[SI-LIST] Re: AW: Glass-Weave Skew / Fiber-Weave Effect

  • From: "Lee " <leeritchey@xxxxxxxxxxxxx>
  • To: <rdawson16@xxxxxxxxxxx>, <billh@xxxxxxxxxxxxx>, <scott@xxxxxxxxxxxxx>
  • Date: Fri, 5 Dec 2014 14:38:41 -0800

The Intel method works if you have a limited number of paths to engineer. 
It is tough to use on a large switch or router with hundreds or thousands of 
paths.

I have struggled with the "how to measure glass spread with respect to skew 
problems" and have not found an answer that I could bet money on.  Instead, 
I am working on materials that are w eave independent.  I think I have found 
some.  Time will tell!

As a rule, Scott an my clients have to be "Right the First Time".  Sound 
familiar?

-----Original Message----- 
From: Randy Dawson
Sent: Friday, December 05, 2014 12:53 PM
To: billh@xxxxxxxxxxxxx ; scott@xxxxxxxxxxxxx
Cc: 'Havermann, Gert' ; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: AW: Glass-Weave Skew / Fiber-Weave Effect

Bill - what are people out there doing, you ask.
One clever solution I am aware of is Intel processors, and NorthBridge 
SouthBridge interfaces (I/O and memory)
The diff pair lanes to these devices are redundant, and I believe there is 
some auto - equalization also incorporated into the driver receiver pairs.
At initialization, the processor selects the valid lanes, and casts out 
those with SI problems.
This keeps the board cost low, using inexpensive material.
Randy Dawson

> From: billh@xxxxxxxxxxxxx
> To: scott@xxxxxxxxxxxxx
> CC: Gert.Havermann@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: AW: Glass-Weave Skew / Fiber-Weave Effect
> Date: Sat, 6 Dec 2014 04:21:39 +0800
>
> Hi Scott:
>
>  That was intended as an open-ended question aimed at "what are people 
> doing?" ... And, "do you index your approach to frequency and cost?"
>
> I thought that if I threw out an example, I might get an answer 
> more-closely aligned with my thought process.
>
> Bill Hargin
> 425-301-4425
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] 
> On Behalf Of Scott McMorrow
> Sent: Saturday, December 6, 2014 4:07 AM
> To: billh@xxxxxxxxxxxxx
> Cc: Havermann, Gert; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: AW: Glass-Weave Skew / Fiber-Weave Effect
>
> bill
> you need to define what an "ultra spread weave" is?
>
>
> Scott McMorrow
> Teraspeed® Consulting - A Division of Samtec
> 16 Stormy Brook Rd
> Falmouth, ME 04105
> (401) 284-1827 Business
> http://www.teraspeed.com
>
> On Fri, Dec 5, 2014 at 3:03 PM, Bill Hargin (Nan Ya, USA) < 
> billh@xxxxxxxxxxxxx> wrote:
>
> > Thanks, Gert/Scott.
> >
> > Question for Scott: How would “ultra-spread” weaves figure into
> > your last paragraph?  I get the “above 28G” point, but have you
> > indexed your approach to frequency? … I’m seeing a potential 
> > Cost/Loss continuum here.
> >
> > Something like:
> > > 3 Gbps, use spread weave*
> > > 10 Gbps, use ultra-spread weave*  (?)
> > > 20 Gbps, use homogeneous resin/glass*  (?)
> >
> > * Or some form of trace rotation.
> >
> > As a follow-on question (for anyone):  As resin-windows narrow toward
> > a lower limit (i.e., with spread glass), how do you deal with resin 
> > flow?
> > Obviously, you use the highest resin content possible, but I’m
> > looking to go deeper than that.
> >
> > Bill Hargin
> > Director of North American Sales / Marketing Nan Ya Copper-Clad
> > Laminates
> > billh@xxxxxxxxxxxxx   â–ª  425-301-4425  â–ª  Skype: bill.hargin
> >
> >
> >
> >
> >
> > From: Scott McMorrow [mailto:scott@xxxxxxxxxxxxx]
> > Sent: Friday, December 5, 2014 9:42 PM
> > To: Havermann, Gert
> > Cc: billh@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> > Subject: Re: [SI-LIST] AW: Glass-Weave Skew / Fiber-Weave Effect
> >
> > Gert,
> >
> > Even flat weaves have skew, as easily evidenced by a picture of the
> > weave that shows gaps in the overlap of fiber bundles in one direction.
> >
> > I've found that the killer problem is skew on line cards causing diff
> > to common mode conversion that bursts as crosstalk within connector
> > PTH via fields and connectors themselves, which are not designed to
> > control common modes.  This was seen specifically in a significant
> > loss of NEXT margin at receivers from Tx or Rx card skew causing
> > excessive crosstalk in the connector pin fields for a well-known
> > standard. This required two solutions, one was to guardband margin to
> > allow for the additional skew caused NEXT.  The other was to use some 
> > skew abatement methods.
> >
> > Doing 1000's of sensitivity runs I've found that this skew sensitivity
> > is much worse on cards than it is on backplanes.  That is, the card
> > skew allowance has much less tolerance than does the backplane or
> > total end-to-end skew.  Where the skew is located is much more
> > important than how much skew there is.
> >
> > To put some numbers to this phenomena, a 10G link had 12 ps of skew,
> > which translates to around -0.7 dB of additional insertion loss.  That
> > is generally not a serious issue for 99.9% of all designs.  However
> > when the effective loss due to crosstalk was factored in, due to diff
> > to common mode and common mode to diff conversion, total additional eye 
> > loss was -3.9 dB.
> > which is a huge impairment.
> >
> > In the end, the only solution for skew, especially at 28G rates and
> > above, is to utilize special techniques to mitigate skew on
> > backplanes, and skew-free materials on cards.  I've measured and
> > characterized dozens of materials and can say that I can easily
> > demonstrate the potential for any woven PCB laminate to have
> > significant skew, even those with spread weaves, except for those
> > laminates that are specifically engineered for zero-skew with matched 
> > glass and resin dielectric constants.
> >
> > Regards,
> >
> > Scott
> >
> >
> > Scott McMorrow
> > Teraspeed® Consulting - A Division of Samtec
> > 16 Stormy Brook Rd
> > Falmouth, ME 04105
> > (401) 284-1827 Business
> > http://www.teraspeed.com
> >
> > On Fri, Dec 5, 2014 at 3:29 AM, Havermann, Gert <
> > Gert.Havermann@xxxxxxxxxxx> wrote:
> > Hi Bill,
> > I've seen it quite often, but I never seen it killing System
> > performance as we work with good margin, and the Silicon accepts even
> > more skew that expected.
> > One Design was not usable due to weave effect skew. It was a TRL
> > Cal.Stucture where the shortest line hat skew exceeding the Phase
> > difference. After that I redesigned with different Material and flat
> > weave Glass, and that worked great.
> >
> > BR
> > Gert
> >
> >
> > ----------------------------------------
> > Absender ist HARTING Electronics GmbH, Marienwerderstraße 3, D-32339
> > Espelkamp; Registergericht: Amtsgericht Bad Oeynhausen; Register-Nr.:
> > HRB 8808; Vertretungsberechtigte Geschäftsführer: Dipl.-Kfm.
> > Edgar-Peter Düning, Dipl.-Ing. Torsten Ratzmann,
> > Dipl.-Wirtschaftsing. Ralf Martin Klein
> >
> > -----Ursprüngliche Nachricht-----
> > Von: si-list-bounce@xxxxxxxxxxxxx
> > [mailto:si-list-bounce@xxxxxxxxxxxxx]
> > Im Auftrag von Bill Hargin (Nan Ya, USA)
> > Gesendet: Freitag, 5. Dezember 2014 06:04
> > An: si-list@xxxxxxxxxxxxx
> > Betreff: [SI-LIST] Glass-Weave Skew / Fiber-Weave Effect
> >
> > Hi Folks …
> >
> > I’m doing a bit of research on glass-weave skew / the fiber-weave 
> > effect.
> > I’ve read the articles/presentations, and understand the nature of
> > the beast, but I’m interested in getting data from the design 
> > trenches.
> >
> > Are you (or do you believe you’ve) seen it in your designs?  What
> > happened, and how did you resolve it?  (E.g., angled routing, low-Dk
> > glass, homogeneous resin/glass, etc.)  What were the characteristics
> > of the material and signals?
> >
> > I have no idea what I’m going to hear in response, but if you
> > respond offline, I’ll hold the info you provide in confidence.  If
> > you reply publicly – I promise not to share your secrets beyond the
> > SI-List …
> >
> > Bill Hargin
> > Director of North American Sales / Marketing Nan Ya Copper-Clad 
> > Laminates
> > billh@xxxxxxxxxxxxx   â–ª  425-301-4425  â–ª  Skype: bill.hargin
> >
> >
> >
> >
> >
> >
> >
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