I was practicing desoldering components with a desoldering heat gun (Quick 861DW) of some boards I salvaged from a broken Sony Bravia HD-Ready monitor.
I applied 400C air flow and used some flux on the pads of the SMD capacitors.
On the first board I practiced with, they all came off nicely without discoloration or anything (in some the plastic did get a bit burnt,) but on a second board I tried with (using the same procedure,) they all started to inflate before the solder melting point and being able to detach them.
Why would that be? Would it be because of the substrate board material? The capacitors seem to be the same type.
Here are some photos of the first board and capacitors that came out well:
Here are photos of the second board and capacitors, they are turned as I had to twist them to release the air pressure before they exploded:
After that I tried with another different board and again they were all removed without problems.