I'm not expert on this but I saw (somewhere) a discussion of
capacitive coupling as an issue. Especially at higher frequencies.
Phil
--- In Homebrew_PCBs@yahoogroups.com, David Cureton <yahoo@d...> wrote:
> Hi Stefan,
> It is my understanding that the copper islands or orphaned
copper is
> removed to help with EMC (or do they call it FCC in the US) approval.
>
> You are probably right in that a fat copper island will not do any
harm.
> However at very high frequencies
> these isolated (in a DC sense) pieces of copper may just have the right
> shape to form L's and C's that become resonant
> and hey - presto , you got yourself an antenna.
>
> Although the chances of a floating piece of copper being resonant is
> probably pretty slim, when designing for EMC you take all the free runs
> that you can get
>
> Also - When I say very high frequencies - the signal cycle times do
not
> have to be high frequencys - they just need fast transition times.
>
>
> Cheers,
> David
>
>
>