[SI-LIST] Re: One stitching via or more vias is better for 25Gbps application???

  • From: steve weir <weirsi@xxxxxxxxxx>
  • To: Leeyuyun <lee.home.61@xxxxxxxxx>
  • Date: Mon, 08 Sep 2014 04:13:46 -0700

Low frequency: lumped capacitance, inductance, resistance.
High frequency:  Wave modes.

Steve
On 9/8/2014 12:35 AM, Leeyuyun wrote:
> Hi, Steve
> Could you help explain
>> I think that you are considering a high frequency problem in low
>> frequency terms
> I do not understand "in low frequency terms", could you help clarify it?
> How to roughly evaluate cavity effect when stitching via close to 
> signal vias?
> Any white paper or material to show stitching via effect?
> When I ask two parties to run two kinds of simulation, including only 
> one stitching vias and more stitching vias, the result from two 
> parties is different. One shows only one stitching is better, but 
> another shows more stitching vias better. How do I make decision which 
> one is correct?
> Thank you
> Lee
>
>
> steve weir <weirsi@xxxxxxxxxx <mailto:weirsi@xxxxxxxxxx>> 於 2014/9/8 
> 上午11:57 寫道:
>
>> It is neither.  It is a description of the physics.  Real engineering 
>> accounts for pertinent physics.
>>
>> Best Regards,
>>
>>
>> Steve
>> On 9/7/2014 6:41 PM, leeritchey@xxxxxxxxxxxxx wrote:
>>> This sounds like a bit of supposiition rather than real engineering.
>>>
>>> Sent from my HTC One™ X, an AT&T 4G LTE smartphone
>>>
>>> ----- Reply message -----
>>> From: "steve weir" <weirsi@xxxxxxxxxx>
>>> To: "Leeyuyun" <lee.home.61@xxxxxxxxx>
>>> Cc: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
>>> Subject: [SI-LIST] Re: One stitching via or more vias is better for 
>>> 25Gbps application???
>>> Date: Sun, Sep 7, 2014 10:43 AM
>>>
>>>
>>> I think that you are considering a high frequency problem in low
>>> frequency terms.  Stitch vias impact the cavity, and when they are in
>>> close proximity to signal vias and traces, they affect wave modes near
>>> those structures.  Thinking about stitch vias and the cavities that 
>>> they
>>> traverse as though they are continuations of the TEM path that 
>>> breaks at
>>> a Z axis transition is not a good approximation.  The Z axis signal
>>> transition injects the signal energy into the cavity.  The various
>>> properties of the cavity:  material, and geometry, including what vias
>>> stitch the cavity surfaces together and where affects how that signal
>>> energy propagates through the cavity in all directions.
>>>
>>> Steve
>>> On 9/7/2014 5:31 AM, Leeyuyun wrote:
>>> > Hi, Steve
>>> > But IL and RL should depend upon the distance / via pad size of 
>>> signal via and gnd stitching via
>>> > If only depend on capacitor vsd via, is the return path loop 
>>> larger to create large inductance?
>>> > Does it fit into 25Gbps application?
>>> > Could you advise what is the benefit of case 1 and case 2?
>>> > Thanks
>>> > Lee
>>> >
>>> >
>>> >> steve weir <weirsi@xxxxxxxxxx> 於 2014/9/7 下午6:11 寫道:
>>> >>
>>> >> The statement is based on the idea that Vss stitching from bypass
>>> >> capacitor Vss vias and IC Vss vias is adequate.  The idea 
>>> concludes that
>>> >> explicit vias corresponding to signal or signal pair transitions 
>>> are not
>>> >> necessary.
>>> >>
>>> >> Steve
>>> >>> On 9/7/2014 2:46 AM, Leeyuyun wrote:
>>> >>> Stitching should be needed when gnd reference plane change
>>> >>> I do not know why you said do not need any stitching vias
>>> >>> I want to clarify my question as below
>>> >>> # means stitching vias, * means signal vias, + means positive 
>>> signal, - means negative signal
>>> >>> 1. Only on stitching vias
>>> >>> +++++++++++++++++*++++++++++
>>> >>>                                    #
>>> >>> --------------------------*----------------
>>> >>> 2. At least two stitching vias
>>> >>>                                   #
>>> >>> ++++++++++++++++*+++++++++++
>>> >>>
>>> >>> ------------------------*------------------
>>> >>>                                   #
>>> >>> For each structure, what is theory behind? What is your 
>>> recommendation for stitching via structure in the 25Gbps structure?
>>> >>>
>>> >>>> "Lee " <leeritchey@xxxxxxxxxxxxx> 於 2014/9/7 上午3:17 寫道:
>>> >>>>
>>> >>>> No stitching vias are needed.  Where did this idea get started?
>>> >>>>
>>> >>>> -----Original Message----- From: Leeyuyun
>>> >>>> Sent: Saturday, September 06, 2014 4:25 AM
>>> >>>> To: si-list@xxxxxxxxxxxxx
>>> >>>> Cc: lee.home.61@xxxxxxxxx
>>> >>>> Subject: [SI-LIST] One stitching via or more vias is better for 
>>> 25Gbps application???
>>> >>>>
>>> >>>> Hi, all
>>> >>>> I am doing 100Gbps (4x25Gps) product now
>>> >>>> How do we put stitching vias when high speed signal change the 
>>> layer?
>>> >>>> This is a differential pair, which has P and N
>>> >>>> Someone told me that one stitching vias is better because P and 
>>> N share the common return
>>> >>>> Someone told me that more stitching vias is better because loop 
>>> inductance could be reduced more
>>> >>>> I am confused which one is better?
>>> >>>> Can anyone help me?
>>> >>>> Thanks, 
>>> Lee------------------------------------------------------------------
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>>> >>
>>> >> --
>>> >> Steve Weir
>>> >> IPBLOX, LLC
>>> >> 1580 Grand Point Way
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>>>
>>> -- 
>>> Steve Weir
>>> IPBLOX, LLC
>>> 1580 Grand Point Way
>>> MS 34689
>>> Reno, NV  89523-9998
>>> www.ipblox.com
>>>
>>> (775) 299-4236 Business
>>> (866) 675-4630 Toll-free
>>> (707) 780-1951 Fax
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>>> All contents Copyright (c)2013 IPBLOX, LLC.  All Rights Reserved.
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>>
>>
>> -- 
>> Steve Weir
>> IPBLOX, LLC
>> 1580 Grand Point Way
>> MS 34689
>> Reno, NV  89523-9998
>> www.ipblox.com
>>
>> (775) 299-4236 Business
>> (866) 675-4630 Toll-free
>> (707) 780-1951 Fax
>>
>> All contents Copyright (c)2013 IPBLOX, LLC.  All Rights Reserved.
>> This e-mail may contain confidential material.
>> If you are not the intended recipient, please destroy all records
>> and notify the sender.


-- 
Steve Weir
IPBLOX, LLC
1580 Grand Point Way
MS 34689
Reno, NV  89523-9998
www.ipblox.com

(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax

All contents Copyright (c)2013 IPBLOX, LLC.  All Rights Reserved.
This e-mail may contain confidential material.
If you are not the intended recipient, please destroy all records
and notify the sender.



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