WORKSHOP VIDEO #26: How to make a simple soldering flux

Flux is a wonderful goo that makes soldering faster and easier. In previous videos we compared different types of commercial flux (Flux off 1, Flux off 2), but did you know it’s possible to make a simple and effective flux at home? We’ll get you started, and don’t miss the giveaway at the end of the video.

Arhi shared his method of dissolving rosin into a solvent. Rosin is an inexpensive processed tree sap, used on violin bows, art, etc. It’s also the primary ingredient in many fluxes. Followup comments revealed an expired patent with a simple flux recipe:

  1. Isopropyl alcohol (60-70% by weight)
  2. Water white rosin (30-40% by weight)
  3. Glycerin (2-3% by weight)
  4. Cationic flurocarbon surfectant (0.01-1% by weight)
  5. Liquid flux is produced using a 20-65% concentration of rosin; at concentrations of 65-80% of rosin, a paste flux is produced

Ignoring the Cationic flurocarbon surfectant, everything is readily available.

A reader donated a kilo of craft rosin, but you can find it a craft and music stores. We powdered it in an envelope with a hammer to it would dissolve faster. The nearest drug store had both isopropyl alcohol (96%) and glycerin. One thing the video doesn’t mention is the alcohol strength. It should be 96%, not  lower strength 70% rubbing alcohol.

We mixed test batches in 3 proportions:

  • Thin – 60g alcohol, 40g rosin. Same viscosity as alcohol alone
  • Medium – 35g alcohol, 65g rosin. Starting to thicken a bit, like cooking oil
  • Paste – 20g alcohol 80g rosin. Quite thick

Glycerin is optional, but is said to prevent the rosin from burning and discoloration under high heat. We added just a few drops, but skip it without worry.

Is it any good? Actually, it beats a lot of the commercial flux off contenders. It barely smokes, it doesn’t smell bad, and it didn’t discolor. The residue can be left on the board, or wasted off with more alcohol or acetone.

If you’re ready to try it yourself, we’ve giving away four 100g bags of flux. Just leave a comment below and we’ll pick the recipients tomorrow. Bonus points for interesting formulation proposals.

A huge thanks to the reader who sent the rosin and made the video and giveaway possible.

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52 Comments

  1. I would try a 50/50 with a few drops of Glycerin. Put in a small jar and use a soft – med stiff brush to apply to your work. I like liquid flux for my electronics work. Paste is just too much of a pain to work with.

  2. Hi Ian,

    There was a time (5-7years back) when I used to use solid rosin as flux. The thing worked good and gave shining round solder joints, but I found that the fumes are very thick and harmful to health(causes mild cough) and secondly the dried up rosin residuals(hard, brittle, dark) are not easy to remove from PCB.
    Does these bad effects are rectified by mixing the alcohol and other chemicals?

    1. In flux-off 2 I tried chips of rosin too :) It worked ok, but left a terrible mess on the PCB. This is much better long-term, and easier to clean.

  3. I did not play the piano very well but I could use my hand for soldering. I would appreciate some flux to test this recipe.

  4. My first attempt at rosin-iso flux works ok for soldering. But it has a bunch of paper fibers from the package the cheap ebay rosin came in: https://picasaweb.google.com/lh/photo/_MT2RopC4gLNBx2a0398DNMTjNZETYmyPJy0liipFm0?feat=directlink

    Now I’d like to get a dispenser bottle with needle tip like the one shown here (not mine):
    https://picasaweb.google.com/109928236040342205185/Electronics#5753933278877530562
    It’s hard to judge visually, but I think the inside diameter of that tip is about 0.3 mm.

    I got a different bottle from ebay with “18-gauge needle tip”. It looks like about 1 mm ID, which works, but is larger than I want (can’t dispense a very tiny amount of liquid).
    http://www.ebay.com/itm/120918900748

  5. I’d like to try replacing some or all of the alcohol with a high smoke point plant oil. There are a few patents from 2011 that use it to make the rosin residue removable with soapy water by disrupting polymerization.

    1. I use a toothbrush to scrub, so not too much alcohol. I prefer acetone (nail polish remover, really) though.

  6. Not interested in the rosin, but when this basic recipe works so well, what do flux manufacturers put in their products and why?

  7. I could deffo use more rosin to thicken my flux! I think i have about 20g of rosin in 110ml of alcohol :(

  8. Very interesting video, thanks. I think I might see about picking some rosin up at a local art store, though I doubt it will be a huge rock like you have.

    I’ve been using a flux pen that I got from Sparkfun and have found that I am not a fan of the smell or fumes.

    I have watched both of the flux offs ( a while ago ) and I think I remember you saying something about testing the Radio Shack flux paste in the future. Did you ever get a chance to do that?

    1. Not yet, I plan to aother flux-off soon with the RS flux, but have not had the time or number of fluxes tp try yet.

  9. I think I’ll have to try this. I have an old, broken Philips video game console that needs to have some parts replaced.

  10. I’ll take some. I wonder how a mix of rosin, IPA, Glycerin, and petroleum jelly would work?

  11. Rosin is also an ingredient in a drawing salve that a friend gave to me 30 years ago. a little bit of the drawing salve on a dirty cut and the next morning the cut is clean. I think I would use it to make flux though.

  12. I saw the flux video you did a while back, so I tried making some flux. I ended up with a mixture that was probably 20% rosin by weight. I wanted a much thicker flux so I decided to let the alcohol evaporate… about 10 minutes later I got impatient and set it on fire and ended up with a perfectly thick flux! Here is my flux in a syringe compared to a syringe full of MG Chemicals flux (http://sphotos.xx.fbcdn.net/hphotos-ash3/601432_3755475138820_398683536_n.jpg).

  13. My first comment is still “awaiting moderation” -I had a link to some photos of flux and dispenser bottles, so I guess it looked like spam. Anyway, anyone know where to get a fine needle-tip dispenser bottle for my new liquid flux? The one I have now has a 1 mm diameter nozzle, which I find is too big for really precise application.

  14. Hi Ian,

    I’ve tried the following :

    Chlorhydric Acid : 10 – 20 %
    2-Amino Ethanol : 7 – 13 %
    Ammonium Chloride : 7 – 13 %
    Stearic Acid : 1 – 5 %

    It was not so bad ..

    I would like to try the ‘Medium’ presented recipe.
    I already have the glycerine and isopropyl alcohol.
    Thank you very much .
    Wish you a nice week end

    Skappy

  15. Can some-one tell me why the store bought solder paste and flux has a limited (suggested) lifespan and they recommend refrigeration? There must be some other ingredients. Second question: that humungo lump ya got there is a little darker than what I was expecting water white rosin to look like, does the grade matter ? PS. would like some for testing, thanks.

    1. That recipe could be much different and require cooling or degrade over time. Prolly this will degrade over time too, but it is easy to make new flux. For hobbyists it doesn’t matter much if quality is a bit degraded over time, for industrial purpose it does. You don’t want to adjust the run everytime because of the flux is different then the last time.

      BTW solderpaste (with solder in it) require cooling to keep the solder evenly distributed in the paste. If it is warmed the solderparticles will float (more) to the bottom.

  16. With a few drops of evergreen or pine it smells even nicer.
    This recipe is similar to one found on a navy electronics
    board I belong to. It’s stuff like this that we use to pass
    the time away from families.

  17. If you still have rosin to give away, I would like to get some. I would love to get away from the expensive commercial stuff. Great video, thanks!

  18. And to think I got mine off a Jeffrey Pine that had leaked these enormous, clear blobs that had the volatiles baked out over a couple summers. I chipped off the contaminated bits, heated the resin over a Bunsen burner and removed what floated to the top. Poured it into a couple metal paste cans with nice metal slip on tops. A whole lifetime supply for an afternoon’s work, it is this beautiful clear golden honey solid, indistinguishable from the professional corked rosin block my dad uses for his fiddle bow. It smells wonderful when heated, removes nicely with 91% isopropyl alcohol.

  19. I am more of a repair-tech and amateur musician. After seeing the video, I had a bit of a different idea. The rosin that musicians use on their stringed instrument bows is pretty highly refined and very in-expensive (~$5.00 for a small block). I keep a pump bottle of denatured alcohol on my bench and several brushes to clean boards etc. I bought a block of rosin from the music shop, got a brush wet with the alcohol and stirred it on the rosin block. Viola (sorry) instant soldering flux. Worked like a charm. No mess, no 24 hours to soften things up and one brush to keep seperate (although not totally necessary).
    I am using acid brushes that are available in most plumbing supply shops and have found that keeping one with long bristles and another with the bristles cut to about 1/2cm will cover most board cleaning projects.

  20. hello
    thank you very much for This valuable information
    I have a question can i use white spirit or thinner in the place of Isopropyl alchol ? because difficult to find him in my country .
    thanks

  21. Hi Ian
    Thanks for the infomation. I ‘ve been having a minor cough problem from no-clean flux. This gives me another path to freedom. I was planning to buy nine dollar solder rosin paste and thin it with 70% alcohol. Now I need rosin rock from a music store, would the Guitar Center in Califonia have it?

  22. would it be smarter to store the rosin as a solid or make it all up in 1 batch and store it as flux

    1. make what you need .don’t store it too long.it degrades with the storage container variables,and humidity,as well as other ambient factors that can’t be listed here as they are vast!
      By the way the hardened rosin one collects from pine trees ( dark reddish, if not brown and shatters when struck will work if you can’t find rosin easily in your area.MAKE sure you don’t collect soft gooey yellow or white-yellow pine sap. It has not hardened yet.Ordinarily it is found in globules near the tree base, on the ground from being years old and shed with the bark from past years.If no globules are apparent on the surface look under a well hardened piece of bark nearer the tree’s bottom with zero fresh sap around it.It is best collected in autumn or winter when no fresh sap ( clear viscous liquid ) is running- if you do get fresh sap on your hands don’t touch your hair or eyes and use ,shortening,butter or as a last resort, mineral spirits or turpentine to remove it-alcohol and soap don’t work like oils to emulsify and remove the sticky stuff.).This is free and as good as most rosins available and usually in your backyard or a neighbour’s yard and goes unnoticed. I use it for many things even varnish ! It is a great sealant for wood and additive for restoration projects on old furniture repairs…

  23. This was a great video!! I’m learning to solder silver and this was very helpful. Thanks. If you have rosin left to give away I would love to have some to try. Thanks

  24. I would like to know where to buy this Brown looking solid gum rosin, who carries it and under what name. In India it is very inexpensive and easily available.
    Please do let me know

  25. In Norway they sell a denatured form of IPA with a blue color. Would this be a problem for the flux?

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