Hi there Ken,

Rather than just give a measurement I'll explain why I keep power &
ground planes away from the edge of the board.

If the board goes into a panel that is scored, you will need to bear in
mind that the edge of the board will have
a slope on it, caused by the V-scoring machine. This is typically 0.5mm
between boards in a panel.
Therefor you will lose 0.25mm (0.01") of the laminate around the edges.

If the board is routed, you will not lose this, but it is always good
practice to keep the same distance away no matter what
method of panelisation.

Once that is done, then you have to think about the solder resist edges.
If you have copper and solder resist
edges at the same distance from the edge you can get nasty things
creeping under it and corroding the board.
You need to leave a gap for an area of solder resist before the start of
your copper areas.

I dare say that this also applies to the bonding of multiple layers, in
order to provide good adhesion of laminates
between the layers.

What this then boils down to is keeping copper about 1mm (0.039") away
from the edge of the board.
If the board is large & has plenty of room then obviously this can be
increased, but should never be decreased.

I dare say that its mentioned in one of the IPC specs somewhere. (I'd
like to know which one?).

There... That's my tuppence...

Hope it helps & doesn't confuse.... TIA - Matt.


>-----Original Message-----
>From:  Ken Patel [SMTP:[log in to unmask]]
>Sent:  Thursday, December 09, 1999 9:13 PM
>To:    [log in to unmask]
>Subject:       [TN] Edge Clearance for power & ground planes
>
>Guys,
>How far my power & ground planes should be away from the egge of the board?
>
>re,
>ken patel
>______________________________________________________
>Ken Patel                       Phone:  (408) 490-6804
>1708 McCarthy Blvd.             Fax:    (408) 490-6859
>Milpitas, CA 95035              Beeper: (888) 769-1808
>
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