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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