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.

[rsjsouza]

I have been using the MG Chemicals 8341 series and it works quite well. However, I always make sure to clean up everything after a job, especially when repairing older equipment where the green film that protects tracks is exposed due to battery corrosion residue, etc.

https://mgchemicals.com/products/soldering-supplies/soldering-flux-paste/

At work we use the Chipquick SMD291 mentioned before and it works alright as well. Although I am not soldering BGAs or anything of the sorts.

[wraper]

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.

Yeah, often it's better to just leave it on the board. Washability should be considered when designing the circuit. If there are any buttons or unsealed relays, PCB becomes unwashable unless carefully done manually. But that won't get flux out from under SMT components and mostly would be just a cosmetic thing.

[tooki]

It bears repeating that no-clean fluxes are only guaranteed to be safe for their stated purposes once heated fully to reflow temperature. When hand-soldering using only the flux in flux-core solder wire, the flux is guaranteed to reach that temperature. But when hand-soldering with external flux (paste, gel, liquid), it may not get heated at all, or may get only partly heated. Unheated or partially-heated flux may be left in an active state and be corrosive. In those cases, flux residues must be removed.

The same applies to many rosin fluxes, which may be corrosive if still wet or pasty. (In tests I’ve done, some liquid fluxes caused no corrosion at all when applied in a thin layer that could dry within a short amount of time, but droplets big enough to take a day to dry caused corrosion.)

My approach is this: when hand-soldering using no external flux, or when using solder paste on a board then reflowed in an oven, I consider cleaning as completely optional. But as soon as liquid or paste flux is used for rework, cleaning becomes mandatory.

[shapirus]

But as soon as liquid or paste flux is used for rework, cleaning becomes mandatory.

Even with cleaning there is no guarantee that the flux will be cleaned completely, no matter how you wash the board, including the ultrasonic bath.
In fact, it's worse: there is almost 100% guarantee that some of the flux will stay, unless all the components are THT and all of them have good clearance against the board's surface.

Thus it is important, if you are hand soldering with an added flux, to make sure that this flux is not corrosive and does not conduct both before and after heating.
...and then, on top of that, you still want to wash the board, because creating an electronic device is an art, and a piece of art must not look ugly and dirty.

[Smokey]

The only time I break out the tacky flux is when I need to hot air rework something.  In that case I'm pretty sure it's reaching the required reflow temperatures.

[Fryguy]

I just visited the Amtech website and found this line in the product description of the STIRRI-V3-TF : This product is designed for a professional consumers. 

A professional consumer ?   

Who here feels addressed ? 

[rsjsouza]

I just visited the Amtech website and found this line in the product description of the STIRRI-V3-TF : This product is designed for a professional consumers. 

A professional consumer ?   

Who here feels addressed ? 

I guess someone was asleep during the page writing. Stirri's page does not have such "safety" disclaimer and states this flux is for "prosumer" customers.

https://stirri.com/products/stirri-v3-tf

[elektryk]

I've never heard about this brand previously, but acquired one for testing.
BROQUETAS BTFO-81-1 https://www.tme.eu/pl/en/details/btfo-81-1h/fluxes/broquetas/btfo-81-1/
It worked when soldering wires and some basic SMD components too. Not sure about conductivity but we will see.
In my opinion bundled needle is a bit too large, I've used 0.7mm instead.

At manufacturer's site they say that it doesn't have to be cleaned.
https://broquetas.com/en/producto/tacky-flux-btfo-81-1/

The residue left is clear, non-corrosive and non-conductive so there is no need to remove it, but it can be easily cleaned with isopropanol, solvent, or semi-aqueous systems.

[EPAIII]

Interesting. Do you have any references on this or is it just your observations and opinion?

I can add my own anecdotal "evidence". I have performed maintenance on PCBs and other electronic assemblies for over 55 years. Often working on items that had been worked on not once, but multiple times before and often by technicians less skilled than myself. The same part often failed and had to be replaced multiple times. Most of the time the flux had been just left where it was after the repair, sometimes in quite thick lumps. Not in even one incident did I ever see any evidence of damage from that flux. If I went to the trouble of cleaning it off, I invariably found the copper traces and component leads totally undamaged from that flux.

So I must ask what do you have, beyond your own observations, to back up your statement that it must be cleaned. Manufacturer's recommendations? Proper studies? Or anything?

I have seen health warnings on the flux containers, but never anything about cleaning parts after use being required or even suggested. I am, of course, speaking of fluxes made for electronic work, not those for general soldering.

It bears repeating that no-clean fluxes are only guaranteed to be safe for their stated purposes once heated fully to reflow temperature. When hand-soldering using only the flux in flux-core solder wire, the flux is guaranteed to reach that temperature. But when hand-soldering with external flux (paste, gel, liquid), it may not get heated at all, or may get only partly heated. Unheated or partially-heated flux may be left in an active state and be corrosive. In those cases, flux residues must be removed.

The same applies to many rosin fluxes, which may be corrosive if still wet or pasty. (In tests I’ve done, some liquid fluxes caused no corrosion at all when applied in a thin layer that could dry within a short amount of time, but droplets big enough to take a day to dry caused corrosion.)

My approach is this: when hand-soldering using no external flux, or when using solder paste on a board then reflowed in an oven, I consider cleaning as completely optional. But as soon as liquid or paste flux is used for rework, cleaning becomes mandatory.

[elektryk]

Personally I've only noticed problems when flux residues were left on a PCB without solder mask (copper gets green after some time) or when soldering wires/connectors.

[BBBbbb]

Have you tried TK-83 (TermoPasty), I like that one a lot.

[elektryk]

I've tried that or something similar but I rather prefer gel fluxes than liquid ones.

[shapirus]

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.

So it has finally arrived. Looks like your regular gel/paste flux, nothing unusual in this regard. Has zero conductivity at up to 2.5 kV, as measured by BM869s in nanosiemens mode and Aneng MH13 megohmmeter, which is already a good sign. Haven't yet tried to solder anything with it. Applied a blob of it to a strip of bare copper and left on a shelf in the bathroom to test for corrosive properties: if there is anything, it'll show itself in a few days at most.

[slybunda]

Am i the only one who has been using pine rosin and mixing it with isopropyl alcohol for home made liquid flux? Not had any issues with it at all.
Also dont get water on the rosin it becomes sticky and very hard to wash of

[tooki]

I tried rosin in alcohol, and while it does technically work, it’s so mild as to be pointless for anything that isn’t gleamingly new — in which case the flux core of the solder would be more than enough, too. It certainly isn’t good enough to use as a rework flux.

[slybunda]

it works surprisingly well for me although i have it in max concentration so maybe that makes the difference?

[T3sl4co1l]

I have some on hand, and use crumbled flakes of it from time to time, mostly when I'm doing something so big that it's not worth using "real" flux on, and the duty is mild.  Tinning a copper-clad board for example, that's already been sanded clean so just needs to stay bright while I work the solder over it.

I do not use it as a solution, and all such products I have tried have been dismal to use: the alcohol pushes away from heat, while bubbling and spattering, leaving nothing under the soldering iron.  It's too mobile under hot air as well.  Gel type is far superior; I would rather use crumbled rosin.  Though it blows away under hot air, if that gives you any idea of the relative annoyance using them... not so bad if preheating the board so it melts on contact.  But yeah, gel type 99% of the time.

Tim

[slybunda]

just did a test right now, put some copper tape on a piece of paper then loaded up the iron with some solder and waited for some time for it to burn off the flux then tried to put the solder to the copper tape but it wouldnt stick. put a drop of the home made flux on the tape then applied the soldering iron and it just flowed onto the tape no issues. so it does work. copper tape has been out of the bag for a while so it wasnt shiny copper more of a duller appearance. shockingly the tape is still stuck down firmly to the paper, a little lifting on the edges where the flux soaked into the paper but this gives me a good idea in using this tape to fix pcb traces and stuff. will have to try it out at some point.
pic attached.

[shapirus]

Tinning a copper-clad board for example

Have you tried "liquid tin"?

[T3sl4co1l]

just did a test right now, put some copper tape on a piece of paper then loaded up the iron with some solder and waited for some time for it to burn off the flux then tried to put the solder to the copper tape but it wouldnt stick. put a drop of the home made flux on the tape then applied the soldering iron and it just flowed onto the tape no issues. so it does work. copper tape has been out of the bag for a while so it wasnt shiny copper more of a duller appearance. shockingly the tape is still stuck down firmly to the paper, a little lifting on the edges where the flux soaked into the paper but this gives me a good idea in using this tape to fix pcb traces and stuff. will have to try it out at some point.
pic attached.

Well yeah, glop on enough and it's fine. A contrived scenario does not, a counterproof, make.  Like I said, there are places where I use it (albeit dry). Copper tape is... almost anomalously clean, come to think of it?  Tape is basically same as my example of tinning a freshly-sanded board.  Try it on dirty terminals, try it on SMT rework, you'll see the issues I mentioned.

Tinning a copper-clad board for example

Have you tried "liquid tin"?

Have not. Frankly I don't do it often enough that I would think it worth keeping chemicals around; I don't happen to have much of a place to store or dispose of chemicals here.  But that might be an option in those circumstances.

Tim

[shapirus]

Have not. Frankly I don't do it often enough that I would think it worth keeping chemicals around; I don't happen to have much of a place to store or dispose of chemicals here.  But that might be an option in those circumstances.

That's almost a life-changing experience when you do need to tin boards (and wires, too!). Like going straight from an old style iron to T12.
Proper disposal is a valid point, though. It, however, can be used and reused multiple times, as there's a lot of tin in it, and it takes a lot of surface plating to deplete it.

[wraper]

I have been using the MG Chemicals 8341 series and it works quite well.

I tried MG Chemicals 8341, and it's probably the best tacky flux I tried yet. The major upside, its residues instantly dissolve in IPA. So can be cleaned like a charm instead of trying to clean something like barely solvable OM-338. Also it's non conductive, has a long work time, no nasty fumes and actually is quite inexpensive. The only downside is its viscosity, so needs either thick nozzle it comes with, or conical, as it will be very hard to squeeze it though a thin needle.

[shapirus]

So it has finally arrived. Looks like your regular gel/paste flux, nothing unusual in this regard. Has zero conductivity at up to 2.5 kV, as measured by BM869s in nanosiemens mode and Aneng MH13 megohmmeter, which is already a good sign. Haven't yet tried to solder anything with it. Applied a blob of it to a strip of bare copper and left on a shelf in the bathroom to test for corrosive properties: if there is anything, it'll show itself in a few days at most.

No corrosion whatsoever in 11 days.

Also tried soldering. Some SOT-23 and a coax cable's shield (which looks like steel) and copper core, with patina -- the piece that I tinned had been exposed to air (indoors) for 8 years. No problems with either. Nice shiny joints, as you'd expect from any good flux. No tendency for bridging, but I have yet to do more soldering, preferably finer pitch, to be certain about this.
Less smoke than with the Mechanic 223 that I used before and the smoke is much less smelly too (though not necessarily less hazardous of course).

I think I have found my new favorite.

up: I never posted a link, here it is: https://www.aliexpress.com/item/1005003474405099.html, variant RL-422-IM. Being a branded product, it will hopefully stay more or less consistent over time.

[shapirus]

I tried MG Chemicals 8341, and it's probably the best tacky flux I tried yet. The major upside, its residues instantly dissolve in IPA. So can be cleaned like a charm instead of trying to clean something like barely solvable OM-338. Also it's non conductive, has a long work time, no nasty fumes and actually is quite inexpensive. The only downside is its viscosity, so needs either thick nozzle it comes with, or conical, as it will be very hard to squeeze it though a thin needle.

It comes in a proper syringe with a plunger, too: opinions may differ, but I think that plungerless syringes that require a dispenser suck. Surprisingly, it's available locally where I live. $15-$20 sounds a bit steep, but I'm now tempted to try it after the positive reviews here, the easy cleaning with IPA being an important point of attraction -- this is not something that you find often, at least in non-conductive fluxes.

[wraper]

I tried MG Chemicals 8341, and it's probably the best tacky flux I tried yet. The major upside, its residues instantly dissolve in IPA. So can be cleaned like a charm instead of trying to clean something like barely solvable OM-338. Also it's non conductive, has a long work time, no nasty fumes and actually is quite inexpensive. The only downside is its viscosity, so needs either thick nozzle it comes with, or conical, as it will be very hard to squeeze it though a thin needle.

It comes in a proper syringe with a plunger, too: opinions may differ, but I think that plungerless syringes that require a dispenser suck. Surprisingly, it's available locally where I live. $15-$20 sounds a bit steep, but I'm now tempted to try it after the positive reviews here, the easy cleaning with IPA being an important point of attraction -- this is not something that you find often, at least in non-conductive fluxes.

I got it for EUR 10 (ex VAT) https://lv.farnell.com/mg-chemicals/8341-10ml/no-clean-flux-paste-10ml-10g/dp/3018420?st=8341
Also it comes in 50ml jar for almost the same price https://lv.farnell.com/mg-chemicals/8341-50ml/flux-paste-no-clean-50ml-jar/dp/4143455?st=8341
It's very cheap for branded tacky flux. Compare it to say ERSA, 3x the price for 5ml 

[VK3DRB]

A few years ago I decided to make my own flux. Why? Because it was fun and I wanted to see how good it was. I took the recipe for the flux from an expired IBM patent dated around 1972.

THE RESULTS

A colleague who is a very experienced electronics technician said my flux was better than a top shelf $60 flux pen after he compared the two on a fine pitch quad flat pack IC. It certainly seemed to reduce the chance of bridging. I made a batch about 4 years ago. Still have not run out and it still works OK.

Pros:
  Low cost
  Better than many expensive liquid fluxes, even for soldering quad flat pack IC's
  Excellent oxide removal and wetting of a solder joint. Helps make a great solder joint.
  An amount in a small bottle lasts a long time.
  Works with lead free or lead based solders.
  Non corrosive according to the patent (I still wash it off using isopropyl alcohol and a toothbrush).
Cons:
  Sticky like jam when it dries.
  You might be accused of wasting your time.

THE RECIPE

Ingredients: Technician grade isopropyl alcohol (readily available), Glycerin (from the local supermarket), Colophony resin (it has to be crystallised and you can find it in some hardware and music stores or on eBay.)

Crush the resin with a hammer. By weight, mix 60-70% isopropyl alcohol, 30% to 40% resin and 2-3% glycerin in a jar. Mix until the resin is dissolved. Put the lid on an leave it for couple of days and restir. Put it in small plastic eye dropper bottle. Put the bottle in a safe place.

An extract from the patent is here (I didn't worry about the surfactant):  https://patents.google.com/patent/US3730782A/en

[Conrad Hoffman]

Tip- always read the data sheet for your flux, then read it again. Some modern fluxes aren't recommended for hand soldering at all. I like Kester, but you tend to have to buy it a gallon at a time. Maybe go in with ten friends and each will have a two-lifetime supply. I use water washable core on new boards and make sure there's no place the stuff can get trapped, spacing components slightly off the board if necessary. Old boards get rosin and a lot of alcohol cleaning.

[Bud]

A colleague who is a very experienced electronics technician said my flux was better than a top shelf $60

A very experienced electronics technician never heard of flux made from rosin dissolved in alcohol?   

I never realised that as a kid I was infringing on an IBM parent 

Technician grade isopropyl alcohol

What the feck is that ?

[tooki]

I never realised that as a kid I was infringing on an IBM parent 

The claim in the patent isn’t the rosin-in-alcohol part of the recipe.

Technician grade isopropyl alcohol

What the feck is that ?

I assume they meant “technical grade”.

The patent itself doesn’t specify what grade of solvent to use. 

It does, however, correctly identify it as non-activated flux. That means it’s useful only for very mildly oxidized surfaces, as found on brand new components. You need the activators for anything beyond that.

[tooki]

it works surprisingly well for me although i have it in max concentration so maybe that makes the difference?

No. I tried various concentrations, from very thin all the way to thicker than honey. Nowhere near as good as any commercial flux.

[elektryk]

The only advantage (to me) was nice smell from such flux.

[tooki]

An extract from the patent is here (I didn't worry about the surfactant):  https://patents.google.com/patent/US3730782A/en

That’s not an “extract”, it’s the whole patent.

[VK3DRB]

A colleague who is a very experienced electronics technician said my flux was better than a top shelf $60

A very experienced electronics technician never heard of flux made from rosin dissolved in alcohol?   

I never realised that as a kid I was infringing on an IBM parent 

Technician grade isopropyl alcohol

What the feck is that ?

Sorry a typo... technical grade.

[m98]

Fluorocarbon surfactants and hand soldering, what could possibly go wrong? Last century was hardcore 
There is a German company that makes "Löthonig", which is basically some modified rosin with alcohol and glycerin. Never actually tried that stuff as a replacement to more modern gel flux paste, maybe it works just as well.

[shapirus]

That's almost a life-changing experience when you do need to tin boards (and wires, too!). Like going straight from an old style iron to T12.
Proper disposal is a valid point, though. It, however, can be used and reused multiple times, as there's a lot of tin in it, and it takes a lot of surface plating to deplete it.

So after trying liquid tin one more time, I'm not so excited. What I disregarded as a temporary glitch the first time I used it, repeats. First of all, it doesn't create the shiny mirror surface that you get with traditional (thermal) tinning methods. Next, it actually solders worse than bare copper (non-oxidated, of course, clean and fresh). Maybe it's just the stuff I got, maybe it is its expected behavior, no clue.

The only positive is that the board tinned with it with the soldered components looks better than a mix of bare copper and solder colors.

[shapirus]

I think I have found my new favorite.

...no .

Having tried it (Relife RL-422-IM) on a freshly etched board with bare copper, no. It's not going to become my go-to flux. It only works well in ideal conditions, that is, when everything is tinned, and much preferably with leaded solder, or gold plated.

As an illustration, I soldered some pin header sockets -- the same stuff that the round socket style IC sockets have, just made as a single row of sockets. They have an exposed round leg between the plastic shell and the thin pin that goes into the hole. It is reachable with the iron's tip between the board and the plastic shell. That part is what I had to solder to the board on the same side where it was inserted (DIY board, no PTH, so no solder wicking from the other side).
With the Mechanic 225 flux, once I touch the trace/pad with a tip that has a blob of solder on it, even if the contact area is small, the solder quickly wicks to wherever the flux was applied and covers everything very nicely without the need to go around and touch things with the tip from all sides. And that is with untinned traces: bare copper. It works really well, just two downsides: lots of very smelly fumes (which seem to cause effects similar to light drunkenness/intoxication -- so ventilation is a must, more so than with other fluxes), and somewhat on the difficult side in terms of cleaning.
The Relife flux that I initially liked doesn't work like that. It spreads only a little and goes further only where you touch it with the tip. It doesn't wick into wherever the flux is. Too bad. The search of holy grail continues.

Speaking of MG Chemicals 8341 mentioned above -- how good/bad is it in the scenario similar to described above? Does it make the solder flow easily without the help of the tip?

Also, there were mentions that the 8341 (unlike 8342!) is not conductive. How was it tested? Did someone here test it with a megohmmeter or a DMM in nanosiemens mode? Please share the results.

[DavidAlfa]

Tested several chinese craps, but this one worked pretty nice, doesn't burn the tip, instantly evaporate or emit nasty fumes, it's  easy to clean with IPA, pretty similar to original Amtech.

I recall buying it from a different store and being absolute ***, then bought this one, actually by mistake (I was decided to never buy Kingbo again), performed great, ordered again few months later and the quality was the same.

https://www.aliexpress.com/item/1005001424090098.html

[shapirus]

Also, there were mentions that the 8341 (unlike 8342!) is not conductive. How was it tested? Did someone here test it with a megohmmeter or a DMM in nanosiemens mode? Please share the results.

You want measurements? Take them youself!

So, the MG Chemicals 8341 is conductive, at least, before heating. I have tested it with a megohmmeter with the probes simply shoved into the flux with the tips as close to each other as practically possible without shorting. Result: ~6.5-7 GOhm.
BM869s in nanosiemens range registers ~0.06-0.07 nS.

Definitely unsuitable for high impedance/high sensitivity stuff, at least when hand soldering. I have no data on the conductivity after heating.

This instantly disqualifies it from the potential holy grail category.

Will see if it is really as good as others have said when it comes to actual soldering and washing.

I got a 50 ml jar, as its price was almost the same as the 10 ml syringe.

[elektryk]

Tested several chinese craps, but this one worked pretty nice, doesn't burn the tip, instantly evaporate or emit nasty fumes, it's  easy to clean with IPA, pretty similar to original Amtech.

I recall buying it from a different store and being absolute ***, then bought this one, actually by mistake (I was decided to never buy Kingbo again), performed great, ordered again few months later and the quality was the same.

https://www.aliexpress.com/item/1005001424090098.html

In my case Kingbo from previous order had more nasty fumes but was also quite more active than actual one (which is BTW weakly active).

[rsjsouza]

So, the MG Chemicals 8341 is conductive, at least, before heating. I have tested it with a megohmmeter with the probes simply shoved into the flux with the tips as close to each other as practically possible without shorting. Result: ~6.5-7 GOhm.
BM869s in nanosiemens range registers ~0.06-0.07 nS.

Definitely unsuitable for high impedance/high sensitivity stuff, at least when hand soldering. I have no data on the conductivity after heating.

This instantly disqualifies it from the potential holy grail category.

Well, to be fair its datasheet mentions the need to clean after use, so not necessarily surprising.

https://mgchemicals.com/downloads/tds/tds-8341.pdf

Overall I found it cleans much easier than the other types I have used, so that is a big plus. Also, for anything high impedance or high voltage I would not rely on leaving residue on the PCB anyways, but YMMV.

[shapirus]

Well, to be fair its datasheet mentions the need to clean after use, so not necessarily surprising.

https://mgchemicals.com/downloads/tds/tds-8341.pdf

Overall I found it cleans much easier than the other types I have used, so that is a big plus. Also, for anything high impedance or high voltage I would not rely on leaving residue on the PCB anyways, but YMMV.

The problem is that even when you clean the boards (I actually wash mine pretty thouroughly by immersing them in IPA, letting them soak, then cleaning with a brush), there is no guarantee that some residue will not remain under e.g. SMD parts or other components that sit flush against the board so that the brush can't reach under them.

IPA only dilutes the flux, or makes it thinner, so that it becomes easier to remove it mechanically, but it doesn't dissolve it in the actual sense of the word -- so if you just soak the board in IPA, let it sit there, then pull it out and let it air dry, then after drying the flux will almost all be there.

So even with cleaning, for the circuits where the fluxes' conductivity, even if very low, may matter, I would still prefer a flux whose conductivity is below the sensitivity of a megohmmeter. At least for hand soldering -- it is said that when the "no-clean" fluxes are heated in a reflow oven to a certain temperature, they lose conductivity.  I cannot verify this.

So, back to the 8341. I have now also soldered some stuff with it and compared it with Relife RL-422-IM and Mechanic 225 that I've also used recently.

- very thick -- a 16 gauge needle with a 5ml syringe is barely enough; also rather tricky to transfer it from the jar to a syringe
- wetting properties are good, better than RL-422-IM, but slightly worse than Mechanic 225
- slightly more fumes and more smelly than RL-422-IM, but much, much more less so than Mechanic 225
- does not boil out or lose its properties as fast as the Relife (which is rather poor in this aspect), stays in place really nicely, so it requires much less frequent reapplication. I think it's actually better in this than the Mechanic, too. This isn't yet a final observation, as I have to do more soldering: I'll soon have a PCB with a few dozens of SMD and a few THT components to solder, and that's going to be a good test.
- very easy to clean indeed: doesn't need a prolonged soaking in IPA, doesn't leave a white powder-like residue in hard to reach spots (the Mechanic does this). The Relife flux is similar, but maybe a little harder to clean, and the Mechanic is quite stubborn (and is a bitch to clean when it gets onto your hands).

Now, I must admit that, with the previous fluxes, before the 8431, I was doing my conductivity measurements wrong! I used the wrong terminal for the negative probe on the megohmmeter, and, while it did show the breakdown voltage (I think), it didn't show the resistance. D'oh! Shame on me. For example, I've now measured the Mechanic, and it does conduct, and it seems to be actually worse than the 8431.
I did, however, use the nanosiemens range on the BM869s correctly, and not all fluxes showed conductivity in that case.

I will make a small PCB consisting of two opposing polygons of a known size separated by a gap of a known width and redo the measurements of conductivity of all the fluxes I have in a controlled and reproducible manner. Just shoving two probes into a blob of flux and measuring if it conducts at an uncontrolled distance between the tips isn't good enough at this point.

[rsjsouza]

Thanks for the comparison; indeed there is never a holy grail of chemicals but a weighted approach based on its characteristics.

So even with cleaning, for the circuits where the fluxes' conductivity, even if very low, may matter, I would still prefer a flux whose conductivity is below the sensitivity of a megohmmeter. At least for hand soldering -- it is said that when the "no-clean" fluxes are heated in a reflow oven to a certain temperature, they lose conductivity.  I cannot verify this.

I am not surprised an instrument is able to get a reading, which is based on several boundary conditions (applied voltage, contact area, etc.), but I would personally not be caught up by a single reading of the unused material. Your proposal to use a more controlled environment for these tests is certainly a more interesting approach. Also, regarding the longer term corrosion and other effects, over the two years that I have been using this flux I have not yet experienced any problems - however I don't live in humid environments which could contribute to this.   

[shapirus]

Also, regarding the longer term corrosion and other effects, over the two years that I have been using this flux I have not yet experienced any problems - however I don't live in humid environments which could contribute to this.

Neither it is very humid here (at least when it's cold), but I have a bathroom for this, and in that bathroom sits a piece of a copper-clad board with some flux smeared on it :).
If there is anything, it will show itself in a few days.

[DavidAlfa]

I remember using this JBC flux, it wouldn't read any ohmic resistance even wet or when placing the probes extremely close to each other.
But when powering the board with 12V or so (Can't remember exactly), after 5-10 minutes a small puff would appear and short  something.
Applied some flux in a proto board, connected to a PSU, had the same behavior, so I never used that flux again.

[shapirus]

Neither it is very humid here (at least when it's cold), but I have a bathroom for this, and in that bathroom sits a piece of a copper-clad board with some flux smeared on it .
If there is anything, it will show itself in a few days.

So after 9 days of MG Chemicals 8341 sitting on a bare copper surface in the bathroom there is a well visible green coloration appearing under the layer of flux.

Now, while the slight conductivity may be fine, the corrosive activity is totally unacceptable.

This stuff, when you compare it to alternatives, isn't worth the money asked, especially in the 10 ml package. I call it unsuitable for anything involving SMD or other components that do not leave a gap above the board that allows to wash the flux residue out completely. At least for hand soldering.

There are lots of fluxes, including cheap offerings from aliexpress, that do not cause even the slightest hint of corrosion when they are left on a copper surface in a humid room for at least several months. In fact, most of the fluxes I tried didn't cause any corrosion, and the only corrosive one (except for the actual acids) was some liquid very active flux specifically purposed for oxidated copper and such.

Easy washing and less stinky fumes aren't worth it for me.

[shapirus]

There are lots of fluxes, including cheap offerings from aliexpress, that do not cause even the slightest hint of corrosion when they are left on a copper surface in a humid room for at least several months.

Time to repeat the experiment. Here goes.

[tooki]

Well, to be fair its datasheet mentions the need to clean after use, so not necessarily surprising.

https://mgchemicals.com/downloads/tds/tds-8341.pdf

Overall I found it cleans much easier than the other types I have used, so that is a big plus. Also, for anything high impedance or high voltage I would not rely on leaving residue on the PCB anyways, but YMMV.

The datasheet is NOT saying that cleaning is necessary — it is a no-clean flux after all — but rather is giving suggestions on what to clean it with if you choose to clean anyway.

[tooki]

Neither it is very humid here (at least when it's cold), but I have a bathroom for this, and in that bathroom sits a piece of a copper-clad board with some flux smeared on it .
If there is anything, it will show itself in a few days.

So after 9 days of MG Chemicals 8341 sitting on a bare copper surface in the bathroom there is a well visible green coloration appearing under the layer of flux.

Now, while the slight conductivity may be fine, the corrosive activity is totally unacceptable.

This stuff, when you compare it to alternatives, isn't worth the money asked, especially in the 10 ml package. I call it unsuitable for anything involving SMD or other components that do not leave a gap above the board that allows to wash the flux residue out completely. At least for hand soldering.

There are lots of fluxes, including cheap offerings from aliexpress, that do not cause even the slightest hint of corrosion when they are left on a copper surface in a humid room for at least several months. In fact, most of the fluxes I tried didn't cause any corrosion, and the only corrosive one (except for the actual acids) was some liquid very active flux specifically purposed for oxidated copper and such.

Easy washing and less stinky fumes aren't worth it for me.

At my old job, I did similar tests with a large number of commercially available no-clean and rosin fluxes (both liquid and gel/paste) from a variety of manufacturers and many of them caused corrosion when tested. (Including MG 8341, which I’ve been using for years.)

I did three tests:
1. applied onto copper PCB and left cold
2. applied to one end of stranded wire (with transparent insulation) and left cold
3. applied to the other end of the same wire and tinned with a soldering iron

Plain and simply, most fluxes are not designed to be left on in the unheated state.

This does, of course, mean that many fluxes absolutely must not be used for tinning stranded wire, since partly-heated flux will wick under the insulation where it cannot be cleaned. Many fluxes that caused no corrosion in tests 1 and 2 caused corrosion in test 3, because some flux got heated hot enough to activate it, but not hot enough to neutralize it!

There are some specific rework fluxes that expressly state that even the unheated flux is non-corrosive. (Please don’t ask me which, I can’t remember! Probably Kester, but not sure.) Other fluxes (like one liquid from Stannol) are expressly for tinning wire, so obviously should be safe for that.

Also, with liquid fluxes, the corrosiveness of the unheated flux often correlates directly to the amount applied: with many fluxes, a thin layer that can fully dry quickly results in no corrosion at all, but droplets or other heavy application that takes overnight to dry thoroughly will cause corrosion during that time.

The no-clean flux cores in solder wire are, of course, safe for hand soldering, since they’re designed for soldering iron use, and the flux will be exposed to sufficient heat to neutralize it, if that’s even needed by the formulation.

This is why I always remind people that no-clean fluxes must be cleaned when used for hand soldering, because you can’t guarantee it’s been heated enough to neutralize it. Only whole-board reflow ensures that. This isn’t a defect as such, because they’re not designed for hand use. They’re designed for reflow, and are safe when used for that.

[shapirus]

This is why I always remind people that no-clean fluxes must be cleaned when used for hand soldering, because you can’t guarantee it’s been heated enough to neutralize it.

Yeah, and cleaning doesn't guarantee that you remove all of it, too. But, frankly, I don't think that the tiny amount that gets trapped under the SMD components etc. is going to cause any trouble in the long run, especially if the board has solder mask. For multi-strand wires, yes, probably. That's where a definitely non-corrosive flux will be better even if it's worse in other aspects (such as cleaning or fumes).

FWIW, most of the fluxes I used were non-corrosive, at least in their original unheated state. But, as I said earlier, it's time to repeat the test for all the fluxes I currently have, which is already in progress. Need to have them all on the same board in the same place in the same conditions for a correct comparison. No corrosion with either so far, but it takes longer, need to give it at least a week or two.

[tooki]

Well, by “cleaning” I mean “actually cause to be clean”, not just “perform a cleaning procedure regardless of outcome.”

I do recognize that this can be hard to do with some components. I’m very glad I have compressed air at work, since that’s super useful for getting stuff out from under SMD parts.

[shapirus]

Time to repeat the experiment. Here goes.

16 days later. Hi-res photos are attached.

Seven fluxes, left to right:

2) MG Chemicals 8341
3) Relife RL-422-IM
4) Mechanic 225
5) Mechanic 223
6) F-2000 (local stuff)
7) Lukey L2010
“Amtech” NC-559-ASM from Aliexpress

Of the above list, numbers 6 and 7 are not usable as fluxes at all -- same result as using no flux at all.

The list starts at number two, because the famous libreoffice calc does not allow to (or I don't know how to) unassign the number 1 from the first row used as header and start numeration in the actual data section.

I also did some quick soldering and conductance (before heating) testing, but the results require conversion from libreoffice spreadsheet to bbcode, so I'll maybe post them later. In a nutshell, 6 and 7 are useless (same as no flux at all).
With 6 and 7 excluded: all are good for soldering experience, except for 3, which among them has worse wetting (yet works quite fine in some scenarios), but is better in terms of the amount of fumes.
4 and 5 are the worst for fumes and cleaning, but are the best for wetting.
2 is the best for cleaning, 3 is slightly worse, the rest are significantly worse.
4 is the worst for conductance (8.5 GOhm in a controlled test that I'll describe later), followed by 5 (18 GOhm), 8 (21 GOhm), 2 (50 GOhm), and 3 (120 GOhm). 6 and 7 are outside of the megohmmeter's range (>200 GOhm).

Corrosive activity -- before heating -- can be seen in the photos. MG chemicals 8341 is the worst gel flux in this regard that I have ever used. "No clean", my ass.
Relife RL-422-IM has only a slight hint of green, F-2000 is corrosive (but it's not a flux anyway), and the rest are non-corrosive, except that the copper under number 8 became noticeably darker.

[Smokey]

Time to repeat the experiment. Here goes.

16 days later. Hi-res photos are attached.
...

...But you left off my favorite flux, TF5000, so I'm going to have to ask you to do that over...  hah!

Epic experiment!  Thanks for doing that.  If you post csv file, or contents here it's trivial to paste that back into any spreadsheet. 

About the flux attacking bare copper... how big of an issue is that really?  I'm only ever using flux over board area that is either soldered or has soldermask. 

[wraper]

...But you left off my favorite flux, TF5000, so I'm going to have to ask you to do that over...  hah!

I tried it quite a while ago. Cannot call it anything better than useable. Nothing exceptional in soldering properties and IIRC it was slightly conductive before reflow.

[shapirus]

...But you left off my favorite flux, TF5000, so I'm going to have to ask you to do that over...  hah!

Feel free to mail me some, as it's not sold here :).

Epic experiment!  Thanks for doing that.

More is coming: I ordered two more Relife fluxes, they'll be here in a week or two.

If you post csv file, or contents here it's trivial to paste that back into any spreadsheet. 

I think of creating a github repo with a markdown-formatted plain text file. Will use a proper yaml file instead of the spreadsheet junk for the raw data and then generate whatever representation I need from that.

Maintaining it on the forum manually will be tedious, especially as more data are added.

I think I'll do that when those new Relife fluxes arrive and I test them.

About the flux attacking bare copper... how big of an issue is that really?  I'm only ever using flux over board area that is either soldered or has soldermask.

Yeah that's a good question. Not much of a problem in practice, I think: most of the residue will be washed away (so much for "no-clean") during cleaning, and then the copper will be protected with either soldermask, or solder. But it's going to be worse for homemade boards without any coating, and worse yet for soldering insulated wires.

[shapirus]

More is coming: I ordered two more Relife fluxes, they'll be here in a week or two.

Both are crap.

I'm not gonna be bothered testing them for any other parameters after I measured their resistance:

1) RL-420S-UV: 83 MOhm at 260 V; <20 MOhm at 2.5 kV
2) RL-421S-OR: 23 MOhm at 260 V; arcs at 2.5 kV

Test setup: a layer of flux ~0.6 mm thick applied over two parallel strips of tinned copper on FR-4, each 20 mm x 2.5 mm, spaced 2.0 mm apart, long sides facing each other (resembling a capacitor symbol).

Other fluxes measured 8.5 to 120 GOhms in the same test.

They can also be easily measured with BM869s (low voltage) in the nanosiemens range.

Requested a full refund for my Aliexpress order on the grounds of false description (which specifically mentions "high insulation" and "no conductivity", albeit the latter is stated along with "no resistance"). Will see what they will have to say lol.

They were packed nicely, though, and had needles included. But who cares if they are useless for what they are advertised for.

[jonpaul]

Geuine rosin, Kester 44

We use only 63/37 Eutectic solder with those flux cores.

Avoid commie china junk solder or wire



j

[tooki]

Geuine rosin, Kester 44

We use only 63/37 Eutectic solder with those flux cores.

Avoid commie china junk solder or wire

Do you even bother reading threads before replying? It’s clear from the original post onward that this thread is about external flux, not flux cores.

I love Kester 44 flux-core solder, but unfortunately Kester stopped making the 44 paste flux many years ago. The liquid version, 1544, still exists but is only sold in large jugs. (There are some resellers that break those down into small bottles, at least in USA.)

Of course, both 44 paste and 1544 would fail shapirus’s requirement to be non-conductive before heating. I don’t think he understands that flux specs refer to the conductivity of the post-soldering residues.

[shapirus]

Of course, both 44 paste and 1544 would fail shapirus’s requirement to be non-conductive before heating. I don’t think he understands that flux specs refer to the conductivity of the post-soldering residues.

Not that I don't understand, but I don't care. I test the fluxes I get my hands on for my specific requirements, which is hand soldering of both THT and SMD parts. And I believe this specific use case is of interest to many electronics hobbyists that can read this, too. Another way of looking at it is worst case scenario testing.

Besides, the two fluxes from my last post are specifically advertised for BGA rework and general repair, which does not guarantee full heating, either (I believe even when using a hot air gun). And hey, they are 500-1000 times (!) more conductive than the other fluxes I tested.

It would also be interesting to test conductivity after full heating, but that would require having a reflow oven, which I don't have, and the motivation to do it, which I also don't have, since I don't do that kind of soldering.

...but I might try something, just for a quick test: for example, set the hot air gun to what, say, 280 °C, heat the PCB with the flux on top from below (to avoid direct blowing on the flux so that more of it stays in place) for, say, 30 seconds, then let it cool and measure what remains. Just to see if the "it must be heated to stop conducting" claims are substantiated, and to what extent, if they are.

[forrestc]

I realize I'm late to the party here but....

Indium TACFlux 020B-RC is pretty much the only flux I use for hand soldering/rework anymore, for the reasons everyone mentions in this thread.   

From the datasheet:

"TACFlux® 020B-RC passes SIR testing in the unreflowed state. Oftentimes during hand soldering and rework, the flux may not be heated properly due to spot heating methods, thus the flux is not adequately activated. TACFlux® 020B-RC is designed to solve this problem and avoid reliability concerns such as dendritic growth over time. "

The 020B doesn't seem to be as active/aggressive as the TACFLUX-089HF, but 089HF needs to be fully heated to pass a SIR test.   Note that there is also a slightly different formulation of 020B which is labeled as tacflux-020 or tacflux-020A or something similar and is either thicker or thinner (can't remember which).

Note that SIR is the test the industry uses to verify a flux isn't going to corrode/cause dendritic growth over a long period, even in high humidity situations.   

[shapirus]

...but I might try something, just for a quick test: for example, set the hot air gun to what, say, 280 °C, heat the PCB with the flux on top from below (to avoid direct blowing on the flux so that more of it stays in place) for, say, 30 seconds, then let it cool and measure what remains. Just to see if the "it must be heated to stop conducting" claims are substantiated, and to what extent, if they are.

So I did exactly that (but 50 seconds and 290 degrees) with RL-421S-OR, the one with higher conductance.

Yes, heating the flux reduces its conductivity, and, in this particular case, it did that to a great extent. That's kind of expected, because what remains looks like plain rosin. No numbers, however, since this test setup can't be considered controlled and repeatable with the flux melting and flowing all across the board.

Still, my primary objective is not to test whether fluxes meet the datasheet specs (and I'm not sure that any of mine, except MG Chemicals 8341, even have datasheets), but to test which of them are more applicable than others for applications where neither full heating, nor full removal of residues can be guaranteed, and find a good go-to flux that I'll be happy with. I've had a device malfunction due to a conductive flux, and I don't want to make that mistake again.

[shapirus]

I realize I'm late to the party here but....

Indium TACFlux 020B-RC is pretty much the only flux I use for hand soldering/rework anymore, for the reasons everyone mentions in this thread.

Nah it's never too late to add new information, especially personal experience (ideally accompanied by numbers), be it good or bad. It'll be useful to someone some day.

[tooki]

Of course, both 44 paste and 1544 would fail shapirus’s requirement to be non-conductive before heating. I don’t think he understands that flux specs refer to the conductivity of the post-soldering residues.

Not that I don't understand, but I don't care. I test the fluxes I get my hands on for my specific requirements, which is hand soldering of both THT and SMD parts. And I believe this specific use case is of interest to many electronics hobbyists that can read this, too. Another way of looking at it is worst case scenario testing.

That’s fair.

My main concern was you trying to get a refund for flux because of it not meeting the claimed conductivity specs, even though you hadn’t reflowed it. That’s not fair unless they specifically said it was nonconductive in a non-reflowed state.

Of course, both 44 paste and 1544 would fail shapirus’s requirement to be non-conductive before heating. I don’t think he understands that flux specs refer to the conductivity of the post-soldering residues.

Not that I don't understand, but I don't care. I test the fluxes I get my hands on for my specific requirements, which is hand soldering of both THT and SMD parts. And I believe this specific use case is of interest to many electronics hobbyists that can read this, too. Another way of looking at it is worst case scenario testing.

Besides, the two fluxes from my last post are specifically advertised for BGA rework and general repair, which does not guarantee full heating, either (I believe even when using a hot air gun). And hey, they are 500-1000 times (!) more conductive than the other fluxes I tested.

Hot air alone is not adequate to achieve full heating. It heats locally, but also blows barely-molten flux all over the place. However, BGA rework is usually done with both preheating from below and hot air (or infrared) from above. And above all, if the balls reach reflow temperature, then the flux between them will also have reached that temperature. It’s only whatever flux has flowed far away that is of concern.

It would also be interesting to test conductivity after full heating, but that would require having a reflow oven, which I don't have, and the motivation to do it, which I also don't have, since I don't do that kind of soldering.

You should reconsider. Reflow in an oven is exceedingly efficient. (And practically mandatory for many modern packages.) A simple $50 toaster oven is enough for basic use.

...but I might try something, just for a quick test: for example, set the hot air gun to what, say, 280 °C, heat the PCB with the flux on top from below (to avoid direct blowing on the flux so that more of it stays in place) for, say, 30 seconds, then let it cool and measure what remains. Just to see if the "it must be heated to stop conducting" claims are substantiated, and to what extent, if they are.

You make it sound as though that’s some crackpot theory… No, it’s how no-clean fluxes are designed to work.

However, I would be leery of your proposed methodology, because it’s quite possible that it wouldn’t heat it evenly enough to draw any conclusions. If you do this, you’d want to do it with a custom test PCB that has solder pads that you can apply solder paste to, so that you can actuate whether it reached reflow temperatures.

Remember: there are TWO temperature thresholds to reach. The first (lower) one activates the flux, the second (higher) one neutralizes it again. If you heat to a temperature that reaches the activation temperature, but not the neutralization temperature, it may be left in a more conductive, more corrosive condition than the unheated state! So the only fair test of this “claim” is to actually get it hot enough to melt solder, since that’s what it was designed for.

[shapirus]

My main concern was you trying to get a refund for flux because of it not meeting the claimed conductivity specs, even though you hadn’t reflowed it. That’s not fair unless they specifically said it was nonconductive in a non-reflowed state.

That's 50/50, I would say. They never said that a full reflow profile was required for the loss of conductivity, either, and they advertised the flux as purposed for general repair work. Many other fluxes with similar claims have resistance on the order of gigaohms before heating, and that sounds fair and reasonable to me. Obviously I will prefer those over the more conductive ones.
These two, however, conduct in megaohm range, and that's a completely different story.

It’s only whatever flux has flowed far away that is of concern.

That's the point. Unless you heat entire board, you can't guarantee that the still conducting residues do not get trapped in some high impedance circuitry where it can cause trouble. I agree that it's not very likely, especially with almost exclusively digital circuits like laptop or smartphone boards, but it may be an issue with sensitive analog devices.

You should reconsider. Reflow in an oven is exceedingly efficient. (And practically mandatory for many modern packages.) A simple $50 toaster oven is enough for basic use.

I don't doubt that. I just won't have any use for it. I don't do repairs, I don't assemble complex boards (or any boards for that matter) on a regular basis. I mostly make one-off devices to try one idea or another, implement something that is of interest to me at a particular time, basically just what a hobbyist does.

You make it sound as though that’s some crackpot theory… No, it’s how no-clean fluxes are designed to work.

However, I would be leery of your proposed methodology, because it’s quite possible that it wouldn’t heat it evenly enough to draw any conclusions.

As I mentioned, it was an idea of a quick and dirty test to get a first rough estimate. It actually worked: I confirmed that heating at least one particular flux greatly reduces its conductivity. It was reduced in all areas that were heated to different temperatures.

Of course, proper testing would require a more complex setup with a corresponding reproducible temperature profile and a board (or whatever) designed to retain a given initial amount of flux in place as it's being heated to be able to measure it in a controlled and reproducible way.

And considering this:

Remember: there are TWO temperature thresholds to reach. The first (lower) one activates the flux, the second (higher) one neutralizes it again. If you heat to a temperature that reaches the activation temperature, but not the neutralization temperature, it may be left in a more conductive, more corrosive condition than the unheated state! So the only fair test of this “claim” is to actually get it hot enough to melt solder, since that’s what it was designed for.

...I don't think I'm gonna be bothered. It's calling for a much more complex test setup that I'm willing to use, and that, in addition, would serve no purpose for my practical application of fluxes.

Yes there is a certain probability that a comparison of unheated fluxes cannot be extrapolated to the same fluxes heated partially or fully. This is a disclaimer that has to be made.

Empirically, however, I've been observing, so far, that partially heated or fully heated fluxes are not worse than unheated ones, and if that is true, then testing unheated fluxes represents the worst case scenario, which I am happy with.

If someone wants to extend testing to partially and fully heated fluxes, it will be wonderful. But not me... at least for the time being :).

[tooki]

It’s only whatever flux has flowed far away that is of concern.

That's the point. Unless you heat entire board, you can't guarantee that the still conducting residues do not get trapped in some high impedance circuitry where it can cause trouble. I agree that it's not very likely, especially with almost exclusively digital circuits like laptop or smartphone boards, but it may be an issue with sensitive analog devices.

I know that. I said that in my original reply up above. As I said there: that’s why I always tell people to always clean no-clean flux (except from flux-core solder) when using it for rework.

[shapirus]

As I said there: that’s why I always tell people to always clean no-clean flux (except from flux-core solder) when using it for rework.

Correct. But cleaning also does not guarantee that all of the residue will be removed. I'm not sure just how much of an issue will the trapped flux be, but even when washing entire boards in ultrasonic bath, some flux easily remains under SMT parts and generally in hard to reach spots.

And it's the combination of this and the fact that we can't, with enough certainty, heat all the flux to where it loses conductivity, that motivates my filtering for fluxes that will be reasonably low-conductive before heating. Once a flux passes this check (many do!), I can look into other parameters.

[tooki]

As I said there: that’s why I always tell people to always clean no-clean flux (except from flux-core solder) when using it for rework.

Correct. But cleaning also does not guarantee that all of the residue will be removed. I'm not sure just how much of an issue will the trapped flux be, but even when washing entire boards in ultrasonic bath, some flux easily remains under SMT parts and generally in hard to reach spots.

As I said above, which you didn’t respond to then, either:

Well, by “cleaning” I mean “actually cause to be clean”, not just “perform a cleaning procedure regardless of outcome.”

I do recognize that this can be hard to do with some components. I’m very glad I have compressed air at work, since that’s super useful for getting stuff out from under SMD parts.

The emphasis is “cause to be clean”. That is, perform cleaning until it is actually clean. Not just “do” a cleaning once, regardless of outcome, and consider it good.

(I once had a roommate who washed dishes like that: he’d run the soapy sponge across a pan or dish and declare it “washed” because he had done the motion, without even looking whether the food had actually been removed!  Super frustrating for me to grab a pan or dish from the cupboard, only to find it still covered in visible, smellable residue from last week’s dinner. Once I didn’t pay attention and started cooking a dessert, then noticed it smelled like chicken…)

[shapirus]

As I said above, which you didn’t respond to then, either:

Well, by “cleaning” I mean “actually cause to be clean”, not just “perform a cleaning procedure regardless of outcome.”

I do recognize that this can be hard to do with some components. I’m very glad I have compressed air at work, since that’s super useful for getting stuff out from under SMD parts.

The emphasis is “cause to be clean”. That is, perform cleaning until it is actually clean. Not just “do” a cleaning once, regardless of outcome, and consider it good.

Sometimes it's easier said than done. Even with ultrasonic and compressed air (I do both, plus brushing) some flux still remains under SMT parts. Easy to check: just heat the washed and dried board, and the remaining flux begins smoking and flowing from under components. Or desolder some components and see what's under them.

I wash my boards with a mix of IPA and ethanol (ethanol is there just to save the more expensive IPA, the mix works about the same as pure IPA). Sometimes, in more difficult cases, I add some purified gasoline. Maybe some chemicals can penetrate and dilute the flux better. I can't justify using (or bying to test) them for home use. Alcohol plus low-conductive flux plus reasonably thorough washing work well enough for me, or I want to believe they do.

[tooki]

In my experience, proper flux cleaners work very noticeably better than pure IPA/ethanol. I wish people would stop relying on those, especially for modern no-clean fluxes which plain and simply are not fully soluble in alcohol. It’s no wonder you haven’t had good luck getting them cleaned out. Modern no-clean fluxes contain ingredients that swell up in alcohol, but don’t dissolve into it, requiring significant mechanical scrubbing to more or less remove.

In contrast, they do dissolve in proper flux cleaners, especially ones designed for lead-free fluxes.

Try a proper, modern flux remover like Electrolube LFFR (my favorite solvent-based flux remover), or for your ultrasonic bath, splurge the whopping $60 for a 5-liter canister of Electrolube Safewash Super (SWAS), which you then rinse off with tap water, followed by a final rinse with DI water or alcohol.

[T3sl4co1l]

A friend said a -- drat, now I forget which brand exactly, but probably any will do? -- window cleaner is effective on flux residues.

Seems like it would be slow, to me, but maybe a solvent-rich variety, or boosted with a little alcohol or ethyl acetate, would cover that.

There are a few different flux chemistries and it stands to reason flux cleaners need similar variation; alcohol works fine for your basic rosin based ones, but other solvents, surfactants, chelators, and acids or bases may prove more helpful for some.  Which is basically to say... try a lot of things and see what works best, but also, just buy the stuff that's recommended and be done with it?

Tim

[tooki]

A friend said a -- drat, now I forget which brand exactly, but probably any will do? -- window cleaner is effective on flux residues.

Seems like it would be slow, to me, but maybe a solvent-rich variety, or boosted with a little alcohol or ethyl acetate, would cover that.

The brand likely doesn’t matter, since the formulations are basically all the same, at least for the standard ammonia-based window cleaner. And my suspicion is that the ammonia is the key ingredient, insofar as aqueous ammonia is basic, and a base is what is used to saponify rosin. (Commercial aqueous flux remover, like the SWAS mentioned in my previous reply, uses plain old sodium hydroxide for that purpose! I assume the remaining important ingredients of the formula are corrosion inhibitors, surfactants, and redeposition inhibitors.) I’m just leery to use cleaners not intended for electronics, because of the risk of corrosion.

I just got a small amount of SWAS from another electronics lab at work, I’ll try it out soon. I’ve used the old Safewash in spray cans before, but they discontinued that recently. It worked pretty well, but not as fast as solvent cleaner. You have to give it time to soak. But since it’s water based, it doesn’t evaporate quickly like solvents.

Aside from the LFFR I also mentioned in my previous reply, I do have bottles of ethanol and acetone at my bench. The ethanol is mostly for cleaning of things that aren’t flux. I do use acetone to remove flux — it’s extremely effective, more than anything else I’ve used — when the materials allow. (For example, I used it yesterday to clean flux from silicone-insulated wire soldered to an all-metal banana socket.) But since acetone damages many plastics, and wipes the markings off many components, I rarely use it on PCBs and the like.

[PlainName]

16 days later. Hi-res photos are attached.

Got some of the Relife 422 stuff with which I did a board last week. Then yesterday I did the same board (well, duplicate) with MG8341, which I used to kind of like before you posted the photo. My result is:

RL422 is a right pain to clean up.

MG8341 is super easy to clean.

I tend to do single boards at a time and treat them as a kind of continuous repair job. I will attach some parts and then clean up that area before moving on, so rather than trying to flood wash the entire board afterwards, I use small amount of cleaner to clean a small area.

The MG8341 is easy to clean because it dissolves quickly in IPA. I will put a couple of drops (or cotton bud load) of IPA on the area to clean, then get some paper kitchen towel and dab it up using tweezers to move it around. The MG8341-loaded IPA is quickly sucked up and nothing seems to be left behind. I think that process successfully gets unused flux from under components too.

So, what I would be interested in seeing is a repeat of your bare copper test but this time with the flux cleaned off. Not cleaned off as in bath washed in an ultrasonic cleaner, but using an appropriate cleaner in the way a repair might be done (because that's the worst case). Dribble or spray the cleaner, wipe with rag/towel/whatever then let's see which corrodes. I think the MG4381 might pass the test after doing that, and some others might not (if they just get spread around rather than actually cleaned off).

(I like the MG4381 except for one feature that has me looking for an alternative: it's lumpy. I can squeeze a few dabs from a syringe and then it's blocked and useless.)

[tooki]

(I like the MG4381 except for one feature that has me looking for an alternative: it's lumpy. I can squeeze a few dabs from a syringe and then it's blocked and useless.)

How old is yours? I have definitely noticed lumpiness in my syringe of it, which is near its end, but I don’t remember it being lumpy when it was new (which was probably 2015 or so).

[shapirus]

Got some of the Relife 422 stuff with which I did a board last week.

Which of them, exactly? They have several 422 fluxes that have different suffixes in their model names and they differ in properties.

The MG8341 is easy to clean because it dissolves quickly in IPA.
I will put a couple of drops (or cotton bud load) of IPA on the area to clean, then get some paper kitchen towel and dab it up using tweezers to move it around. The MG8341-loaded IPA is quickly sucked up and nothing seems to be left behind.

IPA doesn't truly dissolve it, but it thins it very well, so that it becomes really easy to remove it mechanically and/or by soaking the thinned mixture with something, like you do.

I think that process successfully gets unused flux from under components too.

Unfortunately it doesn't. Not for me, at least -- even when I wash entire board by fully immersing it in alcohol, even in an ultrasonic bath. As I mentioned before, that's easy to check: heat the board after washing and drying (even if blowing with compressed air), and it starts to smoke. Some of the flux remains trapped at least under SMT resistors and caps, and I believe generally under the parts that have very small gaps between their bodies and the board. Not an issue (with this flux) for THT stuff.

So, what I would be interested in seeing is a repeat of your bare copper test but this time with the flux cleaned off. Not cleaned off as in bath washed in an ultrasonic cleaner, but using an appropriate cleaner in the way a repair might be done (because that's the worst case). Dribble or spray the cleaner, wipe with rag/towel/whatever then let's see which corrodes. I think the MG4381 might pass the test after doing that, and some others might not (if they just get spread around rather than actually cleaned off).

I'm pretty sure that there won't be any corrosion at all. As you said, and that's my experience too, this cleaning method removes all or almost all of it: you can't see any flux visually or feel/smear when touching the board etc.
I would also speculate that it's the corrosive components of the flux that get solved with IPA most easily. Not sure if that's really so.

A test better suited to real world application would be to solder some SMT parts (fully covering the footprints with the flux first) onto a board without solder mask, with traces passing under components, ideally with components placed individually and in side by side groups, then wipe the excess flux using the spray-and-soak method and leave it to rest for a few weeks or months. Then, to see the result, use a hot air gun to desolder the components. I would expect, but I'm not certain, that there won't be any (or at least significant) corrosion under the components either. That would be an interesting one.

I however lack the enthusiasm to do it at this time. So you, or anyone, are invited to try it: the test steps are straightforward and reproducible and no special equipment or skills are required :).

(I like the MG4381 except for one feature that has me looking for an alternative: it's lumpy. I can squeeze a few dabs from a syringe and then it's blocked and useless.)

Yes, other than the lumpiness, it's a pleasure to work with, that's for sure. I have even ordered some conical Luer lock compatible dispenser tips to solve the needle blocking issue, but haven't had a chance to try them yet.

[shapirus]

(I like the MG4381 except for one feature that has me looking for an alternative: it's lumpy. I can squeeze a few dabs from a syringe and then it's blocked and useless.)

How old is yours? I have definitely noticed lumpiness in my syringe of it, which is near its end, but I don’t remember it being lumpy when it was new (which was probably 2015 or so).

Mine should be fresh enough, but I haven't found the production date specified anywhere on the jar (I have the 50 ml version) or the packaging. Have this lumpiness issue too.

BTW, the sticker on the jar says "made in China". Doesn't look counterfeit though, everything looks as it should. Was yours made in Canada?

[tooki]

BTW, the sticker on the jar says "made in China". Doesn't look counterfeit though, everything looks as it should. Was yours made in Canada?

Either USA or Canada. (I can’t check, I left it at work.)

[PlainName]

(I like the MG4381 except for one feature that has me looking for an alternative: it's lumpy. I can squeeze a few dabs from a syringe and then it's blocked and useless.)

How old is yours? I have definitely noticed lumpiness in my syringe of it, which is near its end, but I don’t remember it being lumpy when it was new (which was probably 2015 or so).

Couple of years now, but it was like that when I got it new. Reason it's old is because the lumps persuaded me to change to a liquid flux, and that's mostly what I've used since.

[PlainName]

Got some of the Relife 422 stuff with which I did a board last week.

Which of them, exactly? They have several 422 fluxes that have different suffixes in their model names and they differ in properties.

RL-422-IM

I think that process successfully gets unused flux from under components too.

Unfortunately it doesn't. Not for me, at least -- even when I wash entire board by fully immersing it in alcohol, even in an ultrasonic bath. As I mentioned before, that's easy to check: heat the board after washing and drying (even if blowing with compressed air), and it starts to smoke. Some of the flux remains trapped at least under SMT resistors and caps, and I believe generally under the parts that have very small gaps between their bodies and the board. Not an issue (with this flux) for THT stuff.

OK, that's believable. Perhaps the fix is a pass through an oven no hot enough to reflow. Bit of a palaver, though.

A test better suited to real world application would be to solder some SMT parts (fully covering the footprints with the flux first) onto a board without solder mask, with traces passing under components, ideally with components placed individually and in side by side groups, then wipe the excess flux using the spray-and-soak method and leave it to rest for a few weeks or months. Then, to see the result, use a hot air gun to desolder the components. I would expect, but I'm not certain, that there won't be any (or at least significant) corrosion under the components either. That would be an interesting one.

Indeed. I'm almost tempted to try that - a homebrew PCB, sans mask, would be easy to do.

I however lack the enthusiasm to do it at this time.

Yes, no problem. Already done more for the cause that I've seen before 

(I like the MG4381 except for one feature that has me looking for an alternative: it's lumpy. I can squeeze a few dabs from a syringe and then it's blocked and useless.)

Yes, other than the lumpiness, it's a pleasure to work with, that's for sure. I have even ordered some conical Luer lock compatible dispenser tips to solve the needle blocking issue, but haven't had a chance to try them yet.

BTDT. So as I can tell, the conical tips just concentrate the lumps from a wider selection. I've gone back to a purple needle (pink might work but let out too much at a time).

[tooki]

Yes, other than the lumpiness, it's a pleasure to work with, that's for sure. I have even ordered some conical Luer lock compatible dispenser tips to solve the needle blocking issue, but haven't had a chance to try them yet.

While those tips are better in general for thick pastes (they’re what I use), they will not overcome the problem with the lumps, which just get clogged at the tip of the nozzle rather than the base.