Bob, heatsinks on a PCB are fun. I usually preheat the solder lugs before I insert it into the board, then I use a solder bridge method. Just put some solder on the iron tip before you place it at the joint, this helps get things flowing. It is a PITA if you ruin pads and lift traces, that's why I don't think I'll build any more fully PCB based components. I like to tweak and soldering and desoldering repetitively is a quick way to trash a board. Hope this helps.
Cheers,
Shawn