I have seen this condition caused by slow cooling.  Are the particular
leads which exhibit the condition also connected to larger traces or to
planes?  Anything which increases the thermal mass of the solder joint
will decrease the rate at which it heats and cools.

>>> <[log in to unmask]> 01/20/98 07:54am >>>
Over the past 2 months we have been experiencing and increase in the
number
of opens on several different fine pitch QFPs.  We believe the problem is
due to poor wetting to the component leads.  On a typical 304 QFP we
find ~
5-10% of the cards have 1 or more lead which is open.  Optically the
open
lead has a coarse, grainy finish, and is surrounded by good joints where
the lead finish has a very fine grain structure.   SEM/EDX analysis of the
finish reveals the presence of large (~20-40 um) Sn grains with Pb
segregated between the grains.  Analysis has not shown any signs of
gross
contamination.

Is there anyone who has seen a similar phenomena and might have a
possible
corrective action?  I can email anyone a picture if you're interested.

Thank you

Jason Bragg

 Jason P. Bragg,
Celestica Inc.
                    Component Failure Analysis
                         844 Don Mills Road, 20/429
                    Materials Analytical Lab
          North York, Ontario, M3C 1V7
                    Internet: [log in to unmask]
          Tel: (416) 448-6203

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