Not simple, but important, that's the bad thing about weave effect: you never
know when it will hit you. And in mass production you will not be able to test
every single trace so it is all about risk management. Knowing laminate and PCB
manufacturing processes helps a lot to find strategies to lower the risk.
BR
Gert
Von: Binayak Shrestha <mailto:binayaks@xxxxxxxxx>
Gesendet: Freitag, 25. Juni 2021 09:34
An: Havermann, Gert <mailto:Gert.Havermann@xxxxxxxxxxx>
Cc: Si-list <mailto:si-list@xxxxxxxxxxxxx>
Betreff: Re: [SI-LIST] AW: [EXTERNAL] Re: A new old topic - fiber weave and low
loss material
Dear Gert,
Thank you for explaining in-depth the different scenarios that can take
place....not so simple!!!
Regards,
Binayak
On Fri, 25 Jun, 2021, 11:13 am Havermann Gert,
<mailto:dmarc-noreply@xxxxxxxxxxxxx> wrote:
Dear Binayak,
keep in mind that the weave effect in grain direction is also depending on the
Laminate manufacturer, and sometimes even on the plant because the pulling of
the weave can be (and in fact is) different.
Another factor is the PCB manufacturer and how he handles a two ply
construction. Some do very accurate registration stamping which gives a higher
risk of weave effects. So even if you would try to do a research on how much
benefit a 2-ply construction would give you, there are still so many unknowns
that you may never come to a single conclusion.
Scott has techniques set up to prevent skew under all circumstances, but that
doesn't mean that this is the only way to reduce the risk of skew in your
system. Finding the right combination of material and manufacturer can have
(almost) the same effect (almost=Murphys Law).
BR
Gert
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Persönlich haftende Gesellschafterin:
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Vorstand: Dipl.-Kfm. Philip F. W. Harting (Vorsitzender), Dipl.-Kffr. Maresa W.
M. Harting-Hertz, Dipl.-Kfm. Dr.-Ing. E. h. Dietmar Harting,
Dipl.-Hdl. Margrit Harting, Dr.-Ing. Kurt D. Bettenhausen, Dipl.-Ing. (FH)
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-----Ursprüngliche Nachricht-----
Von: mailto:si-list-bounce@xxxxxxxxxxxxx ;<mailto:si-list-bounce@xxxxxxxxxxxxx>
Im Auftrag von Binayak Shrestha
Gesendet: Freitag, 25. Juni 2021 06:44
An: Lee Ritchey <mailto:lritchey49@xxxxxxx>
Cc: mailto:scottmcmorrow@xxxxxxxxx; mailto:corley@xxxxxxxxx; ;
mailto:rawilson@xxxxxxxxxxxx; mailto:si-list@xxxxxxxxxxxxx; ;
mailto:si-list-bounce@xxxxxxxxxxxxx
Betreff: [EXTERNAL] [SI-LIST] Re: A new old topic - fiber weave and low loss
material
Dear Lee,
The data provided in the Scott's presentation show that even with 2-ply
construction using spread glass, there can be significant skew in the grain
direction (compared to fill direction) since the spreading effect is degraded
by the pulling of the weave in the grain direction.
Since your data showed less skew in both X and Y directions while Scott's data
showed much more skew in grain direction compared to that in fill direction,
the only conclusion that I think we can arrive at is that - using a 2-ply
construction does not necessarily reduce the skew in grain direction.
Regards,
Binayak
---
Binayak Shrestha
Senior Research Engineer,
C-DOT Centre for Development of Telematics
On Thu, Jun 24, 2021 at 11:32 PM Lee Ritchey <mailto:lritchey49@xxxxxxx> wrote:
We use two ply 1067 on both sides of a centered stripline layer with
very good skew results. Both in X and Y directions.
Lee Ritchey
Speeding Edge
P.O. Box 817
Bodega Bay, CA
94923
408-781-0253
mailto:lritchey49@xxxxxxx
Worry is like a rocking chair
It keeps you busy,
but it doesn't get you anywhere.
I just took the energy it takes to get mad and wrote some blues.
Count Basie
-----Original Message-----
From: Binayak Shrestha <mailto:binayaks@xxxxxxxxx>
To: Scott McMorrow <mailto:scottmcmorrow@xxxxxxxxx>
Cc: mailto:corley@xxxxxxxxx; Lee Ritchey ;<mailto:lritchey49@xxxxxxx>;
mailto:rawilson@xxxxxxxxxxxx; Si-list ;<mailto:si-list@xxxxxxxxxxxxx>;
mailto:si-list-bounce@xxxxxxxxxxxxx
Sent: Thu, Jun 24, 2021 7:48 am
Subject: Re: [SI-LIST] Re: A new old topic - fiber weave and low loss
material
Hi Scott,
Thanks for sharing the video link. It cleared many of my doubts. I was
thinking mechanically spread glass solves the skew problem....not so after
all!
One doubt though - is there any reasonable skew mitigation by using 2-ply
dielectric construction instead of single-ply construction?
Regards,
Binayak
Warm Regards,
Binayak Shrestha
Senior Research Engineer,
C-DOT Centre for Development of Telematics
On Mon, Jun 21, 2021 at 5:54 PM Scott McMorrow
<mailto:scottmcmorrow@xxxxxxxxx>
wrote:
Spread fiber only mitigates skew for traces training in the fill
direction. Traces in the grain direction will still have skew.
https://blog.samtec.com/post/vehicle-for-insitu-glass-fabric-characterization-edi-con-2017/
On Sun, Jun 20, 2021, 11:21 PM Binayak Shrestha <mailto:binayaks@xxxxxxxxx>
wrote:
Thanks Scott and Chuck for the information.
As of now, I normally use mechanically spread glass to go around the skew
issue. In addition, to make the skew occurrence less likely, I normally
tend to go with 2 ply construction.
Thanks,
Binayak
----
Binayak Shrestha
Senior Research Engineer,
C-DOT Centre for Development of Telematics
On Sun, Jun 20, 2021 at 10:15 PM Scott McMorrow
<mailto:scottmcmorrow@xxxxxxxxx>
wrote:
Isola went through a reorganization that included limiting the number of
laminates that they would support. GigaSync was cut at that time.
GigaSync worked, but as stated, the loss was higher than we'd like as was
the Dk. Materials like this try to match the Dk of the polymer to that of
the glass, with some boundary modification also being performed where the
polymer and fibers contact. Unfortunately, glass is still fairly high Dk
when compared to the newer polymers that come in the 2.5-2.8 range. The
better bet will be to either use hybrid stackups with mixed woven and
non-woven materials, or twin-ax cable flyover technology. Ours is
guaranteed to 3.5 ps skew absolute at 6-sigma confidence. Nominal skew is
about 1 ps.
On Sun, Jun 20, 2021 at 9:58 AM Chuck Corley <mailto:corley@xxxxxxxxx> wrote:
So far we've been able to deal with fiber weave skew using a variety of
physical layout and laminate construction techniques while using the
more common existing PCB materials. It probably reduces the demand for
creating a special low skew material while we can manage to keep
continuing to do this fiber weave skew battle by using these
layout/construction techniques with existing materials.
However on the flip side, as the signal speeds continue to increase the
fiber weave skew problem becomes more difficult to handle with the
existing PCB laminates. So special materials like GigaSync may yet be
needed in the future. Perhaps the lack of low loss might be a reason
GigaSync didn't take off. Typically people with high speed signals
which are fast enough to need low fiber weave skew also need low loss.
I agree with you that some type of low loss version of GigaSync would
have been very nice to have. If such a product could also be
cost-efficient and have good manufacturability, it probably would be
hugely successful.
Chuck
---
Chuck Corley
On 2021-06-19 20:58, Binayak Shrestha wrote:
Hi Lee, Corley, and all:figures.
Few years back, Isola had come up with a dielectric in material called
GigaSync with literally no skew (though not a low loss material).
Is there any specific reason why they stopped producing it and stopped
improving it?
Life would have been so easy if a low loss version GigaSync had existed.
Thanks,
Binayak
On Tue, 8 Jun, 2021, 1:29 am Lee Ritchey,
<mailto:dmarc-noreply@xxxxxxxxxxxxx>
wrote:
Ralph,
You would be smart to do this analysis with Isola I-SPEED. It is a drop
in replacement for 23SI at a much lower cost and much better loss
In my opinion, 4000-13SI is about obsolete. I sure would not designBasie
anything new with it.
Lee RitcheySpeeding Edge
P.O. Box 817Bodega Bay, mailto:CA94923408-781-0253lritchey49@xxxxxxx
Worry is like a rocking chairIt keeps you busy, but it doesn't get you
anywhere.
I just took the energy it takes to get madand wrote some blues.Count
material
-----Original Message-----
From: Ralph Wilson <mailto:rawilson@xxxxxxxxxxxx>
To: mailto:si-list@xxxxxxxxxxxxx
Sent: Mon, Jun 7, 2021 12:56 pm
Subject: [SI-LIST] Re: A new old topic - fiber weave and low loss
for
Chuck,
We're in the architecture stage right now on this project. To define
channel
routing requirements, I've already done a "what-if" simulation using
Nelco-13-SI as a baseline.
With its loss tangent and my system constraints, I have come up with
routing guidelines that allow the channel to meet the PCIe-Gen 4 channel
specifications - just barely. I am right at the limits of allowed loss
the channel. I did a sensitivity analysis to maximize theapplication.
routing length I can allow - which is tight right now in this
Hence, my position is any material "as good as or better" than thedonâEUR(tm)t want
Nelco should work (where "as good as" generally means a loss tangent
less than or equal to). Clearly, once we have a final material
selection, have
the stackup defined and the routing is complete we will need to
resimulate to
confirm proper channel operation.
Thanks!
Ralph
On 6/7/2021 12:36 PM, Chuck Corley wrote: Hi Ralph,
There are quite a few good materials now, I would write you a list of
some of the good ones but IâEUR(tm)m not at my desk right now And I
to slight any of the great manufacturers who make these good materials.I've worked with any PCB fab house on
But I can say there are now less expensive materials that are lower loss
than the one you mentioned.
Before you start shopping for materials though, as a first step you
should probably calculate the actual loss that you are willing to
tolerate for your communication links. Once you know what amount of
loss you can tolerate over the actual worst-case trace lengths your
design will have then that will enable you to choose the right material
at the best cost. For example, If your longest traces were actually
fairly short lengths, then you might be able to use a more lossy and
less expensive PCB material for your design and still meet your signal
loss targets. Many designs have short trace runs and may not need more
expensive low loss materials.
Chuck
---
Chuck Corley
On 2021-06-07 08:48, Ralph Wilson wrote: It's been a few years since
stackups and materials for------------------------------------------------------------------
high speed SERDES routing, so I've lost track of what is in vogue and
at
the knee of the curve
in terms of cost/performance. For the current product I'm looking at
we're "only" dealing with
PCIe-Gen 4 (16Gbps). In "the old days" Nelco-13-SI on a 1080/2116 glass
was a reasonably
priced, low loss, reasonably temperature stable, reasonably flat weave
product applicable
to the 2, 4 and 10G channels of the day. What has the industry moved to
these days?
I fully expect some of yesterdays exotic materials may have become
mainstream and affordable.
What materials and glass weaves are at the knee of the cost/performance
curve today that
provide a good environment for 16-25Gbps channels?
Thanks!
Ralph Wilson
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