Good health practices when using Flux

When soldering, the smoke that is formed is mostly from the flux, in short, Flux is a cleaning agent used during the soldering process of components. Its main purpose is to prepare the metal surfaces for soldering by cleaning and removing any oxides and impurities.

The are three main types that we would carry along with some more specific use types:
Rosin Activated, Water soluble, and No-Clean Fluxes. Those can be found here

Rosin is a resin contained in solder flux and can be hazardous to your health . Exposure to rosin can cause eye, throat and lung irritation, nose bleeds and headaches. Repeated exposure can cause respiratory and skin irritations, causing and aggravating asthma. so as little exposure as possible is the best precaution. Use rosin-free and lead-free solders whenever possible.

Water soluble and No-clean fluxes consist of more organic alcohols and acids, but safe soldering practices should still be followed when doing any soldering because there is always going to be fumes and smoke. I dont want to give the impression that No-Clean flux is ‘safer’, as some no-clean flux contains chemicals like methanol among other things which aren’t good to inhale either. When working with any mentioned types you should always read the Material Safety Data Sheet and follow exposure guidelines

Always do your work in a well-ventilated area or if possible use a fume extraction system. Avoid breathing the fumes and smoke by keeping your head off to the side of your work, not right over it. Digi-Key carries a good selection of Fume and Smoke extractors which can be viewed here

I’d like to see a source for this claim since I have never seen this claim before.

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Hi Paul, to be honest that was just more of a general statement I concluded from multiple sites when finding the dangers or Rosin type fluxes versus the others. No doubt the other types may contain Rosin as well so at that point, one needs to look at the specific solder and flux they are using individually rather than trying to compare the whole field of product,

Yes I apologize for the misleading statement, that was well put Kristof, thanks.

Thanks Zach,

I also wouldn’t recommend just a fan on the bench giving a cross breeze. This is certainly better than someone hunched over their work piece with smoke going direclty to their face, however,

A fan for cross breeze would depend upon the size of the space and isn’t advisable for someone soldering for any period of time, such as someone doing assembly professionally.


I agree, I was meaning that in more of a better than nothing type of situation. Of course, a fume extractor would be the ideal way to go about it.

Excellent followup posts by both of you. Thanks @Zach_2893 and @Kristof_2649.

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We are glad to Help Paul,

and to be clear this wasn’t meant as a scare tactic to steer people away from soldering on their own, we get many requests regarding health concerns when using solder/flux so it was purposed to just make people aware of the hazards that may be involved and how to use some safe practices while working.

There are most likely users out there with pre-existing medical conditions like asthma, that soldering/flux fumes can make worse, or If you were to have a job where you are exposed to it 8+ hours a day, obviously they should take heavier precautions. in reality it is probably a small percentage of people who will actually develop these issues from using this stuff but we cannot speak on a person-to-person situation so it is up to them to make the call. Just please be sure to read the MSDS (material safety data sheet) when using such products and follow your occupational guidelines. At Digi-Key we are happy to assist you in locating an MSDS or other safety sheets regarding the products that we carry.

A common misconception we should also address is that using lead free solder means it is safe. This would not be true.
By that I mean there are still bad things in the fumes in regards to the flux whether using Leaded or lead free solder and one should not assume they are good to go just because it is lead free. Again, you always want to refer to the MSDS of a product you are working with.

The best precaution to use is limit the amount of fumes you are breathing in especially if you do routine soldering or rework. As mentioned in the earlier post, avoid breathing in the fumes and smoke by keeping your head off to the side of your work, not right over it, doing that method in combination with a rather inexpensive benchtop fume extractor, ( , in a well ventilated area, is a great short term method. Even better, doing this outside with a cordless iron ( or by using an extension cord if permitting, would be ideal.

If that is not achievable, or you are going to be consistently soldering or doing rework than I would suggest using a more elaborate absorbing setup like the ZEROSMOGELKIT1N-ND

If you are more on the do-it-yourself side of things here are some examples that can be made with some creativity and fairly basic components. We wont get into the entire design but we carry a wide selection of DC fans and power supplies, here are some 12V options for example: DC fans
AC to DC power supplies
exaust fan

thanks for reading

FYI - I’ve been soldering for over 50 years, worked in electronics manufacturing for over 40 years and been Chief Engineer at a small manufacturer for over 30 years.

When my Dad first taught me soldering around age 8 there was no health warning on cigarettes and full on lead pipes and lead paint were still in use (I finally broke my ~45 year nicotine addiction 6 years ago). In the 70’s & 80’s on the manufacturing floor the assembly crew was taking no precautions with handling and using lead rosin core solder. We’d be smoking a cigarette while soldering with no fume extraction. I visited many other small assembly operations over those decades and found it was pretty common across the industry.

It wasn’t until it was noticed that Kester had added a wash your hands after use warning label to the solder rolls that we changed the way things were done. We no longer smoked while soldering to avoid ingesting more lead. Instead we’d solder, wash our hands, then light up a cigarette while using dangerous hydrocarbon solvents to clean up the flux. Growing up at that time we all had lots of lead exposure, although the vast majority was from breathing the lead filled air caused by leaded gasoline. So the amount received from handling solder and smoking/eating at the same time was insignificant in comparison.

The rosin smoke inhaled from solder was insignificant compared to the amount inhaled while burning white pine in our camp fires. So adding exhaust systems didn’t really come into common usage for small manufacturers until the 90’s.

That said, only a science denying fool would argue for returning to the old ways of doing electronic assembly.

My Rules:

  • Don’t use tobacco products of any kind
  • After handling lead always wash your hands before eating or drinking anything
  • Use good ventilation when soldering and don’t breathe in smoke from camp fires
  • Use safer solvents and with good ventilation
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