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April 2001

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Subject:
From:
Douglas Pauls <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 10 Apr 2001 14:41:55 -0500
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Steve,
I have seen this problem before.  What is likely happening is that you are
curing the glue too fast.  The outer layer of the coating skins over,
entrapping volatiles.  They then blow out, leaving a pathway between the
pads.  This pathway can fill with flux, and the solder naturally follows,
creating a short.  I wrote about it in two Process Rx columns in December
98 (Microcanyons), and a follow up column in July 99 (Become One With the
Glue).  And yes, there was a fair amount of drinking going on during title
selection.  I can send you those articles if you are interested.  They also
appear on CSL's website, www.residues.com/library.

The client did are large designed experiment looking at single dot and
double dot application, and different glue curing rates.  They found that
by following the manufacturers recommended glue cure profile, they got the
best adhesion (imagine that, following directions actually works).

Doug Pauls
Rockwell Collins

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