Ingemar,
I remember seeing a similar phenomenon in a former life, maybe 10 yrs ago,
so details are a bit faded. Anyway, it was a contamination issue. There is
a chapter in George Harman's book (Wirebonding in Microelectronics)
describing some Al-Au intermetallic reactions that can get started by a
trace of Cl in the presence of moisture. I remember being able to actually
watch a ball bond disintegrate under a microscope by putting a drop of
water on it. Are you plasma cleaning immediately before going to the bonder?
Are you sure the plasma clean cycle is sufficient to get rid of anything
left from the die bond epoxy cure? Any possibility of contaminants in the
oven or plasma cleaner?
Art Glass

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