We have processed millions of components which use Alloy 42 as a base 
material.  Solderability of these leads is fine under a variety of 
applications.  We had one situation concerning a large number of assemblies 
where problems were experienced due to low joint strength even on 
ANSI/J-STD-001A Class 3 joints.

Cracks were discovered along the Alloy 42 interface.  Low pull strength was 
correlated with certain manufacturers.  During the course of the 
investigation, it was learned that many of our off-shore suppliers 
sub-contracted the plating of the leads which resulted in a range of pull 
strengths from a single supplier.  It was suspected, but never proved, the 
process controls on the Alloy 42 PRIOR to plating played a major role in 
this variation.  It was also learned that some well respected component 
manufacturers do less than you might expect to monitor the performance of 
their packages in this respect; ie pull strength of a soldered lead.

Some of this problem can be mitigated by the strength of the flux and, to 
some degree, the reflow profile.  But your options are limited in the world 
of no-clean. However, the most significant factor was shown to be not only 
the supplier, but which sub-contractor the supplier used for lead plating.

Fortunately, this was only one situation.  However, I suspect the problem 
may be more prevelent as a number of board design, handling, and test 
factors were involved which may have put stress on the joints to initiate 
the cracks.

I would be interested to know if anyone else has seen similar performance 
(low pull strength) with Alloy 42.

Bill Barthel
Electronic Assembly Corp.
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