If so many mcus are defective wouldn't it make sense to have them all removed and swapped for new ones by a machine and leave the testing for a later time? (I don't know if there is a desoldering machine)
Even 37 boards/day is painfully slow with the total number of boards in mind and it must be quite tiring to do it all by hand time and time again.
IT will be by hand again.Even 37 boards/day is painfully slow with the total number of boards in mind and it must be quite tiring to do it all by hand time and time again.
And OP, please remove the TROLL;)
So There isn't any machine that can desolder them.
Then why not making it, perhaps making it fully automated is not an option but what about machining a copper tip with the exact shape for the mcu. A small hole for a thermocouple and series of channels to connect a venturi to suck the solder away. Even doing it by hand that way you could replace hundreds/day.
And to test them you could also make some kind of contraption to speed up things.
In fact being abble to work with metal you could also make frames for the 4 heatsinks that doesn't even need screws so adding a bit of thermal paste is all that is needed to change the boards for testing. If you need it I can make a drawing of what I mean.
I am not disputing your expertise but maybe some fresh ideas would help speeding up things.