While reading some papers on SnBi solder and SAC solder interaction, I
stumbled onto this set of statements in a 2010 paper  Copyright ACI, The
Lead Free Electronics Manhattan Project - Phase II.  

Intermetallic Fracture

. With Cu supplied by the solder, attaching to Ni pads can be problematic

. (Cu1-xNix)6Sn5 intermetallic IMC forms over a layer of Ni3Sn4 at the Ni
pad

. The Ni atoms are substituted on the Cu lattice

. Weak boundary between intermetallics

. Mechanical shock and handling risk

 

The statements were associated with a image "SnNi and SnNiCu intermetallic
compounds found when using SnAgCu solders," IPC/Soldertech Global 2nd
International Conference on Lead Free Electronics. 

 

We don't do much Pb-free soldering.  But all of our boards, or nearly all,
are gold over nickel.  Is this a real concern?  Wouldn't this kill ENIG as a
SAC compatible finish? 



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