Frank,

You are correct in that each application is different and one can use
FR4 in some applications greater than 1 GHz. Loss is an important
factor, but we have seen designers switch from FR4 to a high frequency
material because of dielectric tolerance too. That I'm aware of, there
is no tolerance (or at least published) in dielectric tolerance for FR4
or many other high Tg materials, only on those designed specifically for
RF/microwave applications. Because of that fact, some FR4 boards require
much tuning to get them to work, this adds overall cost to the finished
circuit and in some cases it is cheaper to got to a more expensive
laminate and eliminate tuning. Each application is different and if I
were desining a board I would give FR4 a shot also. Let's face it, if it
works after looking at all costs then there is nothing that somebody
like me (working for a supplier of high frequency laminates) can say to
convince you to switch away from FR4 (but there are cases down to 500
MHz, digital, where the change has happened).

regards
Art Aguayo
[log in to unmask]
www.rogers-corp.com/mwu/
[log in to unmask] wrote:
>
> Everyone seems to have a 1GHz ceiling on FR4.  We routinely go higher than
> that on our FR4 boards.  It all comes down to how much loss you can tolerate.
>
> Frank
>
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