[SI-LIST] Re: Ground clearance at connector vias

Fabrizio,
        There is much work done by the makers of the connectors in modelling the
connectors.
        However my experience is that due to many dependencies you will probably
have to make a test board with optional clearances and configurations as we have
done for our backplanes and connector types regarding 2.5G and above.
        If you are interested and can send you a ppt with some indications of
how to determine impedance match.
        My experience is also that the "screened" connectors are not very well
matched and will require the adation of clearance etc. for compensation.
        I cannot see any good reason for "oval" clearance other than you have
some special crosstalk problem.
Much success
--
Regards,    __________   James G Roberts
           /___  ____ |  jrobert@xxxxxxxxxxxxxxxxxxxxx
 Jim      __  / /___/ /  jgroberts@xxxxxxxxxx
         / /_/ /---| |   Room: BE436, Hilversum
         \____/    /_/   Tel: +31 35 687 4308 Fax: 5976

Fabrizio Zanella wrote:

> I have a question regarding ground clearances for signal vias in a
> backplane connector, like the Molex/Teradyne HSD.  Connector and
> semiconductor manufacturers recommend using an oval ground clearance
> around the differential pairs, to minimize reflections.
> Do you agree with this recommendation, especially at signal speeds of
> 2.5Gbs and above?  Can anyone share their experiences?  How large should
> the clearance be on the backplane?
>
> Thanks and regards,
>
> Fabrizio Zanella
> Principal Hardware Design Engineer
> Broadbus Technologies
> fzanella@xxxxxxxxxxxx
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