flux advice

[algorithm]

What flux do you suggest?

I have lately been looking back on some failed projects and noticing what looks to be flux left over. (on the other side of board, beneath a chip, between legs, etc.)
I worry that this flux could have been the reason these projects failed, a knowledgable friend a long time ago told me flux was conductive.
I am unsure what sort of flux I am even using. I know it is really old though.

Could types of flux cause failure if too much was applied, or if some was not cleaned entirely properly?

Thanks!

[GreyWoolfe]

I use MG Chemicals liquid rosin flux.  I apply it with a small squeeze bottle and an 18 ga needle.  For even more control for small amounts I use a hypodermic needle with the same 18 ga needle.  Both work well and flux doesn't go anywhere I don't want it to go.

[nanofrog]

What exactly are you using?

I ask, as rosin and no-clean fluxes are designed to be non-conductive, and inert if left on the PCB (only become active with heat). Partial cleaning can be bad though, as that can leave the acids behind which will cause corrosion.

Water soluble OTOH, tends to be conductive as well as corrosive. Must be cleaned off, or it will corrode your joints in time (hours), even if it's not conductive. Definitely not the best choice for hobbyist use, and recommend skipping it entirely.

Also, where you're located would help, particularly with links. If you go into your user profile and set your country, your nation's flag will display beneath your userID. Makes things a lot easier for everyone IME.

Flux residues and what to do about them (.pdf) can offer more details if you're interested.

Personally, I use rosin, preferable RMA. There's all kinds of ways to dispense it (disposable or refillable pens, brushes, needle bottles, brush bottles, Bon-Kote brush pen). As mentioned MG Chemicals is good stuff, and available in sizes handy for the hobbyist (125ml & 1L sizes). Not very expensive, and will last you a good while if stored properly.

Other major brands, such as Kester, only come in disposable pens and large bottles (1 gal/4L & larger). Pen's aren't very cost effective, and the latter is usually way too much for a hobbyist to use in any reasonable amount of time (save perhaps a group buy of a large container, and someone is responsible for repackaging it into smaller bottles & shipping it out).

[BillWojo]

What flux would you suggest for occasional hobby use? I look on Ebay and everything seems to be made in China.

BillWojo

[IanB]

What flux would you suggest for occasional hobby use? I look on Ebay and everything seems to be made in China.

BillWojo

MG Chemicals liquid flux as mentioned above. I also have Kester and DeoxIT paste fluxes in small retail containers and both work fine. All are rosin fluxes.

Rosin flux is the kind you need for home soldering.

[nanofrog]

What flux would you suggest for occasional hobby use? I look on Ebay and everything seems to be made in China.

Here you go: MG Chemicals 835 Rosin, 100ml

Don't cheap out on consumables (flux, solder, desolder wick, ...), and get the good stuff to begin with. You'll save yourself endless amounts of aggravation, and dealing with the consequences (i.e. damage) that can come from poor quality supplies.

[zapta]

What flux would you suggest for occasional hobby use? I look on Ebay and everything seems to be made in China.

BillWojo

Chip Quick tacky flux in a syringe package. It status in place instead of running, good wetting, good smell (subjective) and you can leave on the board or clean with IPA.

[T3sl4co1l]

I use a tub of the (clear, orangish) paste rosin from RadioShack.  More of a gel than a paste, actually.  It works surprisingly well.  I like it better than solvent based (dropper or pen) types, which aren't as active, and don't stay where you want them -- the solvent boils off when the iron is applied, which pushes everything exactly away from where you need it.  It's also better than rosin core -- not that I'd ever use solid solder, but 'core' flux is not as active, and you can't apply as much of it.

It feels like a petroleum jelly base.  Ingredients say WW gum rosin, diethylene glycol dibutyl and dymerex rosin.  Probably anything with a similar list, or actually with petroleum jelly instead of, or with, the glycol, would perform very similarly.

Tim

[IanB]

I use a tub of the (clear, orangish) paste rosin from RadioShack.  More of a gel than a paste, actually.

The DeoxIT flux I have is very similar. Obtained from Fry's.

[PedroDaGr8]

What flux would you suggest for occasional hobby use? I look on Ebay and everything seems to be made in China.

Here you go: MG Chemicals 835 Rosin, 100ml

Don't cheap out on consumables (flux, solder, desolder wick, ...), and get the good stuff to begin with. You'll save yourself endless amounts of aggravation, and dealing with the consequences (i.e. damage) that can come from poor quality supplies.

Isn't this the truth. Good quality solder and flux are surprisingly important. I haven't tried that flux yet but just got that exact bottle in a few days ago. Will be trying it soon and will let you know how it goes.

[GreyWoolfe]

Pedro, I predict that you will like it.  I am very happy with it.  I have even given some to a new solderer.  I also hooked him up with some good solder.  Hopefully, he will have taken my advice on getting a Hakko FX-888D to replace his fire stick.

[ice595]

never EVER use plumber's flux unless if you absolutely need to, if you do make sure you do a good job cleaning it up afterwards.
I used plumber's flux to solder a pin header for a 1602 LCD module and guess what?
the I/O pins on the LCD had a fair amount of crosstalk due to the conductive plumber's flux, even though it only ran on 5v logic signals.
I scratched my head for hours wondering why my project worked in simulation but not on hardware.

[T3sl4co1l]

^

Also, tip cleaners, or acidic fluxes (anything with ammonium chloride, zinc chloride or similar stuff in it).  Obviously enough, the salts or acids form ionic (conductive) residues.  They're also much more strongly acidic than rosin (which is, after all, an organic acid, much milder and less volatile than, say, vinegar), which will corrode the joint much more quickly, especially with humidity around (zinc chloride itself is deliquescent, meaning it absorbs moisture from the air so strongly as to form a liquid solution of itself).

Still occasionally worth keeping in mind, for those strange occasions when you have a hunk of dull copper around, or you need to solder to steel.  Tin it first, using the nasty stuff, then clean it up as well as you can!

Often, good old mechanical cleaning does as well.  I've used coat hangers for electro-mechanical purposes (namely... the stuff makes good self-supporting antennas, stiffer and cheaper than heavy copper wire).  Sand or file off any coatings, rust, etc., and try to tin it as soon as possible.  Exposure to air causes oxidation, and it's a time * temp thing (steel will start turning yellow, then other colors, as the oxide layer grows).  In this way, I've had no problems soldering bare steel.  (You're welcome to try the same procedure with stainless, or aluminum, but have fun with that.  Most recommended methods for those require the ridiculously nasty ammonium bifluoride based fluxes.  So, better off with nuts and bolts for those materials.)

Tim

[algorithm]

What exactly are you using?

Marvelous info! thank you!
I am using a nokorode flux that apparently is from novembre 1926. O:
If that age printed on the lid is true, that is insane...

Thanks everyone! great stuff.

[nanofrog]

What exactly are you using?

Marvelous info! thank you!
I am using a nokorode flux that apparently is from novembre 1926. O:
If that age printed on the lid is true, that is insane...

Thanks everyone! great stuff.

That's acid flux, which is meant for plumbing (Nokorode is still around). You should stop using it and get something suited for electronics instead (will save you a lot of aggravation later on from corrosion).

BTW, if you would go into your user profile and set your country, it will display your country's flag under your userID. Makes it a lot easier for everyone, particularly when it comes to posting links.

[Psi]

Chip Quick tacky flux in a syringe package.

+1

this is what i use too

However i wish they would supply a proper plunger for the syringe and not the thing that falls out all the time.

[rob77]

good solder and flux are important for beginners, but later on as the level of experience is growing - the flux is not so critical anymore  - but still very important.

most of the time i get along with the flux core of the solder wire, but when more flux is needed then i'm using either solid rosin flux (old school ) or the cheap-ass gel type flux from china (it states RMA-223 but no-one knows what is it - but works well enough ) and of course all the flux must be cleaned up even if it's "no-clean" - especially valid for the cheap fluxes from china
 

[algorithm]

That's acid flux, which is meant for plumbing (Nokorode is still around). You should stop using it and get something suited for electronics instead (will save you a lot of aggravation later on from corrosion).

BTW, if you would go into your user profile and set your country, it will display your country's flag under your userID. Makes it a lot easier for everyone, particularly when it comes to posting links.

Thank you, and yeah, Im kinda all over the world though. (;

Its a shame I used that flux so much. (laughs)
I will look into the brands mentioned here and get something proper.

The strange thing about the flux is that I never saw corrosion on my old projects. What sort of timeline does it take for that to happen?
The things I noticed that coincided with most failed projects was there was still flux residue somewhere on the board, between components, under components, etc.

Looking back, times when I persistently cleaned the board, those projects worked.
Could just be a "coincidence" though..

[GreyWoolfe]

I used Orange Crush flux for the longest time myself.  I never really had any issues with it.  I did, however, stop and move to MG Chemical rosin flux liquid.

[algorithm]

I used Orange Crush flux for the longest time myself.  I never really had any issues with it.  I did, however, stop and move to MG Chemical rosin flux liquid.

I really enjoyed the flux I had been using for those drastic last resort measures... It was a petroleum based flux. Makes me wish I knew more sooner though. I also read conflicting statements claiming zinc chloride is highly water soluble. Although apparently zinc chloride in aqueous states are not simply solvated and are acidic. Read another source claiming that water+zinc chloride=hydrofluoric acid. O:


yikes.

Thanks again ! I will have to check some of these suggestions out.

[IanB]

Zinc chloride does dissolve in water. When heated under soldering conditions it decomposes to form hydrochloric acid. As already noted zinc chloride and its residues are highly corrosive and should not be used for electronic soldering.

Zinc chloride cannot produce hydrofluoric acid as it contains no fluorine. However some fluxes intended for aluminum do contain compounds of fluorine and should therefore be used with care.

[GeorgeOfTheJungle]

What flux do you suggest?

To desolder I use solder wick well wetted in this water based flux http://www.jbctools.com/flux--product-540.html

[algorithm]

Zinc chloride does dissolve in water. When heated under soldering conditions it decomposes to form hydrochloric acid. As already noted zinc chloride and its residues are highly corrosive and should not be used for electronic soldering.

Zinc chloride cannot produce hydrofluoric acid as it contains no fluorine. However some fluxes intended for aluminum do contain compounds of fluorine and should therefore be used with care.

Thanks for clearing that up.
I was trying to find out about that particularly because I was hoping by some miraculous chance that humid conditions over 10s of years might have eliminated the zinc chloride before I got ahold of this tin. Im no chemist or anything... but the tin is rusted, and it has been left directly in sunlight open for days before, never stored in a temp controlled environment... Considering that zinc chloride is so highly water soluble, I guess this is considered "water soluble flux"?

[IanB]

Zinc chloride isn't going to go anywhere. Like sodium chloride (table salt) it is really quite stable and can sit around for thousands or millions of years without decomposing.

Now although zinc chloride dissolves in water, that flux is not what is normally considered "water soluble flux". It is, rather, "acid flux".

The flux residues can (indeed must) be washed away after soldering, but this requires agitation, brushing and lots of rinse water to do a good job. A quick rinse under a running tap is unlikely to be sufficient.

[T3sl4co1l]

Chemically, zinc chloride is what's called a Lewis acid: it's not an acid in the conventional sense (a Bronsted-Lowry acid, that for example dissolves metals with release of hydrogen), but nonetheless leads to acidic behaviors (electron donating/accepting mumbo-jumbo, but we don't need to go into that).

Easier way to explain it: zinc, like a number of other elements, likes to stick to oxygen.  So it'll latch onto water directly (hence, it's deliquescent: absorbs humidity from the air), and tends to grab hydroxyls (affinity to the oxygen side of the water molecule, but pushing one hydrogen off, leaving OH-), which leaves protons (H3O+) in solution... which is acidic.  It's a mild acid in solution, but enough to do the job with whatever crud is sitting on the metal in question.

If you combine HCl acid and zinc, you get ZnCl2 in solution, which if you evaporate it to crystals (which requires heat, because again, it's deliquescent), gives you the hydrate, not the pure salt.  Even in solid form, it keeps hanging onto those water molecules.  If you try dehydrating it further, it doesn't let the water go easily, and HCl comes off as well, leaving some mix of zinc chloride and hydroxide/oxide.

Likewise, cleaning up the residues should require a solvent to clean up the petroleum jelly base, water to clean up the remaining solubles, and possibly a mild acid to remove the crud that's not soluble in either -- the hydroxides and stuff.  (Mild acetic acid (vinegar) would be fine.  But neutralize and clean it out extremely well.)

Tim