How to Remove White Residue on PCBs

[bostonman]

Over the years I've tried cleaning boards without luck.

Obviously flux residue doesn't come off easily and needs to be plucked off, but, once I clean with Isopropyl, I still get white residue once dried.

At old jobs I'd leave the boards soaking in a isopropyl pan, I'd go over the board with a brush several times, etc... and then blow air to dry off the isopropyl.

Recently with home projects I've tried the electronic spray, but that too leaves white residue. I'm assuming the flux in the solder (and any added) gets dulled by the isopropyl, spreads out, and dries.

Does anyone have a trick to getting a board clean because I've been frustrated over this for years.

[jmelson]

Soak with isopropyl, then brush with an old toothbrush, then immediately wash with water, you will see a white cloud in the water, that is your while residue being washed away.  You may have to repeat several times to get it completely clean.
OR, use water-soluble flux where the boards NEED to be cleaned, it is amazing how clean they come out after just a water rinse.  No solvent needed.
Jon

[all_repair]

After cleaning off with alcohol or flux removal solution, I rinse with distilled water to flush away any leftover liquid.

[HackedFridgeMagnet]

I just use iso and scrub with the toothbrush till its all looks clean when wet.
Rinse the board by orienting it vertically and then squirting copious amounts of iso on onto it. A small river of iso should flow off the pcb.
You probably could use other liquids for rinsing but iso is not that expensive.

[Bud]

A trick that worked for me (someone posted here a few years ago) was to use Spay Nine cleaner instead of isopropyl (for no-clean SMT flux, not rosin flux) . And a toothbrush of course. Rinse with demineralized water after.
It might also work as a second step after cleaning with isopropyl first but i did not try.

[jpanhalt]

Ironically, this thread comes just when I was removing "white residue" from a PCB.  For a little background, I have been experimenting with cellosolves as flux removers.  Later, I found that some commercial removers also contain them.  What limited me was finding a board that had white residue as a positive test. 

I use 63/37 flux cored Kester solder with 44 flux and rarely had a problem removing it cleanly from freshly soldered joints on PCB's with absolute ethanol or absolute ethanol/acetone 3:1 (very approximately).  I settled on testing ethyl cellosolve (2-ethoxy ethanol), because it can be dried easily and quickly with compressed air.  It works neat and almost as well with considerable water (up to 20%).  The board I was working on today was a SparkFun solderable breadboard that was a few years old.  The red solder mask made seeing any residue easy, and I was got a white residue with ethanol. 

Then, I used neat ethyl cellosolve.  It removed the residue completely, but there was a slight haze on a few areas of the solder mask and some connectors after blow drying at room temperature.  A rinse in absolute ethanol gave a nice shiny board with no haze.

I don't know whether the slight haze was from impurities in the cellosolve (technical grade) or something on the board.  The rinse in ethanol removed it quickly.  My ethyl cellosolve was bought over eBay from an American source. It was manufactured by HyMedia Laboratories (India) and was reasonably priced for 500 ml.  That class of solvents is widely used and relatively non-toxic.  The characteristic odor of some floor cleaners (e.g., ZEP stripper) is due to butyl cellosolve. The board ended up needing rework, and for cleaning that, I started with neat ethyl cellosolve, which worked fine.

My procedure going forward will be a wash in ethyl cellosolve using a toothbrush to get into crevices, let drain, rinse in ethanol, and blow dry.

[bostonman]

I've left boards soaking at my old jobs (they had large containers to hold entire PCBs) and they'd still have white residue.

I'll try the other ideas, but seems water can be dangerous for boards that have plastic switches and stuff.

[andy3055]

What kind of solder are you (OP) using? I use 60/40 rosin cored solder and I have no problem removing it with (even) 70% alcohol that you can buy at the drugstore. You have to do it a few times to get rid of the stickiness but it can be done. If you have a tray filled with alcohol and dip the board in it and use a brush, it should work.

[Whales]

Apparently white PCB residues can be caused by a lot of different chemical products, not even necessarily all from the flux:

https://www.kester.com/Portals/0/Documents/Knowledge%20Base/White-Residue-15Apr1988.pdf

[Rat_Patrol]

For SMT or THT?

For THT, I use water wash flux solder and flux paste. Washes right off easily.

For SMT, I still use standard no-clean flux from Chipquik, but I soak in a vat of IPA for 10 minutes, 5 minutes in the ultrasonic cleaner with Branson EC, rinse with DI water, and they are squeaky clean.

[asmi]

I use ultrasound washing machine. Highly recommend! If you do not tolerate high-pitched sounds well, cover it with some box while it's working.

[bostonman]

What kind of solder are you (OP) using?

See attached. This is my stash, but at other jobs, I'm sure it was other types of stuff and I didn't have much luck cleaning.

I use ultrasound washing machine. Highly recommend!

The type of boards/parts has been a combination of through-hole and SMT along with boards that were repaired with parts that (probably) can't get water in them because they are not sealed; so I'd be reluctant to put water on these types of boards.

Do you have a ultrasound washing machine model recommendation? Again though, if a board has things like DIP switches or parts that can be damaged, would water be the best solution?

At an old job we had (over the course of years) hundreds, if not, thousands of power supplies fail in units because it was determined that whatever the board house used to clean the boards was getting up the leads and into the capacitors causing them to short internally. I don't know if it was limited to water or the capacitor was cheap allowing water/alcohol (or whatever cleaning solutions are used) to get inside.

[jpanhalt]

UPDATE
I have finished the prototype I was working on (post #6) and only used ethyl cellosolve to clean up after revisions.  So far, it has worked well with the 44 flux residue.  I have attached a couple of pictures.  I tried to get reflections in one, but was not very successful.  The cleaned boards are as shiny as when I use absolute ethanol or ethanol/acetone.  No white residue was noticed.

The current Kester 5768 flux remover has ethanolamine and diethanolamine in it.  It is sold as a concentrate for dilution with water.  The amines are to provide "saponification," which Kester says is necessary for its newer fluxes.  I suspect one could try those with ethyl cellosolve and a little water.  Maybe simply adding some household ammonia would work too.  Apparently, Kester 5768 cannot be shipped to home addresses by a local distributor.

[asmi]

The type of boards/parts has been a combination of through-hole and SMT along with boards that were repaired with parts that (probably) can't get water in them because they are not sealed; so I'd be reluctant to put water on these types of boards.

Do you have a ultrasound washing machine model recommendation? Again though, if a board has things like DIP switches or parts that can be damaged, would water be the best solution?

At an old job we had (over the course of years) hundreds, if not, thousands of power supplies fail in units because it was determined that whatever the board house used to clean the boards was getting up the leads and into the capacitors causing them to short internally. I don't know if it was limited to water or the capacitor was cheap allowing water/alcohol (or whatever cleaning solutions are used) to get inside.

I wash all my boards, with all connectors, switches, buttons, etc. Never had any failures. I've bought a cheap 6L machine on Amazon, as for the solution, I use BM-5000 General Purpose Ultrasonic Cleaning Solution Concentrate also bought there. This solution is 92% Ethanol, I dilute it 1:10 with distilled water as per instructions, and results are very good - importantly, matte PCB soldermask looks pristine again after washing, something I was never able to achieve using any "manual" methods.

Once out of the wash, I usually either leave them in the open for at least 24 hrs to dry naturally, or put them in an oven at 50-60°C for 1-2 hrs if I want to begin testing boards ASAP. Theoretically one could use a hot air gun set to the 100°C to dry it even faster, but I don't think that's a good idea because moisture + heat + temperature gradient across the PCB is not a good combination.

Most parts are designed to withstand US wash because they are often used at PCBA fabs, but there are some which are not. These are usually components that have intentional openings in the package - like pressure sensors, or humidity - that sort of thing. But since none of the boards I washed had them, so I don't really know details.

Also ultrasound wash acts as a good test of soldering quality due to mechanical stresses induced, so be prepared for some of your tombstones you didn't notice to detach. It happened to me few times, but isn't that often even though I use cheap ZB2520HL reflow oven and not some sort of "professional" one.

[bostonman]

I'll have to look into some of these options.

I agree that some boards are safe to soak, but I had a board from an Agilent scope with 0603 parts, ZIF connectors, tiny fingers that held RF shields (a complete nightmare to reattach the shields), and double sided. I imagine the board would need to be placed onto something so the bottom side of the board doesn't rub causing components to break. This board, however, looked like it had borderline solder connections because I had to replace the ZIF connector and found the pins basically pulled off the solder. This cleaning method would possibly cause many issues.

Trying to clean this board was a nightmare. The tiny fingers that hold the RF shields kept grabbing the acid brush hairs and ripping them off. The board ended up having numerous hairs stuck everywhere.

The current board I've tried cleaning is from a C64. This is certain more durable than the Agilent scope board, however, it has a sensitive RF section, a plastic power switch, and plastic connectors. Not to mention I don't know how well sealed the components are (although I've replaced just about all the electrolytics).

The main thing I don't understand: I've used over a half can of contact cleaner, several amounts of isopropyl (with the board on its side in both incidents so the liquid runs down/off the board), and, instead of letting the remaining stuff sit, I'll use a vacuum cleaner to suck all the liquid off (I don't have an air compressor and figure it basically performs the same function).

After several cycles of the above method, I still saw white flaky residue. My thought is that the isopropyl and spray should drag all the junk to the bottom of the board. This doesn't seem to be the case as I find the white flaky stuff everywhere.

Maybe I shouldn't use contact cleaner and use some sort of flux spray cleaner?

The irony is that I've used brake cleaner, carburetor cleaner, and the contact cleaner, all on various stuff. In most cases, depending on what I'm cleaning, and what I'm using, the cleaner always seems to leave the item shining. Yet, something so simple as flux seems to be a nightmare to remove.

[bostonman]

I'm resurrecting an old thread that I originally started.

Recently I repaired a vintage Commodore mouse with plastic mechanical parts. Due to the plastic and age, I was reluctant to use anything but Isopropyl alcohol. As usual, I grabbed a brush (tooth brush this time), dipped it in the Isopropyl alcohol, and scrubbed all the flux. After drying, not only was the section I brushed white with flux residue, but spread to other areas.

I repeated the wash and got it cleaner, however, some was still sticky. The only thing that seemed to work was using a can of air to wash off the alcohol and dry it quicker.

If I remember correctly, back at my old job I'd leave a PCB submerged in alcohol, scrub it clean, and would still see white residue after it dried.

My assumption would be the Isopropyl alcohol is strong enough that it deludes the flux, scrubbing it clears it away, more fresh alcohol, eats the remaining, and then another dose of alcohol, and it dries clean.

This doesn't seem to be the case. My confusion is what am I doing wrong, and, also, I'd like to put a few bottles of Isopropyl alcohol in a metal pan to wash boards in the future but sometimes the alcohol mixes with the metal and causes the alcohol to become mixed with metal tarnish residue.

Does anyone have recommendations for a pan and ways to stop my boards from remaining white/sticky?

[jpanhalt]

Try the acrylic floor stripper mentioned below.  I use ZEP brand Heavy Duty Floor Stripper which is butyl cellosolve, a little ethanolamine for saponification, and water.  You want a final cellosolve concentration of about 10%.

Oops, I just noticed the date.  I switched from messing with other cellosolves to just using the cheap stuff, because evaporation is not an issue. 

[luudee]

I usually use Acetone and Q-tips.

That works very well for me. Obviously have to take special care with Acetone.

Cheers,
rudi

[thm_w]

Recently I repaired a vintage Commodore mouse with plastic mechanical parts. Due to the plastic and age, I was reluctant to use anything but Isopropyl alcohol. As usual, I grabbed a brush (tooth brush this time), dipped it in the Isopropyl alcohol, and scrubbed all the flux. After drying, not only was the section I brushed white with flux residue, but spread to other areas.

Was this just cleaning, hot soapy water works for that. Windex is another good one to try.

If the flux has been there for 40 years its probably harmless at this point.

[bostonman]

If the flux has been there for 40 years its probably harmless at this point.

No, this flux was due to a repair.

As mentioned, I am sure many of these chemicals will work since many of you had such luck, however, what I find is that boards I repair contain plastic hardware, or something that always forces me to question whether I'll ruin parts as a result of using harsh chemicals.

In all my jobs, everyone uses Isopropyl alcohol and seems to have better luck than me. From what I see, if I place a paper towel over the washed area (let's ignore the static electricity issue) and then use the brush to absorb the liquid by pushing the brush down on the paper towel and/or air blow (in my case I've used a vacuum cleaner since I don't have a compressor but always afraid I may suck a part off the board), it seems to dry much cleaner; but usually still somewhat sticky.

[jpanhalt]

Well, if you use IPA and it works, great.  If it didn't work, as seems to be the case,  keep repeating it.  Maybe your luck will change.

My advice is, if IPA  didn't work, try something different.  You seem to think IPA is less harsh than consumer floor cleaner diluted 1 part to a total volume of 3 parts..  Why?  What do you mean by "harsh?"  How is it measured?

[bostonman]

I've used a few things over the years for cleaning (not PCBs) such as brake cleaner and either electronic cleaner or intake manifold cleaner, and sometimes it ruins the plastic.

For the most part, I've never had IPA ruin anything and would assume letting the PCB sit in a IPA bath would clear away everything. I know that in the past I've poured IPA into a metal pan only to find it got discolored with mixing with whatever metal the pan was made from. So I was wondering what a safe metal pan would be to avoid this.

[thermistor-guy]

I usually use Acetone and Q-tips.

That works very well for me. Obviously have to take special care with Acetone.

Cheers,
rudi

Arctic Silver makes ArctiClean: http://www.arcticsilver.com/arcticlean.htm

It's great for removing thermal grease. It might be useful for PCB residue removal.

[wilhe_jo]

At least for me, the residues are partly cased by my IPA.
Switching to 99% stuff (IIRC the old one was 80% or so) made it way better, but not perfect.

What works best for me for "smart front panels" (front panels made from PCBs with cap-sensors, LEDs,... On their back) is the following procedure:
- get it clean with IPA
- wipe with fresh IPA
- wipe with rs-components quick dry cleaner

This cleaner by rs-components smells suspiciously similar to break-cleaner. Which makes sense, because it would desolve a different type of residue.

73

[Psi]

IPA is annoying for cleaning flux, it gets saturated with flux residue almost immediately and then leaves white streaks on the 2nd or 3rd PCB you clean with it.

You will find it works much better if you have 2x IPA tubs for dirty and clean IPA.
Give the PCB a good wash and scrub with a brush in the 'dirty' IPA tub .
Then do a final rinse in the fresh IPA tub. Rinse only though, don't scrub in the rinse bath or you will dislodge more flux hidden under ICs and create streaks again.
Then immediately blow the PCB clean with compressed air before the IPA has a chance to evaporate and leave flux behind. (Be very careful with this step as you are aerosolizing a flammable liquid).

After you're done with cleaning all the PCBs, make your clean IPA becomes the dirty IPA for next time.
And when you next use it you pour some fresh IPA into the clean IPA tub.