Tore,

   There are always more QUESTIONS than ANSWERS.
You state that much efforts have been placed on this issue yet you have not
specified what those actions are.   Here some are things to consider that
will eliminate what isn't the cause.

        1).   Is there more than one PCBA and/or BGA vendor?   If, so
conduct matrix.
        2).   Is the failure VINTAGE related?
        3).   Is the failure PRODUCT RELATED?
        4).   What plating process does the PCB and/or BGA vendor employs.
ie ENIG?
        5).   Can you duplicate the failure at POST Reliability Testing?
        6).   Have you conducted a MANUAL Shear/Peel Test?
        7).   Have you conducted fault isolation to a SPECIFIC BGA location.
        8),   How did the CROSS SECTION of the BGA look?  ie.  nodules free
and/or size of nodules?
        9).   What did SEM/EDX determine?

   The list goes on and on.   Very painful but necessary to determine
FAILING MECHANISM.

Victor,

-----Original Message-----
From: Tore Jakobsen [mailto:[log in to unmask]]
Sent: Monday, September 23, 2002 1:53 AM
To: [log in to unmask]
Subject: Re: [TN] BGA failure and Rework


Victor

We've put quite a bit of effort into this, but the fact remains.
After removing the suspect components (which fail during test of the
assembled product) we find that some pads on the component are gray/brown.

Further analysis of these darkened pads, show that they probably never
gained a proper intermetallic connection. This kind of fault is a real
problem, as it's one of the faults we cannot detect by any other means than
functional testing. And even then it's not guaranteed the product will
continue working.

We put focus on this problem, due to our customers finding products failing
after thermal stress testing. (The boards were fully functional as they
left our site)

Upon removal, we found several black pads beneath the failing components.

Rgds
Tore

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