Shelf life of flux for soldering electronics

[Andreas Thaler]

The flux I use (no clean) has an expiration date.

The data sheet states that the flux can be used even after the expiration date.

Do you have any experience with this?

 

[koraks]

I've not had flux go bad yet. I never paid attention to expiration dates.

 

[Laurent]

I have some flux for plumbing, that I also use when needed for electronics/electricity, it is over 20 yo, looks awful but still works fine.

 

[koraks]

I have some flux for plumbing, that I also use when needed for electronics/electricity

That's not such a good idea. Plumbing flux is a different animal and will corrode PCB's. Don't use plumbing flux for electronics repairs!

 

[Truzi]

I have flux core solder, and a small container of flux, that are over 30 years old. The last time I used them was about a year ago, and they both seemed fine.

 

[reddesert]

Flux is a reducing agent that works at high temperatures - reducing because its role is to remove oxides. I think at room temperature, flux is essentially inert. If you wipe some flux on an oxidized joint at room temp, it doesn't really do anything, unless you heat it up. So I think it lasts a long time. Like others here, I have used ancient rosin core solder without issues.

This is unlike film developers, for example, which are reducing agents that work at close to room temp, so they have a tendency to oxidize away. (I am oversimplifying the analogy, since of course developers are in aqueous solution and so on, but reduction vs oxidation is the key point.)

 

[Andreas Thaler]

Like others here, I have used ancient rosin core solder without issues.

Flux is hermetically sealed in solder wire.

But what about flux in pens and cans?

Product information from Stannol, Germany:

FLUX
Due to chemical and biological processes, fluxes have a limited shelf life. Alcohol-based fluxes have a shelf life of 2 years, water-based products 1 year, provided the flux is in the original sealed container and stored accordingly. With water-based fluxes, it must be ensured that they are stored above 10°C. Please refer to the container label for the best-before date.

NOTE
For all further information, please refer to the technical data sheets. If you have any questions, we will of course be happy to answer them personally.
Please remember that the times given are best-before dates. This does not mean that the products can no longer be processed after the best-before date has expired. If the products still show good results in your production process after the best-before date has expired, the products can also be used beyond the best-before date. This helps you save resources and also protects the environment.

Translated with Google Translate

German original text:

https://www.stannol.de/fileadmin/redakteur/download/allgemeine-dokumente/Mindesthaltbarkeit_DE.pdf

 

[xkaes]

I just used some electrical solder (not the same as solder for copper water pipes -- that uses flux) to repair a 120v copper electrical wire. I would guess the solder is forty years old and worked fine. It's my soldering iron that's wearing out!!!

 

[koraks]

I think at room temperature, flux is essentially inert.

No, not always. Rosin tends to be inert, but the liquid and paste kinds of flux used today are corrosive at room temperature just as well. Plumber's flux more so than the stuff intended for electronics.

 

[Andreas Thaler]

„No clean“ – do you still clean after soldering?

 

[250swb]

Among a few bottles of flux I have is a water based one from Stannol and nowhere on the bottle does it have a use by date, it only warns it can burn or poison you. I only read that warning just now after using the same bottle on and off for three years. In fact none of my liquid fluxes have sell by or use by dates. I suspect it may be just a ploy to make you buy another bottle.

 

[koraks]

„No clean“ – do you still clean after soldering?

I admit I'm sloppy, but you really should, yes.

 

[Andreas Thaler]

I admit I'm sloppy, but you really should, yes.

What is the reason for this in electronic soldering?

Does this mean that the manufacturer's statement "no clean" is not reliable?

 

[koraks]

What is the reason for this in electronic soldering?

Corrosion. Although it's a minor concern in practice.

Does this mean that the manufacturer's statement "no clean" is not reliable?

It should be taken with a grain of salt IMO.

 

[reddesert]

I assume that liquid water or alcohol based fluxes may eventually suffer some evaporation of the carrier, although if you keep the bottle closed that should take a very long time. It is likely that the manufacturer gives a use-by date to restrict their guarantee of suitability. If you are using it in some industrial process and use 10 year old flux, it's not going to meet ISO 9000 certification or whatever.

AFAIK, paste flux can be somewhat reactive at room temp - it is generally regarded as damaging to paint and lacquer finishes, this comes up a lot in the repair of brass musical instruments - but it's more reactive at high temp.

Even flux in solder isn't "hermetically" sealed. I mean, it's inside a metal alloy, but the requirements to consider something hermetic are more stringent. There's plenty of chemistry and diffusion that could happen while the flux is sitting around inside its tin-lead casing. But in real experience, whatever happens to flux-cored solder over years doesn't seem to affect its usability. Basically, I think age of flux should rank low on the list of problems in the repair of camera electronics.

 

[Andreas Thaler]

Thank you

There is also an old debate about whether leaded solder can be mixed with lead-free solder.

I bought some leaded solder from old stock for my repair work.

And the flux is very helpful when desoldering cables and re-soldering them where there is an existing soldering point. Ideally, the soldering point does not change and everything looks like it was made in the factory.

 

[koraks]

For home/non-professional repairs/projects, leaded solder is just far more convenient to use.

 

[Andreas Thaler]

This is a nice form of flux:

Löthonig - „solder honey“

Home | Löthonig® - www.loethonig.de

Productpage of Löthonig® flux, high quality reduction agent. For inquiries please send an e-mail to service@loethonig.de

www.loethonig.de

 

[f64shooter]

I have a can of soldering flux from over 20 years and it is still as good as new. It is the oily paste type.

 

[albada]

I have a can of soldering flux from over 20 years and it is still as good as new. It is the oily paste type.

Same here. I bought my can decades ago, and it still works like new. It was made by Hercules Chemical Co.
It's labelled "Soldering Paste", but these days, soldering paste is something different -- it's powdered solder mixed with flux used for surface-mount components. What's in my old can is flux.

 

[koraks]

It's labelled "Soldering Paste", but these days, soldering paste is something different -- it's powdered solder mixed with flux used for surface-mount components.

Indeed. The 'powder' is actually tiny globules of tin, and the flux is really good. It also keeps better than what some people say, although it doesn't have the seemingly infinite shelf life of flux. One problem is if you try to dilute this solder paste with something like alcohol or even regular liquid flux, it tends to harden up after a few days. Found this out the hard way....
I use this paste a lot for SMD soldering PCB's, using a hot plate as the heat source. It works really well.

 

[Sirius Glass]

I only use rosin core flux and I have never had rosin core flux go bad. Do not use acid core flux to electronics, acid cord flux us for soldering copper pipes only.