What happens if you solder an IC too hot and too long? Not much until you power up the board. Although, the IC was dead, it still was entertaining to see a nice miniature fireworks as shown in the video.
Unsoldering the IC and replacing it with a new one (this time soldered more carefully) led to a perfectly working system.
There have been two lessons learned: even if there is a lot of work, don’t depend too much on unexperienced students – a failure like this creates more work in the end. And, second, this example shows how quickly things can go wrong when working with hardware. Think of this before adding a component to a safety-critical system.