None, besides the negligible opportunity to create tiny copper burrs
which can embed in the routed edge, Scott. This becomes a concern if
conductors of differing signals or potentials are not edge relieved. If
you are concerned with EMI/RFI moving through the board edge, I have
successfully used the following techniques to edge shield an EMI filter
board:

1) Create the board outline using slots spaced by breakaway tabs typical
of a panelized board (remember to calculate the maximum trap space that
will shield your highest frequency and space the slots below it). Bring
the copper to the edge on both external layers and specify that the slot
be plated on your fab dwg. When the boards are separated, the plated
edges will remain. You can instruct your vendor to perform a secondary
route process after the final plating (SnPb), so long as you provide
tooling holes within your board outline, or separate them in house after
they are assembled.

2) If you have the room, a more economical method is to simply rivet the
perimeter of the board with vias connected to the shield plane. Keep the
via barrel edge-to-edge spacing below the trap distance of the highest
frequency you wish to filter. I hope this helps, Scott.

Chris Taylor
Senior Printed Circuit Designer
LXE, Inc.
125 Technology Parkway
Norcross, GA 30092
voice: (770) 447-4224 X3242
fax: (770) 447-6928
e-mail: [log in to unmask]


>----------
>From:  Scott Buscomb[SMTP:[log in to unmask]]
>Sent:  Wednesday, January 07, 1998 11:50 AM
>To:    [log in to unmask]
>Subject:       [DC] Routed Edge to Copper
>
>What is the reasoning behind setting copper back from the board edge by
>.030-.040 besides tolerancing and the possibility of cutting the trace?
>I would like to bring a copper feature right to the edge of the board
>(trimmed during the routing process) for a shield base. Is there any
>hidden problem with cutting copper w/plating during the routing process?
>
>Any comments?
>Thanks,
>
>Scott
>--
>Scott Buscomb, Senior Designer
>[log in to unmask]
>Techsonic Industries
>1111 Alderman Dr. Ste. 250
>Alpharetta, GA 30005
>770 475-3020 ext.1032
>
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