Jason,
I can't tell you off the top of my head where to get the data from, but I
can tell you that there are studies that address voids in solder joints.
If my memory serves me correctly, the final analysis showed that in most
cases the joints integrity was not effected. In fact, in many cases it was
actually enhanced. The reason was, that in those cases where cracks may
start to propagate in the joint, they stopped at the internal voids. Versus
continuing through the whole joint if it was solid.
Personally, I prefer to see a solid joint. But, given that it may not be
possible in specific cases then past studies and data supports it as being
robust.
These studies were focused on BGA joints big-time.
Bill Yacovitch
Principal Engineer, NPPI
Mercury Computer Systems
[log in to unmask]
-----Original Message-----
From: Jason Gregory [mailto:[log in to unmask]]
Sent: Thursday, February 14, 2002 9:06 AM
To: [log in to unmask]
Subject: [TN] Vacuolar porosity under leads
I have a question regarding vacuolar porosity under leads.
A potential customer has forwarded me some CAD data and will send me some
boards for me to inspect using our 5DX X-ray. His concerns are that during
reflow, the flux attempts to outgas and stops just short of total outgassing
when the joint solidifies. This situation then forms "pockets" in the joint
in the lead/pad interconnect.
My question is this - Has anyone done any studies regarding this phenomena
and if so, does this affect the integrity of the joint? My belief has always
been that the structure and formation of the heel portion of the joint
comprises the actual integrity of the joint and the toe fillet (or lack
thereof) does not play into the lifespan (or strength) of the joint.
Therefore, the lead/pad interconnect would also not be the main point of
contention.
In Alabama, we had some components (QFP48) that had a ground lug on the
bottom part of the package that was soldered to a pad directly beneath. The
lug was approximately 1mm by 1mm and the pad was approximately 7/10mm by
7/10mm. In this case, the porosity dilemma was evident. We would see,
through 3D laminography, that large voids were formed, causing roughly a 40%
or so decrease in actual solder interconnect area. Some playing around with
the reflow profile displayed better results, but never resolved the issue.
Any thoughts/comments would be greatly appreciated.
Thanks,
Jason Gregory
Software Specialist
Sanmina-SCI - Tech Center Austin
15508 Bratton Lane
Austin, Tx. 78728
(512)246-5648
[log in to unmask]
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