Best Solder Flux??

[Mr Simpleton]

So what is THE best solder flux?? And where to get it??

Do I need to use different flux when soldering lead-free??
Clean or no-clean?
Same stuff for solder and de-solder?

I did a quick search on the web but came up with pretty useless information... so I'm turning to the expert mob 

Guess this still holds true: "Stay away from water soluble or no-clean fluxes" from https://www.eevblog.com/forum/beginners/good-solder-paste-and-flux-pen/15/
But why is no-clean to be avoided??

[David Hess]

No clean flux is acceptable on new parts and boards.  If they are old, then surface tarnish will cause problems.

Water soluble flux must be cleaned or it will cause corrosion.

I prefer fully activated rosin flux like Kester 44 for both assembly and rework.

On difficult to solder connections, I use dilute hydrochloric acid or if you can get it, Kester 5520 Copper-Nu.

[suicidaleggroll]

I rarely (read: almost never) have any need for separate flux.  I exclusively use Multicore 60/40 rosin core solder (eg: MM00992), which has plenty of no-clean flux inside and flows with the best of them.  Clean the flux immediately, clean it after a few years, never clean it, it really doesn't matter.  I've cleaned boards soldered with this solder/flux literally 3+ years after soldering them, and there is no visible difference between them and those cleaned immediately (though, admittedly, it is significantly more difficult to clean them after a few days, but soak them in some isopropyl and it comes off pretty quickly).  Definitely avoid the water soluble as it'll eat your board, but no-clean is just fine.  I don't know why marshallh in the link you posted said to stay away from no-clean, all of his pictures, opinions, and evidence was about water soluble.

[sleemanj]

The cheap 10cc flux syringes out of China are very good, usually sold as "Amtech RMA223-UV", they are not real Amtech (like any branded product out of China is real), but the flux inside works very well.

[nanofrog]

Although I prefer Kester (186-18), the smallest bottle is 1 gallon and the disposable pens are pricey for what you get. Fortunately, MG Chemicals Rosin 835 is an excellent RA flux (activated rosin; similar to Kester 1544) that comes in hobbyist friendly sized containers (100ml & 1L).

Also, a fiberglass scratch brush can be very handy at removing heavy oxidation and corrosion.

[VK5RC]

For small jobs,  I vote for Electrolube flux pen e.g. http://uk.farnell.com/electrolube/smf12p/flux-pen-12ml/dp/891186

[GreyWoolfe]

Although I prefer Kester (186-18), the smallest bottle is 1 gallon and the disposable pens are pricey for what you get. Fortunately, MG Chemicals Rosin 835 is an excellent RA flux (activated rosin; similar to Kester 1544) that comes in hobbyist friendly sized containers (100ml & 1L).

Also, a fiberglass scratch brush can be very handy at removing heavy oxidation and corrosion.

I use the same flux dispensed by a small squeeze bottle with a needle on it.  Excellent wetting and cleans easily with IPA and a toothbrush.

[Mr Simpleton]

Thanks all for the information.
So it seems no-clean flux should do the works... and just have to find a local supplier that doesn't want arm+leg for a small bottle.

For those who do not use flux... try flux plus solder wick when removing through hole IC's and this with plated vias. Pure magic

Cheers

[nanofrog]

Thanks all for the information.
So it seems no-clean flux should do the works...

Actually, everything mentioned is rosin based (w/ varied levels of activation, RMA and RA).   

[zapta]

For those who do not use flux... try flux plus solder wick when removing through hole IC's and this with plated vias. Pure magic

Cheers

Yes, good flux is magic. It takes the crustiest solder and makes it flow and shine like mercury.

[marshallh]

MG Chemicals 835P. This is a rosin flux that does not corrode, even if you leave it on for ages. Cleans up with 99% iso.

Do NOT use chinese no clean fluxes. Avoid all water soluble or no clean fluxes unless you can be sure you will properly activate all components of the flux (usually requiring the full heat of a reflow cycle). Just soldering a QFP or something with an iron is going to leave behind lots of corrosive, nasty unactivated flux which will ruin your PCBs in short order.

[zapta]

Avoid all water soluble or no clean fluxes unless you can be sure you will properly activate all components of the flux (usually requiring the full heat of a reflow cycle). Just soldering a QFP or something with an iron is going to leave behind lots of corrosive, nasty unactivated flux which will ruin your PCBs in short order.

I didn't know the the 'no clean' property is conditional. Good to know. Looks like a case of misleading marketing. Should be called 'no clean*' with a footprint at the bottom.

[nanofrog]

Avoid all water soluble or no clean fluxes unless you can be sure you will properly activate all components of the flux (usually requiring the full heat of a reflow cycle). Just soldering a QFP or something with an iron is going to leave behind lots of corrosive, nasty unactivated flux which will ruin your PCBs in short order.

I know water soluble is corrosive after soldering so must be cleaned off, but can't recall anything like this with no-clean formulations.  Everything I can recall had similar results to rosin; active when heated, but not at room temp (flux residue is complete, no issues from a partial cleaning).

Can you elaborate (Chinese origin? rosin content vs. those with zero rosin content?)?

[xavier60]

The cheap 10cc flux syringes out of China are very good, usually sold as "Amtech RMA223-UV", they are not real Amtech (like any branded product out of China is real), but the flux inside works very well.

This claims to be AMTECH Soldering Flux Paste RMA-223-TPF(UV), https://www.ebay.com.au/itm/AMTECH-Soldering-Flux-Paste-RMA-223-TPF-UV-10CC-USA-Free-Needle/262244648798?epid=1040520771&hash=item3d0effc75e:g:W-gAAOSw2s1Uy3cD

What ever it really is, it appears to be real RMA flux. Measured with a high voltage insulation tester, the resistance dips sharply when heated then becomes virtually non-conductive when cooled. This indicates that it's Active.
 Its volume reduces to form a gummy residue which I assume is Rosin.

This stuff, https://www.ebay.com.au/itm/293180883673, has no indication of Activity and does not change its consistency after being heated, just spreads into a greasy mess.
Oddly, using it for hand soldered joints on new components and PCB makes nice joints.

[MarkF]

It has been discussed here:
   https://www.eevblog.com/forum/manufacture/flux-recommendation/msg2687040/#msg2687040

[Miti]

Coming from a manufacturing environment, I can tell you this. Avoid any flux from a bottle unless you can clean it completely afterwards. Both WW and NC are corrosive and conductive, and need immediate removal. Water wash needs, well... washing and no clean needs to be cleaned with a proper flux remover. And hear this out, IPA is NOT a proper NC flux remover.
No clean needs to be activated to stay on the board, and that only happens through a reflow oven. The excess flux that you pour from a bottle can never be activated completely with the soldering iron. The core flux can.
I remember a big fiasco with one of the products we were making few years ago where a coax connector, MCX type if I remember correctly, was hand soldered using excessive NC flux then the area was cleaned with IPA. The connector was carrying 5V to supply an external active antenna. A big number of boards were failing with the same symptom, short inside the coax connector.
I was in charge with investigating what was going on. What I found was that the flux was somehow getting inside the connector and during the functional test it started the electrolysis that created an initial carbon path. Later in the field, that turned into an almost dead short.
My boss couldn’t believe my theory, he thought we were dealing with bad raw parts. I had to duplicate the fault. Using two twisted wires with stripped ends, a drop of flux between them and a 5V power supply, I had a dead short within 15 min or so. The functional test was shorter than that.

Edit: Water wash flux is amazing for assembling new boards; if all the parts are washable, I always use WW flux. I end up with super clean boards, with shiny solder, that work as they should. The NC boards never look... clean. For repairs and wires though, I always use RA flux and clean it as much as I can with IPA.

[Conrad Hoffman]

There is no "best" flux. There is only flux suited to the application. In general I build new boards with Kester 331 water washable and properly wash the boards within a short time after building them. Kester 245 no-clean is really a minimalist rosin and requires no cleaning. It is not corrosive or conductive AFAIK, and as stated in their docs. I use it for some builds and for rework if the board can't be re-washed. For thru-hole and large or old stuff, I still like Kester 44. It's always appropriate to add a suitable (matching) flux if needed. I once watched a certified NASA solderer work and extra flux was almost always used. I use Kester or other established and well known brands. Unknown solder alloys and fluxes aren't worth the risk.

[obiwanjacobi]

For small jobs,  I vote for Electrolube flux pen e.g. http://uk.farnell.com/electrolube/smf12p/flux-pen-12ml/dp/891186

That is what I use too. But I sometimes have need for flux that is less runny - more gel-like.

So 'best' depends on what you're doing IMO.
[2c]

[ConKbot]

Coming from a manufacturing environment, I can tell you this. Avoid any flux from a bottle unless you can clean it completely afterwards. Both WW and NC are corrosive and conductive, and need immediate removal. Water wash needs, well... washing and no clean needs to be cleaned with a proper flux remover. And hear this out, IPA is NOT a proper NC flux remover.

+1 to this. I've had battery management PCBs that were spotless before going to pack assembly come back green and fuzzy a week later because they were poorly cleaned. The rosin residue would have been fine if left as is, or removed fully. But only partially removed, and disturbed by cleaner, it picked up moisture, galvanic corrosion, copper salts pick up more moisture, and the cycle accelerates.

If flux is going to be cleaned, it needs to be cleaned fully. If no-clean or RMA is going to be left, it needs to be heated and activated fully. No middle ground.

[GeorgeOfTheJungle]

https://www.ebay.co.uk/itm/142428156973



 

[eliocor]

CHIPQUICK SMD291
https://www.chipquik.com/store/product_info.php?products_id=310003
in several options: https://www.chipquik.com/store/index.php?cPath=300_310

[glideher]

hey all,  wondering what the best solder with flux core is used for electronics?
is there a specific brand name and is 2% flux in a core the maximum ?
thanks for all the help

[SiliconWizard]

CHIPQUICK SMD291
https://www.chipquik.com/store/product_info.php?products_id=310003
in several options: https://www.chipquik.com/store/index.php?cPath=300_310

I use that too for hand-soldering jobs.

[tooki]

hey all,  wondering what the best solder with flux core is used for electronics?
is there a specific brand name and is 2% flux in a core the maximum ?
thanks for all the help

There are countless discussions about solder recommendations on this forum. Do a search for them.