15 degrees of skew in the weave?!?! That's far outside IPC spec. (5 degrees)
and anything I've seen or heard of. There are many servers (virtually any
Intel design since ~2007) out there with traces routed 10 degrees to the board
edge with no issues reported. I've seen designs where they didn't jog the
traces (routed them parallel to the board edge) with predictable consequences,
high BER.
I would contend that 10 degrees is adequate to mitigate the issue in most
cases. 10 degree routing does introduce a resonance at about 28 GHz so for
very high frequencies other mitigation strategies might be needed.
Jeff Loyer
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Tom Dagostino
Sent: Friday, March 17, 2017 10:22 AM
To: bbakshan@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Glass Weave Skew
Boris
10 years or so Scott McMorrow and I did some testing on glass weave effects and
found a similar 5 to 7 psec per inch change in delay. It is nice to see that
things have not changed much over time.
But I was doing some testing for a customer a couple of years ago, measuring
the Zo of about 70 traces on their board. They had skewed their traces 15
degrees relative to the edge of the board. On 69 of these traces the Zo was
50 +/- 2 Ohms. On the final trace the impedance started at 50 Ohms at both
ends but the center of the trace was over 60 Ohms. It looked like the trace was
following the weave very nicely.
Be careful about your assumptions.
Regards
Tom Dagostino
971-279-5325
tom@xxxxxxxxxxxxxxxxx
Teraspeed Labs
9999 SW Wilshire Street
Suite 102
Portland, OR 97225
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Boris Bakshan
Sent: Friday, March 17, 2017 4:23 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Glass Weave Skew
Hi experts,
Following Eric's paper on designcon and the conclusions regarding the inherent
misalignment of the glass bundles with respect to the edge of the board, could
it be that some of the laminate manufacturers took initiative to help
mitigating the skew problem caused by the way fabrics are built for so many
years?
(
https://www.signalintegrityjournal.com/ext/resources/article-images-2017/410
3/4103_SIJ_GlassWeave.pdf
)
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