If you ever need to move away from FR4 -- I'd go talk to this guy.

Janis59

Joined Aug 21, 2017
1,143
So, what?
Sometimes indeed FR4 is worst of the worse, however 99% of cases it is sure best.
Those rare cases are any of two a) frequencies hardly over into GHz, b) all cases the high resonative (reactive) power is involved. For FR4 the tan delta is 0,03 thus it burns with a smoke if any dare to load it over few kV and few Amps at even so small as 27-100 MHz. Both cases the ultimate cure is Rogers Duroid, expensivish yet worth any cent spent. There are three candidates, one is very well self-cooled but rather much warming, other is very tiny warming but bad cooling, and third is sth between both. The best of them have tan(delta)=0,00003 - its about the same quality or very small beyound as the good ceramic capacitor dielectric have to have.
Rather another idea is to use the so called ceramic substrates (some US firms was demonstrated ar SpaceTechExpo Bremen 2019, may search at exhibition`s homepage), but it is order of magnitude expensiver so I never tried.
 
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