Let the copper melt the solder, not the torch. If you heat the joint for too long, the flux will burn, and the solder may not ...

Copper is a relatively soft metal ... avoid directly preheating the top of the joint to avoid burning the soldering flux.

Copper wire would work better ... as a barrier that helps solder not escape too far away from the pins. Copious amounts of flux likely desired for this one! Hopefully, this comes handy if you ...

without the capillary action of the copper, the surface tension of the molten solder would just form a big blob. They do mention a special “no-flux 96S solder” at 24:20; could that be the secret?