Liquid Flux: Pen vs. Bottle

[richfiles]

I'm a long time electronics hobbyist and professional, but had a question pertaining to the hobbyist side of things, that would be of likely interest to newbies too, so I'll post it here.

I've used both liquid flux and flux pens. Flux pens are pretty easy for hobbyists to get their hands on (thanks Amazon), but often times, I find that the pens are more of a nuisance than just a bottle with a brush. I find the pens either go dry, or dump a ton of flux... I STILL have never figured out how to get a flux pen to flow in moderation! 

The problem, is that for hobbyists, the good stuff (I prefer Kester 951 No-Clean) goes from a dinky little 10mL pen, to a 1 gallon jug plus a hazmat delivery fee. Kester really doesn't have a middle ground... just like the flow on their dang flux pens. 

So my question is: If I want to get away from flux pens and their inconsistent flow, and favor the simplicity of a bottle and brush, are there any brands of flux that offer hobbyist friendly quantities, and are equivalent in quality and composition to Kester's No-Clean flux? Really do not want to deal with high acidity or conductive fluxes, and am quite accustomed to Kester's stuff, but I'm more than willing to try another brand, if they make a reasonable sized bottle of liquid that's more... hobbyist friendly. Seriously, if I had one of the gallon jugs of Kester's stuff shipped, adding the hazmat fee, shipping, etc, it's be close to $60-70, and it's FAR too much for my needs.

I am open to suggestions.

[nanofrog]

MG Chemicals offers small bottles that are hobbyist friendly (i.e. 835 in 125ml bottles, which is RA flux). Unfortunately, they don't offer a no-clean. You can get Kester 951 from eBay sellers however, and I've found Dickie's Garage Sale to sell genuine 186 FWIW.

[jeffaroo]

I've found that most of the problems of the flux pen are due to a pressure buildup of the internal air bubble.  I've taken to burping the pen before use.
Holding the pen upright I remove the cap and using the cap I momentarily depress the tip.  And Bob's your uncle.

[richfiles]

Thanks! Ebay has the common problem of spamming you with a ton is stuff that you weren't actually searching for, requiring you to sift through long lists of "wun hung lo" sellers and add a dozen exceptions to the search... On the other hand, Amazon was really only returning retail products... THAT was exactly what I needed. Someone spitting up and reselling the large jugs into hobbyist friendly sizes. I'd have never thought to look under PS3 and Xbox reflow repair... 

[Audioguru]

For my entire electronics career I never used liquid flux. I used flux-cored solder instead.

[Galaxyrise]

I've been using a bottle with needle after I dumped my bottle+brush all over the workbench.  The flux is something from MG, and the bottle + needle were an inexpensive set I got from the same store I got the flux. It's been an excellent middle ground.

[richfiles]

For my entire electronics career I never used liquid flux. I used flux-cored solder instead.

I hadn't bothered with it much either, till recently. I'd used some ridiculously sticky crud at my job, for soldering 95/5 solder on mil-spec products, but what i've learned, is that liquid, no-clean flux is your friend, especially when working with tiny surface mount stuff. There's NO comparison to how cleanly the solder behaves when you add more flux than the tiny pittance that's bundled inside the core of the solder itself. For normal soldering, I don't need the extra flux, but trust me... If you need to do rework, if you need to solder non standard metals (such as the solder tabs on the housing of micro/mini USB connectors, etc... the flux pays.

[nanofrog]

Thanks! Ebay has the common problem of spamming you with a ton is stuff that you weren't actually searching for, requiring you to sift through long lists of "wun hung lo" sellers and add a dozen exceptions to the search... On the other hand, Amazon was really only returning retail products... THAT was exactly what I needed. Someone spitting up and reselling the large jugs into hobbyist friendly sizes. I'd have never thought to look under PS3 and Xbox reflow repair... 

FWIW, I found it searching for Kester 186.  Bottles from that seller comes up searching for Kester 951 as well. 

As per dispensing it, I use a Bonkote BON-102 brush pen (here). It's precise, so allows you to put flux where you want it, and control how much goes on  as well (valve controlled by squeezing the pen). Well worth the cost IMHO.  Please be aware however, that they're heavily counterfeited, so buy from an authorized retailer (genuine pens go for ~$15 - 20, while counterfeits from China go for a few bucks).

For my entire electronics career I never used liquid flux. I used flux-cored solder instead.

Generally speaking, it's only used on occasion, such as when drag soldering SMD IC's or large tabs on discrete components for example. Otherwise, the flux core in the solder wire is usually sufficient (i.e. 3.0/3.3% flux content by weight).

[free_electron]

brush bottles are crap for flux.  this type : 

here is why :

when using rosin based flux : the rosin solidifes in the whiskers and you get a solid stump instead of a brush
when using no-clean : the carrier for no clean is alcohol. which evaporates slowly cause you can't seal the brush ...
when using water soluble : it pulls moisture from the air into the flux turning the damn thing into soap instead of flux..

that is why these pens are the only workable solution , or using a closable bottle and use separate brushes that you soak in a 50/50 water alcohol solution at the end of the day. and rotate on alternating days.

[richfiles]

brush bottles are crap for flux.

I'd believe it... I imagine those are only good for constant usage, like heavy production line soldering, where you're constantly consuming the stuff. I use a little brush and a bottle cap usually. Squirt a little out into the bottle cap, and brush it as needed.

Caps, valuable for containnig flux for soldering, emulsion lubricant for sliding rubber parts together, and for purchasing goods from wasteland vendors in the "Fallout" games! 

[KL27x]

that is why these pens are the only workable solution , or using a closable bottle and use separate brushes that you soak in a 50/50 water alcohol solution at the end of the day. and rotate on alternating days.

Bottle with a needle applicator seem to be popular, too. I prefer a needle. You can apply a big bead of flux, rather than spreading out a thin layer over a larger area of board.

What I use is a syringe with plastic needle. I tie a knot in a piece of twine and run it through the inside of the needle. Then I melt the back of the needle and close it up around the knot to lock in the string. As long as it isn't stored tip up, it doesn't dry out. No cap. Grab and go. It doesn't clog, run, squirt, drip. It applies a lot or a little flux with a lot of control, and it doesn't snag on sharp leads or whatnot.

After 2-3 refills, the rosin flux I use gums up the syringe, and it's time for a new one.

Flux pens work fine, but the tip isn't always the best shape for getting flux where I want it, and they're kind of pricey.

[KL27x]

No clean vs RA:

By it's very nature, flux leaves conductive compounds behind. You will usually read that the acid "deoxidizes" the copper. In truth it dissolves the copper oxides, leaving behind copper compounds.

An acid core flux leaves these compounds behind in water, which makes the residue conductive. If completely dried out, it would be non-conductive, but the naked salts/compounds are hygroscopic and pull moisture out of the air. Also, the chlorides in the flux promote continued corrosion, particularly a concern on ferrous metals. This chloride embeds in the metal and can't be washed off with water.

A no clean flux leaves these compounds in a bed of a polymer, so they are non-conductive.

A rosin flux is a very long chain acid which also basically turns into a polymer when the solvent evaporates. It just takes a few hours, rather than seconds as with no clean. And then it's completely non tacky. And it is easy to wash off the residue with alcohol and water. No clean flux turns to crap if you ever need to wash the board with alcohol.

There is some debate on whether or not you can leave RA residue on a board, but the MG website and bottle says "non conductive and non corrosive residue." And I have never had any problem with MG 835 residue. I recently have made up a lot of boards that require an exact voltage on a particular ladder, and I found I had to tune many of them. Thinking flux residue might be contributing, I carefully washed some of the boards, and there was no detectable change, so I ordered some higher tolerance resistors. I have never been able to record any conductivity of RA residue.

From the MSDS, the "activators" of common Kester and MG RA flux remains a mystery. It's a secret ingredient. I have read from various sources that it might be long chain organic fatty acids or even halides (like zinc chloride). The fact that MG states that 835 residue is non-corrosive suggests that they are not adding halides.

[Ian.M]

The answer to the brush problem is a bottle with a brush inside.
e.g. http://www.theplasticbottlescompany.com/product/30ml-hdpe-bottle-18mm-spigot-cap-stem-brush/
Make a weighted base to fit it so it cant get knocked over easily.

For a no-drool DIY flux pen, take a chunky hiliter pen, open it and wash out all the ink under the hot tap, then shake as much water out as possible from its fibre nib and adsorbent foam fill.  Flush with IPA, dry 24H in a warm place then soak with runny liquid flux, reseal it and stand it nib down in a sealed jar for an hour to let any excess drip out before capping it.   I made some up approx 5 years ago that still work fine.   They wont put a lot of flux down, but will put a nice even coat on pads etc.  If you need more, or are fluxing irregular surfaces, that's what the brush in bottle is for.

[KL27x]

Confounding the issue of no clean vs rosin, I bought some "rosin core" solder from Mouser, and when it got here, I see "no clean" on the label.

Per Mouser, this is a rosin core, but in the description is says that it's made from rEsin.

The residue looks and feels like rosin but is much more clear. And it washes off similarly to my rosin core solder. (Not like the Kester no-clean flux pen, nor the no clean solder pastes I have used, which are quite the pain to clean up). It is similar to the "purified rosin" cored solder wire I have (made by Indium). Perhaps glowcore is some sort of synthetic rosin.

So I guess not all no-cleans are the same.

Here's an article that seems to support my feeling on no clean. Essentially, that it can be harder to wash off the residue, should the need arise.
http://www.assemblymag.com/articles/84286-why-clean-no-clean
It also suggests that residue becomes problematic at frequencies in the GHz range, where the skin effect becomes strong.

I also found this interesting on AIM website:
RA core solder wire:

RA wire will leave slight to moderate post process residues that may be left on noncritical applications, but should be removed from any critical applications. RA cored wire meets Mil-Spec cleanliness requirements post-cleaning.

RMA cored solder wire:

RMA wire will leave slight to moderate post-process residues that may be left on noncritical applications, but should be removed from any critical applications. RMA cored wire meets Mil-Spec cleanliness requirements without cleaning.

This may be where the "you can leave RMA residue, but you have too clean RA residue" mantra comes from. A military standard.

[nanofrog]

Per Mouser, this is a rosin core, but in the description is says that it's made from rEsin.

The residue looks and feels like rosin but is much more clear. And it washes off similarly to my rosin core solder. (Not like the Kester no-clean flux pen, nor the no clean solder pastes I have used, which are quite the pain to clean up). It is similar to the "purified rosin" cored solder wire I have (made by Indium). Perhaps glowcore is some sort of synthetic rosin.

FWIW, some no-clean fluxes are made from refined rosin, while the others use a synthetic resin, such as an ester.

Indium for example makes both types according to their technical data sheets and sales flyers (open about this information  ). Their CW-802 or CW-807 (& it's variants) are rosin based, while CW-501 is pure synthetic (they call it rosin-free in the .pdf's I have saved).

[KL27x]

Ok. Well, then I definitely like some no-clean fluxes. I like my Indium solder wire (CW-807), and so far I like this glowcore AIM stuff, too. To be honest, I can't see much difference between these flux residues and regular rosin, other than the color. I am not making any RF or life-critical circuitry.

[tszaboo]

I also order the flux in syringe. It works well, even with metal needles, and you have a lot of control of the amount and the placement of the flux. Maybe the top 0,1mm dries out, but that is easy to push out and it is always ready.

[Galaxyrise]

Maybe the top 0,1mm dries out, but that is easy to push out and it is always ready.

Or melt with your soldering iron, which I have to do occasionally.

[LukeW]

Personally, I like high-viscosity syringe-dispensed flux such as the MG Chemicals 8341 or similar.

I wonder if you can buy it in larger bulk quantities and refill the syringe?

[KL27x]

Interesting. I just dug out one of my syringes of 8341-10mL to see why it is I didn't like it. Did some side by sides with MG 835.

1. Slower to apply

2. Despite being unable to apply anything but a humongous amount, it is much less effective than RA on oxidized but otherwise clean copper. This is not really big deal. Most people only solder to bare copper when tinning wires. I just happened to notice because one of my tests was on a piece of unprepped copper clad. The 8341 side spotted in slowly, while playing the tip over the copper. The RA side instantly sucked the solder off the tip like a... well, I'll stop there. I tried again with the 8341, in case the preheating of the board helped the RA side. No, the 8341 was still sluggish.

3. Residue. The RA is almost dry when done soldering. Pretty solid with very little tack to it. You can play a dry Q tip over it without leaving fibers or smudging the residue. And I know that after an hour it will be nearly brittle and completely tack-free. The 8341 residue is clear but it is gooey and sticky. The Q tip is just pushing the sludge around and leaving fibers. I played the iron on it for awhile. Hit it with the heat gun for awhile. Let it cool. Still sticky/gooey and not solid, at all. And by now, I see it has already picked up some random hairs.

4. Cleaning: at least 8341 doesn't turn white when you clean it with alcohol. But it is a lot harder to clean than the RA. I don't think it really comes clean with alcohol. There was still a tacky film, and without some abrasive action and elbow grease, the Q tip is just pushing the film around. Water didn't help. Acetone got it clean.

I don't know how this stuff qualifies as no clean. The amount of solids might be low, but the residue is a dirt magnet. For my uses, I don't like it, yet. Maybe I'll have a job where it shines, one day.

I wonder if you can buy it in larger bulk quantities and refill the syringe?

Filling a syringe with this stuff probably wouldn't be trivial. Not as bad as loading a syringe with solder paste, but it wouldn't be a picnic.

[george graves]

For liquid I use a bottle with a needle applicator - not sure of the needle gauge (22?), but I crimp the end down tightly, so that it's almost closed.  (the larger needle is strong, and won't puncture skin unless you're really ham-fisted.)

It's a great way to dispense kester liquid no-clean flux in sub-droplet sided amounts.  You don't even squeeze on the bottle, the mere act of picking it the bottle up, (and turning it upside down) and bringing it to the PCB is enough to warm the vapors in the bottle(from your hand) that they will expand and push out a tinny, tiny amount of flux.  Works perfectly every time. 

A reservoir of liquid is kept in the needle,  so just turning it over seems to replenish it - so there is no wait time for it to flow.  Also, with the crimped opening, I will get a clog (once ever 2-3 month) - but a small squeeze while upright clears it. I usually only keep it 1/4 full of less.

The only change I want to make is to hot glue (or epoxy) some heavy washers to the underside of the bottle, as tests leads and such are happy to tip it over.

[LukeW]

Can you get any RA in high-viscosity gel like the 8341?

[nanofrog]

Can you get any RA in high-viscosity gel like the 8341?

FWIW, Kester's RF741 rework flux is listed as a no-clean gel, but it's made using rosin rather than a synthetic (40 - 55% of it, according to the SDS).  Do note however, it's activity is that of RMA (equivalent to Kester 245 solder wire).

Never fear though, as it appears you can also make your own.  Just mix your liquid RA with a little carnauba wax (doesn't take much). The solvent/s in the flux dissolves the wax. So as you mix, you'll get a gel.  You can also make a paste by mixing your flux with petroleum jelly (should be able to use this in a syringe with a large enough needle if you wanted).

[KL27x]

^ cool. Just don't use beeswax. It smells terrible at soldering temp. I decided to wax a couple pcb's, once upon a time. Come to think of it, the 8341 fumes have a pretty strong odor, somewhat similar to burning beeswax.

FWIW, I just melted a little paraffin into some RA. It works ok, I guess, but it doesn't spread and stick as good as 8341. I suppose you could load a syringe while it's hot.

[Bryan]

https://youtu.be/9skxEr1eQ9o