Flux Etiquette?

[winterturtle]

Pondering my process with a lot of iron-time imminent...

I've not done much PCB soldering but I have seen discussed the need for a chemical flux solvent to clean after the work to prevent corrosion. I saw this in reference to changing electrolytics on the board of aging automotive computers.

To date I've only ever really cleaned up the remaining residue with a dab of paper towel. Have I been leaving a trail of corrosion-based destruction in my negligent wake?

Wondering what others' process is =)

[sluckey]

Acid core solder meant for plumbing is corrosive and should never be used in electronics. Rosin core solder meant for electronics is not corrosive. Flux is your friend when soldering. In addition to the flux in the solder, I keep a bottle of liquid flux and paste flux right beside my roll of solder. I keep a spray can of flux remover handy. When building a new board, I wash with mineral spirits and/or denatured alcohol. An assortment of small brushes helps.

[acheld]

I've not done much PCB soldering but I have seen discussed the need for a chemical flux solvent to clean after the work to prevent corrosion. I saw this in reference to changing electrolytics on the board of aging automotive computers.

To date I've only ever really cleaned up the remaining residue with a dab of paper towel. Have I been leaving a trail of corrosion-based destruction in my negligent wake?

It depends on the job at hand.   For turret boards, I clean the flux off of the board with denatured alcohol, and it's for appearance only.  Assuming my solder joints have been well done.  And yes, I use plenty of flux (liquid, pen, paste . . .)

PCB's are a different animal, especially when the dreaded surface mount components are in play.   Because all component connections are much closer together, you really want to keep excess flux off of the board -- although rosin based flux is not corrosive (as Sluckey mentions) itself, it can retain moisture in the long term and by doing so cause corrosion.  It also hides mistakes.   So yeah, PCB's need to be cleaned IMO, and the more modern (eg, compact) the board, the more important it becomes.   

If you're interested in surface mount repair, take a look at Northridge Fix on YT.   It's another world entirely.  My hands shake too much for that!

I'd be interested in the brand of flux spray remover that Sluckey uses.   

[labb]

Is flux conductive?

[winterturtle]

I have used Chemtronics Flux Off -- for the automotive PCB board application I mentioned.

I am gonna have to separate all my plumbing and electronics supplies. I feel very dumb all of a sudden...

I checked a cap job I did in mid-2022 -- at least I don't think it looks corrod-ey. I may come behind and try to Flux Off for good measure...

[winterturtle]

Is flux conductive?

I think no?

Though I have demonstrated my dunce-hood in this thread =/

[acheld]

Is flux conductive?

No.

I am gonna have to separate all my plumbing and electronics supplies. I feel very dumb all of a sudden...

Don't feel that way.    In the past, we all used similar products for plumbing and electronics -- well maybe the flux was different -- but lead was in everything.

Now, plumbers don't solder very often it seems like, and if they do, they use pain in the ass solder that has no lead.  Oh boy that stuff is tough to do well (for me, anyway) .

Valve amps -- of course we rely on Kester 44 or equivalent, and different types of flux that may or may not need cleaning, and as long as it looks good and you have a good solder joint, you're ok.

PCB's from the 70's through the 90's, pretty similar requirements.

Surface mount boards -- whole different world with different low temperature solders, magic flux, and a requirement that the work be clean.   You are probably not going to use an iron much -- use a hot air gun instead, or a frying pan to reflow.  And your solder may be a paste.     You probably need a microscope for some of this work, and steady hands.

So each job has become very different over the past 20+ years. 

[labb]

I think that flux is conductive and one need to make sure that you clean good. For sure on joints that are close to each other and not over use. But then I’m just an old builder so could be wrong.

[glass54]

Is flux conductive?

Good question 
I have seen a "swamp" of flux left on PCBs and surprisingly still functional 
In the mid 90's I was locating a silly fault in an audio router, which had "programmable" solderable pads located between FETs, I eliminated the bleeding audio (on one leg of balanced line switcher) by cleaning the pre-used pads with de-natured alcohol. I am not saying the resin core flux is corrosive BUT in can become partially conductive thus creating a bleed of signal.
At that time, I had already done a NASA certified soldering course (Canberra, Australia) where cleanliness of soldering/post soldering is paramount so I always like to leave a soldered joint shiny and free of flux debris. This includes Turret boards, clean is pleasing to the eye.
Its also important to see quality of "wetting" to eliminate dry, improperly flowed joints esp on SMD ICs.
I use a nice clean (new) toothbrush to assist with stubborn flux.
...and alcohol is good BUT don't drink it and use it in a well ventilated area 
Regards
Mirek

[JPK]

I clean all my component leads with DeoxIT D5 and paper towel before soldering. Same with any ground lugs, terminal strips. Then use Kester 951 flux pen to apply flux to anything I solder. I probably should clean turrets on the turret board but I don't. They just get fluxed. The less contaminated stuff is, the better the solder joint.

[HotBluePlates]

... I have seen discussed the need for a chemical flux solvent to clean after the work to prevent corrosion. ...

To date I've only ever really cleaned up the remaining residue with a dab of paper towel. ...

As Sluckey said, you can use alcohol to clean up rosin flux.

I worked briefly at a PC board manufacturing plant.  They used water-soluble flux (mostly) in their solder, and the flux was scrubbed off with distilled water & a small brush.  The board was then thoroughly dried with compressed air before being powered.

You can leave flux, but you can also clean up any residual flux, and manufacturers often do the latter.

Is flux conductive?

I think no?

Flux itself isn't conductive, but it can be sticky.  Could be that dust & other stuff settles on excess flux and starts forming a sneak-path that means the ∞Ω between 2 points something much less than ∞Ω.  Then again, it might take a long time for that to occur.   

[labb]

If you do a Google search of ‘is electronic flux conductive’ it will come back with a ‘yes’

[acheld]

Well Mr. Google is not always correct -- their AI answer programs depend on sources such as forums (including this one).  The answer to that search, of course is not a simple yes/no.

However, for point to point and turret board board construction of valve amps, using a standard rosin core solder +/- additional rosin flux, the answer is a flat no.  Flux is not conductive in these builds.   I'm sure someone will find an exception, but that's what it will be -- an exception.  Yes, you can make a mess and pay for it later.

Obviously, you have to add some context to the answer.  For example, Fender eyelet boards are non-conductive at the factory.   But, add a bunch of solder, flux, time, heat and humidity, and they certainly can become conductive.

PCB's, especially when surface mount components are present, and even more so when non-leaded solder is used (with more aggressive flux!), DO require cleaning after work is done.  Leaving the flux can and does cause problems with corrosion and it can be conductive. 

I've used Chemtronics products over the years, and their website has great information.  Check out https://www.chemtronics.com/essential-guide-to-flux-for-soldering-electronics

[sluckey]

Flux removal is very important with high density boards such as found in computers, cell phones, etc. Not as big a deal with antiquated tube point to point circuits.

[kenzen]

I use q-tips dipped in isopropal alcohol to just clean up the localized flux build up around the solder joints.  I keep a supply of the long wooden stem q-tips for this purpose.

Ken

[shooter]

as Sluckey pointed out, context is everything
If I found flux inside a 300A high density, switch mode PS, it would bother me, on the speaker connections in my trunk, wouldn't notice.