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SolderTip #49: Calibration of Soldering Irons

Question: We have both steady output temperature and temperature variable soldering irons. There has always been a long-standing question as to whether we needed to calibrate these irons to meet certain ISO requirements. Is there any documentation that indicates how we should handle this?

Answer: This is an interesting question with several variables to consider. There is an appendix in J-STD-001 that specifically addresses soldering irons, voltage spikes and temperature considerations. It is Appendix B. In particular you might want to familiarize yourself with Section B-2 Benchtop and Hand Soldering Systems, focusing on Item B.

It states: Temperature controlled soldering equipment (at rest) should be controlled within (+/- 5 degrees C [+/- 9 degrees F]) of the idle tip temperature. Constant output (steady output) tools in compliance with A-2a, d, e, and f may also be used.

So what does this all mean? For temperature variable soldering irons, any calibration being performed should be to check that the temperature on the read out matches the temperature measured on the tip and if not adjust accordingly.

If you are using a steady output temperature soldering iron, or rather one where the temperature is controlled by the selection of the appropriate tip for the application, such as Metcal or Oki Soldering stations, there is no adjustment or rather calibration that can be performed.

This is basically all you can do in the “calibration” of the tooling used. It does by no means calibrate the process or guarantee that a perfect solder joint will be created each and every time. There are too many other variables that cannot be calibrated that affect the process. You have to consider the mass of the solder joint being soldered, the power and temperature of the soldering iron and tip, the time spent on the solder joint and even the skills of the operator. This is why you can have a calibrated soldering iron and still destroy a product. All of these variables have a factor in the final outcome.

Overall, calibration of a soldering iron in its simplest form may appease anyone concerned with ISO requests, but it does not guarantee or calibrate the final process.