Thanks for the responses, both on and off line.
Democratically the consensus amounts to the following:
Multi-hole "Sieve" Design = 2 votes for ...
Reasons: 1. Reduce multi-current crowding around pins.
2. Reduce plane inductance.
Single-Hole "Cookie Cutter" Design = 2 votes for ...
Reasons: 1. Reduce noise coupling to power plane from pins.
Now, they are all good concerns. So, what I'm going to
do is try to combine the two with a suggestion from
Scott and require that the holes through the power plane
are to be larger than the holes through the ground plane.
But, they are not to be so large that the concerns of the
"sieve" design are violated, i.e. current crowding and
inductance are INCREASED.
Again, thanks for the reality check...
Doug ...
----------
> From: Doug McKean <[email protected]>
> To: IEEE Product Safety Technical Committee -
<[email protected]>
> Subject: EMC Design Question for a Backplane ...
> Date: Wednesday, September 24, 1997 6:16 PM
>
> I'm having a lively discussion with one of our
> design engineers about backplane PCB design.
>
> Here's the case:
>
> 1. Multilayer board, let's say 10 layers,
> 1 power plane (+5vdc), 3 ground planes,
> 6 signal planes.
>
> 2. Outside world connections to the
> backplane with several connectors
> across the back of the product.
>
> 3. T1/DS1 product.
>
> I want the +5vdc power plane cutaway, actually
> well away, from pins of the connectors that do
> not use the power plane. I can't draw it very
> well with ASCII. But needless to say, if there's
> a 6-pin connector with 1 pin using the 5 vdc,
> then I want the 5 volt plane cut away from the
> other 5 pins with *one* hole.
>
> Instead, what's being suggested is to punch *five*
> separate holes through the power plane like a sieve
> for each pin not using the 5 volts.
>
> My concern is noise, transients, or ESD coupling
> from the outside world lines to the power plane
> of the backplane and thus to everything connected
> to the backplane.
>
> Am I being too picky here?
>
> What's the standard convention that people
> use out there?
>
