Arduino onboard LEDs, what are the specs/names?

Ordered some 1206 leds, figured a little bigger is better since I'll be hand soldering them.

Now the question is to go at it with traditional rosin core solder or pick up some 'solder paste'.

If I dab a little solder from the rosin core solder wire onto my soldering tip, does any of that flux make it onto the surfaces to clean/wet or does it cook off pretty quickly?