Workshop Video #06: Battle of the solder flux

We broke out 4 different types of flux we had in the workshop and tried them with surface mount parts. Liquid flux, flux paste, syringe flux, and a flux marker are all tested. We used each to solder a 0805 resistor and some pins of a QFP 0.5mm pitch IC to an xQFP protoboard.

Our preferences in order are:

  1. Flux syringe – very easy to work with, low fumes, solder flows really well
  2. Liquid flux – we were surprised that a liquid flux worked so well, it could have been #1 if it created fewer fumes
  3. Flux paste (probably rosin-based) – thick and viscous, kept the solder where we needed it
  4. No flux at all – fine for passive parts like resistors and capacitors, harder to work with on the QFP chip
  5. Kester flux marker – overall this was worse than no flux at all

xQFP protoboards make it easy to prototype with surface mount parts, and are currently available in 0.50mm, 0.65mm, and 0.80mm for $10 each. Single xQFP breakout boards are also available in 0.50mm, 0.65mm, and 0.80mm for $3.

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  1. Hehehe, I showed that flux to Sjaak. :) I use a similar one, but mine needs cleaning (rosin looks really bad under magnification) and sometimes even after cleaning there is some sticky residue but works really well!

  2. Really like the review. Since I’m still fairly new to soldering, I’ve just got some basic flux that came from Radio Shack.

  3. I really appreciate tutorials and reviews like this. It’s well filmed and explained. Just this past year, I decided to invest into learning electronics. I love it. But, reading about it, and then attempting it, is not as good as watching someone do it. Thanks for the great videos!

  4. Yeah my Spark Fun marker arrived this week too but it’s a different one. It’s Kester 2331-ZX. I’m going to see how it works as soon as my Bus Pirate parts arrive. I also have some Kester Paste that I normally use. I’ll report back here after I compare them. Either way I’m still buying the one Ian suggested. Also, go to Facebook and look at There’s a video on surface mount soldering that I think Ian linked way back. In the comments I asked about the the solder and flux he used and he posted an excellent reply. The key to a better wetting action seems to be preheating. Although Ian’s flux probably just has a lower temp requirement.

    Also is that board the .5 or .65?

    1. be aware! that flux is highly corrosive. You need totclean it very well after using or it will be eroded in a few weeks.

      But it does work very well and I like it just as the liquid Ian showed.

      1. This man speaks the truth. 2331-ZX is a superb flux, the best I’ve tried so far and it requires a very small amount to work. It cleans even the worst looking solder blob you have, and makes solder flow really well. It doesn’t fume a lot either. But It’s not a flux to use on bare copper boards because it literally eats them. It also likes iron tips a lot, and it can even corrode solder or other metals if you let it. So yeah, pretty good flux, but be sure to clean everything it touches after use. Thankfully it’s easily cleaned with deionised water, nothing else is required.

  5. Nice breakdown of the different flux types, the new flux pens at Sparkfun are #2331 and it seems to work much better then the older stuff. Also, I dont know if you have tried Bevel or Gullwing tips yet but they really help drag soldering, especially for those .5 pitch high pin count ICs.

    1. I bought a T18-C3 but I’m probably going to get a T18-C2 for my Hakko. And I hope you’re right about the newer flux.

  6. I guess you are using rosin-core solder. That would explain why you get a nice, shiny solder joint without using additional flux. Most solder you can buy for electronics have strands of flux in them, so you don’t need additional flux. When working with SMD you will most likely need extra flux for one of two reasons: either you actually solder the component with the molten solder that’s on you tip (then the flux from the solder wire is already evaporated), or you use very fine solder which can’t deliver enough flux to the joint.
    You can make your own flux at home by dissolving rosin in pure isopropyl alcohol. It works really well, but leaves a sticky residue on the board. When you give it some time to dry it won’t be sticky any more. I have been told that at the time when professionally made PCBs were still unobtainable for the ordinary DIY’er, people used to paint home etched boards with rosin flux so they would stay solderable for a longer time.

  7. @Jay and ferdinandkeil – You’re totally right, I should have mentioned that. All my solder has some flux or rosin in the core, most does. I don’t find it to be enough for SMD or through hole parts though. In this demo I used 0.5mm 60/40 with 2.2% flux in the core. I also use a 0.3mm 60/40 I got in Japan, and I can’t really tell what is in the core because it isn’t in English :)

    It should also be noted that the soldering wick is also coated in some flux.

    @FourthDr – Iron dial is at 380c, but I think it is pretty arbitrary and not a real temperature. I just tweak it till it feels good.

    1. LoL I just came back up from the basement to ask about the temp… Any feelings about lead free solder? I also just bought 20′ of the SparkFun “Special Blend”. Going to test that when my Mouser order comes in too. Note that their “Special Blend” has some sort of flux in it that seems to be liquid. I know this because a lot of it leaked out into the bag it was packaged in. No MSDS on it either so not sure what it is.

    2. 380c is about 700f which is what my old Weller’s tip (PTZ-7) was set to. That was always nice for smaller work on PCBs but would take a bit of time to flow a larger solder joint. That’s where I had already set my new FX-888. Can’t wait until I get my parts in. Maybe I should just look for something to break. :)-

  8. I have some really old flux that I use that is a paste that comes in a little metal tin (it says it is for electronics not plumbing) but it burns and leaves a black messy junk behind that takes a bit of cleaning to use. It seems to work well, but I am wondering if I should get something cleaner? Do you have problems with burnt flux, or maybe my iron is too hot (no temp control). Thoughts?

  9. Great video! Most of my experience thus far has been through hole so flux hasn’t been much of an issue. My FX-888 arrived yesterday and as you can imagine, I’m ready to dive into some smts. Thanks for the video!

  10. Thanks for the video, keep them coming! I just bought some unnamed liquid flux, haven’t tested it yet. It is my first flux so I don’t know what to expect… until I watched this video! Thanks!

  11. So I’m researching flux now… After reading a few spec sheets and MSDS sheets I’ve found that most flux is Alcohol and Rosin. And only 1 – 3% Rosin. Rosin is acid.

    I may try talking to Edsyn tomorrow and see if they know where we can buy this stuff in the US. The only flux I could find on their site is FL88 and the search on their site is broken.

    Also, I accidentally subscribed to this thread and received so many emails that Google decided that it’s spam now. After like 20 of them. Poor clueless Google…

  12. After watching this, I bought some tacky flux from element14. Compared to my flux pen, the tacky flux is way better! Both are no-clean types.

    1. While looking up Tack Flux I found this It’s from the people that make Tacky Flux. Their site is

      Dan I’d like to hear how that flux works for you. After playing around today I am unhappy with the Kester 2331-ZX. The Kester Paste I have does better.

      Also I noted above that I bought a T18-C3 tip for my Hakko FX-888. On smaller tips it covers 4 – 5 pins at once. Not recommended! I may run to Fry’s tomorrow and pick up something smaller. Should have bought the iron there too as it’s about $85.

      1. I think i have the same flux as in that video! It’s certainly made by ChipQuik:

        So far, I much prefer it to the flux pen I have: The flux pen uses alcohol as the solvent, which is very volitile. The flux does seem to get left behind, but without the alcohol it’s very hard to make it flow all around the joint.

        The tacky flux is a sticky gel. It does not evaporate before you even get the chip in place. It also melts when the iron touches it, making it flow all over the join. It’s tricky to get the right amount of flux – way less than I thought! I really much prefer using it to the flux pen, even if the application method is less convenient. I mean, what can beat just swiping over it with a marker?

      2. The other video I mentioned is here keep in mind this guy is a PRO. He’s using a preheater under the board. In his post on Facebook (link above) he answered my questions about what he used. I had forgot that he said he also used Tacky Flux. Also he notes that he’s using the T15-C3 (same tip as mine but for different iron). I still feel it’s too large. I’m also NOT a PRO. I suppose I’m going to order some Tacky Flux tonight and go to Fry’s later and buy a smaller tip or 2.

      3. While I am no where near as skilled as John, you can see from my video that its really not that difficult, after all I solder a FTDI in a matter of seconds with no solder clean up. Its just a matter of getting in there and doing it, it helps if you have a hot air station as you can remove and remount the ic over and over for practice. I think after a few rounds you will get the hang of it!

  13. I have been doing some SMT work for a while and just did not know that the flux really would help that much. One thing I did was strip all the SMT parts off an old board with lots of different types of SMT parts using a heat gun. Cleaned up the board and parts then re-soldered them to get some experience.

    1. Lol, nobody actually mentioned it, so I thought no one wanted it :) I will choose and contact someone in the next few hours.

      1. Oh I’m sorry… MEMEMEMEMEMEMEMEME. lol Parts arrived. I’m starting on the BP board tonight or tomorrow.

    2. I forgot he is an outtakes type and hit stop when it faded, had to watch it again thought i had alzheimers maybe.

  14. Another good video for (mainly) surface mount soldering and reword techniques is this one which is a bit dated and Pace equipment specific but contains quite a bit of useful information.

    1. Pace is great. I took their soldering course back in 1987. Yeah. I’m that old. I plan to watch that later. It’s over an hour long!

  15. Thanks for the video. I’ll have to try out the syringe stuff. I’ve been using some rosin based junk from the 80’s.

  16. Maybe some comments on all the different types of flux out there would be nice, too — e.g. you can get flux at home centers (Home Depot/Lowes), Radio Shack, auto parts stores, and real cheap on ebay from China. Are all these essentially the same thing?

    1. Most of what you find at home centers and such are for soldering copper pipe. Those fluxes are VERY acidic and should not be used for electronics. Never bought or seen flux at Radio Shack. I’d avoid really cheap flux since more than likely it’s poor quality. The good stuff is about $12 plus tax and/or shipping. And It’s pretty much a lifetime supply unless you’re Ian or Sjaak. Even so Ian said in the video his last syringe lasted 5 years or more and he passed it on to someone else.

  17. By the way. I went to Fry’s tonight and while they don’t list Tacky Flux by name on their website, they do sell it. Also they were out. :( But they did have this So I bought a pack! On the actual package it says Tacky Flux! Before the Bus Pirate build I plan to try it and also 1 or 2 of the 3 new tips I bought for the FX-888.

      1. Yeah it’s really great. Way, way better than the 2331-ZX. I’ll probably use my 2331-ZX pen for prepping through-hole jobs. I finished about 1/2 of my Bus Pirate Shield for Arduino tonight with the Tacky Flux. Expect pics of my horrible soldering sometime tomorrow. Even though I’ve been soldering since the late 1970’s this is my first attempt at SMD/SMT soldering.

  18. If you are asking about the reservoir tips then the answer, as far as I can tell, is you cannot buy them from Hakko in the US due to patents on that design. Only Pace and I think Weller sell that style tip in the US.

  19. That does appear to the the right style tip. Interesting. When I looked on the Hakko website not long ago, there was a specific note that said that style tip was not for sale in the US. Maybe that has changed or Plato has some other deal in place? Nice to know in any case. It looks like Mouser, Amazon, etc also sell that style tip from Plato.

  20. Plato makes replacement tips for a number of different irons. This particular tip is listed as fitting the Hakko 936 (among others) so it should fit the most common Chinese clones as well as the 936. I’m not sure about the newer Hakko FX888 but I think it also might work there.

  21. Hi,

    quick warning about the 2331-ZX (from sparkfun) because it’s conductive.

    You need to clean the flux after using it, because it is more conductive that you might think.

    I’ve used this to transplant a super gameboy cpu to a gameboy and it was not working after the transplant. i’ve seen like a electrolysis between cpu pins (SMT) when power was applied. anfter cleaning the board everything was working fine ..

    1. Fully agree with xray. I soldered some PCA8562 LCD drivers to some boards. They are 0.5mm pitch. They looked quite clean but they refused to work with the digits coming on and fading out. A wash in an ultrasonic bath fixed the problem. I tried a brush and IPA + various canned cleaners to no avail.
      It was easy to replicate the failure a light wipe on the pins of the flux pen brought the chip down again

      I also noted it shifts resistor values after soldering until they are cleaned. I have had no issues like this with other fluxes

  22. Is it possible to order that liquid flux online somewhere? the one from Sjaak? (I’m in Norway..)
    I have bougt two types of flux, kester 951, and the usa amtech you tested in the other test, damn be it that those two are ofcourse the worst fluxes :)

      1. That’s the same brand as the goot wick?, maybe I’ll have to ask those who sells that if they can come up with something. Or just stick with the amtech fumes :)

  23. We used liquid flux at work, but with a very tiny needle pipette kind of thing stuck through the lid. We could apply it one drop at a time, and it works really really well. Of course you have to match your flux to your solder – the flux we used worked well with SN995 but we used a different one for lead-based solders.

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