I'm a nuts and bolts kind of guy. (some would say crude)  When I get a
suspect BGA joint, I take a small rotary tool (like a Dremel, only there
are lighter, better units) and a diamond burr (McMaster Carr and MSC
carry these) and go through the part to the suspect joint.  This is fast
and doesn't destroy evidence (if you've got a decent "touch").  You need
to add a few drops of DI water (just use supermarket variety distilled
if you don't have it on hand) to lubricate the cut and get rid of
debris.  Work under a decent stereoptic microscope.  You may want to
practice on another part first to get the hang of it.  This also answers
the question "How do I rework a BGA which has been underfilled?"

Wayne Thayer

>>> [log in to unmask] 5/30/2006 12:11 pm >>>
Hi Jon,

My application is when we encounter an open in a net containing one or
more
of these
entombed solder balls.  We usually can isolate a fault down to a single
net
through our
diagnostics.  We can electrically test the PCB or BGA once we remove
the
BGA, but this
destroys any evidence of the root cause if the problem was in the
solder
joint.  I am
more concerned about cracks and other types of defects in the solder
joint.
I guess that
this could include unsoldered balls (solder paste application defect)
and
insufficiently
melted solder balls (assembly process defect).  If the problem is a
solder
joint defect,
our goal is to understand enough of the source of the defect to
determine
the extent
of any latent problems in the field and work to prevent similar
problems in
the future.

Thanks.

Andy







[log in to unmask] on 05/30/2006 11:29:12 AM

Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please
respond to
      [log in to unmask]

To:   [log in to unmask]
cc:    (bcc: Andrew Shieh/CSP)
Subject:  Re: [TN] solder ball analysis




When you are looking at the balls on the BGA for this analysis, what
features are you looking to find?  Crack? Opens? Unsoldered balls?  I
know
that
Micro-CT imaging can get down to sub-micron feature sizes in  3-D.
Does
that get
you the detail you need?

Jon Moore

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