Alcohol when cleaning flux? - Page 1
Forum section: electronics / beginners

author: PotatoBox
author_rank: Regular Contributor
timestamp: March 01, 2022, 06:52:50 am
content: I’m always confused when trying to clean flux off a pcb? When watching board repair videos, they always used a q-dip dipped in alcohol, and that’s it... a good example of it is here. At 20:25.https://youtu.be/yKAp0tVXRb4Maybe it’s the type of flux and solder (Kester 44) I’m using but alcohol really isn’t enough. It just turns into a sticky mess and I always have to rinse it off with water. It makes repairing traces on pcbs look really ugly and I don’t want to have to wash an entire pcb (It doesn’t seem like Louis Rossmann washes every pcb after a job) just because of a small trace repair. What am I missing?

author: JohanH
author_rank: Frequent Contributor
timestamp: March 01, 2022, 07:00:45 am
content: Flux won't magically disappear with alcohol, you have to physically remove it, for instance with paper towels or by rinsing.I use lint free paper towels, IPA and a brush. First lay paper on the PCB, spray IPA on the paper, use brush on paper. If it's really stuck, first IPA + brush, then paper + brush.

author: ataradov
author_rank: Super Contributor
timestamp: March 01, 2022, 07:06:41 am
content: It also depends on how messy your are in a first place. The area is highly zoomed in, and he had to do a lot of scrubbing to clean the area. But yes, it is absolutely possible to clean the local area only with IPA and Q-tip. I do it all the time for rework. I use MG Chemicals 8341 flux, but I do the same for all types of flux, including plain rosin, and it all works about the same, some needing more work than others.If the area if flooded with flux, then it is indeed better to use a paper towel (still with IPA) to remove majority of the flux, then clean up as needed. On flat areas no additional cleanup is needed in most cases. If you have components, then Q-tip or paper towel wrapped around a toothpick usually does the job.

author: wraper
author_rank: Unknown
timestamp: March 01, 2022, 07:09:29 am
content: I don't see how spraying the paper towel with alcohol is effective. I brush the PCB with alcohol. Then quickly place a paper tower on PCB before alcohol evaporates and then brush on top of the towel, preferably with another brush which is dry, or quickly dry the same brush with another piece of towel first. This way all of the alcohol with dissolved flux is absorbed into the paper towel, and barely any residue is left even after a first cleaning pass. Before doing the second pass, you need to dry the brush with paper towel, add alcohol to it and dry with towel again to not recontaminate the PCB.

author: ataradov
author_rank: Super Contributor
timestamp: March 01, 2022, 07:13:23 am
content: I use small folded chunk of a paper towel. Just enough to cover the finger. Soak that in IPA, then use the finger pressure to scrub the board. I personally don't like toothbrush through the towel method as I feel like it does not give me enough control and I end up using more IPA than necessary as the whole area of the towel soaks it in.

author: PKTKS
author_rank: Super Contributor
timestamp: March 01, 2022, 08:10:50 am
content: Rosin based flux is very sticky...But however.. it is not corrosive as other non activated flux...Small hidden pads retain flux which can only be cleaned with compressed air blows embedded alcohol..I use a small air ball for camera lens to blow pads...Today i rarely use sticky ROSIN..Paul

author: Kleinstein
author_rank: Super Contributor
timestamp: March 01, 2022, 08:19:41 am
content: It helps to remove the alcohol with a dry pater towl of similar, not with an alread wettet one.I usually first brush with some alcohol, than apply some new alcohol and than soak it up with paper or let is flow off the side.One may have to repeat a few times for critical areas.I see little need to clean in between soldering parts of the PCB. So cleaning is only after complete (or at least when one thinks it could be) soldering / testing.

author: Pinkus
author_rank: Frequent Contributor
timestamp: March 01, 2022, 08:55:30 am
content: Can somebody please point me to a place where I can get these pad strips shown in the video. I never saw them before and there would have been helpful in the past so I would like to order a sheet of these.This NorthridgeFix-guy does not ship orders below $100 internationally.I looked at Aliexpress and other places for 'pad strips' but this seems to be unknown. Is there a different term for these?

author: jpanhalt
author_rank: Super Contributor
timestamp: March 01, 2022, 10:40:33 am
content: Alcohol (meaning absolute ethanol) works. I still use it for spot repairs and also use Kester 44 flux for such hand work. A little acetone (20% to 30% by volume) helps.Recently, I switched to ZEP Heavy Duty Floor Stripper diluted with water.* It will work by hand for spot application and probably must be rinsed. It works the best I have seen in an ultrasonic cleaner after reflow with Kester 256 (leaded solder). The boards were spotless, and after rinsing, came out almost dry due to the hydrophobicity of the solder resist.*Sold in many countries around the globe, but noticeably, not in Australia. Probably not needed with dirt floors.Actually, the person I spoke with thought it was perhaps a regulatory thing that ZEP is looking into.

author: jeffjmr
author_rank: Regular Contributor
timestamp: March 01, 2022, 01:50:52 pm
content: I use denatured alcohol with little problem except as noted below.Be careful with acetone. I find it removes the protective film on some PCBs. I don’t know how critical this film is, what it is made from or whether it is for anti-corrosion or insulation but even denatured alcohol changes the look of this film on some PCBs.Maybe someone with more technical PCB knowledge can chime in.Jeff

author: jpanhalt
author_rank: Super Contributor
timestamp: March 01, 2022, 02:38:28 pm
content: That stickiness is probably from what's called a conformal coating. That is not the solder resist. It is applied after soldering for protection from corrosion. So far as I know, it can be almost anything, including an acrylic lacquer, which is susceptible to acetone, MEK, and probably other ketones and esters. That is, solvents in lacquer thinner. Acrylic lacquer has the advantage that it can be soldered through without needing to remove it first.The problem with "denatured alcohol" in the US and probably elsewhere is that it need not be just denatured ethanol.* In fact, it is probably about 50% methanol. The composition varies depending on manufacturer. Check the SDS/MSDS for whatever you buy. Some contain a ketone similar to acetone or MEK (e.g., methyl isobutyl ketone). Methanol and ethanol have different solvent properties.*Years ago, denatured ethanol ("alcohol") was used as a non-taxed solvent for shellac. Today, you can still get it, but it is labeled shellac thinner and is considerably more expensive than big box store "denatured alcohol for fuel." If you want something that is cheap and mostly ethanol, try E85 at the filling station. That probably varies by location. What I have doesn't smell too bad.

author: Terry Bites
author_rank: Super Contributor
timestamp: March 01, 2022, 03:50:35 pm
content: Medium tooth brushMEK- methyl ethyl ketone. Less deadly than acetone.A light scrub and let exess run of board.

author: tooki
author_rank: Super Contributor
timestamp: March 01, 2022, 04:53:25 pm
content: Quote from: JohanH on March 01, 2022, 07:00:45 am^^This.Except that as always, I emphatically recommend using commercial flux remover instead of IPA (which leaves behind white residue with many fluxes, especially modern no-clean fluxes).

author: jpanhalt
author_rank: Super Contributor
timestamp: March 01, 2022, 05:43:13 pm
content: Quote from: Terry Bites on March 01, 2022, 03:50:35 pmHave you checked the PEL (permissible exposure limit), REL (recommended exposure limits), and LD50(rat,oral) for each? MEK is considered more toxic. Its LD50 is lower as are its exposure limits. MEK is nice and evaporates more slowly, which can be an advantage, but acetone is often a better solvent. They are similar.

author: jpanhalt
author_rank: Super Contributor
timestamp: March 01, 2022, 05:47:41 pm
content: As for commercial flux removers, that does not define what you mean. As pointed out earlier, at least one is just IPA. The real difference is total cost, including shipping. Kester's 5779 and 5768 are ten times as expensive excluding shipping costs as homemade flux removers that can be bought locally. Shipping is not cheap.

author: tooki
author_rank: Super Contributor
timestamp: March 01, 2022, 06:23:45 pm
content: Practically every solvent-based flux remover is a blend of solvents.Shipping cost is a red herring: there’s always some locally available product.As for cost, that varies regionally. Here in Switzerland, real flux removers are only trivially more expensive by volume than IPA. But remember that even if they’re twice as expensive, you don’t need nearly as much of it.

author: Renate
author_rank: Super Contributor
timestamp: March 03, 2022, 11:25:13 am
content: Dollar store 91% IPA and a toothbrush.Apply liberally then blow off the excess before it evaporates leaving you where you started.Pat dry with a clean paper towel.Repeat if necessary.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 03, 2022, 09:20:45 pm
content: Quote from: tooki on March 01, 2022, 04:53:25 pmYou probably said previously but please remind us of your preferred commercial flux remover(s). Thx

author: tooki
author_rank: Super Contributor
timestamp: March 05, 2022, 01:02:08 pm
content: I’m not sure if I’ve recommended any specific ones, since availability varies so much by region. Here in Switzerland, the ones I can get most easily are Contact PCC (aka Kontakt LR) and Electrolube FLU and LFFR, as well as Distrelec’s house brand RND (which I strongly suspect is made by Electrolube since it’s also made in UK, can dimensions are identical, as is the smell — distinctively orange due to the orange terpenes contained). I’ve used them all and they all work well. I’ve also used Techspray, which worked great too. They’re all blends of alcohols and hydrocarbon solvents, and all work better than straight IPA.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 06, 2022, 04:06:00 am
content: ThanksElectrolube FLU and LFFR look interesting.Any reasons to use Electrolube FLU vs LFFR? FLU works with both lead and lead free? For lead fee is either any easier to use, more effective at removing flux, less likely to leave residue, less likely to melt/eat PCBs? Either one more human friendly / less toxic?Thanks again

author: David Hess
author_rank: Super Contributor
timestamp: March 06, 2022, 11:23:49 pm
content: I never use only alcohol for cleaning (or thinning) flux. The flux thinner I have is 50/50 isopropyl alcohol and toluene, but where plastic is not present, I usually use lacquer thinner or acetone for removing flux from small areas after rework.

author: tooki
author_rank: Super Contributor
timestamp: March 07, 2022, 12:18:56 pm
content: Quote from: Electro Fan on March 06, 2022, 04:06:00 amI haven’t compared their performance side by side. My understanding is that LFFR simply a more aggressive cleaner. The higher temps of lead-free soldering tend to burn the flux more, making it harder to remove, but moreover, lead free solders generally have no-clean fluxes that are themselves inherently harder to remove.It’s always a tradeoff: more aggressive cleaners remove flux with less effort, but are more likely to damage sensitive components. (The first thing to go is component markings.) Acetone (an ingredient in some heavy duty flux cleaners) is great at dissolving flux, but damages many plastics.Don’t worry about the PCB itself, they can take it.As for residue: flux cleaner dissolves flux, but carrying it away is your responsibility. I recommend the approach of laying down a wipe onto the board, spraying on solvent, and then using a brush with fine, but short (and thus stiff) bristles. That pulls the residue into the wipe. Repeat if necessary. Don’t forget to rinse the brush with clean solvent from time to time.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 07, 2022, 04:49:43 pm
content: Brake Cleaner ??https://youtu.be/d3Qmm6Tegb4

author: David Hess
author_rank: Super Contributor
timestamp: March 07, 2022, 11:00:45 pm
content: Quote from: tooki on March 07, 2022, 12:18:56 pmExcept for plastics, the most sensitive component I have run across are DIP switches if their inside gets contaminated during cleaning. In my experience markings that would be removed by acetone will also be removed by soapy water, or rubbing with a finger.