Restoring dried solder flux paste

[tooki]

I tried various ratios, stirring while cooling vs. leaving it still, nothing made any difference. Nothing at all like the old Kester 44 rosin flux paste I have a tin of, which is clearly a true dissolved mixture, since it can be remelted without any kind of separation, so it's not a suspension or emulsion. From the (many, many) flux MSDSs I looked at, and a few other sources, it's pretty clear that for liquid fluxes, unprocessed rosin can be dissolved in solvent, but that for petroleum jelly based paste fluxes, the rosin is processed first.

[SilverSolder]

Are all paste fluxes based on petroleum jelly, or only some of them?

[jpanhalt]

@tooki

I just bought a pound of gum rosin.  That's about 8X the amount of paste flux I have used in 50 years.  Should last me awhile.

My hypothesis is that your mixture is all wrong.  I suspect something like 1% to 5% petroleum jelly is what is needed, maybe even less.

Should arrive later this week, but an unusually strong Winter storm is brewing, and shipping may be delayed (i'm in a very remote area).  Will test and report.

John

[tooki]

Are all paste fluxes based on petroleum jelly, or only some of them?

No, not all are. Newer flux formulations tend to use other things.

@tooki

I just bought a pound of gum rosin.  That's about 8X the amount of paste flux I have used in 50 years.  Should last me awhile.

I should think so!

My hypothesis is that your mixture is all wrong.  I suspect something like 1% to 5% petroleum jelly is what is needed, maybe even less.

Not a chance. A 99% rosin concoction, provided you found a way to make a stable mixture, would be a solid, not a paste.

Kester SP-44 was 25-50% rosin according to the MSDS. (The MSDS doesn't list petroleum jelly, but other sources say that's what its base was.)

MG Chemicals 8342 rosin flux paste's MSDS says it's just 5% rosin, 10% paraffin oils (which could overlap with petroleum jelly, that being such a loosely defined term), a few % acids, with the balance unspecified.

SRA #135 rosin flux paste's MSDS says it's 30-50% rosin, 20-40% petroleum jelly, and the balance "non-hazardous stabilizers, and water". (That paste has the most similar appearance to the Kester SP-44 of all the still-available rosin paste fluxes I've seen.)

Should arrive later this week, but an unusually strong Winter storm is brewing, and shipping may be delayed (i'm in a very remote area).  Will test and report.

Please do!!! If you do find a way to make a functional rosin flux paste, I think many people would be curious.

(I've seen a few youtube videos claiming to do so, but I am quite certain they're fake, in that they claim to add a small amount of IPA to solid gum rosin to make a paste, but then when they demo the paste, it's a very pale yellow paste, not the dark amber the rosin would be.)

[jpanhalt]

One experiment is worth 1000 expert opinions or TDS's.  Why do you think ChipQuik's TDS's are so vague?  (PS: ChipQuik's use of bismuth in its low-melting solder is a matter of marketing.)

Will report back as weather and the USPS allows.

[tooki]

One experiment is worth 1000 expert opinions or TDS's.

Yet my multiple experiments apparently didn't count?

Why are you being so combative, trying to find something to criticize about every utterance I make?

Why do you think ChipQuik's TDS's are so vague?  (PS: ChipQuik's use of bismuth in its low-melting solder is a matter of marketing.)

Ummm… what? Who said anything about ChipQuik? Even so, how is bismuth "marketing" when it makes up the bulk of the alloy?!?


MSDS's (I didn't say TDS's!) are designed to be vague so as to preserve a manufacturer's exact recipe. All the same, they do offer some insight into what goes into products. Nobody is saying they're complete (since nonhazardous ingredients aren't generally listed), nor detailed enough to be used as a recipe guide.

[helius]

I'm interested in what you find. I have a nearly-full pint tub of Kester SP-44, but it has evaporated into a hard, rock like solid with needle shaped crystals. Is the consensus here that a 50%-50% mixture of (absolute ethanol or isopropyl) and sec-butanol is what's needed to restore it to a paste?

[tooki]

I'm interested in what you find. I have a nearly-full pint tub of Kester SP-44, but it has evaporated into a hard, rock like solid with needle shaped crystals. Is the consensus here that a 50%-50% mixture of (absolute ethanol or isopropyl) and sec-butanol is what's needed to restore it to a paste?

The crystals are normal. My ca. 1990 tin of SP-44 is still a stiff paste. I don't recall it ever being truly soft.

[helius]

Hmm, thanks. The only thing I tried so far was mixing some with a small amount of glycerin and IPA. I wasn't able to mix it smoothly so these don't seem to be compatible with it.

[SilverSolder]

I am super happy with the recipe in the original post - I actually used the flux "repaired" that way today, and it still looks, feels, and works like new.

If you have any liquid flux to hand, it is easy enough to try a small experiment to see if it is compatible with your paste...   this method is strong on the principle "use what you have", in my case at least!

This is what it looks like after 9 months - crystals beginning to form on the top, but it is still buttery smooth.

[jpanhalt]

I am in the same shape as both you guys are with a tub of #44.  It is at least 25 years old.  I just use it and avoid the crystals.  As I recall, I once put it in the microwave or more likely used a heat gun for a short time to remelt the surface -- long enough ago I don't remember .  It still works.  I would not add additional solvents to it unless as a last resort.

Maybe by the weekend, if we are not snowed in, I will have something to report.

[T3sl4co1l]

FYI, I tried melting some rosin into (very old) paste flux of that sort of composition (sublimates acicular crystals); it seems it sunk to the bottom, and remains brittle and gummy.  I didn't try much mixing, just stirring.  Hard to see if it mixed much, everything is pretty brown and opaque...

Perhaps the commercial product is an emulsion, but it doesn't seem to be a solution anyway, if the rosin isn't chemically altered.

I wonder which alterations would do.  Oxidation of unsaturated bonds?  Cleavage of esters?  And what is "activation" anyway?  (I was poking around a little earlier, and found one 1960s patent using light alkyl polybromides -- yikes!)

Tim

[helius]

I think hydrogenation of abietic acid esters is more common than oxidation. Those fluxes would then be categorized as "REsin".

As you found, activators are frequently halides, but not always. Some recent formulas are "halide and halogen free" so their activators are in another class, such as citrates, imides or (pyro)phosphates. They are there to react with oxides and slightly etch the metal surface so solder can wet it better.

The alkyl bromides might be scary from a toxicity standpoint, but the main concern is to avoid corrosion or metal migration in the assembled product. Having the halide ion bound up in an organic molecule makes it less likely to migrate and react with copper.

[T3sl4co1l]

Indeed. In the same patent, they detailed the tests used to qualify formulations -- some MIL and ASTM standards I think they were, where a copper sheet is thoroughly cleaned and buffed (with steel wool), floated on a lead bath (not tinned, at least not thoroughly!) and left to oxidize in air for an hour at 400C, or a minute at 500.  They say the coating is fractional microns of cuprous oxide, giving it a delightful flat brown appearance.  Seemingly even more impressive is using the solder on it, getting significant wetting (measured by how far a blob of solder and rosin, I seem to have missed how much of each -- spreads out).  I know the fluxes I have here, and my patience level, well enough to get out the sandpaper or steel wool if I saw a surface like that.

They also describe a corrosion test, which is vacuum deposited copper on glass: very thin, so when the rosin is cooked on it (how hot and for how long, was garbled, I was just reading the OCR..), if the copper oxidizes much due to air or rosin, it will disappear pretty much instantly; and the affected area is measured optically.

Hmm, hydrogenation should make the "resin" more lipophilic than alcohol-philic (heh, I don't think there's really such a thing as that, it would just be plain hydrophilicity, wouldn't it), that may be why it doesn't mix with petroleum jelly.

Citrates would be like partial esters, I suppose?  Alkylated to get them in solution, but not fully so there's free acids to be active (and the oxygen-studded citrate will be more active than the chunky abietic acid is); and pyrophosphates would be the same idea?  And imides like the uh, whatever the OSP stuff is, probably?  Yeah, I can see that.  Some of those might be pretty easily accessible to the home chemist; hydrogenation a bit less so.  (I imagine Pd:C or such should do the job, and H2 gas is easy enough to generate on demand -- it's one of the easier organic reactions to perform -- but it's a reaction (and subsequent workup, augh, filtering catalyst from sticky sticky resin solution? ) nonetheless, not just mixing raw materials together.)

Tim

[SilverSolder]

Who knew flux was so complicated! 

Presumably the recipes for some old school fluxes are more realistic to execute at home?

[tooki]

Who knew flux was so complicated! 

Presumably the recipes for some old school fluxes are more realistic to execute at home?

Not necessarily. If you can get the ingredients, many modern fluxes are very easy to mix, though it hardly makes sense given how cheaply flux can be purchased.

[jpanhalt]

Sorry for the delayed response.  I had to order some "stuff" (rosin, beeswax, petroleum jelly (Walmart), and stearic acid).  I spent a little time searching for formulations on the web and much less time experimenting.

My control/comparison standard is Kester SP-44 flux (I still have half a tin) and Kester 63/37 solder with SP-44 flux.  The MSPS/SDS for SP-44 shows:
Rosin: 30%
Petroleum jelly (PJ): 40%
Stearic acid: 10%

Another SDS for the same thing is similar but shows a few percentage of benzoic acid and ethanediol + "nonhazardous additions" (presumably petroleum jelly).

My first experiment was to test a simple mixture of rosin and petroleum jelly in the ratio of 8g PJ and 6g rosin (43%).  On heating they dissolved each other to give a clear, light amber color.  On cooling there was no separation of phases.  Although, it was cloudy.  A small amount (0.5g) was removed to test as a solder flux.

 

With arrival of my stearic acid, I added 1g to the mixture, heated and let cool.  The product looked the same as the one without stearic acid and was maybe just a little more stiff (no picture).  Final composition:

Rosin: 39.9%
Petroleum jelly:53.2%
Stearic acid: 6.9%

I wanted to oxidize the surface of some PCB without adding halides or sulfates.  I simply used a flame to get a little disolaration.  I then tested the strips using 63/37 leaded solder without flux core.

Here are the results:


#1: No flux, solder simply balled up and didn't stick.
#2: Rosin+PJ only -- almost as bad as #1, ball fell off and was lost.  Some solder stuck to board.
#3: Rosin/PJ/Stearic acid -- Good adhesion
#4: Control (Kester 63/37 w/SP-44 flux

[SilverSolder]

Interesting experiment!  - does there always has to be some kind of acid in a solder flux, even if it is a mild one, to cut through the oxide layer?

[jpanhalt]

The principle component of rosin is a tertiary carboxylic acid (abietic acid).  So, I'd say, "yes." 

Stearic acid is not that much different, but is softer than rosin.  It has fewer carbons (18 vs. 20) and is a primary carboxylic acid.  I suspect there could be a lot of changes in the formula without affecting performance. 

SP-44 flux has a distinct odor that reminds me of iso-amyl alcohol.  I suspect there are other GRASS (generally regarded as safe) components that aren't on the label. 

[T3sl4co1l]

Possibly it could be a complexing salt, or amine, but this would work more on the copper than the solder (tin and lead form fewer complexes, AFAIK), and probably slower anyway.

This is why, for example, copper (as salts, or slowly with exposure to air) can dissolve in ammonia solution, forming the deep blue tetraamminecopper(II) hydroxide.

There is stannate, and plumbate maybe not so much I think; that is, the metals are amphoteric, meaning they can be dissolved in acid or base.  Lead I think requires high oxidation state (not going to happen in contact with bare metal), tin may be happy enough, not sure.  No idea if these are stable and soluble in organic substances, at soldering temperatures.

Whereas the carboxylic acid complexes, of all the above metals, are pretty simple (in any oxidation state, besides metal of course), and reasonably stable.

Tim

[helius]

SP-44 is the paste form of Kester 44 flux (the liquid form is 1544). It is IPC class ROM1 (rosin, medium activation, detectable halides). The name "44" comes from its halide portion, 0.44% by weight. This is an important part of the formula that is missing in the homebrew test. Note that this would be an organic bromide, not an inorganic type.

Where can a person get alkyl bromides? One source is oddly in degreaser cans. 1-bromopropane (NPB) is a solvent used in some flux removers (which I do not recommend for that purpose as it has been associated with peripheral neuropathy). If someone else wants to experiment with it, I will pay close attention.

[jpanhalt]

My purpose was not to replicate SP-44 (which apparently is no longer available) but to show that rosin and petroleum jelly do mix and remain a stable jell.  I would never consider making, rather than buying a flux.

[T3sl4co1l]

Where can a person get alkyl bromides?

Just call up Max Gergel, obviously.   (Passed author of _Excuse Me Sir, Would You Like To Buy a Kilo of Isopropyl Bromide?_, a not-too-bad telling of the swashbuckling time that was chemical manufacturing during the uh, 40s to 60s I think it was.  Given the title, I don't think we'd have any trouble in this regard...)

Tim

[tooki]

My purpose was not to replicate SP-44 (which apparently is no longer available) but to show that rosin and petroleum jelly do mix and remain a stable jell.  I would never consider making, rather than buying a flux.

I wonder what the deal is with my rosin, since it didn’t end up looking anything like that, and just congealed in a layer under the PJ.

[helius]

Just call up Max Gergel, obviously.   (Passed author of Excuse Me Sir, Would You Like To Buy a Kilo of Isopropyl Bromide?

Thanks for that, I hadn't thought of that book in nearly a week It's full of crazy anecdotes, the best perhaps being when the salesman demonstrates the gentleness of a tile cleaner by gargling with it. Unbeknownst to him, the chemist who mixed the cleaner substituted trisodium phosphate for sodium pyrophosphate, completely changing the pH of the product.

I was so interested in this story that I tracked down the detergent ingredient he mentions, DuPont MP-189. The only information I was able to find is that it is a type of hydrocarbon sodium sulfonate, which is entirely unsurprising given the narrative description.