Address,

     I have a 12 layer, 9 x 9, .062 PCA with 4 50mil pitch BGAs.  Two (2)
     of the BGAs are normal 300+ IO perimeter and full array OMPACs.  The
     other two are 500+ IO Perimeter BGAs with aluminum bodies.

     We suspected shorts on both packages and on several PCAs.  An outside
     lab provided us some excellent and I mean excellent Radio Graph photos
     @ 80KV.

     We found the suspected shorts as well as solder ball voids,
     everywhere.  The BGA pads are .025", again on .050" centers.  I
     estimate some solder voids (air pockets) to be as great as .054"


     As a note, our design does have vias in the BGA pads, however, we have
     soldermasked the solder side for obvious reasons.  Worst case voids do
     have vias in them.  Voids are apparent all over.  The same condition
     was not witnessed on the OMPACs.  This condition is only witnessed on
     the Aluminum Package BGAs.

     I'm going to run some more thermal profiling on these BGAs only, but
     request the following from the group.

     1. What advice can anyone provide on this problem.  Any other angles
        are appreciated.
     2. Are there any thermal profile considerations on these BGAs and what
        changes can be made without influencing changes to the OMPACs.
     3. I'm using Convection Reflow.
     4. Could the solder balls on the package be defective?  I don't see
        this as being a problem.
     5. I know the solder balls are not hygroscopic, so can moisture be
        creating these ball voids?

     Again, any input is appreciated.

     Thanks,

     John Gulley

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