These have a pad on the bottom and so need some serious heat to move them!
You have to "soak" the whole board from the bottom with hot air (approximately 150 deg C). Then you don't need too much heat from the top.
Hi
There are a lot of variables here:
1) How much heat was used to remove the parts from their old boards?
2) Were the parts damaged before they were pulled (over voltage ...)?
3) How were the parts stored after they were pulled (ESD etc)?
4) How well are the temperatures on your hot air system controlled / set?
5) How is solder put down on the new board?
6) How was solder removed from the "pulled" parts?
7) Were leads bent / damaged on the pulled parts?
That's only getting into the obvious parts of the list. If you have parts with ground pads in the middle of the chip, there's a full list just for them....
Bob