:34 PM
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: 10 Layer Board Stack up
>
>
>
>Hi,
>
>It is correct that the layers should be symmetrical, to provide better
>copper balancing,
>
>Power planes are generally defined by
>
>      power integrity / decopling requirement
>
>      impedance requirement
>
>                Routability
>
>Your stack up can be modified as follows
>
>1)Top Signal 1
>2)GND
>3)Signal 2
>4)VCC3.3
>5)GND
>6)VCC2.5
>7)GND
>8)Signal 3
>9)GND
>10)Bottom Signal 4
>
>
>     Routing, switch  the signals between layer pair Top Signal 1 and
Signal
>2  or  between layer pair Bottom Signal 4 and Signal 3
>
>     Don't  switch over routing between  Signal 1/2  to Signal 3 / 4
>
>Incase of more routing layer requirement,  make layer 4 & 7 also routing
>layer , make layer 5 split power plane of VCC 3.3 & 2.5, make layer 6 as
GND
>
>Regards,
>
>Vasudevan D
>Technical Leader - PCB Design, CFT
>Philips Software Centre Pvt Ltd,
>Philips Innovation Campus,
># 01, Murphy Road, Ulsoor,
>Bangalore - 560 008. India
>Tel: +91 80 5579 000 extn : 5030
>fax : +91 80 5546 645
>
>
>
>                      stephanie.goedecke+FromInterNet@
>                      philips.com                                  To:
>si-list@xxxxxxxxxxxxx
>                      Sent by:                                     cc:
>(bcc: Vasudevan Duraiswamy/BTC/CFT/PHILIPS)
>                      si-list-bounce@xxxxxxxxxxxxx                 Subject:
>[SI-LIST] Re: 10 Layer Board Stack up
>
>
>Classification:
>                      2002-12-02 02:48 PM
>                      Please respond to
>                      stephanie.goedecke+FromInterNet
>
>
>
>
>
>
>
>Hi,
>
>generally, the layers should be symmetrical.  The details of the layout
>depend on the
>details of the board.
>
>Stephanie Goedecke
>
>Philips - SP3D Chip Design GmbH
>Petersbrunnerstr.17
>82319 Starnberg / Germany
>
>Phone:  +49-8151-270-160
>Fax : +49-8151-270-200
>
>
>
>Hi ,
>
>In 10 Layer Board stack How Multiple Ground Plane Will be More effective
and
>Why.
>
>Is there any Formula/Thumb rule behind this.
>
>most of my Critical Signal ( CLK)  are Running at Signal Layer 1
>and My Board Stack up is
>
>Top
>GND
>Signal Layer 1
>VCC3.3
>GND
>VCC2.5
>Signal Layer 2
>Signal Layer 3
>GND
>Bottom
>
>
>
>Thanks in Advance.
>
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