FreeLists / si-list / [SI-LIST] Re: fiber-weave effect alive and well?

[Scott McMorrow <scott@xxxxxxxxxxxxx>]

Perry
Fiber-weave effects are alive and well, and IMO should be considered by 
every designer concerned with 6 Gbps or higher differential serial data 
communications channels on PCBs, backplanes, and single-ended skew 
controlled parallel buses.  Jeff's paper is real life, building upon 
about 5 years of good research at Intel.  The method that is used is 
quite valid and will be seen in real designs.  The Intel research is 
able to better characterize weave skew using physical nyquist sampling 
techniques.  Yes, with different trace jogs you will see all sorts of 
potential alignments, but in the worst case you will still find that 
traces can have significant lengths of worst case fiber weave 
alignment.  If you are trying to design systems with 1000's of 
differential pairs, there is a statistical certainty that one or more of 
those pairs will have skew close to the absolute worst case, if not 
designed to compensate for laminate weave anisotropy.

The problem is most pronounced with weaves that have large holes without 
fiber in the weave pattern, but you will also see issues with core 
materials that are often constructed with large diameter fibers, like 
7628 material. The fiberglass the Lee proposes to use does have some 
benefits, however, it does not totally eliminate the fiber weave 
problem.  It reduces it to a lower level.  Unfortunately, it is not a 
widely manufactured laminate weave.

There are patented techniques for improving weave-induced skew, which 
must be licensed.  There are also some non-patented techniques, which 
may also be used that are not quite as effective as the patented 
techniques, but nevertheless can be used to design robust systems.  
There is also some silicon IP that can be used to automatically 
compensate for skew, and is finding it's way into test instrumentation.


regards,

Scott

Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax

http://www.teraspeed.com

Teraspeed® is the registered service mark of
Teraspeed Consulting Group LLC



QU Perry wrote:
> I would be interested to see a link as well.
>
> Jeff's paper on DesignCon2007 is convincing to me that this is something
> we need to pay attention. Real life design will probably not be as bad
> as the theoretical estimate since most of the diff pair routing we have
> on the PCB is not likely to run a long length non-stop in parallel with
> edge. The "jog" as is called in the paper is very common due to vias etc
> and pretty random.
>
> Also from the data we got from PCB vendor, it appears that thinner
> dielectric substrate the worse fibre weave effect as the gap between the
> fiber is larger. Has this been looked at ?
>
> Regards
>
> Perry
>
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=20
>
> Perry Qu=20
>
> Design & Qualification, Alcatel-Lucent Canada Inc.
>
> 600 March Road, Ottawa ON, K2K 2E6, Canada=20
>
> DID: 613-7846720  Fax: 613-5993642=20
>
> Email: perry.qu@xxxxxxxxxxxxxxxxxx=20
>
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=20
>
> =20
>
>   
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx=20
>> [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of=20
>> Aubrey_Sparkman@xxxxxxxx
>> Sent: Friday, September 14, 2007 1:59 PM
>> To: leeritchey@xxxxxxxxxxxxx; rdudek@xxxxxxxxxxxxxxx;=20
>> si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] Re: fiber-weave effect alive and well?
>> =20
>> Would you like to share a link?=3D20
>> =20
>> =20
>> Aubrey Sparkman=3D20
>> Enterprise Engineering Signal Integrity Team=3D20 Dell, Inc.=3D20=20
>> Aubrey_Sparkman@xxxxxxxx=3D20
>> (512) 723-3592=3D20
>> "Discovery consists of seeing what everybody has seen and=20
>> thinking what nobody else has thought." - Jonathan Swift
>> =20
>> =20
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx=20
>> [mailto:si-list-bounce@xxxxxxxxxxxxx]
>> On Behalf Of Lee Ritchey
>> Sent: Friday, September 14, 2007 11:36 AM
>> To: Russell S. Dudek Jr.; si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] Re: fiber-weave effect alive and well?
>> =20
>> We already have a glass weave solution.  Check my column in=20
>> the April issue of Circuitree magazine.
>> =20
>> Lee Ritchey
>> =20
>> =20
>>     
>>> [Original Message]
>>> From: Russell S. Dudek Jr. <rdudek@xxxxxxxxxxxxxxx>
>>> To: <si-list@xxxxxxxxxxxxx>
>>> Date: 9/12/2007 1:10:28 PM
>>> Subject: [SI-LIST] Re: fiber-weave effect alive and well?
>>>
>>> Steve,
>>> =3D20
>>> I agree, Fiber Weave Effect (FEW) has most certainly been=20
>>>       
>> confirmed by
>> such
>>     
>>> research.  However, there is a new change in the wind.  I=20
>>>       
>> have the=3D20=20
>>     
>>> unique opportunity, as a technical liaison, to enable a=20
>>>       
>> technology=3D20=20
>>     
>>> that may put
>>>       
>> an
>>     
>>> end to FWE as a consideration in high-speed designs.  We=20
>>>       
>> all know that
>> =20
>>     
>>> the crux of the matter is the glass weave and its effect on=20
>>>       
>> localized
>> Er.
>>     
>>> Either get ride of the reinforcement layer completely or more=3D20=20
>>> challenging change the fundamentals of the glass weave fabrication
>>>       
>> process (GWFP).
>>     
>>> =3D20
>>> We have taken the more challenging (and fun) approach and have=20
>>> rocked=3D20 the fundamentals the GWFP.  I cannot disclose much the=20
>>> specifics of=3D20 the technology and our partners in such an=20
>>>       
>> open forum. =20
>>     
>>> However, if=3D20 you are interested learning more feel free=20
>>>       
>> to contact=20
>>     
>>> me and we can=3D20 get the proper NDAs in place to facilitate=20
>>>       
>> such a discussion.
>>     
>>> =3D20
>>> RD
>>> =3D20
>>> Russell Dudek
>>> Technology Specialist
>>> Compunetics, Inc.
>>> 700 Seco Road
>>> Monroeville, PA 15146
>>> 412-858-6264
>>> rdudek@xxxxxxxxxxxxxxx
>>> www.compunetics.com <http://www.compunetics.com/> =3D20
>>>
>>> To see where no one notices the contrast of white on white is =
>>>       
> an=3D20=20
>   
>>> indispensable virtue of infinite potential.
>>>
>>> =3D20
>>>
>>>
>>>
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