Looking to buy some flux (pen+paste)

[tooki]

Yeah, I'm pretty sure I didn't try any low temp stuff. Maybe I've managed to avoid their good stuff, but I've tried 3 or 4 different ones and none of them gave even close to the performance I see with AmTech, so I've given up on them.

I haven't used AmTech (no easy, remotely trustworthy source for it here), so I can't say how it compares, but in normal SMD hand soldering applications (mostly drag soldering and rework on QFNs) I found the ChipQuik to work well, similar to others (MG Chems, Stannol, etc). The SMD291NL (not the same as SMD291 without the NL!) is especially pleasant, as it doesn't release acrid fumes.

In what ways and applications did the AmTech outperform the ChipQuik?

[xavier60]

To be avoided are fluxes that either immediately cause current leakage or leave residues that  absorb moisture causing leakage problems later. A Chipquick branded flux that I tried, caused immediate leakage that remained after the PCB was cleaned. It gradually came good on its own. 

Extra: It actually is SMD291, there is possibly no problem when used to reflow SMD rather than for hand soldering.

I just saw the edit, made just after my original reply to you.

What'd you clean it with? If you used just IPA, it's possible that contaminants were left behind, since many (most?) no-clean fluxes aren't fully soluble in IPA. A more thorough cleaning with proper flux remover would make it fine.

As you alluded to, no-clean fluxes have to be fully heated to deactivate them, which isn't guaranteed with hand soldering. In the latter case, you have to do a thorough cleaning. If you cleaned and had leakage, then the cleaning was incomplete.

I usually use turpentine. I realize that it dissolves stuff like rosin and oils but not too good for ionic substances, I use  methylated spirits for that. With this particular PCB. I scrubbed it with all of the above and even water and detergent, yet some leakage remained.
It gradually fixed itself. It was like something got into the fiberglass then slowly evaporated.

[David Hess]

I like using liquid flux with a brush but paste flux works well also.  I have never liked flux pens; they never seem to apply enough.

FWIW, there exist modern no-clean fluxes that are more effective than traditional RA fluxes. There's been a lot of progress over the years. (For example, Kester 275 and 245 no-clean flux cores significantly outperform the traditional Kester 44, according to their wetting specs.)

That may be the case with new untarnished parts, but my own experience is that Kester 44 is much more effective than 245 when doing rework.

[Electro Fan]

tooki, any chance you can describe the similarities/differences between SMD291NL and SRA #312 vs this?
https://www.mgchemicals.com/products/soldering-supplies/flux-pens/rosin-flux-pen/
Thx

[tooki]

tooki, any chance you can describe the similarities/differences between SMD291NL and SRA #312 vs this?
https://www.mgchemicals.com/products/soldering-supplies/flux-pens/rosin-flux-pen/
Thx

I haven’t used the MG Chems rosin flux, so I can’t comment on it specifically. But I’ll talk about other liquid rosin fluxes.

SMD291NL is a no-clean flux gel. As such, it is applied much more liberally, and it has much higher solids content than liquid flux, so it doesn’t burn up the instant you apply the soldering iron. This is what you want for extended operations like SML rework. This particular flux doesn’t produce the acrid, nose-burning smoke that most no-clean fluxes produce, making it vastly more pleasant to use for hand soldering. It’s also exceptionally smooth, being a true gel. Most tacky fluxes are slightly lumpy right out of the tube, this one isn’t. This is the flux I use for drag soldering, clearing bridged SMD pins, as well as for initial soldering of small SMD parts, since the tackiness holds them in place. Of course, this will need cleaning since the board will likely be a sticky mess. Using a fine dispensing needle to let you put it just where you need it will help with that.

SRA 312 is a typical modern no-clean liquid flux with low solids. Perfect for helping solder flow a bit better on fairly new parts and boards, be it through-hole or SMD. But not active enough to cut through the corrosion on really old parts.

As for liquid rosin fluxes, I’ve used a few, including Stannol 400-25 and Almit RC-15 RMA. Their higher solids content means they remain active longer than the no-clean, but only slightly. (A thin brushed-on layer is thin either way!) Rosin fluxes (whether liquid or paste/gel/tacky) are less tolerant of really high soldering temperatures than no-clean fluxes, so if you like to solder very hot, they’re more likely to leave you with burnt residues that are hard to remove. There do exist rosin fluxes designed for lead-free use, and they’ll be a bit more resistant to temperature. The rosin fluxes, due to their typically much higher solids content, will leave far more residue on the board than the no-clean. (But there are exceptions, since there do exist low-solids rosin fluxes, and comparatively high-solids no-clean fluxes.)

Broadly speaking, the liquid fluxes (whether no-clean or rosin) are good for “helping things along”. I’ll brush them onto all the pads of a board before soldering it just to give that little bit of flow. For example, when soldering THT parts, the flux will help it create a nice concave fillet on the component side, too, whereas the solder in the same joint without the added flux will flow through, but might not climb out of the hole and wet the top side pad. Either is fully acceptable by IPC standards, but it’s just nicer.

[Jan Audio]

Why?
I've worked with electronics for decades, and have never needed this. Why do you need flux?

For to solder low quality pin headers maybe ?,
the gold-plated ones solder perfect, not those other ones, yes you can only it wont attach so fast.
I also need a flux-pen only they are very expensive, how long does it take until it is dryed out because of not using ?

[tooki]

Why?
I've worked with electronics for decades, and have never needed this. Why do you need flux?

For to solder low quality pin headers maybe ?,
the gold-plated ones solder perfect, not those other ones, yes you can only it wont attach so fast.
I also need a flux-pen only they are very expensive, how long does it take until it is dryed out because of not using ?

The worst pin headers I ever had — so difficult to solder that I simply threw them out — were some cheap “gold” square headers from Ali or eBay. They simply did not take solder at all. They were a pale gold color. The others I had to throw out were at work: some headers that were probably 30+ years old. They were undoubtedly expensive, name brand items, but just tarnished too much over the years. None of the PCB-safe fluxes at hand were able to cut through it.

I’ve had no trouble at all with recently-made regular silver-colored square headers, no matter how cheap, nor with the more expensive round machined headers (which are gold plated), even from Ali/eBay.

A flux pen should cost around $8, it’s not that expensive. I have had absolutely no trouble with them drying out. It’ll go for years and years as long as you keep the cap on. I’ve got one here from 2015.

Remember that a flux pen is refillable. (You pay around $5 for an empty pen, so most of the cost is the dispenser, not the flux!) When empty, buy liquid flux and refill it with a syringe. (On some pens, the body screws apart, in others, you pull apart the body.) You can buy replacement nibs if the tip gets too raggedy, but a somewhat frayed nib is actually often kinda nice for getting onto pins.

[reboots]

FWIW, there exist modern no-clean fluxes that are more effective than traditional RA fluxes. There's been a lot of progress over the years. (For example, Kester 275 and 245 no-clean flux cores significantly outperform the traditional Kester 44, according to their wetting specs.)

Purely anecdotally, I standardized on Kester 245 (63/37) about 10 years ago and found that its wetting is noticeably poor compared to Kester 44 across a broad range of temperatures and applications. I refined my technique and don't really notice now, except when I have occasion to use rosin flux-core solder and see the improvement.

For flux, I like Chip Quik SMD291 no-clean tack flux in a syringe. (SMD291NL is the appropriate formulation for lead-free.) I find pens tend to flood the area, and the tips deteriorate and/or dry out.

For washing the board I use MG Chemicals 4140 flux remover to dissolve the flux, using a brush for agitation, then MG Chemicals 406B Super Wash aerosol for final cleaning. I recommend appropriate PPE for these chemicals. The Super Wash cools on evaporation, promoting condensation, so I follow up with gentle heating by heat gun or oven to drive out moisture. This admittedly troublesome and expensive regimen leaves the boards perfectly clean.

[tooki]

FWIW, there exist modern no-clean fluxes that are more effective than traditional RA fluxes. There's been a lot of progress over the years. (For example, Kester 275 and 245 no-clean flux cores significantly outperform the traditional Kester 44, according to their wetting specs.)

Purely anecdotally, I standardized on Kester 245 (63/37) about 10 years ago and found that its wetting is noticeably poor compared to Kester 44 across a broad range of temperatures and applications. I refined my technique and don't really notice now, except when I have occasion to use rosin flux-core solder and see the improvement.

Thanks for the info! Have you tried the 275? I wanna say that that’s the one someone else suggested I should try…

For flux, I like Chip Quik SMD291 no-clean tack flux in a syringe. (SMD291NL is the appropriate formulation for lead-free.)

Having tried both, I can tell you they’re nothing alike. The 291 is a fairly typical no-clean paste, whereas the 291NL is a true gel, with a radically different smell during use. (The 291NL is much nicer.)

I actually just sent an email to ChipQuik asking if they have a proper flux selection guide, since their data sheets don’t say nearly enough. We’ll see if they get back to me…

I find pens tend to flood the area, and the tips deteriorate and/or dry out.

Flooding is from impatiently pumping the tip too much. Even so, a flooded board is still easier to clean than one with paste/gel on it. As for the tips, drying out shouldn’t be a problem either.

What brand of pen did you use? I’ve used SRA and Stannol pens, and both are excellent.

I’ve also used an expensive BonKote brush pen, and while I like it, it’s very hard to justify its high cost relative to its durability, which isn’t that great.

For washing the board I use MG Chemicals 4140 flux remover to dissolve the flux, using a brush for agitation, then MG Chemicals 406B Super Wash aerosol for final cleaning. I recommend appropriate PPE for these chemicals. The Super Wash cools on evaporation, promoting condensation, so I follow up with gentle heating by heat gun or oven to drive out moisture. This admittedly troublesome and expensive regimen leaves the boards perfectly clean.

I can’t get the MG chemicals solvents easily over here, so I’ve been using brands I can get here, but also highly recommend using commercial flux remover instead of just IPA.

[reboots]

Thanks for the info! Have you tried the 275? I wanna say that that’s the one someone else suggested I should try…

I haven't, but I'll make a note of it for future experimentation.

Having tried both, I can tell you they’re nothing alike. The 291 is a fairly typical no-clean paste, whereas the 291NL is a true gel, with a radically different smell during use. (The 291NL is much nicer.)

I have both, and didn't notice a huge difference, but that doesn't mean there isn't any. I have observed that both fluxes change color over time, from pale yellow to an eventual dark brown, but have not noticed a drop in performance.

What brand of pen did you use? I’ve used SRA and Stannol pens, and both are excellent.

I haven't had a flux pen in-house for many years, so I can't cite a specific brand. Just not my weapon of choice, sorry! I do like the precision of the paste syringe.

[Electro Fan]

tooki, any chance you can describe the similarities/differences between SMD291NL and SRA #312 vs this?
https://www.mgchemicals.com/products/soldering-supplies/flux-pens/rosin-flux-pen/
Thx

I haven’t used the MG Chems rosin flux, so I can’t comment on it specifically. But I’ll talk about other liquid rosin fluxes.

SMD291NL is a no-clean flux gel. As such, it is applied much more liberally, and it has much higher solids content than liquid flux, so it doesn’t burn up the instant you apply the soldering iron. This is what you want for extended operations like SML rework. This particular flux doesn’t produce the acrid, nose-burning smoke that most no-clean fluxes produce, making it vastly more pleasant to use for hand soldering. It’s also exceptionally smooth, being a true gel. Most tacky fluxes are slightly lumpy right out of the tube, this one isn’t. This is the flux I use for drag soldering, clearing bridged SMD pins, as well as for initial soldering of small SMD parts, since the tackiness holds them in place. Of course, this will need cleaning since the board will likely be a sticky mess. Using a fine dispensing needle to let you put it just where you need it will help with that.

SRA 312 is a typical modern no-clean liquid flux with low solids. Perfect for helping solder flow a bit better on fairly new parts and boards, be it through-hole or SMD. But not active enough to cut through the corrosion on really old parts.

As for liquid rosin fluxes, I’ve used a few, including Stannol 400-25 and Almit RC-15 RMA. Their higher solids content means they remain active longer than the no-clean, but only slightly. (A thin brushed-on layer is thin either way!) Rosin fluxes (whether liquid or paste/gel/tacky) are less tolerant of really high soldering temperatures than no-clean fluxes, so if you like to solder very hot, they’re more likely to leave you with burnt residues that are hard to remove. There do exist rosin fluxes designed for lead-free use, and they’ll be a bit more resistant to temperature. The rosin fluxes, due to their typically much higher solids content, will leave far more residue on the board than the no-clean. (But there are exceptions, since there do exist low-solids rosin fluxes, and comparatively high-solids no-clean fluxes.)

Broadly speaking, the liquid fluxes (whether no-clean or rosin) are good for “helping things along”. I’ll brush them onto all the pads of a board before soldering it just to give that little bit of flow. For example, when soldering THT parts, the flux will help it create a nice concave fillet on the component side, too, whereas the solder in the same joint without the added flux will flow through, but might not climb out of the hole and wet the top side pad. Either is fully acceptable by IPC standards, but it’s just nicer.

Tooki, Thanks!

Any idea what Rel0 means?

And which of these dispensers is easier to work with?

http://www.chipquik.com/datasheets/SMD291NL-10M.pdf
http://www.chipquik.com/datasheets/SMD291NL

[xavier60]

I have just done a test on my SMD291 by putting some between adjacent tracks on Veroboard with an insulation tester connected and set to 250VDC.
Initially the flux is very conductive, it sizzles.
After tinning both tracks with a soldering iron and allowing it to cool, the flux turned into brittle rosin. I could detect no leakage.

[tooki]

Tooki, Thanks!

Any idea what Rel0 means?

That’s the J-STD-004 flux classification. In this case, it means REsin, Low activity, halide-free.

The first segment is the base flux type:
ROsin, REsin, or ORganic
Rosin is the kind made from tree sap, resin is similar, but assembled from synthetic or refined resins, organic means acid based (in the context of electronics, that generally means water soluble fluxes)

The second is the activity level:
Low, Moderate, or High
Low and medium are common in electronics, but medium may require cleaning. High always requires cleaning AFAIK, but you’d only need that for extraordinarily corroded surfaces.

The number is whether it contains halides:
0 = halide free; 1 = contains halides
Halides make the flux work better, but can be conductive or corrosive, and thus may necessitate cleaning. Also less healthy to breathe in.

The most common types of non-water-soluble fluxes in electronics are probably REL0, REL1, ROL0 and ROL1, followed by the moderate equivalents.

Another classification system you often see, especially in USA, is the mil spec QQ-S-571E:
 
R: Rosin, not activated
RMA: Rosin or Resin, Mildly Activated
RA: Rosin or Resin, Activated (RA),
AC: non-rosin/resin (i.e. water washable)

Though the categories don’t line up exactly, a ROL0/ROL1/REL0/REL1 is roughly equivalent to RMA, while ROM0/ROM1/REM0/REM1 is roughly equivalent to RA. (Because the boundaries don’t line up exactly, it’s possible to have, for instance, a REM0 that falls under RMA and a different REM0 that falls under RA. Don’t hold me to this, though!)

Another classification system you often encounter is the ISO 9454-1 system, which uses a very granular system of numbers. Very broadly speaking, ROL0 is 1.1.1, ROM0 is 1.1.3, ROL1 and ROM1 are 1.1.2.W/X/Y;  REL0 is 1.2.1, REM0 is 1.2.3, and REL1 and REM1 are 1.2.2.W/X/Y. (The letter suffixes specify very specific ranges of halide contents.)

And which of these dispensers is easier to work with?

http://www.chipquik.com/datasheets/SMD291NL-10M.pdf
http://www.chipquik.com/datasheets/SMD291NL

Get the -10M, the “manual” syringe. Not only are they slightly cheaper at many distributors (I get it from Digi-Key), but the manual syringe lets you pull back on the plunger to stop flow. The non-manual syringe is the kind of tube actually intended for automatic dispensing systems. They do include a plunger with a little rubber cap that kinda grips into the actual plug in the tube, and while it does let you pull back a bit, you have to be very gentle or you’ll yank the rubber thing off. The manual tubes are just a tad easier to use.

[Electro Fan]

tooki, wow!  Thx for all the info with the explanations - and super concisely presented as you always do.   
I'm going with the 10M and will try your SRA recommendation too.
 

[tooki]

tooki, wow!  Thx for all the info with the explanations - and super concisely presented as you always do.   
I'm going with the 10M and will try your SRA recommendation too.

Honestly, for the flux pen, get whatever is available from whatever distributor you order from anyway, so you save on shipping. Kester 186 has a stellar reputation, I’m sure MG Chemicals is great too, and Chip Quik’s is probably just fine, too. I think any major brand would be OK.

(Amazon carries MG and SRA, and a lot of Kester, but the prices may not be the best.)

[t1d]

I like paste/tacky flux.
I use Amtech = https://www.inventecusa.com/tacky-flux.html
I use model #VS-213-A-TF
It is creamy. I apply it with a syringe.
It cleans fairly easily with iso-propyl alcohol.
It has moderate temp tolerance/scorch resistance.
It causes good flow/wetting of the molten solder. However, it flashes off fairly quickly and must be reapplied.
It does not spatter.
It has a good shelf-life. I keep mine in the refrigerator.
It is not inexpensive and somewhat difficult to source. It is known to be faked = buy direct, or from a registered dealer.
But, I am very satisfied/impressed with it and don't think I will ever find better.
Once I found it and Kester brand solder wire, my soldering results improved instantly/dramatically. No more struggling to get the solder to flow = not applying heat for too long and lifting pads and no more spatter.
Solder Wire = Kester 24-6337-7601 | Sn63/Pb37 Wire Solder, 275 No-Clean, .031"dia., 58 Core