Actually I was not impressed with the video of the QFN being placed on the PS board in an earlier post. I don't think the guy doing the work was really happy with it either. While he got theleads to flow, the was no real effort to get the heat sink to flow. He played with the edges.
Ya you are right that was not the best technique. Check some of the links I posted. I think having read a lot of the specs today and researching stencils etc you can do this fairly easily at home.
The QFN 48 not that small if you have the right tools.
1. The proper stencil for either the chip itself or the pcb land area
2. Heat gun or professional grade soldering iron with a fine tip
If you have a good stencil with the right solder and a steady hand then you can bump the chips with a heat gun then set the chips on the PCB properly and use the heat gun to get your chips mated to the PCB. Or stencil the solder on the PCB and heat the chips carefully with the heat gun and get a good reflow profile going.
110v KADA 852D+ Rework Station Repairing System hot air
http://www.aliexpress.com/item/Freeshipping-soldering-station-Same-work-day-ship-out-110v-KADA-852D-Rework-Station-Repairing-System-hot/532004861.html
http://www.soldertools.net/pages/-StencilMate%E2%84%A2.html
http://www.youtube.com/watch?feature=player_embedded&v=IhUGXEom6IM
http://www.soldertools.net/pages/Metal---Stencils.html