The humbucker bottom plate and cover can act like a heat-sink and it can be difficult trying to heat the solder joint hot enough to remove the solder. If you don’t carefully remove the majority of solder than the solder burrs can damage the coil. Trying to heat the solder joint with a small tip or low wattage soldering iron will be insufficient in removing the solder properly which usually leads to using a screwdriver or kitchen knife to pry the cover off thus damaging the coils. Also using soldering “guns”, the ones with a large coil can de-magnetize the magnets in the pickup.