Hello, 
 
I have seen an increase in problems with electrical testing and it has
been traced to BGAs.
I have a few questions regarding BGA and processes.  I am trying to
understand if the problem is process related (SMT) or do I have a vendor
issue with BGA.
 
1.      Open contact between the ball and the package.  This is verified
by pressing onto the package while testing.  Pressing the package down
causes the board to pass.
2.      Visual inspection reveals the ball not touching the PCBA. (You
may have a ball in  the middle not touching and the balls on each side
are) 
        a.      Question:  With on ball in the middle not touching and
the balls next to it are, is this indicative to SMT process issues or
BGA package issues?
        b.      Question:  What type of inspection can be performed on
BGAs prior to SMT to capture Bad BGA?
                                                               i.
Is the industry standard 100% or Sample inspection for out going quality
inspection?
        c.      Question: Is it easy to identify a BGA that has been
re-balled and if so how?
        d.      Is it customary for distributors to re-ball BGA
        e.      What other test or inspections can be performed to
capture BGA with open contacts?
        f.      As indicated above, pressing down the package causes the
board to pass, how do I detect micro cracking of the solder joint? And
what would cause micro cracking?
 
I am lost at this point and am looking for additional suggestions and
assistance in educating me on BGA.
 
David Harman
 

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