[SI-LIST] Re: Resedn:Mitigating PCB fiber weave effect
- From: JASON MILLER <jason.miller@xxxxxxxxxx>
- To: scott@xxxxxxxxxxxxx
- Date: Mon, 29 Oct 2012 10:04:33 -0400
Tesla
Here is the paper Scott refers to:
http://www.electrical-integrity.com/Paper_download_files/DC10_7-WA1_Miller-Blando-Novak.pdf
Jason
On Oct 28, 2012, at 10:42 AM, Scott McMorrow wrote:
> Tesla
> The information provide by the various authors is complementary. We're all
> looking at the same problem from different viewpoints. There are
> additional papers written about laminate weave crossing causing resonant
> filtering of signals, By Jason Miller of Oracle, and by some authors from
> Ansys. Much good work has been published in this area. At the moment I
> don't have the citations at my fingertips. If you want a quick and dirty
> way to control weave skew without zig-zag routing, turn you board 22.5
> degrees. This is a reasonable compromise.
>
> 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
>
>
> On Fri, Oct 26, 2012 at 6:22 PM, Loyer, Jeff <jeff.loyer@xxxxxxxxx> wrote:
>
>> Hello Tesla,
>> I think the answer you're after is in the paper, but rather hidden. I
>> apologize that this finding wasn't clearer, but there were space
>> constraints and we couldn't detail every interesting thing we found!
>>
>> In the paper, you'll find the following note:
>> "Also note that 45 degree routing is not as effective at mitigating the
>> effects as 13 degrees (see Table 2), and this might not be as effective for
>> extremely long routing lengths."
>> Table 2 then shows that a design rotated to 45 degrees reduced the max
>> skew of a 10" trace from 51ps to 11ps, while a design rotated to 12.76
>> degrees reduced it to 6ps.
>>
>> It's called out more explicitly in the PowerPoint (on slide 18), as well
>> as our suspicion of why 45 degrees isn't best, presented pictorially. We
>> hypothesize that traces on boards rotated to a large angle still have a
>> significant chance of aligning with the "knuckles" (where the weft and warp
>> intersect), thus reducing the mitigation effectiveness.
>>
>> In short, we built boards rotated at ~13 and 45 degrees, to try both
>> approaches, and found the boards rotated 45 degrees didn't mitigate the
>> effect as well. This is a bit anecdotal, but agrees with the physics as I
>> understand them. I personally would not advocate a 45 degree rotation
>> unless shown some compelling evidence of its increased effectiveness and
>> credible reasoning as to why it would be more effective.
>>
>> As far as applicability of rotation angle to the various weaves, figure 19
>> ("Angle vs. Line Length to cross 2 Bundles") was drawn for the dimensions
>> of 1080, as I recall. It indicates a rotation of 2 degrees, relative to
>> that weave, is sufficient to mitigate the effect. On top of that 2
>> degrees, we add some more rotation to account for possible skew between the
>> material and the board edge, which we believe is about 5 degrees maximum.
>> That gives us an angle of 7 degrees to ensure the effect is mitigated. We
>> believe that routing traces angled 7 degrees relative to the board edge
>> should mitigate the effect for all reasonable scenarios.
>>
>> We often actually route our traces at slightly different angles to make it
>> easier:
>> * 10 degrees is a nice round number
>> * ~11.31 degrees allows you to do angled routing but stay on the grid (if
>> you use a 1:5 or 5:1 rise/run ratio)
>>
>> My understanding is that both Cadence and Mentor Graphics tools allow easy
>> angled (and "zig-zag") routing, others may also.
>>
>> I hope this helps,
>> Jeff Loyer
>>
>> P.S.
>> If some of you get multiple copies of this, I apologize - my e-mail's gone
>> wonky today.
>>
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>> On Behalf Of Tesla
>> Sent: Thursday, October 25, 2012 10:02 PM
>> To: si-list@xxxxxxxxxxxxx; Scott McMorrow
>> Subject: [SI-LIST] Resedn:Mitigating PCB fiber weave effect
>>
>> Hi,
>>
>> Today read two two Designcon paper about PCB fiber weave effect
>> 1 The Impact of PCB Laminate Weave on the Electrical Performance of
>> Differential Signaling at Multi-Gigabit Data Rates
>> Scott McMorrow
>> 2 Fiber Weave Effect: Practical Impact Analysis and Mitigation Strategies
>> Jeff Loyer
>>
>> For the method mitigating skew by fiber weave effect. Scott suggest that
>> use-Panel construction at 45 degrees to the weave.
>> Jeff suggest that A rotation of 13 drgree is very effective at alleviating
>> the problem and A 45 degree rotation is not as effective.
>> For the two methods, which is better? Does the rotation method to reduce
>> fiber weave effect applied to all kinds of fiber weave(106,1080, 2113 and
>> so on) or different dense fiber weave may need different degrees rotation?
>>
>> Thanks.
>>
>> Tesla
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>
>
> --
>
> 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
>
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