Oxidation of Tips with Lead-Free Solder

Why do tips oxidize easily when using lead-free solder?

If you have been working with different types of solder for a long time, you may have noticed that lead-free solder oxidizes soldering tips four to five times faster than normal solder wires.

Lead-free solder wires affect the rate of oxidation in two ways. Firstly, lead by itself is an inhibitor of oxidation. The very presence of lead on the soldering tip prevents the tip from getting oxidized readily. By using lead-free solder, it removes this protective layer, exposing the tip to oxygen. (Source)

Secondly, a normal solder wire, or a eutectic solder wire, is a blend of different types of metal that allows the wire to melt at a lower temperature, as compared to the melting points of each individual metal. Removing lead from this mix to make lead-free solder wire, causes the melting point to increase by approximately 30ºC, from 183ºC to 217ºC. This means that a higher temperature is required to melt the solder, leading to a higher-than-normal temperature being set for the soldering iron. Since oxidation occurs rapidly when the tip is hot, having to melt lead-free solder at a higher temperature speeds up the oxidation process.

Oxidation of the tips reduces the heat transfer from the tip to the solder wire. This results in a cycle where a higher temperature is needed to overcome the lower heat transfer, resulting in quicker oxidation, and so on. 

How to prevent oxidation?

Keep the temperature as low as possible
Never increase the temperature to more than what is required to melt the solder wire.

Switch the power off when not in use
The iron continues to heat up even when it is set aside. Make sure to completely turn off the iron or station when you are done with soldering.

Cleaning the Tip
Use wire-type cleaner such as HAKKO 599B which leaves some amount of solder on the tip when cleaning the tip. Some solder residue helps to prevent oxidization.
Remove oxide using the Hakko FS-100 Chemical Cleaning Paste. In the event that the chemical paste cannot remove the oxides, use the Hakko FT-700 Tip Polisher first and then use the chemical paste.

Cover the Tip
After cleaning the tip with a damp cleaning sponge or a dry cleaning wire, make it a habit to cover the tip with new solder at the end of soldering or before putting the soldering iron into position in the iron holder during soldering work.