hi,

this happens to us more than i'd like to admit.  one approach you may
take is to bond the power module to the pwb prior to soldering.  this
essentially fills the void between the power module and the pwb and
eliminates the possiblility of voids forming later.  if this power
module dissipates a lot of heat, the bonding can improve the heat
transfer from the module.

phil crepeau

-----Original Message-----
From: Lum Wee Mei [mailto:[log in to unmask]]
Sent: Monday, August 31, 1998 7:27 PM
To: [log in to unmask]
Subject: [TN] Bubbles from conformally coated board


The test engineer came back to us to complain that bubbles are found
along the edge of the power modules after going through the temperature
cycling tests. This problems are found on both coated boards. The power
modules are mounted completely flushed onto the board and subject to
conformal coating using the diping method. The coated board undergo QC
to ensure all components are completely coated, inlcuding the edges
around the modules.

What could be the problem?

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