Your failure mode of deepest concern is most likely CAF (Conductive
Anodic Filament).  The most common spot for this problem is via to
trace, and the seed is disturbances in the via side wall.  CAF can also
grow along glass filaments within pre-preg from layer to layer.  Failure
potentials are at less than 10% of the 750V/mil.  Laminates are
available with very high CAF resistance if you need to push things.  I
believe there are some BT based materials that are virtually immune, but
1500V is a lot of potential!

Wayne Thayer

>>> [log in to unmask] 9/25/2006 5:06 pm >>>
Should I be using IPC Table 6.1 for conductor spacing for high voltage
in the z-axis of the pcb?
Or should I be using the approximately 750V/mil spec from the laminate
supplier and derate that number?
Board has +/- 1200V.

Thank you.

Kaye Clayo
Sr. P. C. Layout Designer
Keithley Instruments, Inc.
440-498-2862

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