Good soldering flux?

[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.