I have a high wattage iron I use mainly for Cardas binding posts. I think it is 80 watts but don't recall exactly. After the iron is fully heated up, I place the tip firmly against the outside of the post while the wire I intend to attach to it is resting in the opening of the post. (The wire is tinned in advance.). After 5 seconds or so, the interior of the post is hot enough that I can apply Cardas solder to the interior of the opening and it flows quickly and smoothly over the wire and along its sides where it is touching the post. I only use enough solder to coat the wire and have it join smoothly to the post. Then I quickly place the flat tip of a screwdriver on the wire and press it firmly against the wire and post while the solder cools. To be on the safe side, I leave the screwdriver there for 10 or 15 seconds until I am sure the joint is secure. The keys are to make sure there is a good mechanical connection, use enough heat, make sure the joint is fully heated up before solder is applied, and don't let anything move before the solder cools. Works every time.