You remember in the movie "Michael" when the angel Michael said "you can 
never eat too much sugar"?
Well you can never have too much GND plane, and that includes copper pours.

BUT... unconnected copper pour fragments will actually hurt, not help, 
an EMI situation. Make sure those
pieces are actually GND.

Did you put tiny caps on any long runs? Even caps as small as 5pF seems 
to stop a PIC from capturing noise
through a long trace. Just a thought.

4Mhz is so slow that you won't radiate anything either. HINT: if you 
can't hear any noise, chances are great that
the PIC won't capture any, either.

You are on the right track. You will be very successful.
 
--Bob

Rick Thompson wrote:

> Here's a question for the noise experts:
>
> I've designed a 4-layer pcb running a 16LF876A at 4MHz to be used in a 
> VERY noisy environment.  Fortunately there's no A/D functionality 
> needed but there's some timing-critical functions to be upheld (20Hz 
> to 1000Hz CCP events).  Every trick that I could find to make the 
> design immune to EMI has been included or at least considered.  But 
> one consideration that I don't know enough about is the need for a 
> copper pour.  Until now, my understanding is that a copper pour can be 
> considered as a "poor man's ground plane" on 1 or 2-layer boards.  But 
> if my board already has a ground plane, am I going to see any benefit 
> by adding a copper pour on any or every other layer, or am I just 
> wasting my time thinking about it?
>
> Rick
>


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