It helps to use solder paste, a proper dispenser, and a proper SMD hot air knife with appropriate nozzles. Someone recently mentioned a solder wave process using a soldering iron and a largish tip to drag a blob of solder along over the IC legs, relying on surface tension to leave just the right amount of solder on each connection. I did a small amount of this using Pace equipment. The procedure we used is a bit different. Instead of solder, use solder paste.
Solder paste is flux with microscopic beads of solder mixed in.
The solder paste is held in small cartridges mounted in a gun, like a miniature caulking gun. The paste should be new or kept fresh in a refridgerator. Turn down the pressure and turn up the heat until the jet of air is hot enough to turn tissue paper brown in just a few seconds. Make sure the smt pads are clean and well tinned. If they are not clean and shiny, use solvent and brush to clean, or tin as necessary.