Why do tips easily oxidize when they are used with lead-free solder?


The factors that caused tips easily-oxidized when using lead-free solder.
POINT 1 Why do the tips of soldering irons oxidize easily when using lead-free solder?
POINT2 How to Maintenance
POINT 3 Use the thermal recovery efficient soldering irons to increase the life span of the tips.

Point 1. Why do the tips of soldering irons oxidize easily when using lead-free solder?
In general, the melting point of lead-free solder is 20ºC to 45ºC higher than conventional eutectic Lead-free solder oxidizes the tip of the soldering iron four to five times as fast as eutectic solder. Lead, one of the components of eutectic solder, relieves the oxidization of the tips. The lead-free solder, then, speeds up the oxidization. It is unavoidable that the life span of the tip decreases. Besides, the melting point of lead-free solder is approximately 30ºC higher than that of eutectic solder. Determining the preset temperature with little regard for the characteristics of lead-free solder, and leaving the tip at the high temperature of lead-free solder's melting point, speed up oxidization of the tips. Understanding the characteristics of lead-free solder and maintaining the soldering irons in a clean condition is the shortcut to preventing the soldering iron tips from oxidizing.
Point 2. How to Maintenance
Keep the preset temperature as low a possible. (Never increase the temperature to more than what you need.)
How to maintenance
Switch the power off except for long hours of use.
Make it a habit to cover the tip with new solder at the end of soldering.
Make it a habit to cover the tip with new solder before putting the soldering iron into position in the iron holder during soldering work.
Use wire-type cleaner such as HAKKO 599B. Using the wire-type cleaner leaves some amount of solder on the tip when cleaning the tip. Some amount of solder left on the tip helps to prevent oxidization.
Remove oxide using Chemical Paste (HAKKO FS-100).
When the chemical paste (HAKKO FS-100) cannot remove the oxides, use the tip polisher (HAKKO FT-700) first and then use the chemical paste (HAKKO FS-100) so that the solder on the tip restores wettability.
Point 3. Use the thermal recovery efficient soldering irons to increase the life span of the tips.
Set the preset temperature as low as possible to slow the oxidization of the tips. (Never increase the temperature to more than what you need.) The melting point of lead-free solder is higher than that of eutectic solder. Setting the preset temperature with little regard for the characteristics of lead-free solder could raise the temperature of the tip and speed up oxidization. Here, we suppose that you are wondering how one can solder securely with high-melting-point lead-free solder without raising the temperature of the soldering iron. It's the thermal recovery rate that answers your question.
(1) The melting point of solder + 50ºC = the optimal temperature for the tip.(Lately, it is said that the solder melting point + 10ºC or more = the allowable temperature limit of the soldering iron.)
(2) It is also said that the optimal temperature for the tip+ 100ºC = the optimal temperature for the soldering iron.
 
Let us find the optimal temperature for the soldering iron using the formulas above when the melting point of solder is 180ºC.

180ºC + 50ºC = 230ºC
230ºC + 100ºC = 330ºC

The optimal temperature for the soldering iron is 330ºC.

The melting point of lead-free solder is about 30ºC higher than that of eutectic solder. The melting point of lead-free solder, when using the formulas above, is about 360ºC. It is risky to use different types of soldering irons as often as the type of solder changes when soldering the same items.

If the optimal temperature changes in a 30ºC range as often as the type of soldering iron changes, heat-sensitive parts will be negatively affected from the temperature changes. Consequently, both the thermal recovery efficient soldering irons and the thermal manageable soldering irons are required to keep the optimal temperature for the soldering iron for lead-free solder at the same temperature as that of the soldering iron for eutectic solder.

When using the thermal recovery efficient soldering irons, the formula above (2) will be:
The optimal temperature for the tip + about 60 to 70°C = the optimal temperature for the soldering iron The formula above cancels the increased temperature of the melting point of lead-free solder. In this way, the optimal temperature when using lead-free solder can be reduced to a temperature almost as low as the temperature needed for eutectic solder.

One of the soldering irons for lead-free solder that we would like to recommend, which meet the requirements above, is the HAKKO FX-951, FM series. Especially, we would like to recommend the HAKKO FX-951 and HAKKO FX-952 that accept the T12 series, which has 84 variations of standard tips. For detailed information, click the URLs below.