Hi,

Kelly brought up the most serious point... trapped process chemicals, flux or
cleaning solutions.  If the part is soldered into the PWB by pins extending
from the case bottom, bubbles may be the least of your worries.  This kind of
design fubar can sometimes be corrected by bonding the case using a 0.010"
plus mat such as Ablestik's Ablefilm 561K, a flexible, thermally conductive
adhesive film.  By leaving openings in the mat from the joints to the part
edge, you open up a cleaning \ drainage path.

If the part has side mounted leads or terminals, you can bond the part
straight to the board, or you can seal the edge of the part perimeter prior to
processing to prevent entrapment.

In any case, the last resort is to convince Design that a washer or two under
the part would also eliminate the problem.  You might need to adjust the
viscosity so that the coating coats under the part, but does not fill the air
gap.  This should prevent the bubbles as well.

Just make sure you know what is evolving.  Air or solvent is one thing.  Flux
would be another!

Good luck,
Steve Mikell
SCI Systems

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