Is this A Solder Flux that needs to be cleaned?

[iampoor]

To make a short story long I have assembled a few boards with a roll of mystery solder, without realizing it. The product number is of course missing from the solder roll too. All I know is it was manufacture by multicore solders.

http://imgur.com/a/cIde9

The residue it leaves gets thick and yellowy. It also can turn black. I am assuming this is a solder flux that needs to be cleaned off the board? If so, can anyone recommend a good flux cleaner and/or identify what type of flux this is? I know there are many variables in all of this, just figured a greybeard many have an eye for this. I have always exclusively bought no clean flux solder.

I bought the solder at the deanza flea market too, maybe the seller has an account here and can magically give me some insight. Okay, enough wishful thinking. 

[wraper]

Looks like a rosin based flux. You can clean it with IPA, ethanol or some alcohol based flux cleaner for aesthetics, but it's not required. If you use water soluble flux, then cleaning is absolutely required.

[Ian.M]

Looks like it *MAY* be a Rosin based flux core.  However there's no way of telling if its R or RMA that are reasonably safe to leave or RA, some types of which should be cleaned, short of scraping it up and getting it analysed - not worth it for a single reel.

While flux remover on its own does remove the bulk of the Rosin, it typically leaves a thin smear of residual Rosin + undissolved activators across the board surface.  The activators are typically ionic and often hygroscopic, so tend to cause leakage problems in high impedance circuits, and in a high humidity environment, can be more destructive than uncleaned Rosin flux residue. 

Proper cleaning is at least a three step process - first a suitable solvent flux remover to dissolve the Rosin, then a detergent + water or water/alcohol wash to remove the activators and any other ionic contamination, followed by a distilled/deionised water rinse and optionally a final dry alcohol rinse to promote rapid drying.

[iampoor]

Thanks Guys

I am confident its a rosin based flux. The deanza flea market is an electronics swap meet and the seller had 10 or so different rolls for sale.

I was hoping there would be a way to tell if its RA or RMA. From what I have gathered, RA Flux may or may not have to be cleaned, and of course, you need to check the datasheet to find out. 

Ian, thanks, thats some very useful information I didnt know.

I assembled this board a few weeks ago. I am hoping that the cleaning process you have described will still work. The board is not particularly valuable, I just want a long term, reliable build. It would suck for the joints to slowly corrode!

[GreyWoolfe]

FWIW, I always clean up after soldering, it just looks nicer. 

[Ian.M]

If you are leaving flux on boards it needs to be free from readily soluble acids, and if you are shortcutting the cleaning it should also be halide free. 

To attempt to test for acid, you could try scraping as much of the flux residue as you can from the boards, dissolving it in a little Isopropanol  (or methanol  if you don't have any IPA), barely enough to dissolve it, then mixing it with a similar amount of distilled water, and heating it to boiling point.  That would get any water soluble activators into solution and you could then test it with Litmus or Universal Indicator paper to see whether or not it was an acid flux.   If it doesn't contain water soluble acids, it would most likely be safe to simply spot-clean the boards with flux remover or alcohol and a stiff natural fibre brush.  Also, if you know anyone with access to a chemistry laboratory (even school level) or who does their own black & white photographic developing, there's a reasonably simple test for halide ions using acidified Silver Nitrate as the indicator. 

Another simpler test you could do is clean a piece of copper or copper clad PCB to bright copper, and do some test spots: The first one tin a spot heavily then tip off the excess solder, then wash off the flux with alcohol.  The second the same but don't wash off the flux. The third just left as bright copper, then leave it out in the weather for a few weeks, checking it every few days.  If you see any signs of corrosion round the cleaned or uncleaned solder spots, that's worse than the solder-free spot, then you need to clean your boards urgently.

[wraper]

If you are leaving flux on boards it needs to be acid andf halide free.

Flux does not need to be halide free to be no clean.
example

[Ian.M]

I revised that statement while you were quoting me, to emphasise that the problem with most halides is incomplete cleaning. .  Chloride contamination is a serious cause of corrosion of copper alloys.  Unfortunately one of the main etchants used in commecial PCB manufacture is acid Copper (II) Chloride so your boards may even come pre-contaminated.   Non-acid halides aren't a major issue while they are locked up in solid Rosin or no-clean flux residue, but if you wash away the resin matrix and don't subsequently wash with something that dissolves halides, you risk the issues described

[Seaofdep]

Looks like a rosin based flux. You can clean it with IPA, ethanol or some alcohol based flux cleaner for aesthetics, but it's not required. If you use water soluble flux, then cleaning is absolutely required.

I was about to say yup throw back a few IPA (India pale ale) and it will not bother you anymore lol


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[iampoor]

FWIW, I always clean up after soldering, it just looks nicer.

Seems like a good habit to be in too!

If you are leaving flux on boards it needs to be free from readily soluble acids, and if you are shortcutting the cleaning it should also be halide free. 

To attempt to test for acid, you could try scraping as much of the flux residue as you can from the boards, dissolving it in a little Isopropanol  (or methanol  if you don't have any IPA), barely enough to dissolve it, then mixing it with a similar amount of distilled water, and heating it to boiling point.  That would get any water soluble activators into solution and you could then test it with Litmus or Universal Indicator paper to see whether or not it was an acid flux.   If it doesn't contain water soluble acids, it would most likely be safe to simply spot-clean the boards with flux remover or alcohol and a stiff natural fibre brush.  Also, if you know anyone with access to a chemistry laboratory (even school level) or who does their own black & white photographic developing, there's a reasonably simple test for halide ions using acidified Silver Nitrate as the indicator. 

Another simpler test you could do is clean a piece of copper or copper clad PCB to bright copper, and do some test spots: The first one tin a spot heavily then tip off the excess solder, then wash off the flux with alcohol.  The second the same but don't wash off the flux. The third just left as bright copper, then leave it out in the weather for a few weeks, checking it every few days.  If you see any signs of corrosion round the cleaned or uncleaned solder spots, that's worse than the solder-free spot, then you need to clean your boards urgently.

Thanks for those ideas. I dont have access to a lab unfortunately, but I do believe I have some litmus paper. Otherwise I will just order some. I also have some extra copper PC boards around that I will never use. I think I will try the first method and then report back. I bet applying some solder to the copper will be a good way to scrape some flux residue off too!

I revised that statement while you were quoting me, to emphasise that the problem with most halides is incomplete cleaning. .  Chloride contamination is a serious cause of corrosion of copper alloys.  Unfortunately one of the main etchant used in commecial PCB manufacture is copper chloride so your boards may even come pre-contaminated.   Non-acid halides aren't a major issue while they are locked up in solid Rosin or no-clean flux residue, but if you wash away the resin matrix and don'tsubsequently wash with something that dissolves halides, you risk the issues described

Veyr interesting, and good to know for the future. Thanks again!

Looks like a rosin based flux. You can clean it with IPA, ethanol or some alcohol based flux cleaner for aesthetics, but it's not required. If you use water soluble flux, then cleaning is absolutely required.

I was about to say yup throw back a few IPA (India pale ale) and it will not bother you anymore lol


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Too bad those kinds of IPA's tend to make me think harder and become paranoid, unless I consume too many of them. 

[Ian.M]

Odds are its R or RMA flux core.  Acid RA flux core solder is most often used by plumbers and usually comes in much heavier gauges.  There is electronics grade RA flux core solder but its rarely used (typically for metals that are difficult to wet) so don't worry *too* much about your boards.  However, it will only take you a few minutes to boil up the flux scrapings in a clean spoon over a lighter flame and do a litmus test, so its worth it to be certain before you use that reel on any high value repairs.

[nanofrog]

There is electronics grade RA flux core solder but its rarely used (typically for metals that are difficult to wet) so don't worry *too* much about your boards.

FWIW, I like electronics grade RA as it works well with both new and older, oxidized parts (+ reduces consumables I need to keep on-hand).

My favorite is Kester 1544, but Kester only offers it in large containers, while MG Chemicals offers their 835 RA in hobbyist friendly sizes (100ml or 1L). Kester 186 RMA has performance similar to an RA (I have some of this too), and there are companies and eBay sellers that break it down into hobbyist friendly sizes (here; Kester 951 too). 

CML Supply is such a company, particularly for those in the US. They break down other products as well, such as Kester EP256 63/37 solder paste which is the only way hobbyists/small repair shops can reasonably obtain it as Kester only packages it in 500g and 600g containers (jars & cartridges respectively). They also offer RF741 paste flux in a smaller syringe, though Kester offers this in a 30g syringe (and as there's no metal to settle out, it's more forgiving regarding shelf life vs. solder paste). They even offer their own line of disposable pens filled with Kester products, but buying liquid is much less expensive.

CML will also ship internationally via their own website. They also do business through eBay, but they don't offer international shipping from this site. 

I've also purchased from an eBay store, Dickie's Garage Sale (i.e. buy 2 & get 1 free offers available), and it's the genuine article IME (mine uses acetone for the solvent instead of IPA, which was swapped out in 2016). $5.33 shipped for 3.75 fl. oz. would be one example of the b2g1 offer (here), as well as smaller & larger quantities.

[Ian.M]

Yes, but those (apart from Kester EP256) are additional fluxes not RA flux core in solder.  Kester EP256 is a halide free no-clean solder paste.

[nanofrog]

Yes, but those (apart from Kester EP256) are additional fluxes not RA flux core in solder.  Kester EP256 is a halide free no-clean solder paste.

I wasn't claiming EP256 uses an RA flux paste, nor is 951; just that they're other Kester products that are broken down into hobbyist or small repair shop friendly sizes (quality consumables at reasonable prices instead of having to settle for crap/counterfeits). 

Unfortunately, I'm not aware if this sort of thing is available in other parts of the world. 

[calexanian]

+1 for RA flux. You can get away with low impedance circuits not cleaning it, but..... I would clean it anyways. As mentioned IPA works well. If you are more daring you can use brake cleaner, but be sure all your parts are solvent washable. Remove ABS plastics if you are going to go that route. Otherwise a tooth brush and some IPA, then rinse it off in clean IPA afterwards or the board will appear cloudy. shake it good cause it likes to get under the chip and stay wet. I sometimes put them back in the reflow toaster just to heat them up a bit to drive the moisture out of the chips, then brush them again with a clean toothbrush. They will come out looking factory made.

[nanofrog]

+1 for RA flux. You can get away with low impedance circuits not cleaning it, but..... I would clean it anyways. As mentioned IPA works well. If you are more daring you can use brake cleaner, but be sure all your parts are solvent washable. Remove ABS plastics if you are going to go that route. Otherwise a tooth brush and some IPA, then rinse it off in clean IPA afterwards or the board will appear cloudy. shake it good cause it likes to get under the chip and stay wet. I sometimes put them back in the reflow toaster just to heat them up a bit to drive the moisture out of the chips, then brush them again with a clean toothbrush. They will come out looking factory made.

Given you're in the US, you might want to consider Kleen Strip Denatured Alcohol (not the Green version that includes Acetic acid). The reason being it's only made up of ethanol and methanol in up to a 50/50 mix (the methanol makes it denatured). Denatured Alcohol SDS.



I mention this as it's more a bit more aggressive than IPA, yet is still easy on plastics. And to top matters off, it's also inexpensive (~$17 per gallon from Home Depot as of a few months ago). 

[calexanian]

That clean strip stuff is practically useless on PCB's. It leaves conductive residue that itself is hard to remove. IPA is better but you have to flush the board a lot and it will get expensive. True Methanol would be best if you want to stay alcohol. Its not expensive as a company to buy it. Better off using the brake cleaner. It takes very little. Actually my home process is Brake cleaner and a brush. Scrub it. then spray that away. Then dunk the board in distilled water, then hot air dry. Boards look perfect.

[nanofrog]

That clean strip stuff is practically useless on PCB's. It leaves conductive residue that itself is hard to remove. IPA is better but you have to flush the board a lot and it will get expensive. True Methanol would be best if you want to stay alcohol. Its not expensive as a company to buy it. Better off using the brake cleaner. It takes very little. Actually my home process is Brake cleaner and a brush. Scrub it. then spray that away. Then dunk the board in distilled water, then hot air dry. Boards look perfect.

Huh??? 

This particular formulation is nothing but alcohol which will evaporate cleanly. Most any other form will cause problems, particularly the denaturant (naptha or MIBK/methyl isobutyl ketone for example). Incomplete cleaning is also a real problem, regardless of the substance used (e.g. remnants tend to be conductive, and can also cause corrosion issues).

Residues are only left behind if you don't get the flux and other crap completely off the boards IME. Just like IPA, it takes multiple applications of rinsing + scrubbing with a brush with this particular denatured formulation in order to get the junk off as well (uses a good bit of product). Then I do a final run with distilled water, then use forced air and/or heat to dry the board.

Though I like the performance, its less expensive than IPA (~$15 per quart for MG Chemicals 824 shipped). It's more easily ignited however, so greater caution should be exercised when in use.

[Ian.M]

Evaporate a small quantity of your proposed board cleaning alcohol to dryness in a watch glass or polished spoon.  If it leaves a solid or oily/greasy residue, its denaturants aren't suitable. 

[rdl]

...
Given you're in the US, you might want to consider Kleen Strip Denatured Alcohol (not the Green version that includes Acetic acid). The reason being it's only made up of ethanol and methanol in up to a 50/50 mix (the methanol makes it denatured).

141-78-6 Acetic acid, ethyl ester {Ethyl acetate} 1.5 %

Ethyl Acetate and Acetic Acid are two different chemicals.

I don't really see why one is "Green" and the other isn't. Marketing I guess. Without knowing more about the actual solubility parameters of the flux being used, it's hard to say whether one is better than the other for cleaning pc boards.

I think just to have some around for general cleaning purposes, I'd probably go for the green version. Primarily because of the higher ethanol content.