Good soldering flux?

[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