Greetings all,

I'm in the process of generating in-house criteria regarding solder balls
on assembled no-clean SMT boards.  Most of our boards have large conductor
clearances (withno fine pitch devices on most boards).  The IPC-A-610
guideline defines as a defect,  any ball that violates minimum electrical
clearances or are not entrapped in a PERMANENT coating or attached to a
metal contact.

I'd like to hear whether y'all consider a fairly heavy coat of RMA type
no-clean flux (from Kester 244L solder paste), to be a "permanent" coating,
when not run through any post reflow cleaning cycle.  I'm specifically mean
the "squeeze out" type solder balls (typically .005" - .010" in diameter)
that tend to occasionally form along the sides of caps and resistors.
These are greatly reduced by using homebase style pads. proper stencil
thickness, and proper reflow profiling, but still do occur occasionally
(even though I hate to admit it).

Though I would tend to think of "permanent coatings" as applying more to
conformal coatings than to RMA flux residues, I also  tend to feel that the
flux that naturally entraps these ball isn't going to let them loose,
unless shaken like the banshees.  But I'm interested in hearing of any
actual testing or opinions of other OEM's, assemblers, or paste
manufacturers.

Thanks for any and all responses,

Larry Morse
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