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Shelf life of flux for soldering electronics

Andreas Thaler

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Joined
Nov 19, 2017
Messages
4,863
Location
Vienna/Austria
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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?
 
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.
 
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.
 
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.)
 
reddesert said:
Like others here, I have used ancient rosin core solder without issues.
Click to expand...

Flux is hermetically sealed in solder wire.

But what about flux in pens and cans?

Product information from Stannol, Germany:



Translated with Google Translate

German original text:

 
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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!!!
 
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.
 
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.
 
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.
 
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.
 
f64shooter said:
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.
Click to expand...

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.
 
albada said:
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.
Click to expand...

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.
 
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.
 
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