[SI-LIST] Re: 10 Layer Stackup Recommendation for Board with High speed Signals(SERDES/DDR)
- From: "Bill Hargin \(ICD\)" <b.hargin@xxxxxxxxxx>
- To: <prashanth_rajappan@xxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 8 Aug 2012 13:19:05 -0700
Hi Prashanth:
Without having more details, it's probably going to be difficult for someone
on the outside to provide helpful advice here, but here are some general
observations.
The first thing you need to do is nail down how many routing layers you're
going to need. It's not clear what you're planning to do with the top and
bottom layers, or how many layers you need. If you can fit some of your
SERDES signals on those layers, for example - close to the BGAs - that might
not be a bad idea.
Once that's determined - e.g., whether you need 4 or 6 signal layers - you
can start distributing your power and ground planes. It's not a bad idea to
put ground planes near the surface to avoid coupling between power planes
and mounting pads on the top and bottom. At the speeds you're working with,
you might benefit from some power/ground plane capacitance, to pull your PDN
impedance down at higher frequencies. So, mean 4 or 6 signal layers, your 2
power planes, plus 2 ground planes ... Something like this:
4 Signal Layers:
1 - SIG1 - SERDES / DDR2/High Speed Signals
2 - GND
3 - POWER1
4 - SIG2 - DDR2
5 - SIG3 - DDR2 (Pay attn.. to broadside coupling/parallelism on L4-L5.)
6 - POWER2
7 - GND
8 - SIG4 - SERDES / DDR2/High SpeedSignals
6 Signal Layers:
1 - SIG1 - SERDES / DDR2/High Speed Signals
2 - GND
3 - POWER1
4 - SIG2 - SERDES / DDR2/High SpeedSignals
5 - GND
6 - SIG3 - DDR2
7 - SIG4 - DDR2 (Pay attn. to broadside coupling/parallelism on L6-L7.)
8 - GND
9 - SIG5 - SERDES / DDR2/High SpeedSignals
10 - POWER2
11 - GND
12 - SIG6 - SERDES / DDR2/High SpeedSignals
There are eval versions of software that we provide that help with both
stackup and PDN planning that you may want to play around with. Stackup
Planning: http://www.icd.com.au/FX.html ; PDN Planning:
http://www.icd.com.au/PDN_Planner.html .
Bill Hargin
In-Circuit Design, USA
Software & Services for High-Speed Printed Circuitboard Design
(425) 301-4425 ? b.hargin@xxxxxxxxxx
Online: www.icd.com.au
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Prashanth Rajappan
Sent: Wednesday, August 08, 2012 6:33 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] 10 Layer Stackup Recommendation for Board with High speed
Signals(SERDES/DDR)
Hi All,
I am looking for suggestions for our PCB which has high speed interfaces
like SERDES /DDR2/GIGA BIT Ethernet.The current stackup is given below.
Top
GND
SIG1 - SERDES / DDR2/High Speed Signals
SIG2 - DDR2
POWER1
GND
SIG3 - DDR2
SIG4 - SERDES / DDR2/High SpeedSignals
POWER2
BOT
PLease let me know your comments or suggestion regarding the same.
Thank you in advance!
Regards
Prasanth
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