Hi Phil,
What a high P-concentration does is create a weakly adhering Ni/P layer 
between the ENi and the Ni3Sn4 IMC layers—the higher the P-concentration the weaker 
the adhesion.
The P-concentration can be high because of the Ni plating process, but can 
also be driven higher by more Ni dissolving in Sn due to long or multiple 
soldering temperature exposures.



Werner



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