Is 250°C and Mid Air flow ok when reflowing chips?

@md20 yes it is. A few words of advice from me are that you need to watch the temperature closely. Do not rely on the thermometer on your reflow machine. You need to have that temperature on the actual IC not the nozzle. Use a thermocoupler and make sure you get the right temp. One of the resource I've used in the past is this quick guide Metcal-Profiling-for-successfu.pdf