Quote:
Originally Posted by Rick76
There is no need to remove the old solder but you will need to add a bit of fresh electronics grade rosin core solder to the joint. Just reheating is not adequate for a good joint.
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Adding to this advice, if you have a really NASTY looking joint, use some solder wick and remove the old solder, preheat the pad and pin well with the iron, then flow in some fresh solder. My go-to solder alloy is a 63/37 with No-Clean flux from Kester. The higher tin content makes it a harder joint than 60/40 and it tends to wick better. After soldering, clean the flux residue with some denatured alcohol and a toothbrush.