Correct Artur, hence the cracked fet
The hot plate is a great idea, I handn't found that techinque in any of the research I've done. Makes perfect sence though, heat the entire unit up (use the heatsink property of the pcb to your advantage) then deal with the individual part.
What temperature are you using? Do the other components become fragile (movable) at that temp or do you run the plate below the melting point for the solder then use some kind of local heating?