The original question was wrt discretes -- more of an RF question
from the way it sounded. Otherwise, there's no special reason why
frequencies much higher than 500MHz shouldn't go over FR4, since
the main problems are in other areas. We already ship stuff around
at better than 700 MBaud routinely, and Rambus hits near a GBaud.
Package parasitics and device speeds are more of a problem than
the copper is, so long as you can avoid microstrips and similarly
suboptimal tactics.
Now shipping a GHz CLOCK is ugly, but that's mostly because the
delay is hard to contol.
-- D. C. Sessions [email protected]