[SI-LIST] Re: AW: Glass-Weave Skew / Fiber-Weave Effect
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: "billh@xxxxxxxxxxxxx" <billh@xxxxxxxxxxxxx>
- Date: Fri, 5 Dec 2014 15:07:08 -0500
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 âultra-spreadâ weaves figure into your last
> paragraph? I get the âabove 28Gâ point, but have you indexed your
> approach
> to frequency? ⦠Iâm 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 Iâm looking to
> go deeper than that.
>
> Bill Hargin
> Director of North American Sales / Marketing
> Nan Ya Copper-Clad Laminates
> billh@xxxxxxxxxxxxx ⪠425-301-4425 ⪠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, MarienwerderstraÃe 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 â¦
>
> Iâm doing a bit of research on glass-weave skew / the fiber-weave effect.
> Iâve read the articles/presentations, and understand the nature of the
> beast, but Iâm interested in getting data from the design trenches.
>
> Are you (or do you believe youâve) 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 Iâm going to hear in response, but if you respond
> offline, Iâll hold the info you provide in confidence. If you reply
> publicly â I promise not to share your secrets beyond the SI-List â¦
>
> Bill Hargin
> Director of North American Sales / Marketing Nan Ya Copper-Clad Laminates
> billh@xxxxxxxxxxxxx ⪠425-301-4425 ⪠Skype: bill.hargin
>
>
>
>
>
>
>
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