I have seen literally hundreds of thousands of BGAs reballed many I
performed myself, with both convection methods as well as using a
proprietary laser ball attachment process. I was the engineer for these
processes either at companies I have worked for in the past, or with
companies I currently work for (I am a consulting engineer for several
companies as well as being an employee of GD).
If done properly using a controlled method, such as the paper pre-forms
from Six Sigma/Winslow Automation or with solder spheres poured into the
appropriate stencil, in conjunction with a set convection reflow
profile, along with an automated ball removal method (not a hot-air
vacuum method, however) I have never seen a BGA fail prematurely because
it was re-balled. I have seen many fail because the process was not
controlled, however. When critical steps such as pre-bake are skipped
the components will not survive, or their reliability will be reduced.
Use of the wrong fluxes, improper rework methods, improper reflow
profiles, etc. can also cause issues.
I have twice captured field reliability data from BGAs that were
re-balled, both with BGAs reballed using convection and with those
re-balled using laser. Both were instances where a number of BGAs needed
to be removed, re-balled, and replaced. The first instance was to put
the parts on a different PWB, the second instance was to change the
alloy from Sn63 to Kester K100DL, but not to meet RoHS requirements.
In both instances, the re-balled BGAs had longer mean times before
failure than the BGAs that were never re-balled. While I am not
absolutely certain as to why, I believe it is because the SJs on the
re-balled BGAs were superior due to the fact that new balls were added
to the BGA pads that had been essentially pre-tinned during the removal
of the original solder balls and the site prep performed on the BGA
pads.
While working for Analog Technologies in Burnsville, Mn, we developed a
laser soldering machine as well as a process for performing laser ball
attachment using a proprietary oxygen evacuation chemical process (read
about it here www.analog-tech.com). This process removes all oxygen from
around the ball during the laser soldering (no nitrogen is used) leaving
behind perfectly pristine solder balls with no wetting issues. This
process also does not heat up the BGA, CSP, or flip chip itself, because
all of the energy is focused on the solder ball and the pad. This
eliminates two of the four heat cycles necessary to remove a BGA, strip
the old solder, reball, and reattach it.
Analog has been performing BGA original ball attachment and re-balling
for several years now, and we have not seen any, repeat, no issues with
BGAs that were either reballed or attached with laser or controlled
convection processes.
BGA rework and reballing is generally a safe procedure, but only as long
as the process is qualified and controlled. All too often I have been
called in to look at rework processes where it is done with a different
method each time depending on which operator did it, what day of the
week it was done, and how the constellations were aligned. The results
were to be expected including delamination of the die, delamination of
the BGA substrate, popcorning, and other issues.
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Elmgren, Peter (GE
EntSol, Security)
Sent: Wednesday, October 07, 2009 9:37 AM
To: [log in to unmask]
Subject: [LF] Quality/Reliability of 're-balled' BGA devices
Anyone have any experience with the quality/reliability of 're-balled'
BGA devices? Specifically, any experience with going from a lead-free
BGA to a leaded BGA?
Thanks,
Pete Elmgren
GE Security, Inc.
(P) 941-308-8180
(C) 941-465-8991
www.gesecurity.com <http://www.gesecurity.com/>
8985 Town Center Parkway
Bradenton, Florida 34202
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