We have a failure analysis of "dewet" for a BGA ball that is separated from the component substrate.  Does anyone know more about this failure mode?  The part goes through reflow twice, so once while upside down.  It seems unusual, even unlikely, for separation to occur between the balls and the substrate due to the weight of the part rather than between the ball and the PCB.  Other parts on the same board do not have this issue.  Do you have any experience with this problem or how to prevent it?  Or for the future, how to predict it and thus avoid it?  Would vapor phase processing influence the likelihood of this defect?  Any help appreciated!

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