I just gained some experience, I would like to share here.
After I finished the design and test tens of PCB samples of new product (RDM-DMX LED pixel bar luminaire) based on ATmega328P,
I prepared production file and embark to produce 300 samples (6 different models) of final luminaires.
Every thing seemed normal so far since all products successfully passed the individual tests and activation processes.
Then when I put all luminaires together and made a whole system test, the hidden calamity unveiled !
I forgot to set BOD fuse bits in production file !! :/
100 of them were disassembled and reprogrammed again, I happily did it! (5 days rework)
but my real punishment is to rework the remaining 200 pcs of luminairs which are filled with insulation resin ...
There is no way to disassmble them and reach the ISP pins which is burried under insulation resin.
firstly the metal enclosure must be CNC milled , then the insulation resin should be digged.
long days of rework are waiting for me !