[SI-LIST] AW: Re: Fiber weave effect modeling: Stack of materials ...

Hi Al,

we did some skew testboards two years ago using NELCO4000-13 2x2116 (the PCB 
house didn't have the SI-version). It had TRL structures to cover DC - 25GHz. 
When I examined the TRL structures it turned out, that on some boards the 
shortest Thru had skew that made the differential calibration impossible. I had 
to find one "good" line and use this calibration data for all boards.
I cross sectioned one of the bad boards, and yes: it was weave based! 
Based on that I would never use standard weave again. Since that day, I use 
3313 glass style available for a lot of materials (except NELCO). Today I 
prefer FR408HR, FR415, VT461 and Megtron4 Materials, and they are all available 
in flat weave.

BR
Gert


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-----Ursprüngliche Nachricht-----

Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im 
Auftrag von Al Neves
Gesendet: Mittwoch, 10. August 2011 19:02
An: 'JASON MILLER'; 'Lee Ritchey'
Cc: 'Hermann Ruckerbauer'; si-list@xxxxxxxxxxxxx
Betreff: [SI-LIST] Re: Fiber weave effect modeling: Stack of materials ...

Thanks for the informative thread!   

There is always discussion regarding non-homogeneous weave impacting skew, 
period loading (increased loss), mitigating the impact with offset designs,
etc.,    

We are designing our 28Gbpsec Channel Modeling Beta Platform and actually WANT 
LOSS (the purpose of the platform is to introduce loss, ISI, for RX tolerance, 
3D EM analysis, optimization of channels using DFE, FFE, CTLF,
etc.,) but are concerned that the weave impact, even with offsetting the 
orientation of the t-lines against the fibre weave, will impact launch 
integrity and create a virtual connector repeatability problem (we intend on 
using Molex top launch 2.4mm connectors).  

Connector repeatability is important for consistent S-parameter calibration 
(TRL, unknown THRU or SOLR, AFR, etc.,) and T-matrix de-embedding approaches 
used for the platform.

Anyone have insight into how weave impacts launch consistency, specifically
for 2116?   


Products for the Signal Integrity Practitioner
 
 
Wild River Technology LLC  
 
Alfred P. Neves
Founder - Engineer - Business Development
 (503) 718 7172 Office
(503) 679 2429 Mobile
735 South East 16th Ave.
Hillsboro, OR 97123
www.wildrivertech.com
 
 
 
 
 

 
 
 

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On 
Behalf Of JASON MILLER
Sent: Wednesday, August 10, 2011 7:37 AM
To: Lee Ritchey
Cc: Hermann Ruckerbauer; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Fiber weave effect modeling: Stack of materials ...

I just want to mention that there are other considerations when it comes to 
weave effects, such as periodic loading of the trace by the glass weave, which 
don't get simply resolved by the first approach of routing at an angle relative 
to the weave. There are a couple of papers in recent years that I am aware of 
which detailed this:
http://www.electrical-integrity.com/Paper_download_files/DC10_7-WA1_Miller-B
lando-Novak.pdf
http://www.founderpcb.com/upfile/File/2011/SI_Glassweave_Isola_DesignCon2011
%2820110727%29.pdf

On the other hand, tightening the weave or spreading out the glass fabric 
*will* improve the uniformity of the dielectric and mitigate the effect of the 
glass-weave periodic loading.

Jason Miller
Oracle


Lee Ritchey 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
>> Hermann.Ruckerbauer@xxxxxxxxxxxxx
>> Veilchenstrasse 1
>> 94554 Moos
>> Tel.: +49 (0)9938 / 902 083
>> Mobile: +49 (0)176  / 787 787 77
>> 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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>>>   >> Absender ist HARTING Electronics GmbH & Co. KG; Sitz der
>>> Gesellschaft:
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Management
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>>>   >> Alexander Rost
>>>   >> -----Ursprüngliche Nachricht-----
>>>   >>
>>>   >> 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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--
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JASON R. MILLER | PRINCIPAL HARDWARE ENGINEER
PHONE: 781.442.2774 | MOBILE: 617.548.7768
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