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May 1998

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Subject:
From:
Douglas Mckean <[log in to unmask]>
Reply To:
Date:
Fri, 22 May 1998 09:53:40 -0700
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Back when I was working for a telco company, I wrote a paper
that mathematically analyzed FR-4 to an ideal upper limit of
about 850 MHz, IIRC.  We were using FR-4 to an upper channel
freq of 860 MHz for analog and an upper of 1 GHz for ECL based
digital.  Now this is no absolute.  I met some designers that
wouldn't take FR-4 above about 300 or 400 MHz, but that was
their situation.

Our situation with the boards for the analog 850 stuff had it's
downside. There could be a variance of anywhere from 1 to 2 dB
of signal on the same board.  This all depended greatly upon the
mfr'ing processes used and that in turn all depended upon what
exactly the board houses were told by the customer in making
the boards.

I'll stick my neck out and say as with anything, if the proper
information is given and someone is willing to pay any amount
of money for quality checks, you could take FR-4 as high as
you want.

Regards,  Doug

Manfred Huschka wrote:
>
> Fred,
>
> although I am working for a PTFE/woven glass fabric manufacturer, I can tell you that based on many years of
> experience in manufacturing FR4, BT/Epoxy, Polyimide, PTFE, etc. base materials, 400 MHz is still a good
> frequency for FR4 - depending on tolerances.
>
> Some design engineers use FR4 up to more than 1 GHz, whereas other ones use PTFE/woven glass laminates from
> even as low as 200 MHz on.
>
> Regards
>
> Manfred Huschka
> Taconic
>
> --- On Thu, 21 May 1998 08:25:09 -0700  Fred Watt <[log in to unmask]> wrote:
>         Has anybody had any problems with FR-4 at 100 to 200 MHz?  I have several boards from several
> fabrication shops in which the signal loses amplitude above 80-100 MHz.  The boards are controlled impedance
> (50 Ohms) with 5 mil traces and 5 mil dielectrics.  The traces are about 6.5" long.
>         I would appreciate any comments on this subject.  The supplier of the material says that FR-4 should
> be good to 400 MHz.

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