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

  • From: Aubrey K Sparkman <asparky@xxxxxxxxxxxxxxxxxxxxxxxx>
  • To: Michael Greim <mgreim001@xxxxxxxxx>
  • Date: Thu, 05 Jan 2012 13:48:42 -0600

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