6.5" is at the limits of a 200MHz trace on FR-4. Are you sure that a 5 mil
trace is 50 ohms in your application?

> ----------
> From:         Eddie Brunker
> Sent:         Thursday, May 21, 1998 11:34 AM
> To:   [log in to unmask]
> Subject:      Re: [TN] Frequency problems with FR-4
>
> Recently an article appeared in the Electronics Press after the head of
> Multek visited Dovertron in Cork (part of the same group of companies),
> and
> good friends of ours too.
> The article focused on his warnings that at 300MHZ and above, Fr-4 is
> unsuitable and future substrates should be of alternative materials, the
> costs and processing should be considered etc...
> I asked our design engineers to comment on this, and they have no problems
> with FR-4 at 300MHZ which are speeds we use presently. I know of one other
> company using FR-4 at these speeds, and if they are happy with it then so
> am
> I, as they are big league!
>
> Regards
>
>
> At 08:25 21/05/98 -0700, you 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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