Alloy 42 is simliar to Kovar and is used as a "controlled expansion" alloy, 
typically where a low CTE metal is needed (e.g. lead sealing).  The material is 
42% Ni with the balance iron and has a CTE of ~ 5.2 ppm/C.  Solderability-wise 
alloy42, like most nickel alloys, is hard to solder if given a chance to 
oxidize.  

My guess would be either a) the lead frame was oxidized prior to application of 
plating and therefore the plating reflows leaving a non-solderable surface 
exposed and/or b) the "sides" of the leads are "punched out" and not plated (or 
incompletely plated) and the exposed lead material oxidized (e.g. during burn 
in) and is non-solderable. 

______________________________ Reply Separator _________________________________
Subject: Alloy 42
Author:  [log in to unmask] at esdigate
Date:    4/16/96 4:28 PM


We have a customer who says that a previous supplier had problems soldering 
some fine pitch components (15 mil) because the lead material was "Alloy 
42".  They had a tin/lead coating (85/15).  They were also told that many 
component mfgrs are going to be using this material.
     
We are not familiar with this lead material but since it is solder coated do 
not hink it should be a problem.  Anyone have any knowledge or experience in 
this area?  
     
Thanks in advance for your consideration.
     
Leo Reynolds
Electronic Systems, Inc.