It seems to me like you could just use an ordinary syringe in the Z-axis.
Then increment a stepper motor to depress the syringe however many steps it
takes to place an appropriate sized drop of solder on the board. You
shouldn't need to mess with pressurized air or vacuums.
Paul Symansky
Biology
A&S 2009
954.478.7285
http://www.symtechlabs.com [Non-text portions of this message have been removed]