[SI-LIST] Re: Internal package aggressors/PCB routing
- From: "QU Perry" <Perry.Qu@xxxxxxxxxxxxxxxxxx>
- To: "Ray Anderson" <ray.anderson@xxxxxxxxxx>, "si-list" <si-list@xxxxxxxxxxxxx>
- Date: Wed, 17 Jan 2007 11:26:15 -0600
Hello, Ray:
Thank you for sharing your thoughts. Purely relying on 3D/2.5D field
solver does not sounds practical for a complicated BGA. The challenge is
short of full packaging characterization, it's difficult to predict the
worst case scenario in terms of simultaneous switching output (driving)
and input (receiving) noise and how these noise may "crosstalk" into
other sensitive parts of the circuits such as analogue power supply for
serdes transceiver.
Regards
Perry
=======================================
Perry Qu
Design & Qualification, Alcatel-Lucent Canada Inc.
600 March Road, Ottawa ON, K2K 2E6, Canada
DID: 613-7846720 Fax: 613-5993642
Email: perry.qu@xxxxxxxxxxxxxxxxxx
=======================================
________________________________
From: Ray Anderson [mailto:ray.anderson@xxxxxxxxxx]
Sent: Tuesday, January 16, 2007 2:57 PM
To: si-list
Cc: QU Perry; Mark Alexander; Ray Anderson
Subject: RE: [SI-LIST] Re: Internal package aggressors/PCB routing
Perry-
You bring up a very important and timely issue. As you point out it
isn't a trivial matter to accurately model the effects of the return
current loop inside a dense BGA package.
A typical RLC extraction performed by a quasi-static tool may not
produce a model that is adequate for accurately investigating the
effects of the loop in a full package. While these RLC models are quite
good for some purposes (time of flight, reflections, simple crosstalk),
their use in evaluating the effects of return current paths is quite
often dubious.
A full-wave 3D extraction tool such as HFSS or Owave or other similar
FEM tools will produce the most accurate data that includes the effects
of return path imperfections in the generated s-parameters, however it
is currently impractical to perform a full package extraction with this
class of tool due to the vast size of memory required and the run time
involved.
The typical 3D full-wave extractor doesn't handle power planes very
efficiently. For less than 'full package' extractions with a reasonable
# of nets you can analyze the planar structure separately with a tool
optimized for plane extraction and then combine the s-parameters thus
generated with the parameters from the signal net extraction. However,
as mentioned, this still isn't going to get you to a full package with
several thousand nets.
A 'second best' option is to utilize a tool like PowerSI. This can
handle both the planes and signal nets in an efficient manner, and in
theory could extract a full package model given enough RAM in a 'useful'
amount of time (i.e. a couple weeks vs a couple months). This approach
has limited accuracy above about 6 GHz. However as a practical matter we
find the extraction of a full bank model (in the case of our FPGAs that
is either 40 or 64 drivers) to be about the largest model that is
practical. Even if you could generate a full package model in a
reasonable amount of time that accurately models all the return current
effects it would be huge. Assume your chip has only 500 signal nets.
That would be 1000 ports. Now add the ports for the PDNs, that could
easily be another 50 ports. Now take your 1050 port Touchstone
s-parameter model and attempt to do a useful transient simulation in
Hspice or Nspice or ADS or whatever your favorite simulator is. Good
luck!...... This is a huge topic and is something we are currently
investigating.
-Ray Anderson
Raymond Anderson
Senior Signal Integrity Staff Engineer
Advanced Platforms Group
Advanced Products Division
Product Technology Department
Package Design Engineering
Xilinx Inc.
2100 Logic Drive
San Jose, California 95124
(408) 626-6277
-----Original Message-----
From: QU Perry [mailto:Perry.Qu@xxxxxxxxxxxxxxxxxx]
Sent: Tuesday, January 16, 2007 6:48 AM
To: Chris.Cheng@xxxxxxxxxxxx; si-list; Ray Anderson; Mark Alexander
Subject: RE: [SI-LIST] Re: Internal package aggressors/PCB routing
Chris:
You hit this on the nail. I once had a look of a mcm packaging design
from a IC vendor and I saw exactly what you mentioned: jump of return
path all over the place and what strike me the most is at the area close
to flip chip bumps, where large copper clearance cut off the return path
and you get about one ground bridge for every 20 or so bumps, so all the
return current for those 20 signals has to crowd through that bridge
including giga bit signals.
How to model and predict the effects of large return loop on a full
packaging scale as Ray mentioned is something I'm curious. For me it
seems to very difficult to predict where the return current flows for a
complicated BGA packaging. A full wave field solver should help but I'm
not sure whether it can handle the complexity. Probably Ray and Mark can
elaborate a bit more in details ?
Thanks
Perry
=======================================
Perry Qu
Design & Qualification, Alcatel-Lucent Canada Inc.
600 March Road, Ottawa ON, K2K 2E6, Canada
DID: 613-7846720 Fax: 613-5993642
Email: perry.qu@xxxxxxxxxxxxxxxxxx
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