There has been a recent flurry of discussion on Alloy 42.  
We've also seen some post-thermal failures in which Alloy 
42 MIGHT be implicated. I have some specific questions I 
hope someone can clarify. I've just rejointed TechNet and I 
haven't been able to find the last months' discussion in 
the archives. :-)) 

1.  If a leadframe is made from Alloy 42, is there ALWAYS a 
concern that the part will stress-crack after thermal 
cycling, especially on stiffer leaded devices?

2.  Does the exact sequence of plating have any effect on 
the survivability of the device after cycling?  For 
example, do Alloy parts that are overplated with nickel or 
silver, then tin-lead survive better than Alloy 42 frames 
with only tin-lead?

3.  Is there general agreement that this problem reared 
it's head because of the attempt to use commercial parts 
for military or harsh environments?  This would imply that 
engineering is choosing the wrong parts for the 
application, and that the original part manufacturer is 
making 'good' commercial parts. (And further, that an 
'acceptible' mil part no longer exists!)

4. If the root of the cracking problem results from the 
manufacturer allowing the Alloy 42 to tarnish before tin 
plating, is there anything that can be done except for the 
horrific task of trying to solderability test an SMT part? 

Thanks,

----------------------
Richard Huziak
Manufacturing Engineering
SED Systems
Saskatoon, SK, Canada
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