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What tip should I be using to solder wires together?
(lemmy.fmhy.ml)
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Outside of a few specific cases, a standard chisel tip is all you need. Yes, even for surface mount.
The wires found in some thin flexible cables (like USB or headphone cables) are sometimes coated. Solder won't stick unless you get it hot enough to burn off the coating, or scrape it off before soldering.