The reaction, in one paragraph
A soldering tip is a copper body with a nickel barrier and an iron working layer. Copper wets beautifully and dissolves into tin almost immediately, which is why it cannot be the surface that touches the joint. Iron does not wet as readily, but it does react: tin and iron form FeSn2 intermetallic at the interface, and that layer is carried away into the solder bath or the joint.
The rate climbs sharply with temperature. A station held 100 °C above what the joint needs will consume the iron layer far faster than one set correctly, even if both produce acceptable joints on the first shift. Idle time at full setpoint counts too — an oxidised, hot tip is still losing iron.
Why plating thickness alone is not the answer
The obvious response is to plate more iron. It helps, but only if the layer is even. A thick layer with a thin spot fails at that spot: once the iron is breached locally, tin reaches the copper underneath, the tip pits, and the pit grows from the inside. A thinner, uniform layer outlasts a thicker, uneven one on the same joint.
That is why we control plating by measured thickness per batch rather than by time in the bath. Bath time is a proxy; thickness is the variable that matters. The nickel barrier underneath is equally important — without it, copper diffuses outward into the iron layer and changes how it wears.
- Iron layer: the sacrificial working surface that tin slowly dissolves
- Nickel barrier: stops copper migrating into the iron and keeps the interface stable
- Copper body: carries heat; must never be exposed to molten solder
What actually ends a tip's life
Four mechanisms get blamed for a dead tip. Only one is about the iron layer itself:
- Iron breached. Tin reaches copper, the face pits, wetting becomes patchy and then stops.
- Oxidation. The face blackens and stops transferring heat. Cleaning helps; running too hot causes it.
- Mechanical damage. Scraping the face, using it as a pry tool, or grinding it by hand removes the plating outright.
- Aggressive flux. Some flux chemistries accelerate corrosion of the plating at the wetting line.
In practice these arrive together. A tip that is run hot oxidises faster, is scraped more often to clean it, and loses iron faster — so the observed failure is a mixture, not a single cause.
How to read a worn tip
| What you see | Likely cause | What to check first |
|---|---|---|
| Black, dry face that will not take solder | Oxidation, often from high idle temperature | Setpoint and idle / sleep settings |
| One small pit or crater on the face | Iron layer breached locally | Plating uniformity of the batch, flux chemistry |
| Face looks eroded all over, tip shorter | General iron dissolution over a long duty cycle | Plating thickness record for that batch |
| Wetting fine but joint is cold | Poor seating or low thermal contact, not wear | Shank diameter against the drawing (±0.05 mm) |
If the fourth row is your symptom, the tip is not worn — it is the wrong fit. A dimension report and a check of the shank will settle it in a minute.
