I'm curious how well a hot air gun would work for reflowing an entire board. My circuit board has about 250 components (including 0402 passives, and a couple of 0.5mm pitch TQFPs) and it's a bit of a pain to assemble it using a soldering iron.

Here's what I was thinking might work:

1. Apply leaded solder paste via a stencil onto the PCB.
2. Place components using a vacuum pick-up tool. Use a stereo microscope to place the more fine pitched parts.
3. Once all the components have been placed, place the PCB onto a pre-heater and raise the temperature to, say, 100˚C.
4. Start the hot air gun and slowly sweep it over the board as the paste reflow. I could utilize a fixture [like this](http://www.tequipment.net/Hakko999-224B.html) to keep the gun perpendicular to the board and just move the gun in the x-y plane.

It would take some time to sweep the gun over the board and ensure all of the paste has reflowed and during this time the pre-heater would still be on. Could this possibly damage the board? What about all the parts? Are there any other pitfalls that I might encounter or would this method work well?

I know there are better methods to reflow a board, like a reflow oven, but I'm specifically interested in how this method would work.