Soldering Irons and Thermal Recovery

Posted by gm77 19/04/2021 0 Comment(s) 62 Soldering & Rework,

WHAT IS THERMAL RECOVERY AND WHY IS IT IMPORTANT?

You might have come across the phrase 'excellent thermal recovery' when doing your research on which soldering iron to get. What does it mean and why is it important to have a soldering iron with high thermal recovery?

Lower Set Temperatures and Shorter Working Time

A soldering iron with high or excellent thermal recovery is able to revert to its desired or preset temperature faster as compared to a soldering iron with low thermal recovery. It is less affected by changes in temperature, such as tip cleaning between bouts of soldering, where the temperature tends to drop significantly. With high thermal recovery, it takes a shorter amount of time for the soldering iron to heat up, speeding up the soldering process.

A soldering iron with excellent thermal recovery also allows soldering at lower set temperature. Since it is able to revert to the desired temperature quicker, there is no need to set the temperature higher to account for drops in temperature.

Increasing the Lifespan of Soldering Tips

Soldering at lower set temperatures prevents the soldering tips from overheating, which makes it prone to oxidation. A shorter working time also reduces the length of time where the soldering tip is heated up, further contributing to the prevention of tip oxidation. 

Thermal Recovery and Lead-Free Wires

This feature comes in handy when soldering with lead-free solder, as the melting point of lead-free solder wire is approximately 30ºC higher compared to normal solder wire. When soldering with lead-free wires, users tend to increase the heat considerably to account for the higher melting point. This often leads to rapid oxidation of the soldering tip, requiring frequent changing of tips. 

How then do we solder with lead-free wires without increasing the temperature of the soldering iron? Let's look at the following formulas. 

Formula to determine temperature  
Optimal temperature of the tip (T) = melting point of solder + 50ºC
Optimal temperature of the soldering iron = T + 100ºC 
Optimal temperature of soldering irons with high thermal recovery* = T + 60-70ºC 

*Soldering irons with high thermal recovery requires a lower set temperature of ~60-70ºC.


For normal solder wire with a melting point of 180ºC:
Optimal Temperature (T) = 180ºC + 50ºC = 230ºC 
Optimal temperature of soldering iron = 230ºC + 100ºC = 330ºC
Optimal temperature of soldering iron with high thermal recovery = 230ºC + 70ºC = 300ºC

For lead-free wire with a melting point of 210ºC:
Optimal Temperature (T) = 210ºC + 50ºC = 260ºC 
Optimal temperature of soldering iron = 260ºC + 100ºC = 360ºC
Optimal temperature of soldering iron with high thermal recovery = 260ºC + 70ºC = 330ºC 

From this, it shows that the optimal temperature when using lead-free solder can be reduced to a temperature almost as low as the temperature needed for normal solder when using a thermal recovery efficient soldering iron. 

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