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

  • From: Aubrey K Sparkman <asparky@xxxxxxxxxxxxxxxxxxxxxxxx>
  • To: Ken Cantrell <Ken.Cantrell@xxxxxxxxxxxxxxxx>, Mikhail Matusov <matusov@xxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
  • Date: Thu, 05 Jan 2012 11:27:23 -0600

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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>> This e-mail may contain confidential material.
>> If you are not the intended recipient, please destroy all records and
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