What the Flux

[msknight]

Ok – here we go. Flux. I know I’ve got a problem.

For some while I’ve been using Fry Fluxite, applying with a toothpick and cleaning with isoprop and a toothbrush, but it clumps into brown stuff which isn’t easy to get off the board.

You know… I’ve got a funny feeling I’ve been using the wrong stuff for electronics. Please stop chuckling. 

I’m starting to try CW8100 no clean flux pen; not that cheap but so far I like it. I also watched SDG’s flux video and started wondering. I’m reading from things that “no clean” means non-acidic so doesn’t need to be, “deactivated” by heat and is safe to leave on the board.

I’m UK, so that factors into postage and prices.

The CIF No clean can be had from Farnell for about £15, but it seems that quite a bit is applied to the joint and I’m wondering how long 10cc will last at that price. (actually, two tubes+VAT and delivery… £33.20)

The Banggood can be had about £9 delivered for three tubs of 150g (1 tub is £6.45, so three is cost effective) but it isn’t no clean. I’m wondering whether it will just do the same as the Fry when I attempt to clean it off… although I have read some discussions where people don’t bother to clean their flux off. The best I can find on the details is, “IC and PCB for no corrosive” so I’m reading that as non-acidic… because I do wonder how much damage I can do with isoprop and a toothbrush, particularly with the quantities I’ve had to apply to clean off the Fry.

Incidentally, there was another version of the ZJ-18 at 50g and a silly price, but looked to have more rosin.

Refillable flux pens are knocking up towards 3 digits in the UK for anything decent… there are e-bay versions but I do wonder. In among my concerns for that is how long the tips last… and that’s before getting into the discussion of liquid types and mix ratios.

It seems that getting good results for hobbyists who are a little tight on the purse strings, is an ongoing battle. Grateful for anything that people can add to my thoughts please, because so far it seems like the flux is ramping up to potentially be the most expensive part of this hobby.

[jpanhalt]

Water in your isopropyl alcohol (IPA) will make a big difference in its solvent properties.  I use absolute ethanol and may add a little acetone.  Do you use 99+% IPA?

I have been experimenting with lower members of a different class of solvents called "cellosolves."  They seem to work with a surprising amount of water present (up to 50%).  If you look at the datasheets for various household cleaners, such as floor strippers, you may find butyl cellosolve.  That may work for you, but it is slow to evaporate.  A good rinse with IPA will cure that.  If you want to go down that route, I have more information to share.  I currently use ethyl cellosolve, which I don't believe is in household cleaners.   Somewhat related, some automotive brake fluids have also been reported to work.

Edit: corrected typo due --> use

[msknight]

Yes, I'm using this - http://www.farnell.com/datasheets/3165616.pdf - 99.7% minimum... although it is so old I can't remember actually buying it.  It is nearing the end of the 1L can, and I do have some Acetone that I bought recently RS Pro - RS 918-1082 which seemed to be the only thing available as I was about to spend pennies on some capacitors at RS and needed to bulk up the shopping cart.

[tooki]

I’m starting to try CW8100 no clean flux pen; not that cheap but so far I like it. I also watched SDG’s flux video and started wondering. I’m reading from things that “no clean” means non-acidic so doesn’t need to be, “deactivated” by heat and is safe to leave on the board.

No, that is absolutely incorrect. No-clean means the residues are safe to leave on the board after reaching soldering temperatures, which is not guaranteed when using external flux while hand-soldering. I have done testing with a bunch of no-clean fluxes, and all of them cause some amount of corrosion where they’ve been partly heated (hot enough to activate, but not hot enough to neutralize again), as happens towards the edge of a solder joint.

Water in your isopropyl alcohol (IPA) will make a big difference in its solvent properties.  I use absolute ethanol and may add a little acetone.  Do you use 99+% IPA?

Pure IPA is ineffective for many modern fluxes, resulting in the white residue people complain about. Those are salts that aren’t soluble in IPA — but are soluble in other solvents (which is why commercial flux removers work better) as well as in water, which is why some people actually prefer to use a 70% IPA rinse.

IMHO, the performance of commercial flux removers on modern fluxes is so much better than straight IPA that it’s not worth bothering with the latter. My time is worth it, and you also don’t need to use nearly as much of it.

[jpanhalt]

White residue can be a problem.  Here is the best discussion of it I have seen: https://www.kester.com/Portals/0/Documents/FAQs/White_Residue.pdf

Bottom line:
1) Pick a flux that works for you.  I use a classical rosin flux from Kester.
2) Then pick the way you plan to clean it.

As for your 99.7% IPA, water may not be the problem.  IPA may just be the wrong solvent for your flux.   BTW, absolute ethanol and IPA (anything with a greater concentration of alcohol than the water azeotrope concentration) will be hygroscopic.  That is, it will absorb moisture from the atmosphere to approach the composition of the azeotrope.  That has been my impetitus for looking for cheaper and better solvents, as my absolute ethanol is from a large stash I inherited 20 years ago.  Plus, I am looking for a solvent that will work with a little water and help with the salts.

[agehall]

My £0.002:

Flux pens are absolute garbage. They probably have some use but I sure have not found it yet. I went down that route when I started out as it seemed like an easy way to dispense flux but once I had tried “real” sticky flux that pen went into the trash can. Buy and use good flux - it will help a lot. And don’t buy flux from eBay or Banggod - get it from reputable sources. I’m a die-hard AmTech 559 fan but I’m sure many other fluxes works too.

For cleaning, I’ve used IPA (99.9%) and a brush. Takes a bit of work to get the boards clean but it works. Far from optimal though. I think a commercial flux remover would improve things quite a bit but I recently stepped up to doing ultrasonic cleaning with proper cleaning solution and it is amazing. After that, I rinse the boards in IPA and dry using a bit of hot air (hot air station or the oven, depending on number of boards).

[imk]

I find these pretty good, shop around for better price
https://uk.farnell.com/chemtronics/cw8100/dispensing-pen-flux-no-clean-9g/dp/130692?gclid=CjwKCAjw2ZaGBhBoEiwA8pfP_nfryA151n205nJ30hKZrgYpoL0SRLMxsvpuDRZw2h4zzO8iDx4_cRoCWEgQAvD_BwE&mckv=sY3qwPD9Y_dc|pcrid|377975140503|kword|cw8100|match|p|plid||slid||product||pgrid|5262984128|ptaid|aud-132169620549:kwd-1704272756|&CMP=KNC-GUK-GEN-SKU-MDC-Test717

[tooki]

My £0.002:

Flux pens are absolute garbage. They probably have some use but I sure have not found it yet. I went down that route when I started out as it seemed like an easy way to dispense flux but once I had tried “real” sticky flux that pen went into the trash can. Buy and use good flux - it will help a lot. And don’t buy flux from eBay or Banggod - get it from reputable sources. I’m a die-hard AmTech 559 fan but I’m sure many other fluxes works too.

They're not garbage, they're a great way to place liquid flux. And of course, the pen is only the dispenser: the performance of the flux depends entirely on what type of flux it's filled with!!

What is true is that liquid flux and paste/gel/tacky fluxes aren't interchangeable. The latter are much better for longer soldering/rework processes like hot air. But the downside is cost and the amount of residues that must be removed.

Liquid flux is great for when you need short-lived fluxing action. For example, it's perfect for tinning wires, and for helping solder flow through plated through holes just a bit better.

In general, I find myself using liquid mostly for initial soldering, and tacky for rework. My favorite liquid so far is Almit RC-15, and my favorite tacky is SMD291 from ChipQuik (it doesn't create the acrid smoke of most tacky fluxes, but instead smells like roasted hazelnuts!).

[Ian.M]

Your Fry Fluxite is an acid zinc chloride activated paste flux and is absolutely unsuitable for electronics and general electrical work due to its highly corrosive residue and the difficulty of removing that residue from fine crevices e.g. under components or between wire strands.   Its good for sheet metal work, plumbing etc. where the base metal is much thicker so more corrosion resistant, and cleanup with boiling soapy water is practical.  Everything electronic you've assembled with it is a corrosion timebomb - stranded wire is  unsalvageable unless you can cut back the ends at least 6", and PCBs *may* be salvageable if you can wash them in a very hot cleaning solution in an ultrasonic cleaner, rinse with a hot water jet, then distilled water then IPA, shaking off as much liquid as possible between steps, dry thoroughly at 90 deg C then immediately lacquer the board to prevent any remaining residue and corrosion products adsorbing atmospheric moisture again and reactivating the corrosion.

Most Rosin R and RMA fluxes are much easier to clean than so-called no-clean fluxes and if used sparingly, liquid rosin R and RMA halide-free fluxes can usually be left uncleaned except on high impedance or high voltage circuits.  Also, nearly all Rosin fluxes are compatible with each other which makes life simpler if you are working with cored solder or solder paste, and need to add extra flux.

Rough cleaning of Rosin liquid and gel fluxes and Rosin flux from cored solder or solder paste can be done with ordinary commercial grade denatured alcohol, as long as, once satisfied you've got as much flux off as you can, you shake off as much liquid as possible then finally scrub with the far more expensive 99% IPA or proprietary flux remover to remove the denaturants in the alcohol + any flux residue that wasn't readily soluble in the denatured alcohol.  In the UK, look for Methylated Spirits or Alcohol Stove Fuel to get denatured alcohol affordably in relatively small quantities.

Whatever you use for manual flux removal, its essential to use enough solvent for the excess to run off the edge of the tilted board as you scrub, or to blot it up with a lint-free wipe while still wet, so the flux is carried away.  If let dry on the board without thorough rinsing, you'll just redistribute the flux residue and cause major surface leakage problems, worsening as dirt builds up on the residue film.

[tooki]

Just a thumbs up to Ian.M’s great advice. 

[mindcrime]

If this thread has done nothing else, it has persuaded me to order a bottle of real purpose-specific flux remover instead of just blindly relying on IPA. 

[mawyatt]

Agree interesting thread, and very helpful!! For prototype PCBs been using the usual alcohol & toothbrush approach with limited success. Using a proper flux remover as a final scrub & since seems like a good approach as mentioned. What are the popular flux remover solutions that work well and useful for just prototype scrubbing, the one mind crime mentioned seems like a good candidate.

Best, 

[jpanhalt]

I looked up the MSDS/SDS for Chemtronics ES135 and MG Chemicals 4140A and 413B.  Chemtronics was a mixture of hexanes (10-50%), ethanol, IPA, and propyl acetate (0.1-3).  Wonder whether the latter is for fragrance.

MG Chemicals lacked the hexanes, had HFC134A (about 30%, presumably as a propellant), ethyl acetate, acetone, and IPA with or without ethanol.

I wonder whether the cheapest "first wash" might be E85 fuel in the US at <$3/gallon.    You might add a little ethyl acetate, propyl acetate, or butyl acetate to cover the smell and have ES135.

[tooki]

I looked up the MSDS/SDS for Chemtronics ES135 and MG Chemicals 4140A and 413B.  Chemtronics was a mixture of hexanes (10-50%), ethanol, IPA, and propyl acetate (0.1-3).  Wonder whether the latter is for fragrance.

MG Chemicals lacked the hexanes, had HFC134A (about 30%, presumably as a propellant), ethyl acetate, acetone, and IPA with or without ethanol.

In a notebook somewhere I have a handwritten table of various brands of flux removers and their contents, compiled a few years ago from the MSDSes. They vary quite a bit, other than generally being an IPA and/or ethanol base, usually some hydrocarbon (like hexane), and often something else (like orange terpenes or acetone).

Acetone is usually only in the most aggressive ones, and should be considered a cleaner of last resort, since acetone can attack a lot of plastics and inks.

I wonder whether the cheapest "first wash" might be E85 fuel in the US at <$3/gallon.    You might add a little ethyl acetate, propyl acetate, or butyl acetate to cover the smell and have ES135.

Cheap yes, but I'd be very leery of it being pure enough, not to mention all the additives in motor fuel.

What I have used as a first wash is brake cleaner and canned "industrial cleaner" that's similar solvents. But in the end it's just not really worth the effort to keep so many different things around.

[coppercone2]

get a stiff brush (horse hair cut short)

spray alcohol or better yet flux cleaner on pcb

scrub it with the brush like you are scraping paint

dab with a kim wipe

spray fresh cleaner

scrape and dab more, clean your brush by wiping it on a kim wipe after you soak it in alcohol from a alcohol dispenser to keep it clean

continue to use rosin flux which kicks ass

the tool you want is basically a scaler, not a brush.



you get a real short stiff brush so you can do like that video. you need to like poke the residue to dislodge it, it often does not work when you just soak it. the brush should be 3mm long bristles facing towards the front (not a trim down right angle brush) so you can properly scrape

i know the video shows a metal scaler but the same principle works for flux with a brush doing it manually.

good soldering should end the work bench looking like a fucked up trauma ward full of nasty used absorbents. I think the more aggressive fluxes result in higher quality joints, I often see better wetting with less heat and time.

[tooki]

coppercone, you pretty much exactly described my flux cleaning process, including what the bench looks like afterwards! 

[SteveyG]

The CIF No clean can be had from Farnell for about £15, but it seems that quite a bit is applied to the joint and I’m wondering how long 10cc will last at that price. (actually, two tubes+VAT and delivery… £33.20)

I feel it's important to point out that generally speaking, you don't need to apply much flux at all when soldering. Many of the techniques seen on YouTube are contrary to standard soldering practices - that includes my own video comparing the fluxes. I meant to add a disclaimer at the time that I have purposely saturated the pins of the ICs to keep everything consistent.

Unless you do lots of soldering daily, a 10 ml syringe of flux will last a long time - 6 months+.

[bobbydazzler]

Anyone tried an electric toothbrush?

[coppercone2]

yeah but I got paranoid about ESD and it just does not work as well as a stiff brush cut at a sharp angle (think chisel). the scraping action dislodges flakes of flux, which dissolve in the excess alcohol, and are wicked by tissues

if you are brushing it like your teeth its just being tickled. I find you get stuck on burn flux parts, bigger flux deposits, etc. you want to 'plow'


use a grid system to methodically clean it up rather then trying a bulk approach