Soldering Iron Temperature Control

[George Weiss]

The simple soldering iron, what do we do?
Simple: look at the manufacturer’s manual and specs. If it has specs then it can be calibrated. If there is a procedure, then again, it can and should be calibrated. Look at the items usage. If used on sensitive end items, (missiles and such), then do the right thing and calibrate it.
Calibration is based on specs, procedures, standard coverage, (ISO 9000, 17025 etc.).
Some people say, if it is plugged in then calibrate it. I have read that if it is used in the production of end items then it is to be calibrated in areas critical to the production of end items, or at least tested to the point of knowing it works. I have ridden in the saddle for calibration companies who love to collect money for what is nearly a yep-it-gets-hot ship-it calibration. There are soldering iron testers made, which test the tip temperature, and also the tip to ground residual ACV/DCV and low ohms test, being <5 ohms to ground.
The ACV/DCV and ohms test is actually more important because it is an ESD issue, which is very important to some companies. A company like Space Systems Loral or Lockheed Martin, who produce space qualified and defense product need A1 perfect working tools. A company soldering leads on cable harnesses does not care about ESD and should not. ESD is a big compliance issue because auditors love to ding people for easy items like ESD. I think testing a soldering iron with a thermal couple connected to a T/C meter which is calibrated is a good start. Some would say the t/c thermal couple should be calibrated. I would not. I think that using a Fluke multimeter to test the temperature and residual tip ACV/DCV and ohms to ground would be a fair calibration. I think the testing of temperature, from my many, many, soldering iron calibrations is a problematic thing. The process will find many good soldering irons seemingly bad due to LARGE UNCERTAINTIES of the process.
There seems to be a question of do soldering irons get calibrated at all?
The question of can they be calibrated?
The question of calibrate what or why?
Simple: In some applications soldering irons should be calibrated, some not. They Have a clear ESD issue/feature, which degrades, (resistance to ground), and should be checked, which becomes a calibration, (because an Volt/Ohm meter is used, which was calibrated). The temperature verification depends on the model and manufacturer. Some have no clear temperature spec. They basically have to melt solder to function. >700 deg. F. is a great benchmark.
If it was me, I would have a calibrated soldering iron tester on the shelf, and test once a year or when there is a question. Have records of the testing. Label the items correctly/ testing once a day, week, month is testing out of fear only. If you test them, then have a blanket procedure, and keep it simple. They are just soldering irons.
I can ramble on, but there is good stuff in there I think

 

[George Weiss]

Question: Is there any specific requirement by ISO for checking the temp. of soldering irons. I know IPC suggests that the temp. is controlled to +/- 5c. If there is a requirement, how often should it be done, I think daily would be overkill. Thanks
Direct answer: No direct ISO 9000 requirement, The rub comes when you determine that the soldering iron is calibrateable, and the question becomes, "do I calibrate it?" The answer becomes sometimes. Out of fear most people run to calibration service companies and have everything calibrated once a year. A look at the support document for your soldering iron(s) will find several specs, and a industry norm for calibrations is once a year. ISO 9000 is fairly easy. Write what you do, and then do as you write. Simple!

 

[AndyN]

Question: Is there any specific requirement by ISO for checking the temp. of soldering irons. I know IPC suggests that the temp. is controlled to +/- 5c. If there is a requirement, how often should it be done, I think daily would be overkill. Thanks
Direct answer: No direct ISO 9000 requirement, The rub comes when you determine that the soldering iron is calibrateable, and the question becomes, "do I calibrate it?" The answer becomes sometimes. Out of fear most people run to calibration service companies and have everything calibrated once a year. A look at the support document for your soldering iron(s) will find several specs, and a industry norm for calibrations is once a year. ISO 9000 is fairly easy. Write what you do, and then do as you write. Simple!

But George, I think you've over complicated the issue...

I have a soldering iron at home. It has nothing but a plug on the end. I can check it using a temperature probe - which can be calibrated. Are you suggesting that I've just calibrated my soldering iron? It's not capable of measuring anything itself. It has no capability to discern 'go/not go', there's no test it performs. Why would I calibrate it?

If it's working within the specified range for the alloy, good enough!

 

[George Weiss]

The question is raised: Why/Can calibrate a soldering iron?
Short answer: Why = Because it has specs to verify, Can = Because it has specs to verify, Should = sometimes

Observation within question: In the words leading up to the question, there seems to be a belief that it measures nothing, and produces nothing, but just gets hot.
Answer: Calibration is also expressed as Performance Verification, which in the commercial calibration world is what generally occurs. The soldering iron has a purpose, which is supported by manufacturer’s specs. The specs promise a specific performance, which is purchased by the owner of the instrument and documented on specs sheets and manuals. The soldering iron has it’s purpose of soldering, with a confidence of temperature accuracy, (many times, but not always), and generally, but not always has an ESD feature of a grounded tip, to remove ESD damage issues. The calibration of a particular soldering iron would be considered if it is in a use that would impact end product, by the company’s policy the item would likely be tagged NCR, (no calibration required), if calibration was not seen to be needed. An engineering lab, or a research or school facility would likely not calibrate a soldering iron.
In earlier comments a calibration occurs when you place a thermal junction on the tip and check the temperature. It is a basic check, which is likely not NIST traceable, and not properly documented, so causes more issues than corrects. If you do it, document it, and do it correctly.

 

[AndyN]

In earlier comments a calibration occurs when you place a thermal junction on the tip and check the temperature. It is a basic check, which is likely not NIST traceable, and not properly documented, so causes more issues than corrects. If you do it, document it, and do it correctly.

So, if someone documented it, that's a basic check (it would be traceable through the normal chain of comparisons, btw) and would be acceptable?

 

[Al Rosen]

Definition of calibration: Comparing against a known standard.

Andy, if you check your soldering iron with a thermocouple, then you've calibrated it.

 

[AndyN]

Definition of calibration: Comparing against a known standard.

Andy, if you check your soldering iron with a thermocouple, then you've calibrated it.

Al, I get it, but I don't get how a lowly iron is considered to be measurement, inspection or test equipment...I think there's a 'we've always done it that way' aspect here. I'm simply trying to uncover if (proper) calibration and all that entails REALLY applies, or whether it's part of process control and maintenance...that's all.

We read here all the time about conventional wisdoms - stamping documents, quality manuals reflecting ISO formats, torque wrench cal. etc. etc. Some of what is often taken as gospel, simply started off to appease an auditor who didn't know enough to ask the right question.

 

[George Weiss]

There is good calibration and bad calibration.
A temperature check, with a Radio Shack meter and thermal couple probe, which was bought without a traceable calibration leaves you with an untraceable calibration. (bad). Also, if not all specifications are checked, then the test becomes a partial testing of the soldering iron, which would leave the soldering iron in the LIMITED Calibration status. A test procedure, which omitted the ESD feature/spec of about 95% soldering irons, would allow for a claimed full calibration to a written procedure. Because of these frustrating issue(s) some people just ask a calibration house to come over once a year, and put a sticker on it for about $15. It then becomes a valid good calibration.

 

[AndyN]

All good technical stuff George! Of course, you're correct about the calibration being bad if you don't have a cert. And you don't have to go to Radio Shack for your example, either!

The ESD thing is a bit of a red herring though, isn't it? What if I never solder active components? Those which aren't sensitive to electrostatic damage. Connectors, leaded/pth resistors, etc. Why do I have to be worried about ESD grounding then?

I still feel like I'm being thrown a lot of technical stuff instead of being given a straight answer...

 

[gbcqc]

Most of it depends on customer requirements and your inhouse requirements. If your customer requires that you meet IPC J-STD-001 or you company claims to meet the above standard, then you are required to verify calibration and calibrate if necessary. This is for electrical and electronic assemblies. We are required by a customer to meet this standard.

What George quoted earlier looks like is was out of the IPC J-STD-001 (my copy is rev. D). The main thing is how accurate does what you do need to be with the solder you are using and what the customer requires.

That's just my opinion, I could be wrong.