720 is hot... try more like 660-670

If you haven't already... sand the pads in question till they are nice and uniformly shiny.

Use alchohol and clean off the surfaces. Assemble the bits and use some brush on flux.

Make sure your tip is adequately reaching both surfaces to solder.

The only times I've had failures beyond that are
1) Dirty joints causing poor heat transfer
2) Some god awful hideous solder I got from marco one time. Stuff wouldn't stick to anything

True flux usually makes quick work of a troublesome point.

That looks alot like the shit solder I got from Marco. Solder would sit in a ball and not wet and shape to the leads. Either shit solder, or you are not getting heat transfer to the leads. Clean it out, clean up the joints, check your tip, use some flux.. try again.