Hi Gerald - I agree with Wayne, unless you can prove that the cracks are 
not going to compromise solder joint integrity in the product use 
environment, you have no other option than to rework the boards to make 
they reliable. Your analysis shows you exceed the 3% gold maximum limit 
and that you have the AuSn4 IMC phase present with small existing cracks - 
pretty thin ice to be standing on. My guess is that it is more cost 
effective to exercise the rework option rather than research/create a test 
that accurately replicates the field service conditions  such that you 
have acceptable results predictability. Good Luck.

Dave Hillman
Rockwell Collins
ddhillma@rockwellcollins



From:   Gerald Bogert <[log in to unmask]>
To:     <[log in to unmask]>
Date:   10/01/2013 06:05 AM
Subject:        [TN] MIL-PRF-55310 Crystals and Gold Solder Joint 
Embrittlement
Sent by:        TechNet <[log in to unmask]>



October 1, 2013

 

Good morning folks.

 

One of the QPL OCMs that manufactures MIL-PRF-55310 crystals issued a
notice in 2009 indicating that the QPL parts they manufacture must have
the gold removed by a double dip process to preclude gold embrittlement
issues when soldering using SnPb solders.

 

Unfortunately we have an OEM that was not aware of this issue so he
allowed a subcontractor to manufacture circuit card assemblies (CCA)
using surface mount M55310/38 four-termination  crystals without first
having  the gold removed.  The OEM sent out a CCA for SEM/EDS analysis
which showed very small (X3500 magnification) cracks along the SnAu
intermetallic platelets where the concentration of Au was around 5 to
5.6%.

 

To date, the OEM has not experienced any operational failures with the
CCAs,  and in additional to final acceptance testing, the CCAs were also
subjected (on a sample basis) to ESS temperature cycle testing with no
failures.

 

My question is, given that the parts were soldered which created the
SnAu intermetallics, can we depend on passing of the ESS testing to
verify no embrittlement issues or is there some other type testing we
can do to justify leaving alone product the OEM already fielded.  The
assembly can see shock and vibration in the end-use environment and must
operate around 85C. 


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