Myth busting solder-flux cleaning with isopropanol alcohol

[CJay]

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.

It is one of the safer solvents, yes, but it's still worth trying to avoid getting it into your body if possible as it's not good for your liver. Toxicity is low but there's also cumulative damage to consider.

(don't misunderstand me, I use the stuff almost daily and know it's pretty safe but I would feel negligent not to mention the skin absorption and potential damage it can cause)

[schmitt trigger]

I feel embarrassed when i reply to a necro-thread 

But perhaps not. The subject matter is still quite relevant. 

[james_s]

Isopropyl can't be very dangerous, it's the stuff doctors use to clean your skin prior to giving an injection.

[KaneTW]

Isopropyl is used extensively in healthcare and cosmetics for disinfection and cleaning. Don't bathe in it or drink it and the worst you'll get is dry skin.

I wear gloves when using it because my skin gets awfully dry afterwards, but it's really not necessary.

[IanB]

I would feel negligent not to mention the skin absorption and potential damage it can cause

Isopropyl alcohol is sold in pharmacies as "rubbing alcohol" with the specific intent that it shall be rubbed on the skin. It is quite safe, and it is also "safe" to drink, in as much as it won't kill you if you do.

Are you perhaps getting it mixed up with methanol, which is in fact a deadly poison that does get absorbed through the skin and does cause liver damage?

[james_s]

Something that has bothered me is that "denatured" ethanol has (or at least used to have) methanol mixed in to make it toxic so people won't bypass the liquor taxes and drink it. If I deliberately poisoned something in order to keep people from drinking it I'd go to prison.

[free_electron]

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.

i've seen plenty ...

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]
i've seen microcontrollers refusing to boot due to flux residue. especially the water soluble flux. that stuff is in the tens of kiloohms ...


Chemtronix flux-off .  unbeatable !

[CJay]

I would feel negligent not to mention the skin absorption and potential damage it can cause

Isopropyl alcohol is sold in pharmacies as "rubbing alcohol" with the specific intent that it shall be rubbed on the skin. It is quite safe, and it is also "safe" to drink, in as much as it won't kill you if you do.

Are you perhaps getting it mixed up with methanol, which is in fact a deadly poison that does get absorbed through the skin and does cause liver damage?

What can I say, the MSDS specifically mentions it can be absorbed via the skin and that it can cause liver damage, I don't write them, I jsut read them, maybe I've misinterpreted it?

[boffin]

Best solution: Flux cleaner (it's not expensive, widely available). Example MG Chemicals 4140
Cheap solution: 50/50 nail polish remover and isopropyl in a tiny spritz bottle

Look at what's in MG Chemicals 4140

• Ethanol (pure alcohol)
• 1,1,1,2 tetraflouroethane (propellant)
• Propan-2-ol (aka Isopropyl Alcohol)
• Ethyl Acetate (the primary ingredient in more nail polish removers)

[helius]

An anecdote from Nobel laureate Kary Mullis about how you should interpret those warnings:

The worst thing I remember about those days of swelling middle management was when the guy who used to empty the isotope disposal buckets became the "safety officer" and suddenly got a staff, an office, and power.
Safety officers have a vested interest in interpreting everything in terms of various degrees of danger. In order to live for another day and to develop respect for the safety officer, signs were posted everywhere reminding us that everything we did was dangerous. Enclosed with every chemical is a Materials Handling Data Safety Sheet that explains its potential hazards—it's the law. The person who wrote the instructions for sodium chloride must have thought it was a mixture of sodium metal and chlorine gas rather than a completely innocuous compound that people sprinkle on foods to enhance the taste, usually called salt. Sodium and chlorine are pretty serious separately but not when combined into sodium chloride. The safety sheet described in detail the method that should be used to clean up sodium chloride: "Wear rubber boots," it advised. "Wear a respirator. A small spill can be flooded with water. Cleaning up a larger spill may require more than one person." Since I did not want anyone in my lab to suffer serious salt injury, I posted this warning on the wall. This is what happens when government agencies, who have to answer to nobody in particular, run rampant. If you want to have sodium chloride in your lab, you must have safety equipment that would be appropriate for sodium metal and chlorine gas. If you want to have it in a restaurant, you just have to have a salt shaker.

[rhb]

I have now "repaired" a number of pieces of electronics by the simple act of cleaning flux residue off the PCB.

The most recent was an eBay 34401A which arrived completely wonky.   At all settings it just produced a meaningless stream of numbers on the display.  Upon opening it up I observed a 1 cm diameter spot of what appeared to be solder flux in the vicinity of one of the LM358s that perform the integration for the ADC.  The device was slightly misaligned, suggesting a prior repair.

Upon cleaning  off the flux residue with a soft brush and isopropyl alcohol the DMM performs flawlessly and is in spec to the limits of calibration using a new DMMCheck Plus.

Rosin flux is hygroscopic.  It absorbs moisture from the air.  This leads to changes in resistance and capacitance between adjacent traces.  This has become particularly problematic with the switch to 3.3 and 1.8 V logic levels.  The noise margins get very small.  I have "rep[aired" my CD player, a TV remote and 3-4 other devices just by cleaning flux residue from the PCB.  The 34401A is simply the most dramatic example.

[mtdoc]

What can I say, the MSDS specifically mentions it can be absorbed via the skin and that it can cause liver damage, I don't write them, I jsut read them.

Toxicology is all about dosages. Vodka can be absorbed through the skin and cause liver damage too...

Bottom line for IPA is that no one will ever sustain liver damage from skin absorption of IPA using it to clean flux from PCBs.  Even if they were using it with an ultrasonic bath and briefly immersing their hands in it.

[David Hess]

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.

i've seen plenty ...

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.

i've seen microcontrollers refusing to boot due to flux residue. especially the water soluble flux. that stuff is in the tens of kiloohms ...

I should have been more clear; I was only referring to rosin based fluxes.  That water soluble stuff is trouble and should only be used in production.

[David Hess]

I use trichloroethylene break cleaner.

We used to use a lot of 1,1,1-Trichloroethane which is fabulous for removing rosin flux but no more.


As far as reviving an old subject, if the EEVBlog search facilities worked, maybe it would not happen as often.

[ogden]

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

Ethanol is even more aggressive (than isopropanol) to some plastics. Thou, cleaning PCB solutions usually are mix of both and not only. Good idea to check safety data sheets of popular flux cleaner. You will not get exact recipe, but pretty good understanding of contents for sure. One example I know: KONTAKT PCC

[bsudbrink]

I have now "repaired" a number of pieces of electronics by the simple act of cleaning flux residue off the PCB.

I have as well.  Several hobbyist built S-100 bus boards.  Regardless of how well stored (and these boards were well stored) rosin eventually darkens and becomes conductive.  IPA and an old toothbrush was all that was required to bring them back to life.

[rhb]

I tumbled to this living in Houston when a 2nd *very* lightly used VCR died after a year.  I took it apart to see if there were any usable parts and noticed that there was rosin flux everywhere.  There was nothing usable so it went in the trash, but I resolved to test the idea the next time something died.

I *did* have to clean my CD player a second time.   The only solder flux on it was a little bit around the MCU.  But apparently I didn't get all of it and after about a year and a half it died again ("no disc").  The 2nd cleaning did the trick and it's still working flawlessly 2-3 years after the 2nd cleaning.  I'm planning on building an alcohol pressure washer using a 100 psi fuel injection pump with a distillation system so I can reuse the alcohol.

A lot of consumer gear is to difficult to disassemble, so the idea is a flexible wand I can poke into the right places and a few gallons of clean alcohol in the tank.  I work in a thrift store and we throw away a lot of stuff I think this would fix.

[james_s]

I never understood why thrift stores throw away so much stuff. If there was an as-is section of broken stuff that's the first place I'd look when going into one of those places and I know lots of others who would as well.

[rhb]

I never understood why thrift stores throw away so much stuff. If there was an as-is section of broken stuff that's the first place I'd look when going into one of those places and I know lots of others who would as well.

Space.  The volume of stuff can be staggering and I'm in a town of 7500 where most people throw things in the trash.

[james_s]

I guess I'm just a different sort of customer. I completely ignore the rows upon rows of clothing and knick-knacks and head straight for the electronics section, usually leaving empty handed. The best thrift stores are the ones that have a bunch of random junk in unknown condition, I've found all sorts of cool stuff. At one place I got a neat 1970s digital clock that was marked needs repair. Turned out it's electromechanical with a shutter mechanism for the 7-segment digits, only problem was the incandescent lamps that backlight the digits were burned out. It's the only one like it I've ever seen other than a picture I found online of the same mechanism in a clock radio. Most probably just got thrown away when the (easily replaceable) lamps burned out.

[linux-works]

my first job in high school (late 70's) was at a pcb assembly house.   a very small company that had a wave solder line and they made boards for gas station pumps (the digital displays).  I had been soldering a few years already, since I started as a very young kid, but I was surprised to see them use ACID flux (I remember it being pink or reddish and very low viscosity).

we would paint a lot of the flux on the board, the board would be sent thru the wave solder machine (it was all open back then, no cage around it like you'd see in today's big pcb lines) and once it cooled, we'd would work at little kitchen-sink areas, running the whole soldered board under hot running water, scrubbing with a brush and using some kind of cleaning fluid to remove as much of the remaining flux as we could.  we knew it was acid and could not stay on the board, but the boss was convinced that this was the best solution and all joints did come out very shiney, in the end.

it really surprised me to see these handled like dishes in a sink   there was even a dish rack to hold the board vertically while they air dried.

all of us were teenagers (ie, low cost)   I wonder how reliable those displays were.  but the memory of that first soldering job I had will never leave me.  scrubbing boards like dishes, under hot running water - that really surprised me.  it was all low density chips and TH parts and I suppose that once the boards were fully dry, all was well.

the lesson I learned was: acid flux can be used IF you don't let it sit very long and you take great pains to remove it after the process.  but again, this was the late 70's..

[T3sl4co1l]

They probably didn't fare too well -- the metal gets etched by the acidity, inevitably trapping some acid in the pores.  Once sealed over with solder, that still shouldn't do anything; but, if the solder corrodes through, or there's a sneak path through the porosity to an exposed surface, it will fail, some day.

The active ingredient is usually zinc chloride, a deliquescent salt and Lewis acid.  The former means it greedily absorbs moisture from the air, until hydrated to the point it forms a saturated solution.  The latter means it hydrolyzes (breaks down by water), giving HCl (a traditional [Bronsted-Lowry] acid) and a zinc hydroxide crust.  In both cases, the solution encourages electrolytic corrosion, and the acidity accelerates it further.

Tim

[linux-works]

I don't know if the company did a 'sell and run', or if they knew the products would start to fail after X amount of time.  maybe the boards were only meant to last a certain amount of time.  back in the 70's, we didn't have quite the 'disposable' mentality of electronics that we have today; things that broke would be repaired, most likely.  the company didn't appear to be a 'sell and run' kind of thing; the owner seemed to be doing what he felt was the best thing for the process.

it would have been interesting to go back and find out how well the product did.  maybe our scrubbing and cleaning really was enough.  once the boards came off the line, it was less than an hour later that we were removing the acid residue.

I would not repeat this in today's world, of course.  just relating an old past experience.

fwiw, I've had tours of proper high-end pcb assembly houses and the size of the machines used just to clean the boards are larger than my whole living room space   we could not see what was going on inside that machine, but the boards that came out were clean as could be.  modern tech can do a seriously good job at making pcb's, as long as the customer is ok paying for it!

[David Hess]

For precision analog boards, I remember where we had to install a reverse osmosis dishwasher to wash the board *before* assembly to reduce leakage but RMA flux and hand scrubbing in flux remover was completely sufficient.

[linux-works]

speaking of cleaning, when I get a batch of boards with HASL from pcbway (for example), I've found that there is some kind of coating on the solder that makes it really hard to work with.  scrubbing hard with IPA before I even start populating the board seems to work well.

first few boards I made, using pcbway board, were aweful until I realized this.