heating the chip itself with hot air set to 350 C results in a consistent temp of 180 C. So the chip is absorbing 170 C.
So if the solder has a melting point of 158C, I should be good. There is a 20 degree difference between top heat and bottom heat, which is going to have to be acceptable. I may start off with a lower hot air temp, maybe 320 C. That should result in the top heat being 160C and the bottom heat right about 160C. If I don't get good results, I will have to step up the hot air.
I'm not sure if I want the hot air to be 30 degrees hotter than the board temp. I think I would rather have both temps be as close as possible. I could just heat for a longer period of time. That way the heat distribution should be pretty even.