Author Topic: Myth busting solder-flux cleaning with isopropanol alcohol  (Read 119134 times)

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Offline astroschmidt

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Myth busting solder-flux cleaning with isopropanol alcohol
« on: July 22, 2012, 01:12:15 am »
Dave,

could You bust (or confirm) another myth about cleaning PCBs from the solder flux.

I see it often that it is adviced to clean your PCB after soldering with isopropanol alcohol because

a.) the solder flux could oxidize the copper in the long run

b.) the solder flux is not as high-ohm as a cleaned PCB and can create high-ohm connections on the PCB


I believe that it is much better to NOT clean the PCB from (pure rosin!) solder flux, because

a.) Isopropanol is aggressive to some plastics and can intrude into parts creating undesired effects.
It can e.g. dissolve polystyrene capacitors AFAIK

b.) By this dissolving of other materials a potential low-ohm film is spread over the PCB while the rosin itself is very high-ohmig when left untouched at the solder joints.

Please comment

Roger
 

Offline mikeselectricstuff

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #1 on: July 22, 2012, 02:10:51 am »
It depends on the flux. Some fluxes are corrosive over time, although not generally the ones you's normally use. Even good flux, if contaminated can become corrosive - I had a bottle some a while ago that was OK for a while but then started corroding things a few days after application.
Some types will also absorb moisture, so if you have high impedance stuff it can cause long-term problems.
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Offline astroschmidt

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #2 on: July 22, 2012, 02:43:34 am »
It depends on the flux. Some fluxes are corrosive over time, although not generally the ones you's normally use. Even good flux, if contaminated can become corrosive - I had a bottle some a while ago that was OK for a while but then started corroding things a few days after application.
Some types will also absorb moisture, so if you have high impedance stuff it can cause long-term problems.

Hi Mike,

in the days of youth I first used solder intended for plumbers because nothing else was available at the local warehouse and I didn't know about the deifference.
That one of course corroded everything through its halogenated solder.

But I never had any issue with electronic solder with a (non-halogenated) pure rosin flux-core solder.
Even when I sometimes open a case with a 2 decade-old PCB soldered by me I never saw any corrosion.
This is also what the german wikipedia-entry says about rosin ("Kolophonium" as it is called in German)
http://de.wikipedia.org/wiki/Kolophonium#Elektronik.2FL.C3.B6ten
There they even say it is better to leave a layer of rosin on the PCB because it is more protective against corrosion than a cleaned PCB.

Couldn't it be the same with moisture, that a thin layer of rosin protects high-impedance stuff more than it harms?

BTW I only speak of pure rosin flux.

Kind regards

Roger
 

Offline free_electron

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #3 on: July 22, 2012, 02:48:44 am »
rosin based flux is generally not conductive unless you baked it at such high temperatures it turned caramel color or black ...

no-clean flux is just that. no-clean. you can leave it on. no problem

-low solids flux is a flux that under a correctly controlled process totally evaporates. if there is a lot of residue your process is wring and you need to remove it as it can be conductive

- water soluble flux needs to be removed simply because it is hygroscopic and leaves a soap-scum like residue on the board that is conductive.

isopropylalcohol does not attack plastics ( apart from one kind of transparent material that just falls apart like a smashed car window. very weird)  ipa is perfectly safe for electronics.

There are some very agressive fluxes like RA that must be removed as they contain acidic substances. RMA is the most prevalent rosin flux ( RMA ; Rosin Mildly activated. RA = rosin activated )
it is actually not the rosin that is the flux , but another substance in the compound. the rosin is just a carrying vessel for the real active ingredient.

flux works on two fronts :

When activated ( temperature controls this, most fluxes kick in around 100 degree C ) flux is a very reactive element that want to bind with oxygen molecules. It is so reactive it can strip oxygen molecules that have already bonded with copper. So it converts copper oxide back into copper.

The second thing it does is lower the surface tension of the solder. this lets the solder 'wlow' over the to be soldered surface.

under a correct process the flux is given some time to activate and do its work before soder is applied. wave solder machines apply  warm flux to the board first, let it soak for a few seconds as the conveyer moves over a warming plate and the flux is now activated.  then it goes through the solder wave where the flux totally evaporates leaving a clean board.

solder paste works in a similar way. when doing reflow you have a rampup to flux activation, a hold phase to ledt the flux do its work and evaporate for almost 75% and then you ramp up to liquid phase where the solder melts and flow on the remaining flux. if reflow is done correctly there is little or no flux residue and board wash is not required.

boards that have been reworked ( manually touching 1 component ) will have residue and those need washing with iehter solvent based flux removers or water.

the flux in solder wire is a different composition than the flux found in pens or liquid form ( for starters the flux in solder wire is dry powder .. ) it is also more agressive as it has a shorter time to do its work.

and then there are specially formulated fluxes like the gel fluxes or tacky fluxes. those are formulated for rework and the idea is to use a lot of it. so much that there is residue and you need to remove it.
The same goes for pen fluxes. Those are for rework. fluxes for wavesoldering come in 50 gallon drums ... not something to have on your workbench ...

in general :
when doing handwork you will need to clean the board unless no-clean is used
when doing reflow or wave correctly ( note the usage of the word correctly ) there will be no need to clean the board afterwards unless in special circumstances like medical or military stuff where they are extremely anal ( with perfectly fine reasons) .

if you care about the esthetical aspect : clean it up

every kind of flux has its own specific flux remover. some flux removers are broad spectrum. like chemtronics flux-off.
and flux remover need a LOT of remover to wash a board. simply squirting a tiny bit on does not work. it just leaves goopall over the board like a sticky film. you need ot squirt some on , let it soak for 10 seconds, scrub with brush then spray more on to wash the 'spent' stuff off. let the board drip out , spray once more.
apply warm air to dry. NEVER EVER blow air using your mouth . as the flux evaporates it cools down the board which pulls moisture out of the air. human breath contains saliva that is acidic .... you don't wan that on the board.
So : warm air is the way to go. use your reflow hot air gun.


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Any comments, or points of view expressed, are my own and not endorsed , induced or compensated by my employer(s).
 
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Offline astroschmidt

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #4 on: July 22, 2012, 06:03:17 am »
Thanks free_electron for thorough explanation.

Roger
 

Offline ftransform

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #5 on: July 29, 2012, 03:03:47 pm »
I use trichloroethylene break cleaner.
 

Offline dcel

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #6 on: July 29, 2012, 04:49:30 pm »
For rosin cored wire solder, I always clean the flux off the board with lacquer thinner and a wooden stick Q-tip. The reason I said always is because when I started repairing amplifiers, I made the repairs and the damn thing oscillated crazily. Took some time to determine the flux at the repair sites were the problem. Also had the same problem in a large mixing console channel as well. Now, I make the repair, clean the board while the joints still warm ( flux removes easier when still soft ) and then proceed with power up and testing. I have used alcohol before (all that I had avail.) and it takes too freaking long to clean the flux off the board. I wouldn't 'wash' the board in lacquer thinner, it eats plastics, I'm just spot cleaning.

Chris
 

Offline bradleytron

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #7 on: July 30, 2012, 12:50:00 am »
I use trichloroethylene break cleaner.

Just a note to say that I think this stuff is CARCINOGENIC, please check the MSDS sheets for more detail.
 

Offline T4P

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #8 on: July 30, 2012, 01:31:56 am »
I use trichloroethylene break cleaner.

da shit dangerous bro

For rosin cored wire solder, I always clean the flux off the board with lacquer thinner and a wooden stick Q-tip. The reason I said always is because when I started repairing amplifiers, I made the repairs and the damn thing oscillated crazily. Took some time to determine the flux at the repair sites were the problem. Also had the same problem in a large mixing console channel as well. Now, I make the repair, clean the board while the joints still warm ( flux removes easier when still soft ) and then proceed with power up and testing. I have used alcohol before (all that I had avail.) and it takes too freaking long to clean the flux off the board. I wouldn't 'wash' the board in lacquer thinner, it eats plastics, I'm just spot cleaning.

Chris

Eh ... really depends on what sort of alcohol you use. usually pure alcohol (IPA) is pretty smooth for my rosin fluxes
 

Offline ftransform

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #9 on: July 30, 2012, 03:08:58 am »
Just don't get any on your hands (appropriately picked protective gloves) and do it down wind (fan). The stuff is not flammable, so do not worry about motor sparking. This stuff removes the flux like magic and evaporates very quickly. Unfortunately all the awesome solvents are bad for you. I bet liquid butane would work well but unfortunately the canned stuff has a slight odor and its rather flammable.

I would at least dry my IPA with some kind of dehydrator or use the anhydrous stuff (either methanol or ipa) sold as gasoline dehydrator... I remember I fried a video card once after giving it a wipe over with a high concentration of IPA because I did not dry it for long enough. You need to be careful with the dry times on that solvent. I'm pretty sure I used the 95% stuff too...
« Last Edit: July 30, 2012, 04:08:27 am by ftransform »
 

Offline dcel

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #10 on: August 01, 2012, 08:29:24 pm »
Quote

Eh ... really depends on what sort of alcohol you use. usually pure alcohol (IPA) is pretty smooth for my rosin fluxes

99% Isopropyl Alcohol. Is Isopropanol Alcohol better as a flux remover?
Its been a while since I have used it for flux cleaning because being spoiled by the speed at which lacquer thinner takes it off. I'll have to try it again just to make sure I wasn't brain damaged when I used it before. I have used brake clean as well, but NOT that chlorinated shit, yuk, makes me gag. I use the flamable stuff at work and its much easier on the lungs, esp. with the spray and run technique. I've cleaned boards with it also, I have a special can at work just for that, it stinks but does not eat plastics.

Chris
 

Offline ju1ce

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #11 on: August 02, 2012, 10:38:03 pm »
99% Isopropyl Alcohol. Is Isopropanol Alcohol better as a flux remover?
It's the same stuff.
http://en.wikipedia.org/wiki/Isopropyl_alcohol
 

Offline Short Circuit

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #12 on: August 03, 2012, 12:15:43 am »
IPA does not work very well for flux removal.
Although (some) flux removers do contain a certain amount of IPA,
I use Electrolube Fluxclene (MSDS), which contains 10-30% IPA (Propan-2-ol).
So there can be similarities, but not the same.
 

Offline Dread

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #13 on: August 30, 2012, 08:02:08 am »
So what is the best brand of Flux remover?
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Offline IanB

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #14 on: August 30, 2012, 08:06:36 am »
So what is the best brand of Flux remover?

There is probably no simple answer to this.

It's worth bearing in mind that flux cleaner does not work just by rinsing. It requires mechanical action with a stiff bristle brush (or ultrasonic tank in production environments). The flux cleaning solvent is doing a balancing act between dissolving the flux and not dissolving the electronic components. Therefore the flux cleaner cannot be too aggressive and must be fairly gentle in its action.

If you use mechanical assistance then pure IPA or pure ethyl alcohol will work fine with most fluxes.
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Offline ablacon64

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #15 on: August 30, 2012, 01:54:18 pm »
I use mostly IPA but I don't like the results of IPA to clean BGA flux paste, I use Methyl Acetate, very good.
 

Offline amyk

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #16 on: August 30, 2012, 08:40:10 pm »
I use trichloroethylene break cleaner.

Just a note to say that I think this stuff is CARCINOGENIC, please check the MSDS sheets for more detail.
It's classified as a group 2A carcinogen, meaning "probably carcinogenic" and thus in the same group as emissions from deep frying. I'd worry about the other toxic effects of it more than its possibly carcinogenic properties...
 

Offline Fava

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #17 on: July 26, 2018, 07:16:46 am »
I use the Ethyl Alcohol. It clean so good than Isopropyl Alcohol. :-+
 

Offline schmitt trigger

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #18 on: July 26, 2018, 08:35:28 am »
Unfortunately all the awesome solvents are bad for you.

Very true
And few chemicals as potent and as nasty as CCl4.
 

Offline David Hess

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #19 on: July 26, 2018, 10:47:57 am »
a.) the solder flux could oxidize the copper in the long run

I have never actually seen this happen to a point where it mattered even after decades but it is possible.

Quote
b.) the solder flux is not as high-ohm as a cleaned PCB and can create high-ohm connections on the PCB

For most circuits this will not matter.  Where it does matter, extra cleaning steps should be used anyway.

Quote
a.) Isopropanol is aggressive to some plastics and can intrude into parts creating undesired effects.
It can e.g. dissolve polystyrene capacitors AFAIK

I have never had problems with IPA and board mounted parts but some plastics are susceptible although I do not think polystyrene capacitors would be affected.  Some parts like switches or trimmers which contain enclosed areas should be sealed before washing or soldered into place later no matter what solvent is used.

Quote
b.) By this dissolving of other materials a potential low-ohm film is spread over the PCB while the rosin itself is very high-ohmig when left untouched at the solder joints.

See above.  For most circuits this is irrelevant.

IPA does not work very well for flux removal.
Although (some) flux removers do contain a certain amount of IPA,

IPA is not my first choice either but it is inexpensive and less dangerous than most of the alternatives.

The common rosin flux thinner that I have is 50/50 IPA and toluene and it works great.  For better results and when cleaning rework, I use acetone or lacquer thinner.
 

Offline T3sl4co1l

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #20 on: July 26, 2018, 11:41:29 am »


;D

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Offline chris_leyson

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #21 on: July 26, 2018, 12:15:34 pm »
Best stuff I've found is Electrolube "Fluxene", seems to be mainly cyclohexane and some IPA. https://docs-emea.rs-online.com/webdocs/001e/0900766b8001ed27.pdf
 

Offline james_s

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #22 on: July 26, 2018, 02:39:52 pm »
I use trichloroethylene break cleaner.

Just a note to say that I think this stuff is CARCINOGENIC, please check the MSDS sheets for more detail.
[/quote

Don't drink it, just use it to wash the board. I sometimes use a dish of solvent and scrub the board off with a toothbrush.
 

Online CJay

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #23 on: July 26, 2018, 03:39:49 pm »
I've a few tins of Electrolube LFFR, works fairly well.

 Isopropyl alcohol works well too, try not to get it on your skin, it's absorbed pretty quickly and it's *really* bad for your liver...

Rosin flux is pretty stable though, the kind of kit I restore for fun is usually liberally caked in the stuff and on the few I've cleaned off the ~40 year old boards are like new underneath it, no corrosion, they sparkle.
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Offline mtdoc

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #24 on: July 26, 2018, 04:07:14 pm »
Isopropyl alcohol works well too, try not to get it on your skin, it's absorbed pretty quickly and it's *really* bad for your liver...

No, not really. It is very safe and not very toxic. You would literally have to bathe in it or drink it to get any toxic range dosage.

It is less toxic than almost any other common solvent sans water. There should be zero concern for toxicity using it to clean flux from a pcb in the usual manner.
 


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