RE>>qualification plan for BGA soldering... 1/3/97
We have been using IBM's CBGA for nearly 4 years for some high performance
applications. Our computers are mainly mounted in VME chasses, some of which
are in standard office environments, but some are in aggressive airborne
environments. We didn't have the resources at the time for a true, rigorous
qualification of them, but instead were able to utilize a considerable
portion of IBM's reliability data as long as we used consistent assembly
processes. The major component of this was to ensure that we have adequate
solder paste volume for each site.
We have done some testing on our own and found that the only real deficiency
was exactly as George Franck mentioned: they failed at relatively high
vibration levels. An inclusion of an epoxy underfill solved this problem.
We now use 7 or 8 different BGAs (some plastic, some ceramic), and we've
found this same vibration susceptibility (and fix) with all that we've
tested.
We have found BGA technology to be well-suited for our applications and
extremely robust. At the risk of jinxing us, we haven't seen any field
failures related to solder joint problems - and, yes, we would have seen
them! The biggest problem that we've seen with this technology is with the
array via reliability in the PWB. (Consider that these vias are generally on
the small side, and boards with BGAs tend to have more layers.) We had a
significant number of failures initially but have taken steps to minimize
them.
Greg Bartlett
Mercury Computer Systems
Chelmsford, MA
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--------------------------------------
Date: 1/3/97 10:35 AM
To: Greg Bartlett
From: George Franck Jr
Obrien,
I have not run a qualification program for BGA's. As such, I
am only watching from the sidelines, however, I have gleaned the
following information off the technet and other articles in our
library.
It is my opinion that BGAs are good for applications with temperature
ranges of 30deg C and less, 50 deg C being the limit. Applications
basically are room temperature / air conditioned applications. I think
Compaq Computer is still the bigest user of BGA's.
Another big consideration is vibration. Happy Holden of HP-Loveland, or
Fort Collins CO, expressed frustrations with BGA's in (Inkjet?) printer
applications in a posting last year. Too much vibration caused failure
rates to exceed HP's targeted reliability. (I was so impressed that a
consumer electronics firm did reliability studies, that I went out and
bought an HP Ink Jet.)
It has been my observation that most reliability studies of BGA's
confine their use to very beniegn environments, and report excessive
failures in other environments. There are many different configurations
commonly refered to as BGA's which have different reliability levels.
BGA package suppliers are not all the same. Variables, Variables,
Variables. It seems to me that reliability studies usually bring bad
news. Again, these are my observations from the side lines. Success
stories may be suppressed as 'company sensitive' information. Good
luck. I would be interested in following your progress.
Finally, there is a JPL study in progress for NASA to determine the if
BGA's can be used for NASA-type applications. Check this for an idea of
how they set up their experiment:
http://arioch.gsfc.nasa.gov/eee_links/vol_01/no_03/eee1-3h.html
(I hope I typed it in correctly)
--
George Franck Jr
Raytheon E-Systems
Falls Church Va.
"The opinions expressed are those of the author, and are not necessarily
those of the Raytheon Corporation."
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