Hi TechNet! I just love it when someone other than Sir Doug uses the
standard process question answer of "it depends"! Our experiences at
Rockwell Collins very much mirror Peter's experiences with BGA components.
We have achieved solder joint life improvements of 2-3X when underfilling
CSPs. I expect that we will see the same improvement for BGAs when our DOE
is completed (we have surpassed the 500 total cycle mark on the way to 2000
cycles - more news to report later this year). The improvement in solder
joint life is not free - the underfill process is an extra manufacturing
step, adds cost to the assembly, can turn your assemblies into
non-repairable units depending on the type of underfill material used, and
can change some thermal aspects of the area array components. Peter said it
best - an evaluation of what underfill can/can't do you your situation is a
good idea. Good luck - I'm off in search of a morning Coke!
Dave Hillman
Rockwell Collins
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[log in to unmask]@ipc.org> on 05/14/2002 08:01:22 PM
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Subject: Re: [TN] BGA's on ruggedized assemblies...
Our Rockwell friends, through the fumes of Mountain Dew and Coke, will say
"No" if your attachment processes are good enough. Personally, though,
after some early (low level) vibration failures with some third party
designed and assembled boards, I built some more to my own spec and
introduced underfilling as an insurance policy. I hope to be able to
vibration qual test boards with and without underfilling to see if this
process is really necessary.
To answer your question, it depends .... on your processes, the operating
conditions and expected life of the product, and maybe even the board and
BGA materials. Underfill manufacturers claim that using underfill can
improve the fatigue life of BGA solder joints by a factor between 3 and 5,
but it is another process and it involves heating boards an extra time (if
you use the capillary action type underfill) to carry out the underfill
process and cure the material. The no-flow type is applied and cured
concurrently with the assembly of the BGA onto the board and doesn't
involve the extra thermal excursion.
I recommend you try qualifying boards with underfill and without it to see
if you need the extra process. Underfilling is not necessary in all
situations, nor a recommendation, but it won't do any harm either if you
want to use it anyway.
Peter
[log in to unmask] 15/05/2002 05:08 AM
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Subject: [TN] BGA's on ruggedized assemblies...
Hi All!
Gotta question, when BGA's are used on ruggedized assemblies (at least
Level-4, probably Level-5), is underfilling BGA's recommended, or a
necessity?
Thanks, as always...
-Steve Gregory-
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