Where can I find gel flux?

[MarkS]

I'd like a source of a bottle flux that I could best describe as a gel. I've seen videos of people using it, but cannot find it. I bought a flux pen, but I'd practically have to press hard enough to crack a PCB to get anything out of it, and then trying to find the gel flux, wound up buying water thin stuff. This is pricey stuff and I'd like to not guess any further.

[Ian.M]

Gel fluxes generally don't come in bottles as their consistency doesn't permit easy pouring.  If there was no label on it in the videos, the user may have loaded a squeeze bottle from a bulk tub.

Most major component distributors will stock various brands of tacky flux gel in syringes (but check its with a nozzle and plunger for manual application).

[Someone]

Fluxes thin out when heat is applied (to wick) so but every flux syringe I have ever bought has a thickness close to honey (thicker than cream, more runny than toothpaste) at room temperature (have to warm it up from cold storage).

[mariush]

TME.eu has a bunch of fluxes , liquids and gels : https://www.tme.eu/ro/en/katalog/fluxes_100484/    and just gels : https://www.tme.eu/ro/en/katalog/fluxes_100484/?mapped_params=1682%3A1465331%3B


Not sure how many can be shipped by air to US, but some should be.
You can get "tubs" of 100 ml gel and suck it in syringes as needed, for example : https://www.tme.eu/ro/en/details/topnik-zel_100/fluxes/ag-termopasty/art-agt-089/
Or you can get individual syringes, but they're a bit more expensive

SDG Electronics has reviewed some of these and they're good.

I actually use this liquid flux,  in 50 ml bottles : https://www.tme.eu/ro/en/details/flux-tk_50/fluxes/ag-termopasty/art-agt-044/
It's good but liquid, good amount of rosin, doesn't require cleaning but leaves some residue (which can be cleaned with isopropyl alcohol, acetone, other flux removers)
It's also available in bigger bottles, like half a liter for example : https://www.tme.eu/ro/en/details/flux-tk_500/fluxes/ag-termopasty/art-agt-075/

and there's even a version without halides (less strong) in 1 liter bottles : https://www.tme.eu/ro/en/details/rf800_1/fluxes/ag-termopasty/art-agt-043/

[Ian.M]

Louis Rossmann sells individual 30ml syringes of his favourite: Amtech NC-559-V2-TF Tacky Flux.  https://store.rossmanngroup.com/amtech-nc-559-v2-30-cc-16160.html

Its not the best deal if your order can meet a major distributors' free shipping threshold, or if you have a reputable local stockist, but if you are in CONUS, will at least guarantee you wont receive fake grease from China!

N.B. As of Jan 2023, He's in the middle of a move to Texas, so you may have to wait a bit for him to ship.

[artag]

I have an Electrolube SMF12P flux pen.

It's not a gel but the flux is so runny that pressing on the tip (which pushes in, a pump action to wet the wick like many marker pens, which are similar) can make a puddle on the pcb. However for surface mount I usually use a small bottle of BLT 10-75-30-R that I bought many years ago at a radio rally/hamfest  and apply it with a small paintbrush. This flux is also as runny as water. The seller (maybe it was @Robert763 ?) had decanted it into small bottles which made it quite reasonably priced.

I only use these when I have a particularly difficult project, perhaps with tarnished copper. It is quite helpful if using plain braid for desoldering (Chemtronics braid has flux already in it). For most purposes the flux in cored solder or the flux in solder paste is more than adequate. I don't really understand the current advice to use loads of flux. It seems unnecessary.
 

[Bud]

You can buy flux paste in syringes at Digikey.

[shapirus]

Louis Rossman sells individual 30ml syringes of his favourite: Amtech NC-559-V2-TF Tacky Flux.  https://store.rossmanngroup.com/amtech-nc-559-v2-30-cc-16160.html

Any idea if it has any conductivity? I've got some NC-559 from China (yes I know) which is great otherwise, but meaures 5-10 GOhm at low voltage with the probes placed in a blob of flux ~1mm apart. Not good for high impedance/high sensitivity circuitry.
I wonder if it's worth it to try ordering the apparently original flux from the USA.

[artag]

Perhaps I'm unreasonably fussy, but if I had a circuit needing gigohm isolation, I'd expect to have to clean the board rather thoroughly.
 

[Ian.M]

+1.  Louis puts all his repaired boards through an ultrasonic cleaner after rework, so he doesn't care about the conductivity, which is a good thing as he's notorious for the amount of flux he uses.

Also, unless that blob of flux has been heated to reflow temperature for long enough to drive off all volatiles and fully activate the flux, you can *EXPECT* some conductivity - and the same is true for the majority of (if not all) fluxes.

[shapirus]

Perhaps I'm unreasonably fussy, but if I had a circuit needing gigohm isolation, I'd expect to have to clean the board rather thoroughly.

I can see how it can be a problem with high-impedance op amp inputs and high-impedance signal sources. Besides, its resistance is proportional to distance, so it'll be lower where clearances are tighter. I actually experienced problems created by a conductive flux, and even though in that case it was of the order of tens of megaohms, I now avoid fluxes that are even slightly conductive.

I clean all my boards anyway, but some hard to reach spots will always remain uncleaned, so cleaning does not solve the problem completely.

Finally, there are many fluxes that don't conduct at all (at least at low voltages), so there is no reason not to reject one that measures higher than 0.0 nanosiemens. But many of them have other disadvantages: some produce too much fumes, some are very hard to clean with IPA or wash off the hands after an occasional contact, etc. So I am still in search for my holy grail.

[shapirus]

Also, unless that blob of flux has been heated to reflow temperature for long enough to drive off all volatiles and fully activate the flux, you can *EXPECT* some conductivity - and the same is true for the majority of (if not all) fluxes.

This is a valid point. However, between the flux that measures non-zero (I use nanosiemens range of my DMM) and that measures zero, I pick the latter, and there are many of the second category.

Anyway, if someone has had a chance to measure the NC-559 mentioned above, I will appreciate if you simply share the numbers.

I'm not feeling like getting into a discussion on how much of an actual problem the flux conductivity is, since it's a matter of personal preference, to a certain degree.

[ygi]

+1.  Louis puts all his repaired boards through an ultrasonic cleaner after rework, so he doesn't care about the conductivity, which is a good thing as he's notorious for the amount of flux he uses.

Also, unless that blob of flux has been heated to reflow temperature for long enough to drive off all volatiles and fully activate the flux, you can *EXPECT* some conductivity - and the same is true for the majority of (if not all) fluxes.

Considering Louis works exclusively on macbooks boards and those always look rusty/tarnished for no reason (or overcooked if "refurbished" by Apple), it makes sens to ultrasonic them regardless of flux abuse.

[Bud]

I had issues with flux conductivity even in such trivial cases as using it on optocouplers. The board behaived weird until i washed the flux off.

[Ian.M]

Considering Louis works exclusively on macbook boards and those always look rusty/tarnished for no reason (or overcooked if "refurbished" by Apple), it makes sense to ultrasonic them regardless of flux abuse.

There's also the time is money issue - his shop has historically been in midtown Manhatten NY, less than half a mile from the Empire States building, and the Big Apple has historically been notorious for the highest average commercial rents in the USA, so his overheads must have been horrendous.  If using flux by the bucketful saves only five minutes per board, vs taking the time to painstakingly apply just enough flux, and you've got work queued up, with those overheads you'd be mad not to apply it 'Louis style'.

[wraper]

Louis Rossman sells individual 30ml syringes of his favourite: Amtech NC-559-V2-TF Tacky Flux.  https://store.rossmanngroup.com/amtech-nc-559-v2-30-cc-16160.html

Any idea if it has any conductivity? I've got some NC-559 from China (yes I know) which is great otherwise, but meaures 5-10 GOhm at low voltage with the probes placed in a blob of flux ~1mm apart. Not good for high impedance/high sensitivity circuitry.
I wonder if it's worth it to try ordering the apparently original flux from the USA.

Genuine Amtech and Chipquik gel fluxes I tested are no better in this regard. And using them for manual soldering does not guarantee fully heating them to nullify conductivity. On other hand Ersa gel flux (super expensive) and Alpha OM338 are non conductive even in initial state.

[thm_w]

I'd like a source of a bottle flux that I could best describe as a gel. I've seen videos of people using it, but cannot find it. I bought a flux pen, but I'd practically have to press hard enough to crack a PCB to get anything out of it, and then trying to find the gel flux, wound up buying water thin stuff. This is pricey stuff and I'd like to not guess any further.

You get something in a syringe, no guessing required:
https://www.mgchemicals.com/products/soldering-supplies/soldering-flux/soldering-flux-paste/

I'm not feeling like getting into a discussion on how much of an actual problem the flux conductivity is, since it's a matter of personal preference, to a certain degree.

Its a problem only for very sensitive analog circuitry, maybe RF gear, and then beyond that its a matter of personal preference, sure.