That usually means the tip is oxidized and no longer properly tinned, which prevents heat from transferring to the solder. A healthy tip should look shiny, not black and dull.
Here’s what’s going on and how to fix it:
Why it happens
- Oxidation from heat + air – If the tip sits hot without solder on it, it forms a black oxide layer.
- Too high temperature – Running your iron hotter than needed accelerates oxidation.
- Poor-quality or old tips – Cheaper plating wears out faster.
- Not tinning the tip regularly – The solder coating protects the metal underneath.
Why it won’t melt solder
Solder melts from heat transfer, not just temperature. That black layer acts like insulation, so even if your iron is hot, the heat isn’t reaching the solder effectively.
How to fix it
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Clean the tip
- Use a damp sponge or brass wool (better than sponge for less thermal shock).
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Re-tin immediately
- Apply fresh solder while the tip is hot so it coats the surface.
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Use tip cleaner/activator
- If it’s badly oxidized, a tip tinner (flux + solder mix) can restore it.
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Lower the temperature
- Around 320–370°C is enough for most electronics.
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Keep it tinned
- Always leave a thin layer of solder on the tip when idle.
If it’s too far gone
If the tip stays black and solder won’t stick even after cleaning and tinning, the plating is likely damaged—at that point, replacing the tip is the only real fix.
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