Solder joints appearing milky on the surface after switching flux - Page 1
Forum section: electronics / beginners

author: bear
author_rank: Newbie
timestamp: February 14, 2022, 04:32:27 pm
content: I have been soldering withMG Chemicals 63/37 solder with RA fluxand I also used an additional flux as sort of a primer. The aforementioned flux was just a diluted flux with some IPA sold as a soldering liquid for soft soldering with 60/40 class solders. It was always working well, I would always clean the joints after the soldering with IPA. If I ignore the inconsistent amount of solder, joints were shiny and durable (I tend to tweezers to try to poke and pry such joints when I solder some small and annoying parts to make sure there isn't a cold joint).Anyway, I ran out of that flux and decided to useMG's flux pasteI purchased some two years ago, but didn't end up using it as it was too thick (I prefer something between jelly and liquid), but I got my hands dirty and put it into a syringe and started using it, but I started noticing a problem. After I am finished soldering and I clean the joints, the surface is not dull, but rather has a milky look to it.I also had a chance to compare the two where I did everything the same (again, as same as I can), but one was done with an added old flux and one with this new one and only the joint with this new flux looks would look like the photo below (that one used the new flux on all the joints).Any idea what it could be? Is it possible there is some chemical reaction happening or maybe I didn't give it enough time to evaporate?

author: Vovk_Z
author_rank: Super Contributor
timestamp: February 14, 2022, 10:02:29 pm
content: Technical manual says it needs cleaning after use:2. Clean residue with MG 4140 or 413B flux removers.This requirement seems to me typical for all pastes.

author: bear
author_rank: Newbie
timestamp: February 15, 2022, 08:04:55 pm
content: This is something which didn't cross my mind in the slightest.I looked at it and it seems this is almost impossible to get in Europe. Is is possible to say if some other flux remover (besides the straight IPA) can be used? Or, is this the ideal question for the manufacturer?Lastly, I did some more soldering today, and I got some better results, so would it be possible to say such appearance could be caused by something else as well?

author: Zipdox
author_rank: Regular Contributor
timestamp: February 16, 2022, 09:34:20 am
content: IPA is probably your best bet

author: jpanhalt
author_rank: Super Contributor
timestamp: February 16, 2022, 10:04:36 am
content: Here's a study by Kester on "white residue":https://www.kester.com/Portals/0/Documents/FAQs/White_Residue.pdfOlder boards/components may have more oxidation or other dirt for the flux to remove. That leaves more stuff to be cleaned. IPA is generally good. I used to use absolute ethanol and acetone (3:1). That work well, but white residue can be a problem.Spurred by Kester's comments that its newer fluxes may require a "saponifier," and its newer flux removers are water based, I have been experimenting with cellosolves, which tolerate a lot of water, and most recently an organic base like ethanolamine as saponifier. Check out SDS's for Kester 5768 and 5779 flux removers. If you can get an acrylic floor stripper (not cleaner) locally, that might work. Check its SDS/MSDS. If if contains a "cellosolve," which will have a chemical name like butoxyethoxyethanol (generically alkoxyalcohol or alkoxy(alkoxy)alcohol ) Try it neat or even with water, say 1 part stripper and 3 parts water. ZEP floor stripper (an American brand) meets that definition and is worth a try.

author: tooki
author_rank: Super Contributor
timestamp: February 16, 2022, 10:22:48 pm
content: Quote from: Zipdox on February 16, 2022, 09:34:20 amAbsolutely not the best. It often leaves white residue because of alcohol-insoluble salts. Commercial flux removers do a far better job.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 16, 2022, 11:17:26 pm
content: Before gambling on a "commercial" flux remover, be sure to check its SDS/MSDS. Some are not much more than IPA with or without acetone, which has already been mentioned. Neither is very good at dissolving alcohol insoluble "salts." For example (one of many):https://www.mgchemicals.com/downloads/msds/01%20English%20Can-USA%20SDS/sds-413b-a.pdf

author: tooki
author_rank: Super Contributor
timestamp: February 17, 2022, 10:09:21 am
content: Quote from: jpanhalt on February 16, 2022, 11:17:26 pmA few years ago I looked at the MSDS of every commercial flux remover I could find. None of them were just IPA without acetone.There are a few families of recipes, but the most common was IPA and a hydrocarbon, and my experience with such things is that there’s a massive difference in performance over just IPA. Heavy duty flux removers often use acetone as well. Some use additional agents like orange terpenes, and then there are the nonflammable ones that rely on completely different chemistry.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 17, 2022, 11:23:35 am
content: Quote from: tooki on February 17, 2022, 10:09:21 amDid I say or imply that? No.In fact, as posted, my primary remover for years was absolute ethanol and acetone. Why absolute ethanol? It's a much better solvent for nonpolar substances (e.g., greases, oils) than 95% ethanol. It only takes a little water in either ethanol or IPA to change that property. As for acetone, it helps with larger molecules like abietic acid and polymers.QuoteOnce again, we are left to your personal, undocumented experience. How about supporting those assertions with your results or references? Lacking that, just name those removers so others can verify. There are lots of "flux removers" on the market, and I seriously doubt you looked at every one.I have given links to the ones I reference. One thing I have noticed is a trend toward aqueous systems, as illustrated by links to Kester. Those systems seem to always include mono- or poly- alkoxy ethers of diols or triols, The the most common are mono- or di-alkoxy ethers of a diol. I just refer to them as "cellosolves" as that term is easily searched in Wikipedia (https://en.wikipedia.org/wiki/Glycol_ethers). They are all share similarities in solvent strength but vary in volatility.The similarity of the aqueous flux removers to floor strippers (i.e., for removing waxes and polishes, not paint) is striking:Link to several with SDS included therein:https://www.jondon.com/chemicals/floor-care/stripping-removers.htmlLink to ZEP:https://images.thdstatic.com/catalog/pdfImages/96/967064eb-76c7-45eb-ac3f-305ff4810e3d.pdfI intend to try the ZEP product on my next board and will simply use a higher concentration of the cleaner than is recommended for floors. ZEP is a local brand sold at home improvement centers. I am sure there is an equivalent in Europe.One exception in the first link is the "green" cleaner that has N-methyl-2-pyrrolidone (NMP) in it. Kester EP256 paste also has NMP, but I think it can be avoided in a flux remover.EDIT (preliminary): Just hand soldered an SOT23-6 and cleaned with undiluted ZEP floor stripper (link above). There was a fair bit of flux residue around the freshly soldered chip, including some that was well darkened. ZEP worked well. This is just preliminary, and I wouldn't expect white residue under those conditions. As expected, the ZEP did not evaporate fast, even with compressed air, so I dipped in ethanol to clean it off and dried. ZEP is already less than 30% butoxyethanol. The other listed component is ethanolamine at a ratio of about 2:1 to 6:1 (cellosolve:ethanolamine)(using the SDS ranges). Those who are interested may consider diluting the floor stripper with distilled/deionized water. I have been using ethoxyethanol as it is more volatile, but I did this experiment for those who are reluctant or cannot buy chemicals. Crummy macro picture attached.

author: tooki
author_rank: Super Contributor
timestamp: February 17, 2022, 03:35:42 pm
content: Quote from: jpanhalt on February 17, 2022, 11:23:35 amWell sure, you absolutely did! What else did you mean by the following sentence, if not that?!?Quote from: jpanhalt on February 16, 2022, 11:17:26 pmQuote from: jpanhalt on February 17, 2022, 11:23:35 amI did forget to specify that I meant only solvent-based (non-aqueous) flux cleaners. But I didn’t claim to look at every flux remover on the market, just the ones I could find. And since it’s not an exhaustive list of every solvent based flux cleaner in existence (i.e. there will be some that aren’t on the list), it’s impossible to provide evidence of my claim, since that’s asking me to prove a negative.All I said was that I didn’t come across a single one that was simple IPA and acetone. (I was hoping to find a fairly simple recipe I could reproduce for cheaper. I didn’t find one.)

author: jpanhalt
author_rank: Super Contributor
timestamp: February 18, 2022, 08:55:07 pm
content: Just FYI, while looking for flux cleaner prices, I came across one that is pure IPA + HFC-134A freon as propellant:https://www.techni-tool.com/product/565CH307-MCC-BACJG?gclid=EAIaIQobChMI-omE_oqK9gIV4R-tBh1ojQM6EAQYBCABEgLvJ_D_BwEThe real purpose for this post is to update on using ZEP floor stripper. I finished the assembly of a PCB with a few additional parts (SOT23-6's and 805's). The original had been cleaned with solvent and toothbrush, but some flux and white stuff remained between pins of narrow pitch devices. I decided to try ZEP at the same final concentration of cellosolves as the very similar Kester 5779 and 5768 flux cleaners are recommended to be used at. A 1:3 dilution of ZEP (i.e., 1 part ZEP and 2 parts water) was used. I was skeptical, but 3 minutes in my Bransonic 12 cleaner was all it took. Rinsed in tap water from Lake Erie,* then another 3 minutes in distilled water in the Bransonic. First observation is that the PCB after a water rinse ends up almost dry, except for water trapped under components. Solder resist used by Oshpark is quite hydrophobic. I suspect that is part of the reason for adding a surfactant.The boards were immaculate and shiny. Absolutely no trapped flux was seen with my dissecting microscope. The Kester products are about $100/gallon in single gallons. ZEP is about $10 per gallon. Since a water rinse is probably mandatory, I have decided there is no purpose in pursuing the more volatile alternatives. Of course, the smell is ZEP doesn't compare to good ethanol with or without acetone.John*ZEP probably uses the same water.