Soldering flux is (or at least, should be) one of the ubiquitous features of any electronics bench. It serves the purpose of excluding oxygen from a solder joint as it solidifies, and in most cases its base is derived from pine rosin. Most of us just buy flux, but [pileofstuff] is having a go at making his own.
He starts with a block of rosin and a couple of different solvents. Isopropanol we’re happy with, but perhaps using methanol for something to be vaporized within breathing distance isn’t something we’d do. At about 25% rosin to solvent ratio the result is a yellow liquid flux, which he tests against some commercial fluxes. The result is a reasonable liquid flux, something which perhaps shouldn’t be too much of a surprise, and is a handy piece of information to store away should we ever be MacGuyver-like stuck in a pine forest with a need to save the day with electronics.
It would be interesting to try the same technique but with a solvent selected to soften the rosin for a paste flux, and perhaps any chemists among our readership could enlighten us about just what rosin is beside the heavy fractions left after extracting the volatiles from pine resin.
In the past we’ve taken a close look at how solder really works.
I’d like to see it with ethanol as something that would be homebrewable. Or just tested with everclear
With distillation you can get to nearly 96% ethanol I’m not sure what a home setup could reach (not that I’d recommend anyone try DIYing a pot). But BigClive has some sort of home distilling device.
And I believe anhydrous magnesium sulphate (baked Epsom salts) can dehydrate the mixture to even purer ethanol.
Is there a reason other than taxes that IPA is so often used instead of ethanol?
Taxes.
You can drink ethanol, so it is taxed an alcoholic beverage in most places.
Sometimes you can buy denatured ethanol, but in most places it is cheaper and easie to just use isopropyl alcohol. Denatured ethanol has some stuff in it that is supposed to make you puke if you drink it.
In Germany, I find it cheaper to buy denatured ethanol than to buy isopropyl alcohol. Grocery stores carry denatured ethanol as a fire starter for charcoal barbecue grills. It is over 97% pure ethanol. I use it to clean PCBs and as a solvent for shellac. The denatured ethanol costs about 2 Euros per liter bottle. You can buy isopropyl alcohol in Germany, but the stuff you can get is intended for cosmetic or medical use and has to meet different standards – it costs about 4 times as much as the denatured ethanol. That’s about 8 Euros a liter for isopropyl – and none of the stores in the small town I live in carry it.
I find the smell of ethanol pleasanter than isopropyl alchohol. Not that I’d drink either one straight, or that solvents smell like perfume. As a solvent, ethanol is one of the least “stinky.”
Denatured ethanol usually has bergamot oil in it (the same stuff as in Earl Grey tea), to make it so bitter as to become undrinkable. That’s what causes the nice smell. It also tends to have some methanol in it, to make it toxic.
Interesting about the bergamot oil, I drink Earl Grey to calm my stomach when it’s upset. I guess the concept of too much of a good thing is universal.
Denatured ethanol may at one time have used bergamot oil, but it seems that there’s substance callen “denatonium” that’s used these days.
It takes far less denatonium to make the stuff undrinkably bitter.
Denatured ethanol:
https://en.wikipedia.org/wiki/Denatured_alcohol
Denatonium:
https://en.wikipedia.org/wiki/Denatonium
If you read the general guidelines for denatured ethanol, “making it toxic” is actually NOT a goal, and could probably attract some fines.
The goal is to stop people drinking it, not to kill those that inevitably do.
However since it’s not made for consuming, it doesn’t have the same high standards for purity, so some degree of residue is ok.
I live in the Netherlands and it’s a bit weird with the chemicals. The hardware stores around me sell thinner (advertised as such) without thinner, ammonia (advertised as such) without ammonia (looks, smells and acts more like dish soap), and so on. It’s so weird.
Kind of annoying when you need the actual ingredient for something. I buy isopropyl online but it’s crazy expensive. Indeed about 8 euro’s a liter. Can’t even buy it in any local store. Acetone is also crazy expensive if you want a normal bottle. Mostly sold as makeup cleaner.
I didn’t know fire starter liquid was ethanol, so thank you for that. I’ll try that out.
Not all barbecue starter fluid is ethanol. The stuff sold locally as “bio” starter fluid is ethanol. Check the label and see what it says.
I order my 99.9% at cee-bee-cleaning.nl. 50 euro will get you 9 liters of the stuff (in 1L bottles) which works out to 5,55 a liter.
As for acetone, modern nail polish remover doesn’t contain any acetone anymore, you really have to hunt the labels of the cheapest stuff.
Hardware store might have Acetone since it’s used as a cleaner.
Acetone is a solvent used for diluting paint or cleaning not-quite-solidified paint off clothing and other things. Most paint stores have it; expect to pay $10 to $20 for a gallon.
From wikipedia, “In soldering metals, flux serves a threefold purpose: it removes any oxidized metal from the surfaces to be soldered, seals out air thus preventing further oxidation, and improves the wetting characteristics of the liquid solder.”
The removal of oxidized metal means that the flux is acidic, and should be completely removed after the soldering is done to prevent corrosion. A hallmark of poor quality electronics is residual flux.
@Bob You can simply buy 96% denatured ethanol from Kruidvat (Alcohol Ketonatus). 3 euro or less.
I have a few tins of ‘kolofonium’, which is basically rosin. I crush up a bunch of it and mix it with the denatured ethanol. Wait a few days for it all to dissolve, and you’ve got yourself a quite reasonable flux. I think I probably am at 15% kolofonium/ethanol or so. Works for me. 25% would probably be better.
I use this self-made flux all the time. Didn’t even realise that it was something out of the ordinary.
Thats 3€ for like 100ml. Crazy. I bought some 99.99% isopropil from amazon.26€ for 6 liters. Very expensive still, when you only need like half a bottle. Still better than paying 15€ for a single bottle. Did get ‘free’ shipping though …
Rosin is also used by violinists, and I actually won some once with a dangerous prototypes giveaway. I used kruidvat alcohol to make a bottle of flux. Still have to increase the concentration sometime. Solders quite good, but my biggest issue is that it sticks really bad … Like rosin ;p and it crystalizes. So the bottle is always a mess…
“Alcohol Ketonatus”
I once mentioned this to someone from the US, and she immediately said “Ah, you must be Dutch.”
Apparently, we’re the only place that sells alcohol ketonatus. :)
Werkenmetmerken also has it on sale frequently, box of 12 1L bottles for 60 euro at the moment which gives 5 euro/bottle.
If you look/wait around 5 euro per bottle is quite achievable. Acetone is also best ordered online nowadays.
A few years ago, I ordered everything at deoplosmiddelspecialist, but sadly they went out of business quite messily due to supposedly personal circumstances and resultant mismanagement. Luckily I had no orders at the time, quite a few people got screwed when they went under. They had everything I wanted for usually the best available price.
The ‘bio’ paint thinner, ‘bio’ wasbenzine and ‘bio’ turpentine is super annoying. IIRC the hardware stores got pushed to sell less environmentally polluting solvents, and that ‘de parel’ eco trash is now all you can find in any hardware store. I have a sneaking suspicion all the bottles are filled with nearly the same stuff, just a random fraction hydrocarbons and alcohols in slightly different ratios. I no longer trust any solvents from hardware stores.
As fuel for alcohol stoves, the bio-ethanol from Action is quite nice, burns way better/cleaner than spiritus. Never tested it as a solvent yet.
Go to a hardware or car supply store, and look at the ingredients of gas line antifreeze.
Where I am, the most popular product is called Isoheet, and is mostly isopropyl alcohol.
Ah here in the UK denatured ethanol is called methylated spirits. Now I know what you are talking about, the penny has dropped!
And have you tried to buy any recently? I went to the regular places (supermarkets, B&Q and Wickes) recently in search of some and came back empty handed…
I want to know what makes those fluxes that stay relatively liquid even at soldering temps – the ones people are always using to float around extra small smd components until the solder grabs.
The problem with alcohol based fluxes is that the alcohol evaporates long before the rosin and/or solder melts.
But the alcohol is just the carrier, nothing more, nothing less. Rosin is a solid. It melts and does its work when you heat it. But the problem is in the application. You are trying to get tiny shards of a hard material close to your pins. But breathe too hard, and they move and you have to reposition them again. And the more pins the component has, the more tiny shard you have to place, the more work if you breathe too hard, or tap a bit too hard with your soldering iron. It’s a hassle, and I’d even say: a chore.
If you dissolve the rosin in ethanol, you can apply it with a syringe or a small brush. So very much easier. If the alcohol evaporates, the rosin stays behind. And it forms a film on the things that you want to solder. I don’t see the problem of the alcohol evaporating.
Searching for “flux” on some websites like Farnell returns dozens of results, making me wonder which one(s) i should pick!
Should i use different ones for different usage, like desoldering vs soldering, though hole vs surface mount components, hot air station vs soldering gun ?
As a hobbyist, mostly you shouldn’t.
You should use solder with a flux core. That will work and be proper for most things.
If you are soldering with hot air or using a soldering oven then you should be using solder paste that contains the proper flux as well as the solder.
“Flood it in flux” is the way people solder who haven’t learned to use a soldering iron.
Hard agree, makes me cringe to see the number of youtube ‘experts’ who soak stuff with flux, even some people who call themselves professional and claim to make stuff ‘better than factory’ (when it’s obvious to anyone with eyes that it’s far worse).
Put the time and effort in, learn to solder, use the right tools and consumables and you’ll get a far better result.
Flux has a purpose. It exists and is manufactured for a reason. If, for example you are reworking a BGA package, you need flux.
If you are reworking existing corroded solder joints, you need flux.
If you’re mixing a low melt bismuth based solder into a lead free solder to lower its melting temperature, you need flux.
If you are replacing a component on a populated board, you probably need flux.
You don’t need flux if you’re soldering through-hole components on an unpopulated board or doing a quick THT cap replacement and you’re using rosin core solder.
If you’re doing SMD rework, which the vast majority of people who do electronics repair work are doing, then you do need flux.
When you’re soldering sub millimetre pin pitch qfn packages on a populated board, you can’t use solder paste. You’d likely end up causing solder bridges on neighbouring SMD resistors and smoothing caps, particularly if they’re 0402 packages.
You’re going to apply solder to the pads, use flux to prevent poor solder joints and apply localised hot air. The flux most people use also has tacky properties which help hold tiny 0402 components in place, for example.
I’m tired of seeing people complain that people are using flux. It’s 2024 and soldering technology has moved on from the 80’s. In the vast majority of electronics repair cases, flux will be needed.
For the hobbyist populating their own virgin boards it isn’t needed. For any kind of rework, it is necessary.
Correct soldering requires the right tools for the job. Complaining that people are using too much flux really highlights a lack of experience in performing any level of rework on devices made after 1990.
It is exactly as you have written.
When I read the title of the article, I knew instantly that there would be a comment from someone claiming their superiority for rejecting the evil of flux.
Good luck to those trying to remove a short between two 0201s without flux.
Absolutely. I find the “people who use flux don’t know what they are doing” attitude hilarious. Sure, if you never rework anything, then there’s enough flux in your solder as long as you don’t heat it for too long. You can try to use new solder to touch up a cold joint, but it just leaves you with too much solder on your connection. If you go to remove it, you might cook it again burn off the flux and then you have to start all over.
“Complaining that people are using too much flux really highlights a lack of experience in performing any level of rework on devices made after 1990.”
Gee, thanks, I guess I’ve been doing it wrong for nearly 40 years* and counting.
Snark aside though, you write some sense, flux has its place, never claimed it doesn’t, the skill is in knowing where, when and how much to use.
There is such a thing as too much, beyond what’s needed to make a decent joint it becomes just a waste of flux as well as potentially problematic because it increases the difficulty of cleaning fully and, when you have hygroscopic fluxes which can become corrosive over timep, that can cause real damage if it’s gotten under a BGA for example.
Wiping it down with an alcohol soaked bit of tissue just doesn’t cut it, hells if I’d been seen doing that at one repair facility I worked at I’d have been on a disciplinary if not sacked.
If you need to add flux with your solder wire or paste then your wire/paste and or technique is crap.
We really don’t need to discuss the youtube experts who apply flux paste to brand new THT boards before soldering with flux cored solder wire.
* Started off repairing the original IBM PCs and so many oddball competitors which never flew, worked though 8088, 286, 386, 486 and the Pentiums through to very recent Core i stuff , also built a business unit repairing Apple gear back in the 68K and Power PC days but that’s a long and unpleasant story of malicious litigation.
if you work with smd you need flux no matter how you solder
Nope. I do SMD by hand with a soldering iron using only fine (lead free) solder with just the flux in the solder.
Let’s see you do some bga chips without flux… I do GPU repair and it’s essential if you need to reball the core or memory
” “Flood it in flux” is the way people solder who haven’t learned to use a soldering iron. ”
Hard disagree. While components don’t need their own personal swimming pool of flux, for tiny SMD components or large pin-count devices, it is often useful to have a large blob (compared to the component’s size) of flux nearby, particularly when desoldering components.
Just because you don’t use the method doesn’t mean no one else knows what they’re doing.
Hard agree. Flux is a tool, use the tools available to you. If you don’t need it, great! But it’s not like we’re running out of Flux and we need to conserve as much of it as possible. As long the flux gets cleaned off after the board work is done, it genuinely doesn’t matter.
Well, this is not a hack, it is widely known and I did it several times. I have rosin forever and to make new flux, I just dissolve some in ethanol. Could be 2-propanol, too, but I do not see a good reason, as ethanol is even cheaper and more available in my country than isopropanol.
“Isopropanol we’re happy with, but perhaps using methanol for something to be vaporized within breathing distance isn’t something we’d do”
What makes you think breathing in isopropanol is any less harmful?
Reason to keeping a small fan in one’s work area.
The skull and cross bones on the methanol bottle label which the isopropanol bottle doesn’t have.
a small amount of glycerin to reduce stickiness
When I read “from scratch” I thought what was coming next was going to involve bleeding a pine tree.
😂
Also thought “from scratch” would involve common household ingredients
I kind of miss the smell of rosin flux.
yes… The Smell Of Napalm In The Morning
https://www.youtube.com/watch?v=Jts9suWIDlU
Fun Fact: Isopropyl alcohol is metabolized by the liver into Acetone. It’s diluted down to at least 90% in pharmacys and grocery stores so it isn’t absorbed into the bloodstream transdermally.
Depends on the country. In Canada I can walk into my local grocery store’s pharmacy and buy 99% isopropyl alcohol all day long.
Flux is usually necessary, at soldering temperature it reduces the oxide film on many metals back to the metal which is solder-wettable. Some assembly houses use nitrogen atmosphere in-process to prevent oxidation.
I once tried tartaric acid (as a glycerin paste IIRC) and it worked fine. But it attracted ants – too much … :((.
I made some pine tree based flux for doing a period-accurate rebuild of an edison phonograph. (No electronics, but the amplifier horn was made of sheets of steel that had been lead-and-flux soldered together.) The stuff in rosin is terpenes, turpentine being one mix of terpenes. They’re pretty bioactive and kind of nasty chemically. They’re a very broad family of chemicals, with thousands of individual components. It’s a little like coal tar but from trees.
My understanding is the rEsin from pine trees contain terpenes but the rOsen has had the terpenes removed making it hard and crushable instead of gooey.
Been there about 5 to 7 years ago. I needed flux, was to expensive or unobtainable and I had to make myself after seen it on the Internet how easy was to make it. It worked, but I cannot remember the proportions (maybe i added IPA to crushed rosin until it disolved completly). It was sticky and after soldering I had to wash the electronics with IPA. The brush I used got a stiffy after a while and no amount of IPA fix it back.
If I’m soldering a ring togerther rem sizing it how do I get the soldiers to stuck.
Rosin does not just exclude oxygen. It is an acid that strips oxides so that metal _can_ be soldered. But it is only active when heated. At room temperature it does not have a corroding effect. So when you are told not to use acid core solder, because it would corrode the PCB traces, rosin is acid too! It just doesn’t corrode the PCB.
Interesting comment. So why are we told to clean flux residue? Is it some kind of urban legend?
Consider acetone?