Good soldering flux?

[elektryk]

Which flux has actually the best price vs quality ratio?
I have been using Kester TSF6502, it was nice but now it has poor availability in my country.
Some years ago I've also bought Kingbo RMA218 from China, it needs cleaning but worked also good. I've bought it again recently but unfortunatelly some ingredients (or manufacturer) must have changed and now it works very poorly (I even stopped using it).
I'm currently using Alpha OM338, it is active enough and easy to clean, it could be the best of mentioned here but the smell of it is in my opinion terrible. It'd  be nice to find something similiar but with less aggressive fumes...

[wraper]

Some years ago I've also bought Kingbo RMA218 from China, it needs cleaning but worked also good. I've bought it again recently but unfortunatelly some ingredients (or manufacturer) must have changed and now it works very poorly (I even stopped using it).

It's not even clear who made the original thing, not to say 100 of its counterfeits.

[T3sl4co1l]

Beats me -- as mentioned, you get whatever you get from China, if it's anything at all like the name (let alone datasheet) suggests, or actually similar to some other name-brand product they're aping, who knows.

A good general strategy with such markets is: consider your money wasted.  Don't spend any more than you can afford to simply and completely throw away.  Anything you get in return, is then a welcome surprise, a gift to yourself as it were.  There's nothing to be disappointed by, because you already threw away the money.  Right?  So, if you get a product roughly as described (it's flux, but not the right kind), that's a pleasant surprise; and if it's exactly what you wanted, a remarkable surprise!

Even if such products are, you know, just a couple bucks each, but to get some modest degree of confidence that you're buying at least one of the thing you want, you should plan to purchase several at once, from a diversity of suppliers, across marketplaces (shop on Ali and Amazon and etc.; try to make sure they aren't all myriad storefronts of the same underlying companies -- gibberish brandings proliferate).  And since the results of such a purchasing campaign will vary from trial to trial, if you need a certain quantity of that product, you should further plan on buying multiple at a time -- so you have a reasonable supply until the next time you need to do the same thing.

Maybe you can buy one of everything and go back and get more of the one thing that worked, but you don't know what the chances are, of the storefront remaining up at all, or the product being the same next time.

So, you can see it quickly adds up to an expensive endeavor, both financially and in terms of time spent shopping and reviewing/testing.

The cost of a name-brand product feels much less painful, all considered.

To that end, I'm currently using a tube of this, https://www.digikey.com/en/products/detail/chip-quik-inc/SMD291/355201 and it's lasted over a year so far (maybe a couple? I forget when I got it), so, that $15 price tag is well more than amortized to me.

Tim

[shapirus]

Which flux has actually the best price vs quality ratio?

I'd say it mostly depends on your local availability, unless you're willing to pay for shipping and/or minimum order to get something well-known from global stores like mouser, digikey etc.

Otherwise, we can discuss what's available on aliexpress, but often times the impressions about a specific product stay relevant for only so long, because at some point the product can change, and they will sell a completely different stuff with the same sticker.

FWIW, for now, I'm half satisfied with Mechanic (that's at least somewhat of a brand) 223 and 225. I don't see any real difference between them.
What I like: they work well for soldering. They don't leave burnt hard to remove residue. They don't conduct. They don't cause corrosion (the "copper plate in the bathroom" test).
What I don't like: the fumes are stinky, which is perhaps a good thing, as it forces you to use a fume extractor or at least a fan to blow or pull them away from direct inhaling. They are somewhat stubborn to clean: need to be left soaking in IPA for some time, then they become gel-like and can be removed with a brush, but even then, after drying, some white powder-like substance remains stuck in hard to reach spots. I'd much prefer something that is diluted and not just thinned by IPA.

There is also that fake "NC-559-ASM-UV" from ali. Non-corrosive, too. Works well for soldering, easier to clean than the two mechanics mentioned above, but is a bit conductive: few GOhm at low voltage with 1-2 mm between the leads. Some would say that the fluxes conductivity is to be measured after heating. I would answer that it does not apply for hand soldering: you can't heat all of the flux and some will remain trapped in hard to reach spots, which may cause issues in high impedance circuits. Therefore zero conductivity both before and after heating is important.

I have ordered one more from ali: the "Relife Green". It hasn't arrived yet. There are hopes that it may turn out good, will see. It is also somewhat of a brand name, so lower risk of getting a different stuff under the same name.

Also worth watching, even if old:

[elektryk]

Yea, no risk no fun...
I know a company where they tried to incorporate some charger modules from China, the funny thing was that with each delivery they got something different and then abandoned this idea.

Is that SMD921 active enough to solder so-called NOS components? I've got a bunch of old components with oxidized legs. Especially silver plated ones can be difficult to solder.

Anybody tried this?
https://www2.mouser.com/ProductDetail/Chip-Quik/CQ4300-2OZ?qs=Wj%2FVkw3K%252BMDhZZtwx%2F2ZXA%3D%3D
https://www2.mouser.com/ProductDetail/MG-Chemicals/8342-50G?qs=6SAGcVcpVil6QxsjfUWJgQ%3D%3D


shapirus I've seen that video but I'm also afraid that the same situation will occur like with my RMA218 but with such price I can buy sth. to test it.

[wraper]

SMD291 is the worst tacky flux I tried ever. Wetting not that good, when heated bubbles as hell, leaves ton of awful sticky residues, somewhat conductive. Worse than most of Chinese counterfeits.

[T3sl4co1l]

SMD291 is the worst tacky flux I tried ever. Wetting not that good, when heated bubbles as hell, leaves ton of awful sticky residues, somewhat conductive. Worse than most of Chinese counterfeits.

Are you sure--?  That sounds like a counterfeit product to me.  Or maybe it was really old and absorbed moisture or something.  What I have, hardly bubbles on heating (say, if I put some under a QFN to solder in place, it doesn't wobble around as it heats up), it does contain volatiles which sizzle off quickly under the soldering iron, and, I don't have anything to measure really low leakages but it at least doesn't show up on my ohmmeter.

Can't say about older deposits (absorbs moisture and then becomes conductive, maybe?), also it's winter (dry) here so I wouldn't expect a fair test even if I had, but, I usually clean things off anyway, as the softer consistency washes away easily with IPA or flux remover.

Is that SMD921 active enough to solder so-called NOS components? I've got a bunch of old components with oxidized legs. Especially silver plated ones can be difficult to solder.

Heh, much of my inventory by now could be considered "NOS"... I've got chip resistors from 2010ish, they definitely don't stick as well, but some flux (any kind, really) perks things right up again.

Can't think if I have any silver plated parts or leads around right now, that are also tarnished, and that I would want solder on... maybe some switches? Oh let me check...

Just testing right now, with a surely "old stock" carbon comp resistor, 82k 10%, with very obviously grayed leads: a drop of said flux on the lead, then heating with 370°C soldering iron touched further up the lead, shows the wetted spot turning silvery in about five seconds.  Mind, this isn't all that challenging of a task; the same is true of some straight pine resin I have here (which I do actually use a little of here and there, when I'm tinning things that are large enough not to be worth using something good on, and that aren't super dirty to need mechanical cleaning anyway, nor a more active flux).

...Aha, I have some old (Russian, ex-soviet?) fuse holders here, the sprung terminal is tinned, but the side contact is not, and is fairly badly tarnished.  Let me see:
- Rosin core solder... I get a blob that seems to be in contact, but it looks rough, isn't strong, and doesn't spread out at all.  I think if I use a lot, I could eventually clean it up, but it'll be a mess, and I'd rather sand it down if that were the case.
- SMD291: putting a couple drops on the terminal and heating, the solder-blob area does seem to consolidate and flow, and there is a subtle change to the tarnished surface; almost more like, the surface crud is separating from the metal, maybe, but only in patches.  Looks like I can rub through the crud to tin it, but it's not so active that it'll just dip and coat in one shot.
- Pine resin: doesn't look like it does much of anything, or much more anyway.  Main advantage, I have a ton of it.

After heating with this combination for a minute or two, and wiping off the excess, it does look like the tarnish has been removed, at least in relevant patches.  Let me see if I can get a meaningful photo of this...





There's some texture in the background that's been added by the camera/app, just... ignore that.  The backside view with the bright spot, the difference in albedo is so dramatic it looks tinned, or nearly overexposed, but it's actually bare silver with its subtle yellowish tint.  On the front side, it's easier to see the color against the solder around it.

Note that the fluxes didn't flow all the way around, the resin in particular kind of staying in place.  So there's only a small "etch" spot on the back side as you can see.  Obviously I'd do a more thorough job if I were intending to make a proper connection here.

I don't have any strongly activated or aggressive fluxes to try and compare, but I'm sure something would cut through much faster.  I don't have much old junk laying around like this so it's not something I have to deal with; consider a stronger one if that's the case.

Tim

[wraper]

Are you sure--?  That sounds like a counterfeit product to me.

Counterfeit from Digikey?

it does contain volatiles which sizzle off quickly under the soldering iron

I'm talking about hot air and IR (bubbling) and not good (in comparison to good fluxes) for soldering iron too (other issues). This sort of flux albeit can be used with soldering iron is not meant for it. Especially slighty conductive ones (most of them are) as they cannot fully activate with soldering iron.

[T3sl4co1l]

Are you sure--?  That sounds like a counterfeit product to me.

Counterfeit from Digikey?

Beats me?  I mean, I use it fine.

You hadn't mentioned where you got it from, so, that covers one thing.

Maybe you were just using it wrong?  I wouldn't assume so (but, I wouldn't completely assume not until shown otherwise).

I gave illustrations of successful use, which you are free to contradict, but, I guess if you're letting it stand, my description should be considered priority?  But then why raise paranoia over something you aren't confident about..?

Tim

[wraper]

I gave illustrations of successful use, which you are free to contradict, but, I guess if you're letting it stand, my description should be considered priority?  But then why raise paranoia over something you aren't confident about..?

I don't know how badly it was oxidized but it's a poorly tinned lug. I did hell a lot of soldering, and SMD291 is not even close to be in the same league as OM-338 that was mentioned, ERSA, Edsyn, Kester, Amtech tacky fluxes I used. Even most of Chinese stuff is better as far as soldering goes, without considering other issues they may pose.
EDIT: just remembered it has a short working time for a tacky flux.

[EPAIII]

Well, I have tins of Kester flux that are older than most people reading this. It still works great. The fact that I have not emptied them is nor a lack of use. I use them all the time. But when I see the internet videos on how to solder, I see so much flux that is wasted, that it isn't funny. Gentlemen and ladies, when watching those videos, DIVIDE the amount of flux that you see being used by a factor of 10. And then do that a second time. What remains is about the amount that is really needed. And a tin or bottle will last a long, long time. I have worked in electronics for all my life. Frankly I have never had to buy a second bottle or tin of flux for a shop in my entire career. NEVER!

OK, you can't get Kester. I always used paste flux but recently (for me) purchased a bottle of liquid. It is GC Electronics 10-4202. It works great. The only problem I have had is the brush is too large. It carries too much to the job. I have to stroke the brush against the neck of the bottle several times to reduce the amount. As I said above, divide by 10 then divide by 10 AGAIN. And you will have about the right amount. And a bottle or tin will last 20, 30, or 40 YEARS of constant, daily use.

And stick with NAME brands that have been around for several decades. And NOTHING from China.

[luudee]

Hi Guys !

I just recently bough STIRRI-V3-TF flux from Amazon. Apparently this is the latest and greatest stuff from Amtech.

It does the UV light-up, and sweet smell. It is a no-clean flux.

I do light repair and development work, including 0201 components and small BGAs.
So far I absolutely love this stuff !

Cheers,
rudi

[EPAIII]

Oh, you mentioned easy to clean.

They make flux remover. Again, GC is one brand.

https://gcelectronics.com/~gcelectronics/switches-2/flux-remover

I have used it. It works. It isn't cheap.

I have also used alcohol. It also removes flux, but you need to either use more or scrub with a brush (old toothbrush is great). And it is a lot less expensive. I like the 91% variety, but lesser concentrations also work.

Both work on every flux I have ever used.

[Smokey]

I've been using this stuff.  Works really well so far.

https://www.digikey.com/en/products/detail/sra-soldering-products/TF5000/10709784

[T3sl4co1l]

I gave illustrations of successful use, which you are free to contradict, but, I guess if you're letting it stand, my description should be considered priority?  But then why raise paranoia over something you aren't confident about..?

I don't know how badly it was oxidized but it's a poorly tinned lug.

Regarding that, specifically, I wasn't trying to tin it, that just happened incidentally in places, in the course of trying things out.  The point was to show how the tarnish changed, if at all.  (I can actually solder things, surprising as that may seem.)  I didn't take a before picture, but the backside view gives some idea what it looked like on the front (basically that, but without the rainbow, uniformly brownish).  The contrast between dry (natural, unfluxed), fluxed, and tinned, is stark, proving that fluxing has done something.

The way you speak, seems to suggest the product is utterly useless, and this proves it's not.

I guess your point is more to the relative success, which I can't speak to as I haven't used those other products before, let alone side-by-side.  My point is more to absolute success, and if nothing else: something is better than nothing.  I guess as your framing is relative, I shouldn't expect acknowledgement of this point.  I (and I expect, other readers too) would just appreciate an indication of your frame of reference.  Not everyone is maximizing throughput in a factory, some people just need something that works, you know?

Tim

[wraper]

I've been using this stuff.  Works really well so far.

https://www.digikey.com/en/products/detail/sra-soldering-products/TF5000/10709784

It solders OK, although not the best. However it's slightly conductive. So I would not recommend it for using with soldering iron due to incomplete activation. Unless you can do very sophisticated cleaning, like with ultrasonic bath as Just brushing with IPA won't remove it from under MLCC and chip resistors.

[wraper]

The way you speak, seems to suggest the product is utterly useless, and this proves it's not.

It's not utterly useless, it works. However it's absolutely subpar for what it costs, I'd call it acceptable if it was $2 for 10ml syringe.
Edit. Also it came with a huge amount of air bubbles mixed in, and pictures on internet show the same. It results in it continuing oozing out for like a minute after you stop pushing the plunger, which is another annoyance.

[T3sl4co1l]

Oh, you mentioned easy to clean.

They make flux remover. Again, GC is one brand.

https://gcelectronics.com/~gcelectronics/switches-2/flux-remover

I have used it. It works. It isn't cheap.

FWIW, the MG Chemicals blend at least, boasts ethyl acetate, acetone and isopropanol on the label.  Acetone and isopropanol tend not to be aggressive towards electronics (with acetone being the more suspect of the two), and are usable by themselves; probably the EA, being a little bit more, Idunno, oily maybe, helps them out just a bit.  If you find a cheaper source of EA, you might blend your own.  What percentages, not sure, but equal parts might be a good enough start.

Rosin is also soluble in MEK, if you're so inclined, but it's likely to affect more components (markings, and electrolytic capacitor seals, being the most susceptible), so, use accordingly, and at your own risk.

It should also be soluble in aromatics too? -- I've not tried personally.  Toluene, xylene, etc. are discouraged for use on electronics anyway, so I don't care.

Speaking of solutions; the worst fluxes I've ever used are the solutions in alcohol.  Such as flux pens, and bottles with a needle on top.  The alcohol bubbles off aggressively, it migrates strongly away from a source of heat, and the rosin used tends to be, it at least smells like damn near pure pine resin, mildly activated or processed if at all.  Not worth paying anything for that (can make it yourself if you want, scrounge for some blobs of sap under a pine tree, get your lifetime supply in one fistful).  At a minimum I would say, a flux should have some kind of oily, glycol or gel base (I think polyethylene glycol is a common ingredient in these?), which are usually what the pastes and "tacky" syringe products have in them.

Tim

[elektryk]

I've tried rosin dissolved in alcohol, stock and self made, both of them not convinced me so much.

For desoldering job I use local "AG Termopasty" product, not as active as OM338 but still better than natural rosin.
BTW Cynel makes decent solder wire.

Locally I can also aquire Warton Metals Future HF Rework Jelly Flux and Warton Brown Jelly. The first one was recomended by one guy on YT. Does anynone here tried them?

And about cleaning. I've got 3l ultrasonic cleaner but sometimes boards are to big to place them or have elements that won't stand isoprophyl bath, so in such situations easily cleanable flux is prefferable...

[Smokey]

I've been using this stuff.  Works really well so far.

https://www.digikey.com/en/products/detail/sra-soldering-products/TF5000/10709784

It solders OK, although not the best. However it's slightly conductive. So I would not recommend it for using with soldering iron due to incomplete activation. Unless you can do very sophisticated cleaning, like with ultrasonic bath as Just brushing with IPA won't remove it from under MLCC and chip resistors.

They don't give conductivity in the data:
https://www.sra-shops.com/pub/media/docs/srasolder/sds/sds-tf5000.pdf
https://www.sra-shops.com/pub/media/docs/srasolder/datasheet/tds-tf5000.pdf

Is this something that caused you a specific problem?  Was it a circuit that was especially sensitive to leakage or something?  After hot air rework, I've left components submerged in blobs of this stuff on mostly digital boards and I haven't seen anything I would call an issue due to stray conductivity.

[wraper]

I've been using this stuff.  Works really well so far.

https://www.digikey.com/en/products/detail/sra-soldering-products/TF5000/10709784

It solders OK, although not the best. However it's slightly conductive. So I would not recommend it for using with soldering iron due to incomplete activation. Unless you can do very sophisticated cleaning, like with ultrasonic bath as Just brushing with IPA won't remove it from under MLCC and chip resistors.

They don't give conductivity in the data:
https://www.sra-shops.com/pub/media/docs/srasolder/sds/sds-tf5000.pdf
https://www.sra-shops.com/pub/media/docs/srasolder/datasheet/tds-tf5000.pdf

Is this something that caused you a specific problem? Was it a circuit that was especially sensitive to leakage or something?  After hot air rework, I've left components submerged in blobs of this stuff on mostly digital boards and I haven't seen anything I would call an issue due to stray conductivity.

For me personally no, but I also do not use unverified flux on sensitive electronics either. But if you start soldering some sensitive analog electronics, you may experience problems. I check all new fluxes I use for resistance, and most of them are slightly conductive, including Amtech and Kester fluxes I tested. It's anecdotal evidence but IME white colored, creamy tacky fluxes are not conductive even in inactivated state. But translucent fluxes generally are slightly conductive.  By that I mean you may have resistance in  Megohms between traces. Of course leakage will depend a lot on actual trace configuration, not just flux type, its amount and proper activation during soldering.

[Smokey]

Good excuse to get an ultrasonic cleaner I guess

[shapirus]

For me personally no, but I also do not use unverified flux on sensitive electronics either. But if you start soldering some sensitive analog electronics, you may experience problems. I check all new fluxes I use for resistance, and most of them are slightly conductive, including Amtech and Kester fluxes I tested. It's anecdotal evidence but IME white colored, creamy tacky fluxes are not conductive even in inactivated state. But translucent fluxes generally are slightly conductive.  By that I mean you may have resistance in  Megohms between traces. Of course leakage will depend a lot on actual trance configuration, not just flux type, its amount and proper activation during soldering.

I've had an actual problem with a flux in this regard. It was a water-soluble flux for which a multimeter showed resistance about IIRC ~10-30 MOhm, maybe even less, with leads ~1mm apart (I still have it, I can re-measure it later if I want).

I used it in a circuit that included the well-known Chinese LM399-based voltage reference module, which allows to select one of 6 output voltages using jumpers, and my "wrapper" circuit had several small relays to short the respective sets of jumpers on a repeated pressing of a button.

The flux got under the relays and became trapped there, and, because of stray conductivity, the voltage readings from the module were actually off. It was impossible to wash the flux away from there, so I had to remove the relays, wash the board, and replace the relays (with new ones because I failed to desolder them without damage -- ouch), using a non-conductive flux.

Of course I didn't measure the flux beforehand. It was marketed as "no-clean", so I assumed it would be fine. One of local brands, so no use mentioning its name here.

Lesson learned, now I never use fluxes that show any sign of conductivity on anything that can even remotely be affected by it.

[lezginka_kabardinka]

Firstly you need a good flux capacitor to store it in 😛

[EPAIII]

While most circuits can function quite well with the flux left in place, even with thick gobs of it, I would never assume that a flux that is marked as "no clean" would be perfectly safe in all circumstances. In fact, I would not even know what exact meaning to assign to that claim beyond it perhaps not containing a strong acid which would eat at the traces and wires of a circuit. In other words, a flux intended for electronic work.

I also had a problem with relays on a PC board once. I did some repairs and then washed the flux off with the flux cleaner that I mentioned above. But I was not careful and some of the dissolved flux washed into the relays, which were not sealed, and on the contacts. It acted like an insulator and the low level signals were attenuated. I had to wash those relays with generous amounts of the flux cleaner about a half dozen times or more before I got it all out.

You do need to be careful when washing flux off your boards.

For me personally no, but I also do not use unverified flux on sensitive electronics either. But if you start soldering some sensitive analog electronics, you may experience problems. I check all new fluxes I use for resistance, and most of them are slightly conductive, including Amtech and Kester fluxes I tested. It's anecdotal evidence but IME white colored, creamy tacky fluxes are not conductive even in inactivated state. But translucent fluxes generally are slightly conductive.  By that I mean you may have resistance in  Megohms between traces. Of course leakage will depend a lot on actual trance configuration, not just flux type, its amount and proper activation during soldering.

I've had an actual problem with a flux in this regard. It was a water-soluble flux for which a multimeter showed resistance about IIRC ~10-30 MOhm, maybe even less, with leads ~1mm apart (I still have it, I can re-measure it later if I want).

I used it in a circuit that included the well-known Chinese LM399-based voltage reference module, which allows to select one of 6 output voltages using jumpers, and my "wrapper" circuit had several small relays to short the respective sets of jumpers on a repeated pressing of a button.

The flux got under the relays and became trapped there, and, because of stray conductivity, the voltage readings from the module were actually off. It was impossible to wash the flux away from there, so I had to remove the relays, wash the board, and replace the relays (with new ones because I failed to desolder them without damage -- ouch), using a non-conductive flux.

Of course I didn't measure the flux beforehand. It was marketed as "no-clean", so I assumed it would be fine. One of local brands, so no use mentioning its name here.

Lesson learned, now I never use fluxes that show any sign of conductivity on anything that can even remotely be affected by it.