i have seen this forward wave tickling trick on youtube, and tried today.
it worked sometimes!
soldering tiny pins using a standard iron.
sometimes it did not work. a few PCB traces moved off due to heat.
these are 0.4 mm pitch for the pins! 100 pins. new microchip USB microcontrollers.
for the bottom one, only half of the pins is soldered. traces have to be cut, and connected to the upper deck using magnet wire.
but the soldering is much better, all pins connected correctly.
the top one PCB still has a few shorts, i have measured most of them but it is very tiny stuff. two of the rows are nearly perfect, all pins soldered cleanly.
i guess the problems relate to a little as 0.1mm alignment error, very difficult to do for human, without any help (such as a lens magnifier).
and the wave soldering trick requires a special tip normally. it did not really work, just a little.
the PIC on the left has "only" 64 pins, more easy, 0.5 mm pitch. now the plan is to power them up in the near future.