When I was employed at Motorola I operated the Bump machine which was
designed to make LGA's into BGA's. We found at Motorola that we could
save thousands of dollars every year by reworking or re-balling our own
BGA's. However it took some fabrication of make shift tooling. 1st a hot
plate with a counter sink to hold the back side of the part and ensure
no solder was depositied to the casing was used to reflow the existing
solder and ball's. Then by using a small square of ESD safe manilla
folder the ball's and solder would be skimmed off the pads and into the
hot plate leaving a flat tinned surface. Then a hand held manual screen
print was created with a counter sunk holding device and a stencil with
apetures the same configuration of the solder pads. a small amount of
solder paste was squeeged over the apetures leaving sufficient paste
deposited on the pads. Then the component was placed into another make
shift tool that worked a lot like the dollar toys were the main object
is to shake and maneuver the hand piece until all the balls are in their
perspective holes. Upon careful removal of the top layer of the device a
BGA with wet solder paste and balls could then be sent through the
convection oven to reflow. As this was done by make shift tooling often
additional reflow on an open belt with a dental pick or exacto was
required to ensure propper ball alignment. then of course the parts had
to be propperly cleaned of all flux residue. We re-balled BGA's of all
types, microprocessors etc with metal casings. no ceramic or plastic
casings were ever done. Technology may have come farther than this in
the last 3 years but at the time parts were often flown into the
facility on special order to have us re-ball and send back as not very
many had this capability

Pro's once the tooling and training is in place you can save dollars
$$$$
Con's if the person performing the operation is not percise you will
continually see shorting issues and if not cleaned properly most pick
and place machines will have a difficult time reading and placing the
re-worked component. Other cons can include the reduction in component
integrity due to the several cycles of heat application  required to
complete the above mentioned process. To my knowledge there is no rule
that speaks against re-work of this type for class 3 however this kind
of re-work may need to be classed with re-work of assemblies which
requires documentation prior to being performed rather then the re-work
of an unsolderable component which does not require documentation.

>>> [log in to unmask] 11/9/2004 4:23:51 PM >>>

November 9, 2004

We have an OEM who has some de-laminated PWA'S with some BGA'S
installed.  He wants to salvage the parts and have them re-balled.  I
have no direct experience in this area.  How does one re-ball a BGA?
What types of BGA can be re-balled?  What are the pros and cons on
re-balling?  Is this an acceptable repair method for Class 3 product?
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If not, why not?


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