Starting in 1993, while working at Amdahl Computer Corporation, I worked
with a group evaluating BGA solder joints using various substrates, ball
types (eutectic and high temp) with small and micro vias in SMT mounting
pads, and soldering processes. Our first estimate for acceptable voiding was
in the range of 15 to 25%. After running many thermal cycles to failure
tests, the number 20% worked well dependent on voiding "spread" or
"proximity". In cases with one large void (approximating 20% of ball
volume), failures were higher than if smaller voids (spread throughout the
sphere) were encountered with the same voiding volume. This was true to the
extent about 30% failures were encountered to near none, relatively
speaking. Also, after x-sectional and SEM/EDX analysis (of void contents),
it was found that failures were dependent on whether flux residues were
found and its composition (carboxcyclic acid, or?).
I don't have all the numbers anymore as the data became Amdahl property.
There are few of the original cast left to assist. However, the cycles to
failure testing and void analysis techniques are "standard" and the numbers
are reasonably easy to obtain. For this reason, the people I work with, and
myself, are currently supporting the 20% maximum voiding number.
I know there are more recent, and much more in depth, studies being, or
having been, performed. I agree there is a definitive need for such
information as it is critical to solder joint quality and long term
reliability just as with other device types.
Sincerely,
Earl Moon
################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe: SUBSCRIBE TechNet <your full name>
To unsubscribe: SIGNOFF TechNet
################################################################
Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################
|
