In a message dated 3/1/2001 4:34:40 PM Eastern Standard Time,
[log in to unmask] writes:

This is a product where the board size cannot be
increased to solve the problem, so we're pretty much constraint to pad
reduction and relocation of vias? Any ideas on what's the minimum distance?,
is there an IPC standard for issues like this?

Trace to Board Edge

Jorge, make sure you know what you really need for trace-to-board-edge
distance.

I would first recommend you check with your UL file to see if there are
limits or constraints (if UL is even a factor). Second, determine whether
trace-to-edge spacing can be an issue at assembly. Third, is there an
application/installation issue? (e.g. grounded chassis or rack rail distance
to the nearest trace).

With those thoughts aside: Determine what the minimum airgap requirement is
from the respective trace(s), then add to that your maximum manufacturing
tolerance for score line location AND your maximum tolerance for trace
location (image registration with substrate, including material mechanical
dynamics). The IPC does comment on these measures.

If your required airgap minimum is 5-mils, and your profile tolerance is +/-
5-mils and your trace locational tolerance is +/- 3-mils, I would see your
absolute minimum distance becoming 13-mils. But again, check-out the
environment that will be around the board edge at assembly -- and then in the
field -- for practical needs that will likely increase this starting-point
measure.

Bob Lazzara