[SI-LIST] Re: Impedance Controlled Board Production Vs Normal Board Production

  • From: Scott McMorrow <scott@xxxxxxxxxxxxx>
  • To: Rajan Hansa <all.si.list@xxxxxxxxx>
  • Date: Fri, 06 Jan 2012 09:44:30 -0500

+/- 10% of what nominal baseline impedance?




Scott McMorrow
Teraspeed Consulting Group LLC
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On 1/6/2012 2:45 AM, Rajan Hansa wrote:
> guys don't you think that if impedance variation is under 10 % then we
> shouldn't worry much about it.
> My analogy is that for 10 % impedance variation return loss is more than
> -20 db and effect of this return loss is less than 0.5 db on insertion loss
> which is quite acceptable when we compare it with losses due to attenuation
> on  insertion loss.
>
> Correct me if i am wrong or am I missing something ???
>
>
> On Fri, Jan 6, 2012 at 3:51 AM, David Siadat 
> (dsiadat)<dsiadat@xxxxxxxxx>wrote:
>
>> I agree with Aubrey's statement.
>> If you do not specify Impedance Control design (possibly for each
>> layer), then traces on the layer with not enough copper material will
>> have more than +/-10% impedance variations even if you specified its
>> characteristic impedance in your request!
>>
>> -David
>>
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>>   On Behalf Of Aubrey K Sparkman
>> Sent: Thursday, January 05, 2012 11:49 AM
>> To: Michael Greim
>> Cc: Ken Cantrell; Mikhail Matusov; si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] Re: Impedance Controlled Board Production Vs Normal
>> Board Production
>>
>> Michael,
>>
>> A fab house only has to meet the specifications in the contract.  I
>> would
>> say the company got what they specified.
>>
>> My point was that an impedance only specification is often inadequate.
>>
>>
>> Aubrey
>>
>> On 1/5/12 1:16 PM, "Michael Greim"<mgreim001@xxxxxxxxx>  wrote:
>>
>>> There needs to be an interlock between the fab house and
>>> design team.  If different construction methods are employed
>>> and they aren't checked then offending engineer is really getting
>>> what they deserve.  Check twice, or more, and cut once is
>>> a lesson often learned quite painfully.
>>> -Michael
>>>
>>> On Thu, Jan 5, 2012 at 10:27 AM, Aubrey K Sparkman<
>>> asparky@xxxxxxxxxxxxxxxxxxxxxxxx>  wrote:
>>>
>>>> Ken,
>>>>
>>>> What you say is true.   What hasn't been mentioned is the risk behind
>>>> specifying only the impedance.
>>>>
>>>> Mikhail makes a good point about specifying the board stackup
>>>> CONSTRUCTION.  I have seen failures when impedance only was
>> specified.
>>>> The design went out as a dual stripline with 4 mil cores between the
>>>> signals and their respective reference planes and a 12 mil prepreg
>>>> between
>>>> the two signal layers.  The pcb house was given permission to use 5
>> mil
>>>> cores since they didn't have 4 mil cores in stock.  For the 2nd
>> build,
>>>> the
>>>> pcb house outsourced the design to another house which used 8 mil
>> cores.
>>>> Trace widths and prepreg thickness were adjusted appropriately so
>> that
>>>> both board thickness and impedance specifications were met.
>>>>
>>>> Any guesses about the performance of the boards in the 2nd build?
>>>>
>>>> Aubrey Sparkman
>>>> SparkRight Solutions
>>>>
>>>> On 1/5/12 10:36 AM, "Ken Cantrell"<Ken.Cantrell@xxxxxxxxxxxxxxxx>
>>>> wrote:
>>>>
>>>>> Mikhail,
>>>>> I'm not disputing anything that you said, just pointing out that:
>>>>> "If I, as a designer, know the process and materials used by the
>>>>> particular
>>>>> manufacturer
>>>>> well enough" is a big If.  That's a mature designer talking.  Not
>>>>> something
>>>>> a relative beginner would know or even be able to accomplish.
>>>>>
>>>>> 2cents
>>>>> Ken
>>>>>
>>>>> -----Original Message-----
>>>>> From: si-list-bounce@xxxxxxxxxxxxx
>>>>> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Mikhail Matusov
>>>>> Sent: Thursday, January 05, 2012 9:05 AM
>>>>> To: si-list@xxxxxxxxxxxxx
>>>>> Subject: [SI-LIST] Re: Impedance Controlled Board Production Vs
>> Normal
>>>>> Board Production
>>>>>
>>>>>
>>>>> I don't think those who responded understood the question correctly.
>> I
>>>>> think
>>>>> the OP was asking whether some degree of impedance control can be
>>>> achieved
>>>>> by precisely specifying the board's stackup, width of the traces,
>> and
>>>>> process tolerances without explicitly asking the manufacturer to
>>>> control
>>>>> impedance. For some applications it just boils down to the cost. If
>> I,
>>>> as
>>>>> a
>>>>> designer, know the process and materials used by the particular
>>>>> manufacturer
>>>>> well enough I should be able to specify the board in such a way that
>>>> the
>>>>> impedance will end up in  the right ballpark. In fact, I use this
>>>> method
>>>>> for
>>>>> non-critical designs.
>>>>>
>>>>> =======================
>>>>> Mikhail Matusov
>>>>> Senior Hardware Design Engineer
>>>>> Square Peg Communications
>>>>> Tel.: +1 (613) 271-0044 ext.231
>>>>> Fax: +1 (613) 271-3007
>>>>> http://www.squarepeg.ca
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> ----- Original Message -----
>>>>> From: "Loyer, Jeff"<jeff.loyer@xxxxxxxxx>
>>>>> To:<si-list@xxxxxxxxxxxxx>
>>>>> Sent: Thursday, January 05, 2012 10:22 AM
>>>>> Subject: [SI-LIST] Re: Impedance Controlled Board Production Vs
>> Normal
>>>>> Board
>>>>> Production
>>>>>
>>>>>
>>>>>> Perhaps I'm the only one who is finding it ironic that, on a
>> "Signal
>>>>>> Integrity" reflector list, "Impedance Controlled" isn't considered
>>>>>> "Normal".  I haven't had the luxury of not specifying impedance
>>>> control
>>>>>> since a small 33MHz PCI card design, many years ago.
>>>>>>
>>>>>> I'm afraid Jayasuryan that you won't find the answer you're
>> looking
>>>> for
>>>>>> on
>>>>>> an e-mail thread, or it is going to be a long, drawn out, painful
>>>>>> affair.
>>>>>> You have a lot of work to do to understand what impedance control
>> is
>>>> and
>>>>>> how it relates to signal integrity.  I would recommend starting
>> with
>>>> the
>>>>>> books that have been listed many times on this list.  You can also
>>>>>> search
>>>>>> the archives for "impedance control" to find discussions about
>>>> different
>>>>>> opinions on how much is enough.
>>>>>>
>>>>>> Good luck in the new year,
>>>>>> Jeff Loyer
>>>>>>
>>>>>> -----Original Message-----
>>>>>> From: si-list-bounce@xxxxxxxxxxxxx
>>>> [mailto:si-list-bounce@xxxxxxxxxxxxx
>>>> ]
>>>>>> On Behalf Of steve weir
>>>>>> Sent: Monday, January 02, 2012 6:23 AM
>>>>>> To: si-list@xxxxxxxxxxxxx
>>>>>> Subject: [SI-LIST] Re: Impedance Controlled Board Production Vs
>>>> Normal
>>>>>> Board Production
>>>>>>
>>>>>> Suppose as you like.  Hope as you might.  What you don't contract
>> is
>>>> not
>>>>>> guaranteed.
>>>>>>
>>>>>> Steve.
>>>>>> On 1/2/2012 5:56 AM, Jayasuryan KG wrote:
>>>>>>> Dear Experts,
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Happy New Year!!
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> I have question regarding the impedance controlled board
>> production!
>>>>>>> Is there any special process to produce impedance controlled
>> board
>>>>>>> rather than the normal production?
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Suppose if I go with normal production for a  impedance
>> controlled
>>>>>>> board
>>>>>>> (the design has been done to meet the impedance) what are the
>>>> possible
>>>>>>> issues can happen?
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Looking for your immediate response. Thanks in advance.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Best Regards,
>>>>>>>
>>>>>>> - Jayasuryan
>>>>>>>
>>>>>>>
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>>>>>>
>>>>>> --
>>>>>> Steve Weir
>>>>>> IPBLOX, LLC
>>>>>> 150 N. Center St. #211
>>>>>> Reno, NV  89501
>>>>>> www.ipblox.com
>>>>>>
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>>>
>>> --
>>> -Michael.
>>>
>>> We will either find a way or make one   - Hannibal
>>>
>>> In the middle of every difficulty lies opportunity   - Al Einstein
>>>
>>> If you think you can do something or you think
>>> you can't, in both cases you are probably right   - H Ford
>>>
>>> If you're not getting the results you want with the
>>> current approach, move on and try something else.  - A. Fleischmann
>>>
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