EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: banedon on April 02, 2018, 06:40:54 pm
-
Hi guys
I have a fairly basic question:
How do you guys go about cleaning flux from PCBs in a home environment? Up until now I've been using Servisol IPA (http://uk.farnell.com/servisol/200005000/cleaning-solution-ipa-1l/dp/3821560 (http://uk.farnell.com/servisol/200005000/cleaning-solution-ipa-1l/dp/3821560)) which seems ok, but seems to take multiple attempts and some time to get flux residue off of boards.Because of this it's made me doubt my methodology.
This is what I do after soldering:
For small areas near the edge of a PCB I dip a brush into the IPA and scrub from the inside of the board towards the outer edge (with as much firmness as the components area will tolerate) , let it dry and then do so again until I cannot feel any tackiness on the board.
For larger areas I do the the above, but will generally pour IPA over that side of the board and scrub.
I don't at any time use anything else to clean the PCB in question. Should I be? I've heard people on forums and in videos say they use water to wash the IPA off.
Personally, I wouldn't have thought this wise, unless perhaps it was ionised water?
And, no, I don't have an ultra sonic cleaner ;)
Any advice welcome :)
-
Ionized or distilled? I don't do much, but I recently bought an ultrasonic cleaner, just a cheap one, and it works well for this. I still have to go at some areas if the flux is very thick and has set for a long time. I was just using plain tap water and dish soap.
-
I use hust tips (https://www.amazon.co.uk/Sunwin-Reinigung-Zelletten-L%C3%B6sungsmittel-Supersize-Spezialformat/dp/B00OIWXUGC/ref=pd_bxgy_229_img_3?_encoding=UTF8&psc=1&refRID=90K92XVZA2KS8RXHSHTZ (https://www.amazon.co.uk/Sunwin-Reinigung-Zelletten-L%C3%B6sungsmittel-Supersize-Spezialformat/dp/B00OIWXUGC/ref=pd_bxgy_229_img_3?_encoding=UTF8&psc=1&refRID=90K92XVZA2KS8RXHSHTZ)) and IPA work very well
-
What type of flux are you using? Some fluxes are not supposed to be cleaned so that could lead to your struggle.
-
Hi
I use No Clean Flux Dispensing Pen. In case it makes any difference; The solder I use is Multicomp 50/60 Rosin 5 core.
-
The best method may depend on your flux. I use various no-clean fluxes, which are generally safe to leave as-is but do form a sticky residue.
I use MG Chemicals 4140 flux remover with a toothbrush to dissolve the flux:
https://www.mgchemicals.com/products/solder-and-accessories/flux-removers/flux-remover-for-pc-boards-4140 (https://www.mgchemicals.com/products/solder-and-accessories/flux-removers/flux-remover-for-pc-boards-4140)
Then MG Chemicals 406B Super Wash to cleanse the board, since the flux remover leaves its own residue:
https://www.mgchemicals.com/products/cleaning-products-for-electronics/cleaners/electronic-cleaners/aerosol-electronic-cleaners/electronic-cleaners-superwash-406b (https://www.mgchemicals.com/products/cleaning-products-for-electronics/cleaners/electronic-cleaners/aerosol-electronic-cleaners/electronic-cleaners-superwash-406b)
The Super Wash is a highly volatile aerosol which cools on evaporation, promoting condensation in humid environments. I use a heat gun to evaporate any condensation.
This rigmarole may seem labor-intensive and expensive. But it produces factory-clean boards, without the crusty residue IPA can sometimes leave.
I have heard that ultrasonic cleaning can damage sensitive electronics (e.g. crystals and semiconductor bond wires) unless you use a purpose-built unit which varies the transducer frequency.
-
What type of flux are you using? Some fluxes are not supposed to be cleaned so that could lead to your struggle.
And what flux would that be? If you're thinking of no-clean, that means it can be "safely" left, not that you shouldn't clean it.
-
As I understand it what is going on here is that the IPA is dissolving the flux fine. However the IPA then evaporates away leaving the flux behind. So you finish with what looks like a clean board but it's sticy to the touch as it now has a fine layer of flux all over it.
So you can either repeatedly drown the board in IPA and mop it up once a bit of a scrub has mixed the flux with the IPA or you can rinse the board in water while the IPA is still wet and holding the flux in solution. IPA, Water, IPA, Water, with drying in between can work or multiple passes with LOTS of IPA which you quickly scrub then mop up to soak the dissolved flux into the drying pad, leaving less to distil out onto the board.
As to using tap water it will highly depend on how "hard" or soft your water is, how well you mop up most of the water as to what it leave behind when you air dry it.
When I use water, I then air dry the board with the hot air solderer on 100*C before powering it on.
Ultrasonic baths sound like the ticket though.
-
If you're thinking of no-clean, that means it can be "safely" left, not that you shouldn't clean it.
"No-clean" doesn't mean much of anything, beyond "you can safely leave the residue on there." It doesn't mean "you should clean it, though, if you can." It doesn't mean "it can be cleaned with alcohol." In fact some no-cleans should be actively avoided if it is your intention is to actually clean the board. You have to do your own homework on what you're buying when you buy "no-clean" flux. This is one pretty good reason to use rosin flux if you can't be bothered to become an expert in every new no-clean flux-o-the-week.
In general there are low solids no-cleans, and there are resin based no-cleans. Most of the resin based no fluxes should clean much like rosin. Low solids should be left alone unless you use the appropriate cleaners. Again, no-clean is an industry thing, and there are no hard rules. Rosin fluxes come in 3 kinds which have specs that were set over 50 years ago.
In PCB manufacturing, no clean flux means less cost and work to produce esthetically clean-looking boards. But if a customer actually requires cleaning, this same board may take MORE work and effort and cost to clean than a rosin flux. But the manufacturer will do it anyway, because it is less expensive than changing over the equipment to use a different solder paste just for the few customers who require cleaning.
Don't let the name fool you. Rosin fluxes can also be left on the board in most cases. Of course the manufacturer wants to give off the suggestion that their proprietary PRODUCTS with margins only limited by what people are wiling to pay are saf-ER to leave on a board than a precisely spec-ed COMMODITY (rosin flux) of which the price is dictated by an open market by dubbing their completely unregulated (and more importantly, proprietary) formulas as "no-clean." The manufacturer can put w/e they want in a "no-clean" flux, as long as the customer keeps buying it. If they can make a flux with cheaper ingredients, they can increase their margins. There is no open market to drive the price down. If the resulting board works, it works. But put alcohol on any old "no-clean," and you're taking a gamble. Some of them react badly. And now you really DO have to clean it off. And it won't be easy.
All that said, I bet this is your main issue:
let it dry
Solvents are so named because stuff dissolves in it. If you let it dry, the stuff not only comes out of solution, but now the little ionic schmoo* that was trapped in the resin and was floating around in the alcohol (or had been dissolved in the water content of the alcohol) has now become a hard deposit clinging directly to the board for dear life. Do not let solvent evaporate on the board without removing as much as possible by blotting.
*ALL fluxes leave behind metal salts, which would be conductive if wet. But the main component of flux residue is a water insoluble resin whose job is to contain this conductive schmoo and render it safe enough to work, but maybe you shouldn't eat it.
-
Many thanks for the in depth explanation. I suspect that you're right with regards to em just letting it dry. I'll blot the stuff off in the future.
Any suggestions on what to use or is it just down to whatever comes to hand that seems sensible?
-
The best way is to use water soluble flux, and then just wash the board in running water, possibly scrubbing with an old toothbrush.
This gets them squeaky-clean. Trying to wash no-clean flux off boards is a royal pain, the stuff just DOESN'T want to come off.
Jon
-
OTOH You *MUST* wash off water soluble flux - if you leave it it typically causes severe corrosion. Any trapped flux under components is a major problem.
Rosin fluxes are fairly friendly to use for prototyping labs, repair shops and hobbyists. Cleanup is quite predictable - reasonably dry alcohol will dissolve the rosin fairly readily, although a couple of rinses with blotting in between may be needed to get the rosin concentration low enough to avoid stickiness, and the ionic residue concentration low enough to avoid streaking and surface leakage. Blot the brush you are using as well to avoid rosin buildup.
-
The best way is to use water soluble flux, and then just wash the board in running water, possibly scrubbing with an old toothbrush.
Don't let the wife see you, but I keep an old head from an electric tooth brush for cleaning PCBs. I also have one for my alloy wheels on the car.
Because tooth brushes can get rid of hard to reach embedded in dirt so well, such as in your teeth, they work quite well, the electric tooth brush just makes it so much easier and effective.
Obviously be away that an electric tooth brush is fairly violent for a PCB, so be gentle and careful.
-
I have ultrasonic toothbrushes, too...
-
I use only rosin flux or resin based no clean flux which is compatible with rosin flux.* And I only clean the board if I'm going to apply a conformal coat. The usual reason I'd want to do this is for a board that is not going to be in an enclosure and which will be handled/touched directly and receive contact with human body schmoo like oil and sweat. Most any other case, I just leave the rosin flux residue on the board.
For cleaning rosin flux residue, any alcohol works fine, with a brush and blotting. Adding some acetone will speed things up if the residue has fully dried/cured. I use denatured ethanol because it's convenient for me, and the odor isn't as objectionable to me compared to iso. If you use 99% isopropyl, there's almost no water in it. Ethanol with 5% water content might dissolve the conductive metal salts a little bit better. But I can't say that makes any real difference. As long as you blot, most of these salts should end up in your blotter, whether that is paper towel or kim wipes or Q tips.
*Specific example I use is AIM glo-core no-clean. In my estimation, it is pretty similar to rosin flux, but the residue isn't brown/yellow. And it mixes/reworks back and forth with rosin flux just fine. Indium makes some good purified rosin flux solders which remove the color, as well. I only ever tried these due to availability. I'll preferentially stick with rosin. I use RA liquid flux, and I don't want to run into any compatibility/cleaning issues.
-
I've had trouble getting alcohol to completely dissolve flux in the past and have used acetone instead. Is there any concern with using acetone instead of alcohol?
Sent from my iPhone using Tapatalk
-
Kestrel 62/38ish with a rosin core, or MG Chemicals no-clean paste for me. With paste there is generally so much less solder by volume and hence flux that there's not much to clean, and even then it's more an aesthetic choice in most cases anyway. TH with rosin leaves a clear coat, and I typically just leave it; alcohol makes it frost up, and removing it takes forever in my cleaner. For cleaning, when needed and feasible, I use a small frequency sweeping Elma ultrasonic cleaner with cheap 70% Walgreens IPA and the heater disabled. (Heating any alcohol just seems like a patently bad idea.) Still, despite paying some attention I did at one point destroy a bunch of SMD Omron relays in it; they weren't potted and didn't appreciate being immersed in the cleaner in rubbing alcohol for 20min. :palm: The worst part actually wasn't the destroyed relays, but rather that they sorta kinda worked, when they felt like it, which led me to spend a crazy amount of time tracking down the root cause of the erratic behavior. Replaced the relays, opened one of the old ones up and... unpotted. A face, meet hand moment.
-
Is there any concern with using acetone instead of alcohol?
I've noticed that every plastic component and connector I have tested has been acetone resistant. There are some components that have glued pieces/covers which are susceptible, though. Piezo buzzers are the example I have experienced. Acetone would make the covers fall off. But alcohol would do this, as well.
Acetone evaporates so fast, you might want to mix with alcohol. Don't let it evaporate off the board.
-
The best way is to use water soluble flux, and then just wash the board in running water, possibly scrubbing with an old toothbrush.
That’s bad advice. Water soluble flux is, for all intents and purposes, unsuitable for home use. The cleaning requirements are so demanding that they can’t realistically be reliably performed at home. Moreover, water soluble flux categorically cannot be used with some things, notably stranded wire. The flux wicks up where it cannot be cleaned, and will inevitably cause corrosion.
A home user is much better advised to either use rosin or no-clean flux. Cleaning either is optional, and is basically cosmetic.
-
No clean flux pen (rosin) + 99.9% IPA (both from RS) + multiple wash and rinse. No residue, no sticky, least risk. Works nicely even on my shitty hand made boards:
(https://i.imgur.com/TWaIR7H.jpg)
Don't solder trimmer resistors, trimmer caps, switches, relays until after wash though.
I use tap water to rinse which I will be shot for no doubt, then leave it on the radiator to dry for a bit.
-
I just use Fantastic and tap water to get the heavy flux off then alcohol to rinse .Then dry this a heat gun.
-
It very much depends on your tap water. If you are in a hard water area, or are working with sensitive high impedance circuits, and are water washing, it would be sensible to do an extra rinse with distilled or demineralised water to avoid leaving mineral deposits.
Also, the final alcohol rinse is important for boards you don't want to heat-gun the s--t out of. Both Ethanol and Isopropanol form azeotropes with water, b.p. 78.1°C, 95.5% and 80.4°C, 87.7% alcohol respectively, so as long as your alcohol is *DRY* - >97% for Ethanol and >90% for Isopropanol (and kept that way - dispense from your bulk container into a working bottle, and keep both tightly stoppered when not in actual use), and the board is well shaken and/or blotted top remove as much rinse water as possible before flooding it with a spray of alcohol, then draining it thoroughly, you can guarantee that there will be no water left under components with only moderate heating under 85°C. If it doesn't smell of alcohol you can be pretty much certain the board is properly dried.
Obviously, Isopropanol is preferable but even commercial grade 95% denatured alcohol is better than skipping the final alcohol rinse - as long as its undyed and the denaturant isn't ionic. It will still remove nearly all moisture from the board.
If you are particularly parsimonious and are cleaning a batch of boards, put the next uncleaned board in the catch tray you are using for the alcohol rinse runoff, or save the runoff in a sealed bottle for initial defluxing.
Incidentally, when you mention using a regional brand of propritory household chemical like S.C. Johnson's fantastik, its helpful to note exactly which product you are using and what its label says about its composition, as there are often several different formulations of varying degrees of suitability for the 'off-label' usages that are typical of our trade/hobby.
-
The reason for your issue has already been described so I wont repeat whats already been said.
I perform rework regularly at my day job, I use Kester no-clean gel flux. I don't have the luxury of being able to fully dismantle everything for thorough cleaning. My cleanup strategy is to apply IPA to the area to be cleaned, then use a kimwipe (lint free paper towel) and a small paint brush to agitate the flux. The kimwipe wicks the IPA/flux off the board and stop its spreading to what would otherwise be clean sections of the PCB. Unless I've gone overboard with flux it will usually only take 2-3 cycles to fully clean the area leaving minimal residue.