Hi Bev,
Just like George, I am struggling getting an understanding of you problem.
To me, 'head-on-pillow' solder defects are almost always caused by 
insufficient peak temperature.
If these HOP's occurred essentially near the center of the BGA, you have your 
answer,
If the HOP's are distributed over the whole array, than the root cause is not 
insufficient peak temperature unless the whole reflow process is too low.



Werner



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