# Soldering iron tip is black and will not take solder: clean and tin it

> Fix a soldering tip that repels solder: clean it on a brass wool or damp sponge, tin it with fresh solder and do not leave it hot and dry.

Canonical: https://roboticsengineering.in/fix/soldering-iron-tip-black-wont-take-solder-tinning/ | Published: 2026-11-03 | Updated: 2026-11-04

**Clean the tip and coat it with a little fresh solder right away.** A tinned tip transfers heat well.

## What the message means

Oxidation forms a black layer on a dry hot tip. Solder will not wet it, and heat does not move into the joint.

## Fix it in this order

1. Wipe the tip on brass wool or a damp sponge.
2. Melt a little fresh solder onto it so it looks shiny.
3. Use the right temperature for the solder, and do not run it too hot.
4. Tin the tip again before you put the iron away.
5. Use tip tinner for a badly oxidised tip.
6. Do not file a plated tip, since the coating protects it.

## Why it happens

Hot bare metal reacts with the air and grows an oxide layer. Solder wets clean metal but not oxide, so on a black tip the solder balls up and the heat has no good path into the joint. The hotter the tip and the longer it sits dry, the faster the layer builds.

Tinning coats the clean tip in a thin film of solder that keeps air off it, and the flux in the solder helps remove light oxide. That is why the order matters: clean first, tin straight away, and tin again before you switch off.

## If you see this, do this

| You see | Do this |
| --- | --- |
| Black tip, solder balls up | Clean and tin. |
| Tip is pitted and worn | Replace it. |

## Related

[cold solder joint](https://roboticsengineering.in/fix/soldering-cold-joint-dull-grey-intermittent/), [loose contacts](https://roboticsengineering.in/fix/loose-breadboard-contacts-intermittent-robot/).

Last reviewed: November 2026. These are the usual causes and the order that finds them fastest. Test on your own board; clones and cables differ.

## Why this happens

Solder bonds to clean metal. A hot bare tip is clean for only a moment, because the iron plating on a copper core reacts with the air and grows a dark oxide layer. Solder then refuses to wet the surface and rolls into a ball. Because the oxide is a poor conductor of heat, the tip may be at the set temperature while the joint stays cold.

Typical temperatures show why waste heat matters. Tin-lead solder of the 63/37 type melts at about 183 degrees C, and lead-free tin-silver-copper types melt around 217 to 220 degrees C. Irons are often used between 300 and 350 degrees C for hand soldering. Running much hotter than that speeds up oxidation without making the joint better. Flux inside the solder wire clears light oxide, and that is why you tin straight after cleaning.

## How to confirm the cause

- Look at the tip. Silver and shiny is good. Black, dull or crusty is oxidised. Dark pits through to copper-coloured metal mean the iron plating has worn through and the tip is finished.
- Touch a little fresh solder to the cleaned tip. If it spreads into a thin bright film, the tip is good. If it beads up and slides off, the surface is still oxidised.
- Check the set temperature on the station display. If your iron has no display, note whether the solder melts within a second or two when touched to the tip.
- Check that the tip sits fully in the heater and is tightened. A loose tip makes a poor thermal contact, even when it is clean.
- Notice how long the iron sits unused between joints. Long idle periods at full temperature are the usual cause of recurring black tips.

## Worked example

A routine for reviving a tip, written as steps:

```
1. Set the iron to your normal working temperature, not higher.
2. Wipe the tip through brass wool (or a damp sponge) to remove loose oxide.
3. Feed fresh flux-core solder onto the tip until the whole working face is shiny.
4. Wipe once more and add a small fresh drop of solder.
5. Test: touch a pad. The solder should flow and spread within 1-2 seconds.
6. Before switching off, leave a rounded blob of solder on the tip.
```

## Common mistakes

- Filing or sanding a plated tip, which removes the protective plating.
- Using a very wet sponge all the time. The sudden cooling stresses the tip; brass wool does not cool the tip as much.
- Leaving the iron at maximum temperature while you think or search for parts.
- Using thick blobs of old solder as a heat bridge instead of keeping the tip clean.
- Pressing hard on the pad. Pressure damages the tip and the board, but does not move more heat.

## If this did not fix it

- Worn tip: dark pitting that cleaning does not remove means the tip needs replacing.
- Heat loss to a large copper area or a thick component leg; try a larger tip or preheat the board.
- Dirty pads or component legs. Oxidised copper does not wet either, so clean the work too.