1, BGA solder issue:
cold solder.
short solder.
solder bubble.
2, solve method:
verify stencil design open hole.
change indirect material e.g solder paste etc.
re-test reflow profile and make sure the top temp. above 225, but under 235 degree. and the time should be above 20 second.
before production mast bake 24 hours.
and can dip the flux first.