I have looked at some data sheets for QFP processors and they say the max temp should only be 200 degrees. I can't drag solder at that temperature I don't think.
For one thing, not all chips are made equal. Some are more sensitive than others.
But when it comes to soldering with an iron, but the 200 degrees is not w/e temp you set the iron to. 200C is very reasonable to do by drag soldering.
You set your iron higher (300-350C, typically) so that the joint will reach about 200 degrees.