solder paste recycling - Page 1
Forum section: electronics / general

author: loki42
author_rank: Frequent Contributor
timestamp: October 08, 2025, 04:21:19 am
content: What do people do with expired solder paste? I've got some that's currently lurking in the solder fridge that I'd like to get rid of in a responsible manner.I have regular pick ups of scrap metal (aluminium & steel) but I don't know if scrap dealers would take paste. Australian recycling options would be great.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 08, 2025, 02:12:31 pm
content: Have you tried using the expired solder paste? Might still be usable. Maybe not for commercial boards, but for non-commercial/hobby projects, where one can afford to try and tinker around, might be usable. I'll donate it to any nearby maker's club/ham radio/hobbyists in your area.

author: jpanhalt
author_rank: Super Contributor
timestamp: October 08, 2025, 03:54:20 pm
content: I bought my solder paste (Kester brand) during Covid. It was delivered to me at the back door of a local distributor and had a 6-month expiration date. I used it last Spring (May, 2025), and it still worked. It doesn't take much liquid flux or 99% IPA to change the viscosity a lot. That time, I didn't have a stencil and just used small dots for a few SMD's. It's kept sealed with desiccator or in syringes in freezer bags in a refrigerator.Try it. It's probably a lot more forgiving if you are not using a stencil.

author: jayx
author_rank: Regular Contributor
timestamp: October 08, 2025, 08:13:57 pm
content: In the UK, solder paste suppliers offer recycling, for examplehttps://www.ams-electronics.co.uk/shop/alpha-soldering/alpha-reclaim-service/alpha-solder-recycle-service/I guess if you google "solder paste recycling" you may find the same in your country.

author: Mangozac
author_rank: Frequent Contributor
timestamp: October 08, 2025, 10:30:01 pm
content: Quote from: jpanhalt on October 08, 2025, 03:54:20 pmLoki42 is doing volume production. Once paste has been out on the stencil for some time it's no good and not worth the process risk of mucking around trying to mix in IPA or flux.We've built up a stockpile of dozens of jars of waste paste over the past few years. Chemtools at leastusedto take it for recycling by a third party but I have a feeling they don't do it any more. We have been intending to try a local battery recycler but it's not a high enough priority so we just keep filling the shelf with used paste jars

author: law
author_rank: Regular Contributor
timestamp: October 09, 2025, 01:25:19 am
content: Yeah I asked Chemtools last time I had a chat to them and they said they don't take it, and to check with local council or metal recycler. I haven't done either of those things and now too have started a small stockpile....

author: jpanhalt
author_rank: Super Contributor
timestamp: October 09, 2025, 04:31:14 am
content: Quote from: Mangozac on October 08, 2025, 10:30:01 pmSorry, I didn't get that impression from the original post. If that's the case, I agree. One must follow the expiration date.As for disposal, it's understandable why waste places don't want a paste. Would It be practical to have a solder pot to heat the paste in to make solid billets or slugs of waste solder for disposal?

author: loki42
author_rank: Frequent Contributor
timestamp: October 09, 2025, 09:05:35 am
content: The jar / the connection is growing... you might have the right idea that i could just warm up the whole thing until it's solid and then any scrap metal dealer would take it. They pay for aluminum and I assume would for tin.

author: Mangozac
author_rank: Frequent Contributor
timestamp: October 09, 2025, 11:06:39 am
content: Apparently people used to just put a wok over a gas burner, scoop all the paste in and let the flux burn off. You can imagine the horrible mess it would create!

author: jpanhalt
author_rank: Super Contributor
timestamp: October 09, 2025, 11:57:02 am
content: Some people can make a mess cooking scrambled eggs. That doesn't mean it can't be done without the mess.

author: jmelson
author_rank: Super Contributor
timestamp: October 10, 2025, 03:26:41 pm
content: Quote from: Mangozac on October 08, 2025, 10:30:01 pmI found that the magic solvent for adjusting viscosity is Butanol (the 4-carbon alcohol). It has much lower vapor pressure than the other (lower-carbon) alcohols. It only takes a few drops to make the paste flow like new. The other problem is that the solder beads fall to the bottom and the flux rises to the top, and if you don't mix well, all the flux gets used up first, leaving the paste very stiff and with poor wetting on later uses. But, I have had fairly good results rejuvenating old paste.Jon

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 10, 2025, 03:49:06 pm
content: If your production facility also uses a solder pot for tinning wires, that can be a good use for old paste, but you need to let the flux fumes burn off first, ideally outside

author: jpanhalt
author_rank: Super Contributor
timestamp: October 10, 2025, 07:04:52 pm
content: Another way to simplify the flux removal would be to dilute with IPA (assuming the flux is soluble in it), let settle, decant, dilute again, and so forth. If your solder is lead-free, then the waste is also lead free. And, if its rosin, it could probably be dumped on the ground or regular waste collection. Worst case, let the IPA evaporate then all you have is some rosin to dispose. I suspect 2 cycles or 3 at most would give a sediment that would quickly burn off its residual flux.That of course assumes a rational EPA or its equivalent.

author: J_C
author_rank: Contributor
timestamp: October 11, 2025, 08:18:09 pm
content: Are there any legal restrictions on resale in Aus? If not, sell it on ebay, prominently stating the expiration date and it might help to mention potential uses and thinning options.Price it cheap enough and someone will bite, then even if there's no profit to be made, you still got rid of it.

author: Stray Electron
author_rank: Super Contributor
timestamp: October 12, 2025, 09:18:51 pm
content: Quote from: J_C on October 11, 2025, 08:18:09 pmThis.It would help is you told us what kind of solder paste it is. I've used solder paste that is decades out of date (good brands like Kester) for my own personal use and I've never had a problem with it as long as the container is still in good condition and not rusted or damaged.If it's just rosin you can give it to someone that makes cast bullets. It works GREAT for fluxing molten lead but I don't know how the synthetic fluxes would work. They're probably fine for bullet casting but they might attack the brass when it's assembled into a cartridge. But if I doubt that that would matter if the ammunition is going to be fired soon and not left in storage.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: October 18, 2025 10:42:34 pm
content: As far as I know, you can simply look into your pot and see whether the paste is still good. As long as it's an homogenous paste, it's good. If the balls sink to the bottom and the flux floats on top, then it becomes more difficult to work with. Some people go as far as mixing in their own flux when the solder paste "dries out". But overall, it depends on what you're doing. For a hobbyist which occasionally reflows a few boards, I'd say just keep on using it, and you will notice when your flux goes bad. If you're in some production environment, then it's probably not worth it to risk a lot of rework on a batch of PCB's, and I'd be more cautious, but I would not treat it as waste just because it's "good by" date has expired. The date is only a guarantee from the manufacturer that the paste will be good up to that date. It does not mean that suddenly something bad happens the day after it expires.But if you have to recycle it. Here in The Netherlands you can bring stuff to a recycling center for chemical waste, and it's free for all "household" users. If you don't have that option, then melting the paste into a blob of solder (which burns off most of the flux) already reduces the problem a lot, and it may even be reuses in a tin pot as others suggested here.