Good soldering flux?

[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.

[Gediminas]

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.

I was looking for same thing, same requirements. The best I found so far is TermoPasty Flux Gel, no clean flux.
It is paste/gel flux. I could not measure any conductivity before and after heating (with Brymen BM869S in nano Siemens mode).
If left on pure copper - no  corrosion after several weeks.
After heating, flux remains soft and newer becomes hard. It is half soluble in IPA, but still quite easily can be cleaned with it from the board.
It will flow underneath the parts and you will definitely will not be able to fully remove it from there. But so far I did not notice any problems while using this flux.
Here is the link where I bought it: https://www.tme.eu/en/details/topnik-zel_14/fluxes/ag-termopasty/art-agt-088/

[shapirus]

I was looking for same thing, same requirements. The best I found so far is TermoPasty Flux Gel, no clean flux.
It is paste/gel flux. I could not measure any conductivity before and after heating (with Brymen BM869S in nano Siemens mode).
If left on pure copper - no  corrosion after several weeks.
After heating, flux remains soft and newer becomes hard. It is half soluble in IPA, but still quite easily can be cleaned with it from the board.
It will flow underneath the parts and you will definitely will not be able to fully remove it from there. But so far I did not notice any problems while using this flux.
Here is the link where I bought it: https://www.tme.eu/en/details/topnik-zel_14/fluxes/ag-termopasty/art-agt-088/

Sounds interesting. We have this one available locally. Sold for ~$5/10ml, so not exactly cheap, but I think I'll give it a try, thanks for the idea.

[Gediminas]

I was looking for same thing, same requirements. The best I found so far is TermoPasty Flux Gel, no clean flux.
It is paste/gel flux. I could not measure any conductivity before and after heating (with Brymen BM869S in nano Siemens mode).
If left on pure copper - no  corrosion after several weeks.
After heating, flux remains soft and newer becomes hard. It is half soluble in IPA, but still quite easily can be cleaned with it from the board.
It will flow underneath the parts and you will definitely will not be able to fully remove it from there. But so far I did not notice any problems while using this flux.
Here is the link where I bought it: https://www.tme.eu/en/details/topnik-zel_14/fluxes/ag-termopasty/art-agt-088/

Sounds interesting. We have this one available locally. Sold for ~$5/10ml, so not exactly cheap, but I think I'll give it a try, thanks for the idea.

Yes, it is not particularly cheap, but my use for it is BGA/QFN packages, this sort of things. For regular soldering often is enough flux in the solder wire itself, or I use simple rosin diluted in alcohol.

[shapirus]

Sounds interesting. We have this one available locally. Sold for ~$5/10ml, so not exactly cheap, but I think I'll give it a try, thanks for the idea.

Okay, let's begin.

Corrosion test start date:




Conductivity test: >200 GΩ at 2.58 kV at 52% RH, outside the display range of the meter.





Consistency: medium thick sticky gel without any lumpiness that I could notice so far.

This one looks promising.

[PlainName]

Just noticed the datasheet for that has the following:

Activators used to produce the fluxing agent allow for leaving its residues after the soldering process on the package (provided the production process does not include the washing phase)

What might be the problem with washing, or is that just poorly phrased?

[shapirus]

Just noticed the datasheet for that has the following:

Activators used to produce the fluxing agent allow for leaving its residues after the soldering process on the package (provided the production process does not include the washing phase)

What might be the problem with washing, or is that just poorly phrased?

I guess the meaning is that it's fine to leave the residues even if the board isn't washed.

[forrestc]

What might be the problem with washing, or is that just poorly phrased?

Most no-clean fluxes must either be left alone after soldering (no cleaning at all) OR fully cleaned without leaving any residue behind.

The reason why is that the most common no-clean chemistries rely on encapsulating the active components in the flux residue.   The "plasticized" flux residue is what traps the corrosive elements, and if you disturb it by partial cleaning you open yourself to corrosion.

When using no-clean fluxes, partial cleaning is often/usually worse than leaving residues alone, provided the flux has all reached it's activation point as specified in the datasheet.   

[tooki]

Indeed. And not just for no-clean fluxes, but for rosin flux, too.

Just the other day I wrote this in another thread (about why a manufacturer left flux reside on the hand-soldered connectors in an expensive product):

As for flux residue: ehhhhh… as a perfectionist I also like to deliver pristinely cleaned boards. But pragmatically, there is no reason to clean residue like JBC leaves behind, and there are good reasons not to clean. As long as it is rosin or no-clean flux, then it’s safe to leave behind. These aren’t sensitive RF circuits, and the easy, quick ways to clean PCBs (like ultrasonic) aren’t necessarily good when you’ve got connectors and cables/wires, which is what they’ve hand-soldered. In a white paper about white residues, Kester (the solder manufacturer) says this about cleaning rosin flux (which applies to no-clean as well): “Typically rosin fluxes, including most activated types, have insulation resistances in the 10¹⁰ ohms or higher. The problem arises when it is required to remove the residue either because the assembly will operate hot (above 65°C) where the rosin becomes tacky, or the rosin might flake off and get between electrical contacts, or just for aesthetics (not a good reason for cleaning).” (Emphasis mine.) It also mentions that “Rosin, with its high insulation resistance, keeps the halides dormant but if the rosin is removed, leaving some halide salt behind, corrosion is possible.” This means that incomplete cleaning is worse than no cleaning at all.

[PlainName]

How annoying. I thought trying to make an educated choice of solder was bad enough, but this sure mitigates against taking an interest in flux too!

[Smokey]

... "incomplete cleaning"  pretty much describes most attempts I've made to clean a hand soldered board.  I never want to use as much IPA as it apparently necessary.  Usually end up with white residue over more of the board than originally had flux from the soldering.

[shapirus]

Usually end up with white residue over more of the board than originally had flux from the soldering.

Not all fluxes leave it. MG Chemicals 8341, for example, is one that doesn't. It's pretty easy to wash it off completely, and in that regard it's quite different from many other fluxes.

[tooki]

... "incomplete cleaning"  pretty much describes most attempts I've made to clean a hand soldered board.  I never want to use as much IPA as it apparently necessary.  Usually end up with white residue over more of the board than originally had flux from the soldering.

The amount and technique are one thing, but another aspect, and I cannot emphasize this enough, is this: IPA is not a good cleaner for many fluxes. This has been argued on the forums ad infinitum, and some people refuse to accept it and dismiss it as nonsense, but there is a reason commercial flux removers exist, and why they contain ingredients beyond IPA.

No amount of IPA can flush away compounds that aren’t soluble in alcohol. And some compounds benefit from synergistic action of solvent combinations, dissolving in the combination better than they can in any of the constituent solvents alone.

Yes, some fluxes do clean up perfectly with IPA, but many do not. And warm IPA in an ultrasonic cleaner performs way better than when used for hand cleaning. But my point is that it is not universally successful for hand cleaning as many people wrongly insist. Commercial cleaners do better, and even among them, I’m sure some fluxes respond better to some cleaners and vice versa.

[Zucca]

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. "

You did not mention it cost more than gold



datasheet

6 months shelf life.

[PlainName]

You did not mention it cost more than gold

It would be no good for use on audio kit if it wasn't.

[shapirus]

And warm IPA in an ultrasonic cleaner performs way better than when used for hand cleaning.

I can confirm this. Still, since IPA does not dissolve many (most?) fluxes, but only thins them, mechanical action like brushing may still be required, but it's much less work than after soaking the board in cold IPA without ultrasonic.

Mixing IPA with a petroleum solvent (speaking of stuff that can be easily obtained for home use and is not overly toxic etc.) improves the results even further. It's harder to dispose of afterwards, though. Not that you're supposed to flush even pure IPA down the bathroom drain anyway, but petroleum solvents are way worse in that regard.

[Zucca]

And warm IPA in an ultrasonic cleaner performs way better than when used for hand cleaning.

I can confirm this. Still, since IPA does not dissolve many (most?) fluxes, but only thins them, mechanical action like brushing may still be required, but it's much less work than after soaking the board in cold IPA without ultrasonic.

Mixing IPA with a petroleum solvent (speaking of stuff that can be easily obtained for home use and is not overly toxic etc.) improves the results even further. It's harder to dispose of afterwards, though. Not that you're supposed to flush even pure IPA down the bathroom drain anyway, but petroleum solvents are way worse in that regard.

Interesting discussion, are we talking about >90% IPA here? IMHO high concentrated IPA vaporize away... so according to physics if we then warm up liquid IPA it will become gas even faster...

[shapirus]

Interesting discussion, are we talking about >90% IPA here?

The label on what I use says "99%"

IMHO high concentrated IPA vaporize away... so according to physics if we then warm up liquid IPA it will become gas even faster...

Of course it will. That's why it has to be forcibly removed together with whatever it's now mixed with before it has a chance to evaporate.

Here's how I do it, for example:

1) soak/ultrasonic/brush/whatever the board
2) remove the board from the solution and shake the remaining IPA off/use a paper towel to wick it/use compressed air to blow it off
3) repeat step 1, maybe with less operations (e.g. only soak and brush) in a fresh portion of IPA, then repeat step 2.

Dirty IPA+flux mixture can be saved for later reuse, of course. No need to dispose of it right away, especially the one left from step 3.

[Zucca]

Thanks it makes sense. I will give it a try in my ultrasonic cleaner with IPA and heater on ... I need to buy a gallon of 99% IPA somewhere... (fun fact if you google "IPA gallon" only beer shows up).

EDIT: I found it, some other interesting MG products here

BTW I need to do my homework to see if I can harm the board with the ultrasonic c. ... I remember some relais or other components could fail?

use compressed air to blow it off

I have a dentist oil free air compressor under my bench... (mainly for my Metcal DS-1).
I normally clean/brush with IPA and then drag with compressed air the junk off the metal pins/soldering joints on to the PCB areas where the "junk" can sit, on solder mask areas for example.

It goes back what tooki was saying... cleaning should be for the electronic not for the eyes.

Thanks eveybody for the nice discussion, I will buy a MG Chemicals 8341  once I am done with the current SMD flux.

[shapirus]

Thanks eveybody for the nice discussion, I will buy a MG Chemicals 8341  once I am done with the current SMD flux.

Let us know how it works for you.

For me, the experience is less than pleasant, and not because of its conductivity (which is low enough) or corrosive properties (bad, but hardly significant in practice, provided that the boards are either washed or oven-reflowed), but because of its lumpiness. Whatever gauge of the needle I use, within reason, or a conical syringe tip, it keeps blocking. I really hate that.

Otherwise, it's good stuff.

[shabaz]

Whatever gauge of the needle I use, within reason, or a conical syringe tip, it keeps blocking. I really hate that.

There are a couple of solutions for that : ) (I use the same stuff, 8341).
Solution 1: Use a metal tube nozzle, quite wide (I'm using 1.5 mm hole), and when it's near a hot air tool (i.e. just gently warmed) it will auto-unclog : )
Solution 2: When using a fine flexible plastic nozzle, I use a wire (e.g. through-hole resistor, or any bare wire), poke it around in the end a bit and then it egresses in a fine thin line (if that's what you want, ideal for small SMDs).

Photo shows the metal nozzle I use. Also shows a couple of other fluxes which I've not used yet, but hope to try out sometime.

[eliocor]

Composition formula of the MG suggested cleaner (4140) for 8341 flux: the IPA content is only from 1 to 5%.
The most part is ethanol

[shapirus]

Composition formula of the MG suggested cleaner (4140) for 8341 flux: the IPA content is only from 1 to 5%.
The most part is ethanol

As a matter of fact, whenever I wrote "IPA" in previous posts, I actually meant a 1:1 mix of IPA and ethanol. I forgot about that, but that's what I'm actually using for board cleaning. The reason is that ethanol is cheaper, and IPA, well, everyone uses it, so I do too.

I haven't noticed any difference between the mix and pure IPA in the washing ability.