Gregg,
Destructive tests, whether useful or not, are slow and expensive. I have
tried various ways to evaluate solder joints, but the number of
variants of lead size, lead type, pad properties, grain size, solder
compositions etc was so abundant, that the idea of quality checking by
means of solder destructive tests was abandoned. Instead, we hope that
advanced 3-D X-ray analysis methods will be developed for incoming tests
or final inspection. Some authors mean, that these methods will provide
more data in less time than do traditional cross sectionings and shear
tests. 3-D X-ray is fast and non destructive and will pay back in the
long run. First, one needs collect a large number of X-ray
laminographic slice images from the chip or gull wing solder joints.
These images are then used for meshing in 3-D modeling and producing
high speed reconstructional algorithms. One can draw a parallel with our
new 3-D automatic, contactless inspection machine. In a few seconds,
this machine performs dimensional measurements on hundreds of balls on a
BGA, and presents the results in a number of ways, histograms, tarts,
tables, curves etc. The coplanarity of component is measured in seconds.
Same way, many hope that the 3-D X-ray laminography will be useful for
evaluation of solder joints. In the end, you may have a register of
references for gullwings, SOTs, BGAs and so on, which makes it possible
to check a large number of solder joints in reasonable time. One may
make a comparison with the hundred-year old method of solder joint
inspection: visual inspection. Experienced eyes can get a surprising lot
of information out of just looking in a microscope. Strong and reliable
solder joints pass, and suspect or weak or unreliable joints are
rejected. The 3-D X-ray laminography would compensate for what the human
eye can't see. Like CATscan of a human body.
Maybe, students could work with the development of the mentioned method?
I have not followed what happens here. I saw the first articles 10 years
ago. A lot must have passed since then. Is the method used daily
somewhere? Is the machine affordable?
Inge
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gregg A. Owens
Sent: den 16 mars 2007 19:05
To: [log in to unmask]
Subject: [TN] SMT Solder Joint Strength
Dear Technetters:
Again I have a student asking a good question for which I don't have a
reply.
What IPC standard(s) or test method or methodology does one apply to
test or evaluate the strength of a SMT solder joint adherence to the
land (such as a chip or gull wing).
Thanks,
Gregg Owens, MIT
MTTC, Inc.
Mira Loma, CA 91752
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