For those of you designing or building burn in boards, are any of you
building them on Thermount material?  One of our customers has shown an
interest in this material for their burn in boards and we're trying to
decide if that's a wise move or not.  Most of their boards use 0.8mm and
0.5mm BGA's and have traditionally been built on Polyimide.  The problem is
that some percentage of them develop low voltage shorts in the field.  Hole
to internal traces may be as low as 3 mils when drill wander and material
movement are at their worst but normally it's maintained at 6-mils or
better.  The boards are tested at 40 volts prior to shipping and all pass
but some number of them will develop the field problem.  CAF is suspected
but I'm not so sure.  The field failures develop in days or weeks rather
than months.  I suspect rather than CAF it may be due to the resin system
itself.  I understand that most Poly manufacturers use a common Poly resin
from Ciba and that it has been suspected of developing this low voltage
shorting issue (sulfur content I believe).

Anyone out there have any comments about the situation itself or comments
regarding Thermount (85RT and 55ST)?

Thanks,

Mark Mazzoli

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