Has My Flux Expired?

Has My Flux Expired?
What specific attributes occur in an expired flux? How do you know if a flux is bad and shouldn't be used? Are there any simple tests?
Board Talk
Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting.
Process Troubleshooting, Failure Analysis, Process Audits, Process Set-up
CEM Selection/Qualification, SMT Training/Seminars, Legal Disputes
Phil Zarrow
Phil Zarrow
With over 50 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes.
Jim Hall
Jim Hall
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.


Welcome to Board Talk with Phil Zarrow and Jim Hall of ITM Consulting. We're the Assembly Brothers.

Today we are coming to you from the elegante ballroom high atop Mount Rialto. Where the air is thin, and everything else is too.

We're here to talk about electronic assembly, materials, equipment, components, practices and procedures. Who knows what else.

So Jim, what else? What kind of question do we have today?

Well, this comes from P.H. A very caustic question.

You have a very acidic tongue to say that.

Trying to keep up with my brother. Beyond the printed expiration date, what other criteria are used to judge whether a flux is expired or contaminated? What specific attributes occur in an expired flux?

How do you know if a flux is bad and shouldn't be used? Are there any simple tests one can do to test fluxes?

You better go first on this, because we are talking about PH here. And I am not talking about the person.

I am talking about what I might say. So go ahead Jim.

Well certainly, always respect the expiration date on any material you buy. My general feeling is, if you have any question don't use it. We are talking about creating electronics.

We are talking about making the solder interconnections, which are very critical. Lots of things can go wrong as people will point out. Flux is one of the three things you need to make a solder joint.

You need heat, metal and flux. Don't take any chances. If it is expired, don't use it.

Other attributes, I even hate to say it. Well, one thing we know that can happen with flux is the solvent can evaporate. You would typically see an increase in viscosity.

Maybe a change in color, change in aroma. I don't know. Simple tests? I don't know simple.

You can certainly do wetting tests, wetting balance, copper mirror. Things like that. The standard tests they use to qualify fluxes.

I don't know how simple you perceive them as. Wetting balance of course would be the best. That is what its basic job is to do, is to promote wetting, clean the outsides.

Other than that, keep your fluxes from getting contaminated. Keep them covered so that they can't evaporate.

Keep them in properly sealed containers so that contamination can't get into it. I can imagine that there are things that can go undetected until you get bad soldering and poor quality solder joints, and all the other things resulting from degraded properties of your flux.

Well, I think the bottom line is, as you said in the first place Jim, follow the expiration date. There is a reason the flux manufacturers put it on there. They know their chemistry.

They tested it extensively. They're not putting it on there "Let's put it up a few months earlier so that we can con these bozos into buying more flux." You know, it is not an evil conspiracy here.

On the other hand, I have heard of people selling their flux to third world countries. Geez, just go by the expiration date. The only other thing I'll add, hey P.H. clean out your refrigerator and clean out you medicine cabinet too. Expired flux.

Alright, enough said on that. I hope we made the point. Yes, you've been listening to Board Talk and just remember if you can't laugh at yourself we certainly will.

And whatever you do, however badly expired your flux is, please don't solder like my brother.

And don't solder like my brother.


J-Std.004B Appendix B-8 provides instructions on extending flux shelf life beyond the expiration date.
Timothy O'Neill, AIM
Regarding Mark's comments, make sure the readers know there is a typo and "taste" should be read as "test". We don't want anyone tasting their flux!
Keith Aschliman, Franklin Electric Inc.
Acid number and specific gravity deviating from the range listed on the Technical Bulletin are quick and easy tests to determine if flux has changed over time.
Mitch Holtzer, Alpha Assembly Solutions
The issue is not as simple as this. We have some fluxes that didn't post an expiration date on them what so ever. I called the company that produced them and they told me that they don't put expiration dates on purpose. They also told me that most flux producers just put a 2 year expiration across the board (seems true with other types of flux we buy).

What I ended up doing is implementing a 2 year test date on flux with no expiration. For flux with expiration, we test it and extend for another 2 years. For the most part its it wetting test. We have also had no issues with extended flux expiration dates and have been doing it for many years. This is also a common practice in the military (where I got my initial experience). Granted, we solder mostly terminals and only a few boards with thru holes and all of this is hand soldering.
Erik Kallstrom, USA
Maybe this is more "old School", but back in the day, (I'm talking early 90's), we used to use a hydrometer to measure the specific gravity of the flux. We'd measure the flux right out of the bottle, so we had a reading on known good flux. And then we would set limits up, and taste the specific gravity every shift. We would change the flux out when it fell below acceptable limits. Does anybody do this anymore?
Mark Hoch, Behr-Hella Thermocontrol Inc., USA

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