Why does my soldering iron tip turn black and not melt solder?

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Short Answer: The tip is oxidized — you've been running it hot without keeping it tinned with fresh solder.

Detailed: A soldering iron tip is copper plated with iron. At high temperatures (350°C+), exposed iron reacts with oxygen to form black iron oxide. Solder won't wet (stick to) oxide.

Prevention:

  • Always keep a small blob of solder on the tip when idle

  • Use brass wool (not a wet sponge — thermal shock cracks tips)

  • Set temperature to 300–330°C for leaded solder, 350–380°C for lead-free

Fix (if not pitted):

  1. Clean with brass sponge

  2. Apply fresh rosin-core solder

  3. Wipe on damp sponge (quickly)

  4. Repeat until solder flows evenly

If tip is pitted or has holes: Replace it. Tips are consumables ($2–10).

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