In a message dated 5/7/99 3:00:30 PM Pacific Daylight Time, [log in to unmask]
writes:
<< As many of you, I have been concerned and questioned voiding %
and volume plus all the rest. However, I keep coming back to
one thing haunting. What's in the voids?
In other times, I found horrific problems with residual flux
entrapped in the voids. This often was effected by solder
termination area contamination. The flux remained in the joint
trying to do what was intended - fight the infection. Often,
this resulted in failures as the solder joint continued to fail
as it was "erroded" away.
Certainly, X-Ray points the way to what is to be X-Sectioned.
Beyond that, some type chemical analysis technique needs to
examine the residue left in the void. I have graphic evidence
of this phenomonom as, probably, do most of you. Does this
continue to be an issue in the BGA world as it did/does in the
PLCC/QFP arena?
Earl Moon >>
Hi ya Earl!
Haven't heard from you inna while...was wondering when you'd get back into
the fray! Anyways, about these voids. On the ones that you have found
contaminated with something, where were they? Up inside the ball, or more
down towards the ball/pad interface?
It goes back to how the void was created in the first place. I've read and
heard that many times you stand a very good chance of creating voids if your
reflow profile isn't what it needs to be, and that seems pretty logical to
me. Perhaps if you don't give yourself enough time to drive all the volatiles
off the way you should, and then spike the crap out of the board, zoom it out
of the oven to cool down quickly, I can see where you would have a good
chance of creating a bubble or two inside the joints.
To me, a good sized BGA with it's connections buried deep inside beneath the
body is going to take quite a bit longer to have all the volatiles driven off
the way a gull wing part or "J-leaded" part does, simply because the interior
of the BGA is not getting the benefit of the convection heating and swirling
air he way the other parts do...it's getting it's heat from the radiation of
heating package body and the PCB...am I off base here?
So what I'm saying, is that maybe you need to stretch the profile out for a
longer period of time on a board that has BGA's on it so you can be sure that
all of the volatiles are driven off, and that you've given enough time to
truely preheat things thoroughly. Instead of the normal 4.5 to 5 minute
profiles that most of us are used to, maybe it should be more like 5 to 6
minutes or whatever...heck, I'm just thinking out loud here.
I just think that instead of worrying how big a void can be and live with it
when you see it in a x-ray, we need to really figure out what's causing them
and not do that anymore...then we won't need an x-ray.
I can't afford one anyway...you guys get all the fun toys! (sniff, sniff....)
-Steve Gregory-
P.S. Did any of you check out that ERSA inspection system that Paul told ya'
about? ( http://www.ersa.de/inspec.htm ) I'd take a look at it if I were
you...no kidding, it's one of the coolest pieces of inspection equipment I've
ever seen!
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