Many years ago, there was a guy in New England selling a photo-optically
triggered vibratory system for that very purpose.  The problem was, as John
pointed out with his bearing problem, the vibration may or may not help
self-alignment during reflow, but you don't want it (and this $25K system
could not prevent)  vibration during cooldown.  Besides crappy looking joints
there is a good chance of void formation.
All of the oven people have known about the vibration-aiding-alignment
scenario for years and, as competitive as reflow ovens were and still are,
not one has ever offered it as an option.  Why? Because they know it is
likely harmful.  Vibratory assist during repair is sometimes done since you
can cease vibration during the cooldown portion of the profile cycle.  Note
that Conceptronic offered vibratory assist on their series of repair stations
but not on their ovens.  They knew!
Of course, there is the matter of principle - the oven should not be relied
upon to compensate for the sins of the pick and place.  If a pick and place
machine is properly programed, calibrated and maintained, it should be
putting that component down properly.
Leave the good vibrations to the Beach Boys!
Regards,
Phil Zarrow
ITM Consulting
Durham, NH  USA
www.ITM-SMT.com
Tel: 603-868-1754
fax: 603-868-3623
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