Without seeing your particular application, I can't "shoot from the hip"
for an answer, except to say that you will likely need to do statistical
reliability testing of some kind to determine how serious your problem
is.  If the cost of doing that might exceed the cost of replacing the
parts, and you're convinced the replaced parts will meet the user
requirements, then its obviously more economical to just replace rather
than analyze.

The statistical reliability test design process consists of determining
a way of getting a metric on the reliability degradation caused by the
cracks you are observing.  This can range from a simple calibrated pull
test to a carefully designed HAST (Highly Accelerated Stress Test)
involving temperature cycles and/or vibration cycles.  Determining what
kind of test would be most economical and relevant requires a
knowledgeable person to go over the design and its intended use.

>>> [log in to unmask] 5/4/2006 6:00:38 am >>>
We have some right angle SMT fine pitch butt joint two row connectors
that
due to excessive
force placed on them have caused cracks in the solder joint.  We have
worked out the mech. issue to relieve
the pressure.  I have some joints that just show a crack in the joint
and
others that there is a clear break.  Each
connector is $7.00 ea.  and we have seen this on~100 connectors.  My
questions are the following:

      1)  The original thinking was we could just use our BGA rework
machine to blow hot air on the cracked
            joints, remelt the solder and the joint would be good
again.
But then do I have to worry about
            a possible lead coplanar problem?  Since I'm reflowing the
entire connector will that really be
            an issue or the damage is done and the leads that are
cracked
are now "bent" and I need
            to worry about it?

      2) Would the answer to the above question change for different
senecios:

            a) Entire row has a clear break
            b) Only a few solder joints are cracked (out of 50) but no
clear break
            c) Only a few solder joints are cracked but some have a
clear
break

      3) The connectors are in a row of 5, should I also reflow
connectors
that do not show any sign of
            cracks, even thou other connectors in the row have cracks?
The
assumption is that the
            parts that are not cracked have seen the same stresses as
the
ones with cracks.

      Thank you as always.

Best Regards,

Mike Forrester
LeCroy Corporation

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