Hi Tom,
The failure description is classical 'Black Pad' with the separation at the 
enriched Ni-P+ layer between the ENi layer and the Ni3Sn4 IMC layer.
In terms of P%, the difference between weight% and atomic% is very roughly a 
factor of 2.
P percentage is not the whole story, continuous IMC layers will give less 
brittle failures than 'lumpy' ones.
Also remember, ''Black Pad' is not an all-or-nothing proposition—the more 5P 
the weaker the interface. Thus, one interface not severely loadind is fine, 
while the same interface more severely loaded will show brittle fracture.



Werner



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