Hi Richard. This is a bit late but hopefully it can help out others who have the same issue.
The melting point for lead-free solder is ~220C, depending on the actual alloy. That means you need to get the logic board, IC and solder to that temperature in order to get the solder to "flow". Setting your hot air station at 220C doesn't work for several reasons:
- Unless you have calibrated your hot air station, it could be off by as much +/- 20C, especially lower cost stations.
- The measured temperature of a hot air station is somewhere within the metal tube, before exiting via the nozzle. This will depend on the station but this means that the actual air temperature hitting the logic board will be significantly lower due to heat loss as it passes through ambient air.
- Finally, to bring the board temperature to the melting point, you have to apply more heat to take into account all of the losses. You also have to find a good balance between being too hot to melt plastics near your target and not hot enough that it takes too long causing collateral damage.
Ultimately, you have to experiment with your station and your technique but most techs doing mobile repair use 360-380C.