Yesterday, I had the great pleasure to solder a tiny 4 x 4 mm op amp with 16 legs (AD8336).

I figured out that the best and fastest way to do it is

1. to put solder with the soldering iron on every contact of the electronic board (top side)
2. heat the bottom side of the electronic board with a heat gun
3. use a needle to test if the solder is melted
4. if it is melted place the op amp on the electronic board
5. apply some vertical force on the op amp for proper contact and heat for 1 to 2 more minutes
6. done