Anyone make their own rosin flux? What's it like?  - Page 1
Forum section: electronics / beginners

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: February 04, 2025, 05:16:53 pm
content: Thinking of getting into making my own flux. Tired of paying high prices for low-amounts of name-brand fluxes (Chipquick, Amtek), or having incredibly difficult-to-remove fluxes with no-name brands of fluxes. I've been doing some research, and it seems like Rosin is the the bestbase(or PolyEthylene glycol?), with some-sort of alcohol (ethanol, isopropyl alcohol) being common solutions to dissolve the rosin. Additionally, it appears that citric acid, PEG (Poly ethylene glycol), and lactic acid are commonactivators, with commonsurfactantsbeing stearic/oleic acid.Does anyone here make their own flux? What's your recipe? How easy is it to clean from your PCB, and does conductivity pose a problem for your circuits?

author: shabaz
author_rank: Frequent Contributor
timestamp: February 04, 2025, 05:30:48 pm
content: I don't see the need if you're in a country where you can readily buy decent known brands of flux at low cost from reputable suppliers (and a single pot/syringe/bottle would last you years if you're not doing production volumes), however it's described here:https://www.eevblog.com/forum/beginners/make-your-own-flux/

author: Terry Bites
author_rank: Super Contributor
timestamp: February 04, 2025, 05:35:02 pm
content: Are you a violinist?

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: February 04, 2025, 05:39:24 pm
content: Quote from: Terry Bites on February 04, 2025, 05:35:02 pmNope, but I saw that raw rosin is super cheap from musical instrument stores. It's kinda what sparked this idea... as well as the fact that I hate cheap fluxes.

author: Faranight
author_rank: Unknown
timestamp: February 04, 2025, 05:55:50 pm
content: I bought rosin and some stearic acid. Both can be used as a soldering flux, but I was curious to know how a mixture of the two would behave. So I melted a hefty amount of them together in a 1:1 ratio. The resulting substance was very sticky and very unpleasant to work with, so I mainly use it to solder wires since I made so much of it because it flows somewhat better than pure rosin. I don't ever use it on PCB's.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: February 04, 2025, 06:09:17 pm
content: Quote from: Faranight on February 04, 2025, 05:55:50 pmBased on some research papers that I've been reading, this appears to be due a high amount of residues left behind. Typically longer-chain carboxylic acids (such as your stearic acid) will be more "sticky" and leave more residue. If you have swapped it for a low boiling-point alcohol (ex. ethanol), or decreased the percentage of stearic acid, it would have been better. But also, rosin itself becomes sticky as well at high percentages.For industrial PCB making, it seems that most flux mixes are typically low-residue and use compounds that readily dissolve in water.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 04, 2025, 06:16:01 pm
content: Here's a thread from a while back:https://www.eevblog.com/forum/repair/restoring-dried-solder-flux-paste/msg3484434/#msg3484434My comments begin at #22. Bottom line, you can do it with beeswax, rosin, and a little stearic acid. It still won't match Kester #44. I show some examples.Moreover, for the amount you should use of Kester #44 might be cheaper than the cost of heating the soldering iron. (Please, that is being hyperbolic. No need to show actual calculations.)PS: Dissolving a little #44 in amyl alcohol or similar has occurred to me, but I haven't tried it.Edit: I just skim read what I wrote previously. Petroleum jelly and beeswax can be used as needed to control the viscosity at room temperature. Apparently, I used PJ to get a soft paste.Edit2: If worried about residue, you might consider formic acid. Upon reading a thread this morning about OSP v. ENIG or HASL for PCB's I tried to find out what exactly was the organic in OSP. Most I could find was an MSDS that said formic acid + other stuff. Of course, formic acid may affect your eyes more than stearic acid.

author: MathWizard
author_rank: Super Contributor
timestamp: February 04, 2025, 10:53:33 pm
content: I want to try local trees, like Spruce and Pine, and see if a little bit of their sap/turpentine, dissolved in ISP, does anything. Maybe they don't have the right chemicals or enough of it, but I'm just curious. If you are at a party in the woods, and the stereo needs repairs, what else would work as flux. I'd at least try scratching/sanding the surface 1st. And I'd be soldering with a hot nail or hot knife I guess.

author: themadhippy
author_rank: Super Contributor
timestamp: February 04, 2025, 11:09:22 pm
content: Quoteas if anybody would have a hot knife at a party in the woods

author: coppercone2
author_rank: Super Contributor
timestamp: February 05, 2025, 12:28:07 am
content: I think that is Rosin flux, to get RMA or RA flux, you would need to add some activator chemicals.Citric acid might be one.I wonder if you can make something more aggressive then commercial RA flux but less bad then plumber flux to solder rancid shitI do like the more active flux (RA) but I noticed, especially on HV circuits, you really gotta clean it good. I saw arcing occur on a 100V rail after doing a half assed cleanup after replacing a capacitor.I think what you want to avoid is chlorine atoms though, even though they solder good, it does not work well with electronics partsRMA and RA really help on old equipment to work go as smoothly as new equipment, with increased cleaning requirements.

author: 44kgk1lkf6u
author_rank: Regular Contributor
timestamp: February 05, 2025, 01:37:04 am
content: I tend to take a different approach. I often use solid rosin. It is not very easy to remove. But it does not corrode nor does it conduct electricity. I leave it on.

author: PGPG
author_rank: Frequent Contributor
timestamp: February 05, 2025, 11:10:44 am
content: Quote from: LooseJunkHater on February 04, 2025, 05:16:53 pmI was doing it when as a child I was making my first PCBs (around 1970).Recipe - just add to alcohol crushed rosin until it dissolves no further.I didn't cleaned it from PCB. It was said that it protects tracks from the influence of the atmosphere.Those time I didn't know what conductivity is

author: thephil
author_rank: Regular Contributor
timestamp: February 05, 2025, 11:17:56 am
content: I have "made" my own flux: just dissolved some dry rosin (crush before adding) in IPA until the thickness looked right. Works fine. Is it worth it? It was fun and not much effort but of course just buying it works just as well. Have not yet tried from scratch – i.e. stealing sap from trees...

author: FrankE
author_rank: Regular Contributor
timestamp: February 05, 2025, 11:23:20 am
content: I bought some rosin several years ago and tried dissolving it in IPA 99. It didn't dissolve.

author: coppercone2
author_rank: Super Contributor
timestamp: February 05, 2025, 12:49:20 pm
content: did you heat and agitate it?

author: jpanhalt
author_rank: Super Contributor
timestamp: February 05, 2025, 01:51:12 pm
content: Quote from: FrankE on February 05, 2025, 11:23:20 amAbietic acid, a principal component of rosin, is soluble in acetone, pet ether (low molecular weight hydrocarbons), diethyl ether , and ethanol according to Wikipedia (attachment).When dissolving solids there are thermodynamic and kinetic factors. That is, a substance may be soluble, but dissolve very slowly. Heating is one way to speed up the process. Pulverizing the solid to increase its surface area is another. Lastly, if a substance is insoluble in water, a little water can affect solubility enormously. You mention it was 99% IPA. If that is accurate, it may not be an important factor, but it is worth considering. Solvent properties of absolute v. 95% ethanol are quite different. For example, the former, but not the latter dissolves fats readily.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: February 05, 2025, 08:27:56 pm
content: I once read a guy making his own flux from a combination of citric acid and water, combined with anything to increase it's vicosity, such as glycol or even honey. It's easy to wash of and clean this type of flux, but because it's acid based, you also have to clean the PCB after soldering, as leaving the acid on the PCB will lead to corrosion over time.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 05, 2025, 09:15:25 pm
content: Honey is licking good. It has plenty of reducing sugars in it and may work great. I don't normally lick my PCB's. Strawberries are high in ascorbic acid (Vitamin C) . It's a reducing agent. Either recipe might make an environmentally friendly flux for my leaded solder. Neither contains bromide as Kester 44 does. I like that little activation, because I always clean my board afterward.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: February 05, 2025, 09:36:13 pm
content: I've read a few research paper on this topic of making flux since starting this thread (in other words, I'm NOT AN EXPERT), butthis articlewas quite interesting and provided some general guidance on fluxes, specifically for BGA or other fine-pitched soldering. The article minimally focused on rosin, but instead primarily focused on resin or alternative bases for flux, due to residue of rosin. It also focused on the importance of using highly volatile compounds, to again, reduce residue. I tried to find some articles with specific flux recipes which are easy to clean (ie. highly water-soluable, so that I could use simple distilled water to clean the leftover flux) and use readily-available ingredients, but came up mostly empty-handed. I'd imagine this information would probably be more within patents.Some interesting things discussed in the ScienceDirect article include the conductivity vs corrosiveness vs viscosity vs volatility of additives and how it all effects residue, wetting (relates to surface tension), and activity level (ability to remove oxides; activator) of the fluxes. Most of what was discussed went way-over my head, but some general guide that I picked up for making my own trial flux includes:Solvent: Normal solvent-amount for low-residue = 60-99% (NOT LESS)Activator: Less than 1% activator willnothave enough fluxing action, whileabove9% can lead to significant residueSurfactant: Less than 1% recommended____________________________________________________________________________________________________________________Based on some YouTube videos and research papers that I've read so far, I'm thinking of using maybe 15% rosin (base), 80% ethanol/isopyopyl alcohol (solvent), 5% citric acid or lactic acid (activator), and less than 1% stearic or oleic acid (surfactant). I feel this solution will likely be too-liquidity for typical through-hole soldering, but for reflow of QFN's or similar SMD's it may perform better and be easier to clean. Of course, I'd need to make a small batch and try it out.The rationale for these ratios comes from within the above-linked ScienceDirect article, while the specific compounds comes from their availability & volatility (ethanol, citric/lactic acid, and stearic/oleic acid are all READILY AVAILABLE for cheap).

author: jpanhalt
author_rank: Super Contributor
timestamp: February 05, 2025, 09:47:48 pm
content: Why try to make your own with Google AI so-called information? Kester 44 is 0.44% halide (bromide and/or chloride). It's been a standard and is less than the 1% quoted.Is your interest in making reliable circuits or selling flux?

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: February 05, 2025, 10:15:40 pm
content: Quote from: jpanhalt on February 05, 2025, 09:47:48 pmI provided the source of my comment, maybe read it first before claiming something to be AI.Quote from: jpanhalt on February 05, 2025, 09:47:48 pmNever used or heard of Kester44 before but it appears to be relatively expensive for the amount you get. I've had a number of circuits fail before of leftover flux which is a PITA to remove. If I can easily make my own flux from readily-available materials that performs well, why-not make it? Plus, it's a learning experience.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 05, 2025, 10:58:05 pm
content: Removing excess flux is easy. Every commercial board manufacturer deso it. I've posted pictures of my boards with no "white residue."What's your real goal? Moreover, the need to remove common commercial fluxes may not exist except in specific circumstances.Get on with what you really want to do and leave solder and solder fluxes to the experts.

author: shabaz
author_rank: Frequent Contributor
timestamp: February 06, 2025, 12:26:50 am
content: Indeed. Life is too short to go off on unnecessary endeavors for little benefit.Better to concentrate on doing what you actually want to do.Good flux is inexpensive, you won't need to use a lot, and it's not a pain to remove (if you wish to remove it). You're basing your decision on making flux off incorrect premises.Why not ask here what your peers do, and learn from it? (most don't make their own flux!).I bet Kester is excellent (I have not used it, but have seen the recommendations many times), and if you're not doing production volumes, it's a safe bet you won't spend more than $10 per year or so on consuming flux for your projects. Is that really worth cost-reducing further?The attached photo shows a pot of flux that I use (not suggesting you use it over any other recommendation; I'm suggesting it's one of the ones I use that I'm happy with) - it's a top brand too, it costs less than $15 and it lasts years (applying a thin film onto a PCB..). Granted more is consumed with certain SMD soldering techniques, but there a syringeful of similar-priced flux can again last a year or more when prototyping (I certainly don't expect to make production volumes by hand).As for cleaning.. ask for recommendations if you're having problems with it. I can certainly suggest what works for me, and so can others.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: February 06, 2025, 05:06:56 pm
content: You know what, I think you're right. Realistically, I go through such a small amount of flux per year (like you said, less than $10) that it probably doesn't make sense to waste my time and effort trying to devise my own, when it would have the potential to perform much worse than commercial offerings (in wetability, corrosiveness, cleanability, etc.).Thank you.

author: tooki
author_rank: Super Contributor
timestamp: February 06, 2025, 06:23:22 pm
content: Quote from: jpanhalt on February 04, 2025, 06:16:01 pmKester 44 paste flux (SP-44) was discontinued almost 20 years ago. There isn’t even much NOS left.

author: tooki
author_rank: Super Contributor
timestamp: February 06, 2025, 06:28:16 pm
content: Quote from: LooseJunkHater on February 06, 2025, 05:06:56 pm100%. I went through the same process of researching it and experimenting, and the results were disappointing. It’s easier and cheaper (especially when you consider the value of your time) to just buy a good flux.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 06, 2025, 06:49:31 pm
content: SP-44 is what I use, and the tin is still at least half full. I'm set until 2050. I will remember to have it in my coffin -- I wonder if it can stand that much heat?Kester still advertises 44 rosin flux-cored solder and calls it "activated:"https://www.kester.com/products/product/44-flux-cored-wireThe formula may be a little different. The current analysis shows chlorine at 0.5 ppm and doesn't specify its form. Bromo-compounds are below detectable levels.

author: Shock
author_rank: Super Contributor
timestamp: February 06, 2025, 08:22:57 pm
content: Aside from the composition and viscosity at room temp, you also have to consider the evaporation rate or working time, intended alloy, the activation/deactivation working times and temp, if residue remains hydroscopic, if fumes/solids reactive, cleaning method, toxicity to the operator. Lots to consider in a good flux.

author: tooki
author_rank: Super Contributor
timestamp: February 06, 2025, 08:29:16 pm
content: Quote from: jpanhalt on February 06, 2025, 06:49:31 pmI’m fully aware that Kester 44 solder wire is still sold — it’s my favorite solder, which I use every day at work.Nonetheless, the 44pasteis unavailable to anyone who doesn’t already have it, so it’s not useful in terms of purchasing advice for today. (Sadly. I liked SP-44. I still have half an old tin of it.) There are really similar-looking products from MG Chemicals and Chipquik that are still available today.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 06, 2025, 09:24:08 pm
content: Does the MG SDS say what's in it? My sexperience is that MG is more secretive than Kester was, but even Kester is trying to hide more now. As one example, its recipe for 5768 water-based flux remover was in the SDS/MSDS. That has now seemed to have changed. A seemingly older version is still available on the site for a local supplier:https://gokimco.com/products/kester-5768-bio-kleen-flux-remover-1-gallon-63-0000-5768dated 2017. That is, of course, why I started using ZEP acrylic floor stripper for that-.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: February 06, 2025, 10:10:55 pm
content: Quote from: jpanhalt on February 06, 2025, 09:24:08 pmWow, the observation of the ZEP acrylic floor stripper having some of the same ingredients (in lower concentrations) is an amazing observation! I've previously hadsomemild success with the Zep Citrus Cleaner in my ultrasonic cleaner, which is slightly better than hot water, but still not great. Guess when I run out of the Citrus Cleaner, I'll give the acrylic floor stripper a try.It makes me kinda want to look at a bunch of the commercial flux cleaner products, compare SDS's, and see if there are cheaper products in-stores, advertised for different uses... But again, that may end up sending me down the same rabbit-hole of wanting to create my own flux lol_______________________________________________________Edit: Wow, it looks like the Branson ultrasonic cleaning fluids also contain a significant amount of the ethanolamine, as does the Kester 5768...

author: jpanhalt
author_rank: Super Contributor
timestamp: February 06, 2025, 11:02:04 pm
content: Dilute the stock ZEP product 1 part ZEP to 3 parts total. No need to measure accurately, and you have the same stuff. I was amazed after my first try. Be sure to clean thoroughly with deionized water. The boards glisten. I use an old ultrasonic for about 1 to 2 minutes in the cleaner. The rinse is about the same. Don't go too long in the initial ZEP cleaner. The rinse time doesn't seem to matter much.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: February 07, 2025, 04:06:33 pm
content: Quote from: jpanhalt on February 06, 2025, 11:02:04 pmI've never used any professional flux cleaner products before, but with your ZEP cleaner, do you feel it works "good enough" at room temp, or do you generally heat it up to 50C+?

author: RoGeorge
author_rank: Super Contributor
timestamp: February 07, 2025, 04:57:01 pm
content: The advantage with rosin as flux, either solid or dissolved, is that you don't have to clean the board afterwards, because rosin is a very good insulator, and it doesn't corrode the traces.On the contrary, many commercial fluxes must be cleaned after soldering, or else the leftover flux might be very conductive and disturb the circuit, or might corrode the traces in time.As for preparing your own rosin based flux, don't overthink it. Crush some solid rosin and pour the dust in a small glass bottle, together with some alcohol. Add more rosin until it thickens.Long ago, we as kids at a pioneers' club (the equivalent of today's maker's clubs) were using medicinal alcohol, because it was the only one available as kids. Medicinal alcohol didn't work very well as a solvent for rosin, and some residues were always on the bottom of the bottle. Not sure if the precipitate-like residues were the result of some chemical reaction, or just impurities from the rosin.However, the resulting solution was en excellent flux for soldering, and at the same time an excellent protection cover for the copper traces at the same time.We used to hand made PCBs and etch them ourselves, with fumic nitric acid (very strong HNO3).After rinsing with tap water, then drying, we were painting the entire PCB area with dissolved rosin (dissolved rosin was about as thick as a paint). Once dried the layer of rosin, it was keeping the copper traces shiny forever, and also serve as an already applied layer of flux at the soldering pads.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 07, 2025, 06:04:14 pm
content: Quote from: LooseJunkHater on February 07, 2025, 04:06:33 pmI don't heat it intentionally. It gets a little warmer in the ultrasonic during the 1 to 2 minutes. As for how it works, I'd say excellent, not just good enough.I used to use neat organic solvents, namely absolute ethanol and sometimes added acetone for difficult residues. I still use that for spot cleaning after minor rework or adding things, like button switches, that I do not want to have retained water. When I first tried ZEP, after water rinsing under a faucet, the board is virtually dry. Solder resist is hydrophobic, and the only water left was a tiny bit under components. I blow dry with compressed air from an oilless compressor. That's breathable air, not gas from a can of compressed gas/ difluoroethane. No haze is left; whereas, with the neat solvents, they may leave a slight haze after evaporation unless they are completely fresh. I was rinsing 2 or 3 time to get rid of it. Also, "white residue" left by organics does not occur.I have checked the MSDS/SDS sheets for a few other water-based cleaners, and they have similar mixtures of the same classes of chemicals. Namely, they are mostly hydroxy ethers (aka glycol ethers, e.g., cellosolves,https://en.wikipedia.org/wiki/Glycol_ethers) and a little ethanolamine to raise the pH.I started using that ZEP recipe based on the MSDS/SDS from Kester for its aqueous cleaner, not by hit or miss testing of every household cleaner I had. That is my go to. I have not used neat solvents for full-board cleaning since I started using ZEP a few years ago.ZEP is only a brand name, numerous other products have virtually the same recipe. In speaking with a chemist at ZEP, I was told it is not distributed in Australia. He did not know why, but given its utility for cleaning and polishing floors, I suspect there are equivalent products there, assuming enough people do that there.

author: JoeS
author_rank: Newbie
timestamp: March 26, 2025, 09:22:06 am
content: Got some old sap from a vintage collecting tin. It worked fine. Residue cleaned up with acetone. Good in a pinch, but prefer the stuff I use in the injector. Don't have a fume extractor. Stunk up the garage

author: Co6aka
author_rank: Unknown
timestamp: September 21, 2025, 06:17:57 pm
content: I've been making and refining fluxes for a long time. Beware of the voluminous "witchcraft recipes" polluting the 'net.I use the purest "white" rosinpowdercommercially available. The more color rosin has the more unwanted stuff it contains. Don't hack up your pine trees or whatever. Buying powder saves you time and toil for a small toll.I use at least "99%" IPA. I've tried lab grade "pure ethanol" but it's more expensive and I saw no difference. Basically, you don't want any water in your flux as it immediately turns to steam and splatters when soldering.I use small airtight glass jars. Don't make huge batches unless you'll use it up right away. Fill the jar 1/3 with the alcohol, add about 1/3 rosin powder, and cap the bottle. It takes a while for the rosin powder to dissolve. Agitate, and you can warm the jar in hot water.Adjust the concentration as desired by adding small amounts of rosin powder. Different concentrations have different uses; experiment. For the tackiest flux, add small amounts of rosin powder until saturated, then add a few drops of alcohol and agitate/warm. Repeat until all rosin powder is dissolved. If you weigh, count and record it's easier to remake. If you use different rosin you'll have to recalibrate.To make "activated" flux add adrop(or more as neededfrom a dropper) of glacial acetic acid (no water!) and agitate. Don't use "vinegar" as it contains water. Acetic acid evaporates and/or cleans off with water. Don't use citric acid as it doesn't evaporate and leaves solids behind that must be cleaned.And for the love of everything sacred to anyone, don't use petroleum jelly or similar!And skip the glycerine, antifreeze, hand sanitizer, borax, vodka, etc.As for additives, I haven't experimented with surficants, cationic or otherwise, but they're probably worth tinkering with. Otherwise, there's "MS2 Dross Eliminator" and other dross reducers also probably worth tinkering with.