Hi Boris,
Most Laminate Vendors are aware oft he skew problem and try to solve it in
different ways. Some solutions were just found "by accident" (spread Glass/flat
weave was initially designed to improve Laser drilling!), some were done on
purpose (matching the dk of Glass and Epoxy).
Routing at an angle to eliminate the risk of skew has been around since many
years. I recall a Paper from Siemens more than 10 years ago, and they found 15°
angle to be perfect, but this comes at a cost because you loose Panel space,
and at some angles you create periodic loading.
Erics paper was about how to quantify the amount of skew a certain trace
geometry will see in the worst case (some years ago Bert Simonowich had a nice
paper about another attempt to quantify that, it must be still on his webpage).
Once you know the worst case skew, you can calculate the maximum length of a
straight routed diff-pair and you can check your routing for potential issues.
The "artefact" that Eric talks about in the summary is a well known effect in
textile industry and should be known by every person who ever owned a cheap
T-Shirt: the fabric isn't perfect, and isn't equal in warp and fill direction.
And based on the process and common Loom machines that are out there, I doubt
that there is any way to make the fabric inhomogeneous in both directions. I
believe that one could invent a loom that does that, but given the low quantity
needed, I doubt that anyone ever spend some Millions on this new technology.
Just my two cents.
BR
Gert
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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Boris Bakshan
Sent: Friday, March 17, 2017 12:23 PM
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-2017/4103/4103_SIJ_GlassWeave.pdf
)
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