Phil,
One suggestion is to look at the amount of resin on the surface of the
board.  Often times, when tracking occurs along the fibers of the
reinforcement, the buttercoat, or the thin layer of resin at the top of the
board that seals off the fibers, is very thin and may expose the glass.  If
so, then the fibers can wick contaminants into the bundles by capillary
action and is impossible to get out.  Tracking then follows those
contaminants.

Doug Pauls
Rockwell Collin

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