You should periodically check your soldering iron tip temperature as a part of your process control system to ensure that it is operating within its specifications and meets/exceeds defined tolerances. Please note that when measuring the temperature you must figure the tolerances of both the soldering iron or station and the measuring device into your measurements, because the tolerances will stack. When measuring soldering iron tip temperature you can account for the tolerance stack using the Root-Sum-Square method.
There are a variety of tip thermometers and station testers for measuring the actual operating temperature of your soldering iron tip. This blog will focus on testing with a tip thermometer. Make sure the device you’re using has a valid calibration certificate with acceptable traceability.
You should also take precautions to mitigate unintentional measurement errors. The first way to avoid error is to take your measurements in an area free of air currents or drafts (for example, from an air conditioner or a ceiling fan). Also, replace sensors every fifty or so times you take measurements: sensors oxidize as you use them and, as a result, they conduct less heat over time, which in turn reduces the accuracy of your measurements.
Furthermore, the same person should always take the measurements under the same conditions to avoid any errors resulting from changes in conditions or measurement techniques. Before testing you should clean the soldering iron tip so that it is free from oxidation and other deposits that can alter your tip temperature measurement and reduce accuracy of the reading. Place the soldering iron tip on the sensor of the tip thermometer and apply a small amount of solder as you would when soldering.
Hold the soldering iron tip horizontally with regard to the sensor and minimize movement to ensure maximum contact between your soldering iron and the sensor — an angle or movement can and often does reduce the tip thermometer’s accuracy.
Press the soldering iron tip to the sensor and wait long enough for the temperature reading to stabilize at its highest point — this is especially important if your tip is narrow or sharp. Some tip thermometers and station testers have a “max hold” feature which will display only the highest temperature reading. Repeat the measurement three times in the same position and record the highest tip temperature. Use this number to discover whether your soldering iron tip is operating within its specifications and meets/exceeds tolerances for accuracy and stability.