It appears as if you had checked most of the common failure modes. The fact
that the "dot" was flat, indicates the components are not adhering to the
component. This is most likely due to a surface contamination.  The most
common contaminant we have observed is a silicone contamination on the
component. This can be from a mold release agent used in the component
molding process or Si-compound migration from other parts of the facility.
If you would like we can discuss further off line.

Brian J. Toleno, Ph.D.
Sr. Applications Chemist
Loctite Electronics
15051 East Don Julian Rd
Industry, CA 91746
Ph: 626-968-6511 x304
Cell: 626-390-9562

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