Hi Werner,
My problem is that I agree with you whole heartedly.  Why come up with a
complex explanation to a simple problem?

We receive BGAs which have been pulled off of boards from all over.  We see
the same phenomenon on most components we receive.  All from different
sources and different manufacturers.

At first I attributed the problem to the conversion of semiconductor
assemblers to no-clean fluxes. Then I began looking into the possibility
that they are just escapees which slip through the cracks.  Now I am
wondering if they made it out of assembly with good ball attach and then
were degraded by test sockets which can stress the solder balls while they
are at elevated temperatures.  Regardless of what the root cause of the
problem I guess the real question is:

If you pull a BGA from a board (with a proper hot air reflow system) and
find a bare nickel pad on the component who's fault is it?  As long as it is
not a function of the removal process then I believe the responsibility is
that of  the component manufacturer.  I believe the failure analysis (at the
board level) is complete.  The component failed due to an open which was
caused by a poorly attached solder ball (at the component).  My experience
tells me that the nickel should never become exposed just by heating the
solder balls to the molten state and then lifting the component from the
board.

Do you see any reason why the board removal process would expose a bare
nickel pad of a good BGA?

-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Wednesday, February 17, 1999 6:43 PM
To: [log in to unmask]; Russ
Subject: Re: [TN] Defective BGAs?


Hi Russ,
Well, your problem comes down to two possible causes:
1) no solderability; your tests seem to exclude that.
2) inadequate soldering process; it certainly is possible that the solder
balls were never properly attached to the component. Your problem is not
likely related to shear strength of (or crack propagation in) nickel-tin
intermetalics, but the absenceof any IMCs which are the by-product of a good
intermetallic bond resulting from good wetting. Solder attachment strength
to
nickel is about half that to copper.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask]

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