Good Morning Technetters,

I have been reading this forum for some time now and have thoroughly
enjoyed learning from group
(including the lesson on good and bad puns).

I am hoping that the collective wisdom can help me out again.  We are a
manufacturer of embedded
computer boards for the military industry.  As a result, these board tend
to be fairly complex, very dense,
and very expensive.  Some of our boards are conformally coated and the BGA
components are underfilled.
The conformal coat is removable with solvent and the underfill is
reworkable at solder rework temperatures.

My problem is failure analysis of the solder balls that may be embedded in
the underfill.  Thusfar, we have
not had a significant problem, but I am still stuck with the dilemma of how
to analyze a solder joint problem
without destructive cross-sectioning of the very expensive PCB assembly.

On boards without underfill/conformal coat, we have had good success in
many cases with optical imaging
under the BGA package (Ersascope).  On the underfilled boards, we have
tried acoustic imaging and
several X-ray systems, but none seem to provide the resolution necessary to
determine a possible solder
joint problem.  Due to the cost of these assemblies and our need to provide
the utmost in product reliability,
I would like to consider any means of analyzing a suspect solder joint,
without having to cross sectioning
the board unless I know that there really is a solder joint problem (as
opposed to a component or
PCB/HDI problem).

I was wondering if any Technetters have come upon a similar problem and
found a solution.
Thanks!


Andrew Shieh

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