For prototyping, or when reworking a PCB and in need to (re)solder small SMD packages, everyone suggests first to fix opposite corner pins with a gentle touch of a solder, and then do the rest of this juvelry work. Probably it works Ok with reasonably big SMD packages.This time I needed to fix a fleа size SSOP-20 (0.65mm pitch) on a minimalistic SMD-to-DIP adaptor. Certainly adaptor board did not want to stay still on my desk. But the worst thing was - how to hold that SSOP-20 well positioned while grubbing the soldering iron and then trying to touch pads _on_the_opposite_sides_! Mind you I have steady hands and am used to deal with tiny things right from my childhood.The solution came easy in the form of a sticky tape. I luckily had an aluminium one at hand. I believe that a paper one, used widely by painters - will do the job equally well.
I used a little soldering iron with the fine round tip. The tip must be clean, hot and well covered by the solder. All connections were covered by a pine rosin dissolved in alcohol. Other liquid flux would probably work as well - just make sure you clean the board thorogly afterwards.
Seldom there were shorts - those were easy to roll away from the case and make them disappear. I just had to shake off all excess of the solder from the soldering tip before.
My beloved one suggested to use a small drop of glue in order to hold the tiny case in place. In production this technic is used widely. But somehow I felt more comfortable with that sticky tape - I was not dependant at all on the time needed for the glue to bound.
For those curious readers: the chip was 10-channels 10-bits DAC.