[SI-LIST] Re: Fiber weave effect modeling: Stack of materials ...
- From: Michael Greim <mgreim001@xxxxxxxxx>
- To: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
- Date: Tue, 9 Aug 2011 17:04:01 -0400
Hi Lee,
Do you have a link to this paper? Thanks.
-Michael.
And all this science they don't understand
Is just my job six days a week.....
We will either find a way or make one -Hannibal
In the middle of every difficulty lies opportunity -Al Einstein
On Tue, Aug 9, 2011 at 4:48 PM, Lee Ritchey <leeritchey@xxxxxxxxxxxxx>wrote:
> I've been on vacation, so come late to this discussion. There are three
> glass weaves that are irregular enough to cause skew problems with
> differential pairs as has been shown in papers presented at DesignCon.
> These are 106 ,1080 and 7628. We've tried various ways of nesting multiple
> plies of these to avoid this problem. Doesn't seem to work all that well.
>
> There are some very simple fixes. One is to route the PCB traces at an
> angle
> to the weave or cock the PCB on the fabrication panel. Both work, but are
> either a hassle or expensive.
>
> A much simpler approach is to use a glass weave with uniformly distributed
> glass. These are readily available. 1067 replaces 106. 1086 replaces
> 1080. 3313 in two plies replaces 7628.
>
> We've done many tests and demonstrated that the skew problem goes away with
> the use of these weaves. I've got a paper that shows the difference
> between
> 1080 and 3313. It is dramatic!
>
> Lee
>
>
> --------------------------------------------------
> From: "Hermann Ruckerbauer" <hermann.ruckerbauer@xxxxxxxxxxxxx>
> Sent: Friday, August 05, 2011 1:44 AM
> To: <si-list@xxxxxxxxxxxxx>
> Subject: [SI-LIST] Fiber weave effect modeling: Stack of materials ...
>
> > Hello *,
> >
> > the original thread is already old, but I would have one more question
> > on this one:
> > Will stacks of multiple materials statistically help to reduce the effect
> > ?
> >
> > "Standard" 1080 looks not too good, but if 2x or 3x 1080 is stacked this
> > could statistically reduce the effect.
> > I would not expect that material production and manufacturing is so
> > accurate that a stack of 3 material will result that always the same
> > structures are overlayed.
> > I would more expect, that there might be a statistical distribution for
> > High volume manufacturing where a part of the final boards will have
> > this worst case, and on other there will be a statistical distribution
> > of different combinations how the materials are overlayed in the stack.
> >
> > Does anybody have more than a feeling on this assumption ?
> >
> > Thanks and regards
> >
> > Hermann
> >
> > EKH - EyeKnowHow
> > Hermann Ruckerbauer
> > www.EyeKnowHow.de <http://www.eyeknowhow.de/>
> > Hermann.Ruckerbauer@xxxxxxxxxxxxx
> > Veilchenstrasse 1
> > 94554 Moos
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> > 77<%2B49%20%280%29176%20%20%2F%20787%20787%2077>
> > Fax: +49 (0)3212 / 121 9008
> >
> >
> > schrieb Lee Ritchey:
> >> The 1086 weave used in laser drilled PCBs is the replacement for 1080
> and
> >> the 1067 weave is the replacement for 106 weave. They both look like
> the
> >> Nova product and are not subject to patents or single sourcing. 3313 is
> >> similar and yields a 4 mil core using a single ply of glass.
> >>
> >> From: bala
> >> Sent: Tuesday, January 18, 2011 12:42 AM
> >> To: Lenkisch, Andreas
> >> Cc: Lee Ritchey ; Loyer, Jeff ; si-list@xxxxxxxxxxxxx
> >> Subject: Re: [SI-LIST] AW: Re: AW: Fiber weave effect modeling
> >>
> >>
> >> http://bethesignal.net/blog/?pB
> >>
> >>
> >> On Tue, Jan 18, 2011 at 2:00 PM, Lenkisch, Andreas
> >> <Andreas.Lenkisch@xxxxxxxxxxx> wrote:
> >>
> >> that's really strange, I got the feedback from the PCB shop (Europe)
> >> that this material is "quite expensive" (about two times more than
> >> traditional glass weave). The answer is already half a year old. I will
> >> ask again.
> >>
> >> Andreas
> >>
> >>
> >>
> >> -----Ursprüngliche Nachricht-----
> >> Von: si-list-bounce@xxxxxxxxxxxxx [mailto:
> si-list-bounce@xxxxxxxxxxxxx]
> >> Im Auftrag von Lee Ritchey
> >> Gesendet: Montag, 17. Januar 2011 19:42
> >> An: Loyer, Jeff; si-list@xxxxxxxxxxxxx
> >> Betreff: [SI-LIST] Re: AW: Fiber weave effect modeling
> >>
> >>
> >> One thing I forgot to mention in my last response was that the reason
> >> we
> >> switched to 3313 weave was cost reduction, not signal integrity.
> Prior
> >> to
> >> this material becoming available we achieved 4 mil cores using two
> >> plies of
> >> glass cloth. Our fabricator suggested we switch to 3313 and achieve a
> >> lower
> >> price. I'm not sure why some fabricators would suggest the PCB would
> >> cost
> >> more.
> >>
> >> In the bargain, we got the flat weave and much better impedance
> >> profiles as
> >> well as far lower differential skew.
> >>
> >> My guess is you won't get the new weaves unless you insist on them.
> >> Fabricators don't like to expand their inventories unless they are
> >> forced
> >> to. Guess that is like all manufacturers!
> >>
> >> --------------------------------------------------
> >> From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
> >> Sent: Thursday, January 13, 2011 1:31 PM
> >> To: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> >> Subject: [SI-LIST] Re: AW: Fiber weave effect modeling
> >>
> >> > I don't think the elimination of standard weaves is straightforward.
> >> I
> >> > wholeheartedly agree that "flat" weaves exist and are a very
> >> attractive
> >> > solution but, at the time we wrote our paper, they cost about 2x
> that
> >> of
> >> > standard material. I don't know if the difference is still that
> >> high, but
> >> > I doubt it's insignificant.
> >> > For many designs, the cost differential is outweighed by the
> >> benefits.
> >> > For others, it is not. 10 degree routing, ugly as it may appear and
> >> as
> >> > time consuming as it is, can be attractive if it saves significant
> >> money.
> >> >
> >> > On the other hand...
> >> > There may soon come a point where bus speeds increase such that it
> is
> >> > impossible to avoid routing parallel to the board edge for
> >> problematic
> >> > distances. At that point, flat weaves will be a more palatable
> >> option.
> >> > For instance, just breaking out of a large device plus routing into
> a
> >> > connector might require 2" of length that can't be angled. For a
> >> 40GT/s
> >> > bus, that's probably unacceptable. Then, the choice gets clearer.
> >> >
> >> > For now, many of us are in the grey area where the option of using
> >> flat
> >> > weaves, and getting rid of our funky angled routing, isn't
> clear-cut.
> >> >
> >> > Jeff Loyer
> >> >
> >> >
> >> > -----Original Message-----
> >> > From: si-list-bounce@xxxxxxxxxxxxx
> >> [mailto:si-list-bounce@xxxxxxxxxxxxx]
> >> > On Behalf Of Lee Ritchey
> >> > Sent: Thursday, January 13, 2011 10:22 AM
> >> > To: Havermann, Gert; si-list@xxxxxxxxxxxxx
> >> > Subject: [SI-LIST] Re: AW: Fiber weave effect modeling
> >> >
> >> > I recommend you use neither of those weaves with high speed serial
> >> links
> >> > due
> >> > to there negative effect on skew. The best weaves are known as
> >> "flat"
> >> > weaves. The best are 1067 (replaces 106), 1086 (replaces 1080),
> 2113
> >> and
> >> > 3313. These are so uniform you don't need to worry about weave
> >> effects.
> >> > These weaves were developed to make laser drilling blind vias more
> >> uniform
> >> > and happen to be great for SI purposes!
> >> >
> >> > You also don't need to route your PCBs on a 15 degree angle to the
> >> weaves,
> >> > which is painful to do and wastes materials, so long as you stick
> >> with the
> >> > weaves listed above.
> >> >
> >> > Lee Ritchey
> >> >
> >> > --------------------------------------------------
> >> > From: "Havermann, Gert" <Gert.Havermann@xxxxxxxxxxx>
> >> > Sent: Wednesday, January 12, 2011 6:31 AM
> >> > To: <si-list@xxxxxxxxxxxxx>
> >> > Subject: [SI-LIST] AW: Fiber weave effect modeling
> >> >
> >> >> this is a great paper, many thanks for sharing it with the si-list.
> >> >>
> >> >> please allow me a question. I understand that the 106 and 7628
> >> Prepregs
> >> >> are used to predict the dk values of "pure epoxy" and "close
> >> proximity to
> >> >> the Glass bundle".
> >> >> Do you think that the "pure epoxy" value is always the worst case
> >> that I
> >> >> have to expect for my diff pair? If I (for instance) would only use
> >> 7628
> >> >> Style everywhere, will there even be areas "in pure epoxy", or is
> >> the
> >> >> weave dense enough that the worst dk is somewhere between the
> >> calculated
> >> >> min. and max. value?
> >> >>
> >> >> BR
> >> >> Gert
> >> >>
> >> >>
> >> >>
> --------------------------------------------------------------------------
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> >> >>
> >> >> Von: si-list-bounce@xxxxxxxxxxxxx
> >> [mailto:si-list-bounce@xxxxxxxxxxxxx]
> >> >> Im
> >> >> Auftrag von Bert Simonovich
> >> >> Gesendet: Freitag, 7. Januar 2011 21:55
> >> >> An: si-list@xxxxxxxxxxxxx
> >> >> Betreff: [SI-LIST] Fiber weave effect modeling
> >> >>
> >> >> Hi all,
> >> >>
> >> >> Recently there were discussions on PCB fiber weave effect. I
> >> recently did
> >> >> a study and published a White Paper titled, "Practical Fiber Weave
> >> Effect
> >> >> Modeling".
> >> >>
> >> >> Abstract:
> >> >> Fiber weave effect is becoming more of an issue as bit rates
> >> continue to
> >> >> sore upwards to 5GB/s and beyond. Due to the non-homogenous nature
> >> of
> >> >> printed circuit board laminates, the fiberglass weave pattern
> causes
> >> >> signals to propagate at different speeds within differential pair
> >> traces;
> >> >> causing timing skew and mode conversion at the receiver; leading to
> >> >> reduced bit-error-rate (BER) performance; and increased EMI
> >> radiation.
> >> >> The
> >> >> relative dielectric constant (Dk) surrounding a trace ultimately
> >> >> determines its propagation delay. This paper delves into the issue
> >> and
> >> >> presents a novel approach to practically establish worst case
> >> min/max
> >> >> values for Dk and use them to model this effect using ADS circuit
> >> >> modeling
> >> >> software. A PCIe CEM
> >> >> Rev2 case study is used to practically demonstrate the model and to
> >> >> explore the design space.
> >> >>
> >> >> Here is the link: http://lamsimenterprises.com/White_Papers.html
> >> >>
> >> >> Thanks to Jeff Loyer, Istvan Novak and Gustavo Blando for there
> help
> >> in
> >> >> clarifying some results of their prior published work on the
> >> subject.
> >> >>
> >> >> I hope you find it useful.
> >> >>
> >> >> -Bert
> >> >>
> >> >> Lambert (Bert) Simonovich
> >> >> Consultant and Founder
> >> >> LAMSIM Enterprises Inc.
> >> >> Web Site: http://lamsimenterprises.com
> >> >> Blog: http://blog.lamsimenterprises.com/
> >> >>
> >> >>
> >> >>
> >> >>
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Best Regards,
Michael C. Greim
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