not to step in a place I don't beloing, between werner and Vladimir, but how 
about "dark line defect" instead of "black pad"?

Similar phenomenon for a different reason.

We went through this a while ago, wondering why suddenly boards from a very 
good ENiG supplier were looking like black pad, all that P on top of the pad.  
Changing reflow profiles to reduce TAL and max temp, reducing rework cycles 
made it all go away.  All that extra time at temperature just continued the 
Ni/Sn reaction, leaving P behind.  Quantities of Ni in the Sn tipped us off that 
we weren't starting out with black pad, but we were ending up with it.

I do get why people don't like ENiG, but we've done very well with it by making 
sure we use good suppliers.

Pete

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