I have been successful soldering BGA parts using a hot air rework station, I got one new for ~$600 with an integrated air compressor that I use all the time. Before I had the electronic one I didn't have the worst luck with butane torch style "soldering irons" with the tip removed which ends up amounting to a tiny hand held uncontrolled temperature hot air rework station. I never tried soldering anything so small with that though. The air flow tends to bump parts around if they aren't registered just right and 0.5mm is very small to register right by hand.