[SI-LIST] Re: Internal package aggressors/PCB routing

  • From: "Mark Alexander" <mark.alexander@xxxxxxxxxx>
  • To: <Chris.Cheng@xxxxxxxxxxxx>, "si-list" <si-list@xxxxxxxxxxxxx>
  • Date: Fri, 12 Jan 2007 12:48:08 -0700

Chris,

You're correct that there are multiple coupling mechanisms within the
package substrate.  For this reason, nearest-neighbor coupling is not
our exclusive metric for ensuring the signal integrity of our package
design.  However since nearest-neighbor coupling is a significant
factor, it is one that we find useful.

-mark





-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Chris Cheng
Sent: Friday, January 12, 2007 11:08 AM
To: si-list
Subject: [SI-LIST] Re: Internal package aggressors/PCB routing

Ray,
I wish crosstalk in packages is as simple as flagging the neighbor =3D
traces.
Unlike most of the PCB boards, large BGA packages tends to use a lot of
=3D
blind and buried vias. Power and ground planes are highly meshed and =3D
with evil degassing holes. A lot of times I found the crosstalk does not
=3D
come from the traces to traces coupling but rather from the current =3D
return path overlapping each other on the reference planes.=3D20
A while ago there was a thread about someone challenging the need for =
=3D
ground via drills for return vias. I have used an example in package =3D
crosstalk and I will use the same here. Every time a group of slow speed
=3D
nets hundreds of mils aways switch, the victim line take a huge glitch.
=3D
If you purely use the seperating distance to estimate the crosstalk, the
=3D
amplitude will be near zero. What really happen was there was =3D
insufficient return vias on the reference plane for those slow speed =3D
signal and the return current decided to take the nearest vias which is
=3D
right next to the critical victim lines.=3D20
I believe that's exactly why Al Ruehli and friends developed PEEC to =3D
estimate those crosstalk for TCM modules back in the 70's. Because they
=3D
realize the return path is just as critical as the signal traces =3D
themselves in a highly meshed substrate. Things just don't change that =
=3D
much since then, electrons move the same then and now, =
unfortunately.=3D20

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Ray Anderson
Sent: Friday, January 12, 2007 10:08 AM
To: si-list
Cc: james.f.peterson@xxxxxxxxxxxxx; scott@xxxxxxxxxxxxx;
jmartinson@xxxxxxxxxxxxxxxxx; Ray Anderson
Subject: [SI-LIST] Re: Internal package aggressors/PCB routing


Jerry-

I can't speak how other silicon vendors provide the data, but we perform
a full package extraction on all of our package designs to generate RLC
data for nets operating below about 1GHz (for MGT nets we provide
s-parameter data). We typically generate mutual coupling data for the 4
nearest neighbors since we feel that crosstalk coupling from lines more
than 4 away from the victim contribute negligible crosstalk. The L and C
mutual coupling values are available in IBIS .pkg file format as a data
item we make available for each package type. Given that data you can
simulate or calculate crosstalk voltages.

Besides the standard IBIS .pkg file format we can also provide customers
the data in a number of other formats upon request (with > 4 neighbors
coupling if desired).

-Ray


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
=3D3D20


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