Fellow TechNetters:  Recently having a problem with solder fillets on various SMT assemblies, we
are observing an outgassing in the concave portion of the solder fillet of various resistor package
sizes.  Specifically, 0603, 0805, and 2010 packages.  The outgassing is either a slight, hollow bump
or a "blowhole" and always in the center of the fillet.  If we observe the condition, we switch the reel,
and the problem generally goes away.

It is only happening with resistors, not any other SMT package.  The observations have now occurred
in two separate facilities, with the reels of resistors having date codes from 2009 thru 2011.  We have not
changed solder paste, using a no-clean paste from a major manufacturer.

Is anybody having issues with SMT resistors?  Can anyone shed any light on this absolutely random issue?

Your thoughts and comments are greatly appreciated.

THANK YOU,
Bill

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