Why a rosin flux advertised as paste/cream came rock solid? - Page 1
Forum section: electronics / beginners

author: bassmothership
author_rank: Contributor
timestamp: August 31, 2024, 03:23:38 pm
content: This was my first time buying flux to do repair work on old tape machines and I got this from Amazon.jp (in the picture).The product's name on amazon.jp: [Soldering Flux, Rosin Flux Paste 30g Solder Paste Soldering Cream, Rosin Paste Flux, Mobile Phone Computer Repair Manufacturing Rosin Paste 30g SFD H05] but it's rock solid hard.Could anyone please explain what's going on?I've read about getting bits of it and mix in IPA and use as flux, but once it solidifies it's going to get rock hard again on the pcb.Already missed the return date so what should I do? Should I just throw this in the garbage?Is there any use for this?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 31, 2024, 03:26:44 pm
content: Looks like 100% pure pine rosin.Hope you didn't pay much for it. Considering you can get it free from nearby trees, if you don't mind a little cooking.Tim

author: SteveThackery
author_rank: Super Contributor
timestamp: August 31, 2024, 03:31:48 pm
content: It is mis-described; it should not refer to 'paste' or 'cream".However, you have received a legitimate product. Rosin at room temperature is a hard, clear substance, exactly as you have received. It is the same stuff that you get inside multicore solder. It will melt under the heat of a soldering iron and act as a flux. When the joint cools down it is left behind as a hard, translucent substance.To use it you should dissolve a little bit of it in IPA. When you have made the joint, you should use IPA and a stiff brush (such as a toothbrush) to clean the joint. This applies even when the rosin was delivered via the multicore solder.So there you go: what you have received is a tin of pure rosin. It behaves as a gentle acid when molten (hence working as a flux), but becomes inert when it sets solid. The biggest shortcomings are that it burns and gives off fumes at higher soldering temperatures, and that it needs cleaning off if you want a flux-free joint.Personally I prefer the type of flux that comes in a syringe - it doesn't burn so easily and doesn't give off noticeable fumes. It also works just fine with multicore solder, giving you a mix of two different fluxes.

author: bassmothership
author_rank: Contributor
timestamp: August 31, 2024, 03:35:58 pm
content: Quote from: T3sl4co1l on August 31, 2024, 03:26:44 pmI don't know what is considered expensive. I paid 1,660 ien, about 15 usd for this

author: IanB
author_rank: Super Contributor
timestamp: August 31, 2024, 03:44:22 pm
content: Normally, the soldering flux that comes in containers like that is a soft gel-like paste.It seems like you were shipped the wrong product, or a wrongly described product.I would try buying a different product, but look for a product that specifically says "Rosin paste flux for electrical soldering".

author: bassmothership
author_rank: Contributor
timestamp: August 31, 2024, 03:46:11 pm
content: Quote from: SteveThackery on August 31, 2024, 03:31:48 pmSo "good news" then. I will try to use it and take this experience as a lesson.I'm starting to practice repairing old cassette multitrack machines. There are some PCB contacts and traces that I damaged and need to repaired, so that's where I will be using the flux for the moment.Do you have any advice on that?

author: Ian.M
author_rank: Super Contributor
timestamp: August 31, 2024, 03:52:21 pm
content: It also isn't 'solder paste'!Why would you expect an Amazon product name, from a Chinese 'alphabet soup' brand name seller to be an accurate description of the product? They are notorious for spamming keywords to get a higher search ranking, and frequently mistranslate Chinese to technical English. If the seller's other items aren't predominantly electronics related, they probably don't even know what paste flux is meant to be like.Rosin dissolved in IPA makes a reasonably good liquid flux, but it has the same disadvantage as other alcohol based liquid fluxes - unless you let it dry at least enough to thicken up the heat from the iron tends to drive the flux away from the joint. Applied sparingly with a small brush, there isn't much cleanup required, and the residue dissolves easily in common solvent based flux removers.Also, what do you think happens to the residual solid flux from the flux cores of your solder? That will also form a hard crusty ring round your joint . . .

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 31, 2024, 03:53:07 pm
content: Quote from: bassmothership on August 31, 2024, 03:35:58 pmThat's about 10 times what it's worth.Most people would put that stuff in the bin for chemical waste disposal.It's also annoying stuff. There are a gazillion brands of pasty fluxes around. The "flux pen" with thin liquid clear flux is quite popular.

author: bassmothership
author_rank: Contributor
timestamp: August 31, 2024, 03:53:13 pm
content: Quote from: IanB on August 31, 2024, 03:44:22 pmIt's so weird.The description is wrong but now looking at the picture closely, it clearly doesn't look like gel at all. It indeed looks like it's completely solid, you can even see the pieces and cracks on the surface like glass,

author: IanB
author_rank: Super Contributor
timestamp: August 31, 2024, 03:53:22 pm
content: Quote from: bassmothership on August 31, 2024, 03:46:11 pmPersonally, I would not try to use it. It needs to be a soft, almost liquid, paste, that you can apply to the joint using a toothpick or some other small item.

author: IanB
author_rank: Super Contributor
timestamp: August 31, 2024, 03:59:49 pm
content: I have been very satisfied with this product:

author: Stray Electron
author_rank: Super Contributor
timestamp: August 31, 2024, 04:00:46 pm
content: FWIW pure pine tree rosin makes a pretty good flux for cleaning the lead when I cast lead bullets. Otherwise, you got taken!

author: coppice
author_rank: Super Contributor
timestamp: August 31, 2024, 04:04:41 pm
content: Quote from: bassmothership on August 31, 2024, 03:23:38 pmAll rosin flux gets rock hard on the PCB. Even the stuff that has been softened with something not too volatile, so it stays a paste for a long time in the tin, goes rock hard after the heat of soldering drives the solvent away.Make no mistake. This stuff is high class rosin flux. It must be. It says so in Chinese. Maybe it was made a few years ago, stored in warm conditions, and dried out. Have you tried pouring a little isopropanol on it, to see if the surface will soften?

author: IanB
author_rank: Super Contributor
timestamp: August 31, 2024, 04:07:14 pm
content: Quote from: coppice on August 31, 2024, 04:04:41 pmI think the humour here might get lost in translation?

author: bassmothership
author_rank: Contributor
timestamp: August 31, 2024, 04:11:54 pm
content: Quote from: Ian.M on August 31, 2024, 03:52:21 pmNow I see the problem isn't that I got the wrong product, it is that the subject of flux itself has way more things to be learnt before one can think about buying anything.This stuff is even more confusing with all the scattered stuff on the internet and personal bias over brands etc.Where do one go about to learn properly about this stuff? Where to get the basics?

author: IanB
author_rank: Super Contributor
timestamp: August 31, 2024, 04:20:32 pm
content: No, you definitely got the wrong product.The Deoxit/CAIG product I listed would work fine for you. It is a properly formulated, reliable, soldering flux. If you can find some, I would suggest getting it.

author: SteveThackery
author_rank: Super Contributor
timestamp: August 31, 2024, 04:20:41 pm
content: Quote from: bassmothership on August 31, 2024, 03:46:11 pmWell, I guess it's good news in that you have, indeed, received some proper flux. The downside is that it's a lot more faffing about than using a modern flux paste from a syringe (I can't remember the brand of mine but it works great). Also rosin burns more readily than modern solder paste, so you need to make the soldered joints reasonably quickly, before it has all burnt off. It does give off fumes (smoke) as it burns, which doesn't bother me in the slightest and has done no apparent harm after 55 years, but if you are concerned, some sort of fume extraction might be advisable.Therefore, if it were me, I would probably put it aside and order some flux paste in a syringe.Quote from: bassmothership on August 31, 2024, 03:46:11 pmOnly in the most generic sense. If you have damaged some tracks, you can repair them using thin, solid core wire. You will need to carefully scrape off the flux resist (typically a green coating) from the undamaged ends of the track that you want to join back together. Then you tin the newly exposed copper by melting a little solder onto the two ends. Normally the flux inside the solder is sufficient for this task (because you have only just exposed the copper traces and you have given them a light scraping). However, if you wish you could apply a little extra flux to the newly exposed copper before tinning it.Cut your solid core wire to the approximate length (err on the long side) and solder one end to the track. Form it to the shape of the original track, cut it to the correct length, and solder the other end. Sometimes the track leading to a component leg (such as a connector or other electronic device) has been damaged. In that case, I recommend removing most of the solder from the pad in question using desolder wick. This will expose any ragged remains of the old track which you can pull off with tweezers. When the pad is nicely clean, tin it with a little solder and then solder the patch wire to it.There are loads of online sources explaining PCB repair so I won't repeat it here. All I would say is that the patch wire is much thicker than the original trace so is prone to being disturbed when handling the board. That is why I always advocate finishing the job with a layer of conformal coating from an aerosol. Failing that, apply little dabs of glue to your patch wire. Both methods will protect the wire from being disturbed accidentally.If you are replacing a long length of track consider leaving the insulation on the patch wire. In that case try to find some wire where the insulation doesn't shrink back excessively when heated.TLDR: the main message from me is that yes, youcanuse that solid rosin flux if you don't mind mixing it with IPA, but it burns quite easily, gives off fumes, and leaves blobs of glassy brown resin behind which you need to clean off with IPA and a toothbrush. Too much bother, I reckon.

author: bassmothership
author_rank: Contributor
timestamp: August 31, 2024, 04:21:15 pm
content: Quote from: IanB on August 31, 2024, 03:59:49 pmHere in Japan there's none of the flux brands I see people from English speaking countries talking about on the internets.Due to regulations, I guess?I see the chinese [Zmart Solder Flux AMTECH AMTECH NC – 559 – Asm BGA PCB NO CLEAN PASTE Soldering CC]. I've heard that's the fake AMTECH NC 559, right?

author: bassmothership
author_rank: Contributor
timestamp: August 31, 2024, 04:27:10 pm
content: Quote from: IanB on August 31, 2024, 04:07:14 pmYes, I cannot tell whether it's sarcasm or an inference.

author: IanB
author_rank: Super Contributor
timestamp: August 31, 2024, 04:30:45 pm
content: Quote from: bassmothership on August 31, 2024, 04:21:15 pmI'm sure you can find products like these in Japan:https://www.hakko.com/english/products/hakko_fs210_fs211.html

author: bassmothership
author_rank: Contributor
timestamp: August 31, 2024, 04:59:17 pm
content: Quote from: SteveThackery on August 31, 2024, 04:20:41 pmThanks a lot for the info.

author: bassmothership
author_rank: Contributor
timestamp: August 31, 2024, 05:01:02 pm
content: Quote from: IanB on August 31, 2024, 04:30:45 pmYes, I can find it here.The Hozan brand on the picture is quite popular in Japan:https://www.hozan.co.jp/E/catalog/Soldering_Tools/H-722_728.htmlFrom the composition which would be better for this type of job?

author: IanB
author_rank: Super Contributor
timestamp: August 31, 2024, 05:02:45 pm
content: You might want to get answers from other people. I'm not the best expert on the subject.Rosin flux was traditionally used with tin-lead solder. Such solder flows well, works at lower temperatures, and does not need a very aggressive flux.The newer lead-free solders work at higher temperatures, do not flow so well, and may need more aggressive chemical fluxes to make good joints.If you are going to be using lead-free solder, then you may need to check the data sheet for the solder you are using, and see what flux is recommended by the manufacturer.Soldering became more complex in modern times.

author: tooki
author_rank: Super Contributor
timestamp: August 31, 2024, 05:14:06 pm
content: Quote from: bassmothership on August 31, 2024, 04:21:15 pmNo, you probably just don't know where to look. (I thought the same thing about fluxes and other things in Switzerland 10 years ago. Turns out I just didn't know who distributed what, and that in fact there's a huge variety available.)Anyhow, you can easily order many good fluxes by mail, for example:https://www.digikey.jp/en/products/filter/flux-flux-remover/266Just add it to your next project order so you come up to the 6000 yen minimum for free shipping.

author: coppice
author_rank: Super Contributor
timestamp: August 31, 2024, 05:20:44 pm
content: Quote from: IanB on August 31, 2024, 04:07:14 pmHey, I gave you an accurate translation. I didn't lose anything.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: August 31, 2024, 06:20:12 pm
content: What's wrong with the old reliable rosin?! I use it for over 50 years and even now have a substantial piece of crystallized rosin for special cases. I've just made a simple experiment: I took a couple of wire bits and dropped a bit of melted by soldering iron rosin on top of these (see photos below), than I carefully (rosin is brittle) connected the wires to my high resistance shielding box and measured the resistance between two wires held together by a bit of hardened rosin. The result is close to the leakage of the box itself, less than 10fA at 10V or over 1Pohm (=1000Tohm). Try it with any other flux please, including all no-clean varieties. And yes, if needed, IPA removes it nicely.CheersAlex

author: Siwastaja
author_rank: Super Contributor
timestamp: August 31, 2024, 06:38:25 pm
content: Quote from: Alex Nikitin on August 31, 2024, 06:20:12 pmNothing, if you don't use lead-free. And if OP is planning to repair old devices, that's a viable exemption to use good old leaded solder - and rosin flux.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: August 31, 2024, 06:45:28 pm
content: Quote from: Siwastaja on August 31, 2024, 06:38:25 pmIt works perfectly fine with a good lead free solder (my personal favorite for many years is Stannol HS10, 95.5% Sn, 3.8% Ag, 0.7% Cu with Rosin flux).CheersAlexP.S. - I would agree that for repairs of old equipment, like tape decks etc, a leaded solder is a must, I have a reel of Sn62Pb36Ag2 with Rosin flux in my draw for that very purpose.

author: tooki
author_rank: Super Contributor
timestamp: August 31, 2024, 06:48:25 pm
content: Quote from: Alex Nikitin on August 31, 2024, 06:20:12 pmNothing wrong with it, other than not being particularly active. Fine for parts/boards that have little to no oxidation, but insufficient for more troublesome oxides. Those need a rosin flux that contains activators.Well that, and the fact that rosin in crystal form is difficult to apply.

author: Bud
author_rank: Super Contributor
timestamp: August 31, 2024, 06:51:47 pm
content: Quote from: Doctorandus_P on August 31, 2024, 03:53:07 pmOnly morons would do that. And i omitted the "fucking" qualifier for the morons part because i am in a sunny mood today.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: August 31, 2024, 06:57:43 pm
content: Quote from: tooki on August 31, 2024, 06:48:25 pmI suppose it takes a while to get use to it, on the other hand I personally almost never use a liquid/paste flux, only hard rosin, either in the solder wire or as crystals... .CheersAlex

author: bassmothership
author_rank: Contributor
timestamp: September 01, 2024, 04:11:24 am
content: Quote from: IanB on August 31, 2024, 05:02:45 pmThat's interesting.

author: amyk
author_rank: Super Contributor
timestamp: September 01, 2024, 06:57:25 am
content: Skip to 11:40 of this video to see how solid rosin is used for soldering:https://youtu.be/watch?v=AeL-nnhE7xo

author: SteveThackery
author_rank: Super Contributor
timestamp: September 01, 2024, 10:21:19 am
content: Quote from: amyk on September 01, 2024, 06:57:25 amIreallydon't agree. I don't think the iron should be used to carry the fluxorthe solder to the joint.

author: Ian.M
author_rank: Super Contributor
timestamp: September 01, 2024, 11:31:48 am
content: He's using a soldering gun, and you can hear the trigger clicking as he goes from the rosin flux to the board, so he's limiting the heat to avoid prematurely burning off the flux. It wouldn't go so well with a conventional temperature controlled iron set in the typical soldering temperature range, or with a 'firestick' - you'd have to be a bit quicker getting the flux to the board to avoid cooking it, and its much harder to carry significant quantities of flux at a higher bit temperature. A better technique for soldering irons is to get a good blob of rosin stuck on the end of a toothpick or small bamboo skewer, then use the iron to melt a little off the blob directly onto the pad. Carrying solder on the bit is an acceptable technique when there is supplemental flux pre-applied to the board.

author: RoGeorge
author_rank: Super Contributor
timestamp: September 01, 2024, 11:58:34 am
content: The pic in the OP is not flux, that's solid rosin. I won't call that "flux". Often, the solid rosin is the base ingredient to prepare some of the no-clean flux formulas, but that's a different thing.In practice, I find solid rosin as very, very good for soldering. Very good insulator (unless you burn/carbonize it with a too higher soldering temperature), doesn't require cleaning (doesn't attack copper with time - while some more aggressive flux formulas might corrode/oxidize later if not cleaned after soldering). If you want to clean the solid rosin leftover (though this is not mandatory), let it solidify then break away or scratch it away with a metal needle, then rub the PCB with isopropyl alcohol.Another quality is that it's dirt cheap to buy. The solid rosin can also be dissolved in isopropyl, add it to alcohol until it flows like honey, then spread it with a brush over the entire PCB, as a DIY cover mask, then let it dry/solitify. That will protect bare copper traces (for home made PCBs, to protect against oxidation and/or humidity). The protection layer helps with soldering, too.I prefer solid rosin for through hole components, particularly when using a soldering gun. When using a soldering iron instead of a soldering gun, and/or working with small SMD components, I prefer flux. Another aspect, for Pb free the soldering temperature has to be higher, which will make the solid rosin more difficult to use, but for SnPb alloy + THT + soldering gun, the solid rosin is the best.

author: tooki
author_rank: Super Contributor
timestamp: September 01, 2024, 12:00:51 pm
content: Quote from: amyk on September 01, 2024, 06:57:25 amI’m sure many, many people here have seen DiodeGoneWild’s videos. He makes a point of using janky tools as a sort of schtick.But as Ian.M says, this only works because he’s using a transformer-type soldering gun, where the tip is only heated when the trigger is held. This means he can heat the tip a little bit to melt some flux and transfer it to the joint before heating the tip up to soldering temperature. This method will not work at all for anyone using a normal soldering iron, because the rosin will burn off right away. Consequently, it is inapplicable and inadvisable to practically everyone in electronics. Soldering guns are a largely obsolete device that are not really suited to most of today’s electronics.

author: tooki
author_rank: Super Contributor
timestamp: September 01, 2024, 12:20:39 pm
content: Quote from: RoGeorge on September 01, 2024, 11:58:34 amI’ll just repeat what I said above:Quote from: tooki on August 31, 2024, 06:48:25 pmFYI, when you are using pure rosin as your flux, itisyour flux. It’s not “rosin vs flux”. What you mean is “rosin vs commercial flux”. I do agree with you, though, that selling pure rosin as “flux” is borderline fraudulent, insofar as it isn’t what most people expect.I have used pure rosin dissolved in alcohol to protect bare copper PCBs, just as you describe. And it works great for that. But that is the only thing I use it for. It is markedly inferior to commercial fluxes for anything else.What is interesting is people calling pure rosin “cheap”, in that this seems to vary wildly by location. Here in Switzerland, in USA, and probably in many countries, it’s sold primarily for string instruments (violins, etc) and is not particularly cheap. (I got mine at an apothecary, and it wasn’t cheap either. I wouldn’t say “expensive”, but not cheap enough to bother.) Every single person I’ve ever seen use it (or who says they use it) for soldering has been from Eastern Europe, so I guess it must be cheap there.Also, today I discovered that they make rosin for string musicians that hasmetal added to it. I put it in whatever the musician equivalent of “audiophool” territory is once I saw that the iron used isn’t just any ordinary iron, but “meteoric” iron… (I don’t doubt that metal powders could have a real effect. But IMHO the “meteoric” iron, as well as the wording of the effects, make me extremely skeptical. Especially in the homeopathic amounts used, since the rosins don’t exhibit any visible difference in appearance from ordinary rosin.)

author: coppice
author_rank: Super Contributor
timestamp: September 01, 2024, 12:36:15 pm
content: Quote from: tooki on August 31, 2024, 06:48:25 pmNot being very active is the main reason rosin has been so popular. It does a great job on parts that have not exceeded their use by date, and if the cleaning process leaves a little rosin residue you don't come back 5 years later to a corroded mess caused by that residue.

author: tooki
author_rank: Super Contributor
timestamp: September 01, 2024, 01:12:48 pm
content: Quote from: coppice on September 01, 2024, 12:36:15 pmBut almost always, when people say “rosin flux”, they do not mean unactivated rosin, they mean ordinary RMA flux, like in traditional rosin-core solder. Those do not cause corrosion in ordinary circumstances, even after decades. Unactivated rosin fluxes (type R) are fairly exotic outside of aerospace and military.Certainly I would contest any claims that rocks of rosin are, or ever were, a “popular” flux.