5 Things to Know Before Buying PCB Brush Cleaning Machine

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John_ITIC

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PCB Ultrasonic Cleaner Recommendation?

« on: October 19, , 11:09:10 pm » I would be interested in purchasing an ultrasonic cleaner that absolutely removes all traces of flux residue off of my PCBs. I have found that at 5 Gigabit/second signaling rate, flux residue has a negative impact on signal integrity. Cleaning with flux remover, isopropyl alcohol and tooth brush improved the SI but I can still see under microscope that there are still traces of flux residue between vital IC pins. My USB 3.0 protocol analyzer showed packet error count go down from to 100 after the manual cleaning. It is very hard to get to the pins in question so I'm looking for "the best" solution (not necessarily the cheapest solution).

I have gone through earlier threads regarding ultrasonic cleaners but have not been able to figure out which one to get. My board is 120x100 mm so I don't need a large unit. I want a unit that works with IPA and that does not damage ICs via too much power.

Any recommendations? Links to relevant reviews etc. ?

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georges80

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #1 on: October 19, , 11:52:20 pm » Most inexpensive (ebay) ultrasonic cleaners seem to work just fine in my experience. They have stainless steel basins, so no issues with IPA.

More importantly you'll need to determine if the flux you have on the boards is water or IPA soluble - some of the no clean fluxes can be an issue to dissolve. I presume these are hand/home assembled boards?

I'd also suggest a source of compressed air to then blow-dry the boards after their wash.

cheers,
george.

rx8pilot

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #2 on: October 20, , 12:32:27 am » IPA or any other flammable liquid is NOT recommended. The ultrasonic action can ignite.

There are specific detergents for PCB cleaning from Alconox and others.

Only consider units with frequency sweeping the reduces standing waves. Not only does that clean more effectively, it prevents damage to the PCB. It is possible to make very small scale damage to semi-conductors so the power and time should be considered.

There is a lot of subtlety in the process....temperature, power, frequency, detergents, etc. You should heat the system and de-gas each day and after adding fluid.

I used a single system with detergent followed by an aux tank with DI water. The PCBs were completely resudue free and it was easy.

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #3 on: October 20, , 02:09:02 am » Yes, these are hand-assembled / reflow assembled prototype boards. I'm using various fluxes for various use:

1) Sticky rosin-based flux for BGA reballing (Zephyrtronics). Very gunky stuff. Cleans up well with regular flux remover.
2) MG Chemicals no-clean flux paste. Not actually using but has a tube.
3) Leaded, no-clean MG chemicals p, solder paste. For general board reflow.
4) Amtech NC-559-ASM flux paste, for BGA reflow (rework).

I also have a no-clean flux pen, not sure what it is but use it for general hand soldering. "Water soluble".

Regarding damage due to ultrasonic cleaning; is there any scientific study made on this? I have heard such rumors but not actually seen any proof of damage. Various YouTube videos say such IC damage is a myth.

Are there any entry-level professional units with the mentioned frequency sweep functionality, that are intended for PCB cleaning? I suppose jewelry units may work but may have side-effects such as component damage... Pocket-Sized USB 2.0 LS/FS/HS Protocol Analyzer Model A with OTG decoding.
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jwm_

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #4 on: October 20, , 04:13:03 am » This reminds me of something silly I did once.

I got an ultrasonic cleaner made for jewlery and decided to use it to clean some PCBs. Distilled water seemed to work well, and it had a stainless lining, so I decided to try something stronger. So i load it up with acetone (you see where this is going) and turned it on.

I came back a few hours later and reached for it to open the lid and the thing was basically taffy. my fingers poked through the lid like it was soft rubber. As you can guess, the ultrasonic vibrations atomized the acetone so that it infused into every plastic part of the machine. It was actually kind of odd. It wasn't pure ABS or it would have disolved into a mush pile, it more became like soft latex or something so there was some component of the plastic left with very different properties.

rx8pilot

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #5 on: October 20, , 07:00:22 am » As for scientific evidence...I am not sure. It sounds plausible and I don't have the resources to truly understand or test the long term effects of ultrasonic cleaning. Shortly after using the ultrasonic process, we had an unusually large number of failures that we could not figure out. I stopped using the ultrasonic cleaner and by chance the circuits were totally re-designed at the same time. I never went back to look for the origin of the problem which could have been any number of things. I won't blame the ultrasonic since I have no actionable data. If I felt the need to go back to it, I would allocate some time to make sure I was not creating a long term reliability problem from mechanically stressing the brittle materials IC are made from. One thing for sure is that aqueous ultrasonic cleaning is a molecularly violent process. A LOT of energy is focused on a very small area. It was a short lived experiment that was abandoned without a final conclusion.


I use the Crest D for most stuff. It has been reliable and primarily used on small machined parts as part of the surface prep for plating. Not too expensive, heater, de-gas, varbiable power, digital timer. I don't know of any off the shelf unit that is specifically for PCB's.
http://www.ebay.com/itm/NEW-Crest-CPD-27-Liters-Benchtop-Ultrasonic-Cleaner-Heat-Timer-Degas-/?hash=item1c4eb4a003:m:mVTmLkYMSrHTEWd4Hnz2b1Q

I used a few of the detergents from Alconox http://www.alconox.com/ and they seemed to do a great job. Hot DI water rinse is usually needed.
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crispy_tofu

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #6 on: October 20, , 10:08:31 am »

The ultrasonic vibrations atomized the acetone so that it infused into every plastic part of the machine. It was actually kind of odd. It wasn't pure ABS or it would have disolved into a mush pile, it more became like soft latex or something so there was some component of the plastic left with very different properties.

That's amazing.  Must have been quite surprising, too! 

Shock

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #7 on: October 20, , 11:53:47 am » Crest Ultrasonic Cleaners are the go to brand in the industry. Branson EC (Electronic Cleaner Concentrated
Cleaning Formula) is the detergent designed for cleaning PCBs (flux, rosin etc).

It's a good idea to get the tray with it, you need to suspend your PCBs in the middle of the cleaner not resting on the bottom.

You use distilled water and a tiny amount of Branson EC. Then flush with clean distilled water or IPA if you want to speed up drying time and/or displace water under components prior to drying.

A heated ultrasonic cleaner gives best results and you should avoid ones that have complex controls as all you need to do is turn it on, set the temp, monitor the time and perhaps flip your pcb half way through. A cooking timing or your smart etc means you can leave it unattended in the next room and not worry about noise or chemical issues and just come back to it when it's finished.



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dave_k

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #8 on: October 20, , 12:11:50 pm » I have had excellent results cleaning PCBs with Electrolube Safewash SWAS, both manually and in a ultrasonic cleaner. Best of all it's biodegradable and if diluted sufficiently can be tipped down the sink (read the MSDS).

http://www.electrolube.com/products/cleaning/swas/safewash_range_-_aqueous_cleaning/

rx8pilot

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #9 on: October 20, , 09:43:28 pm »

It's a good idea to get the tray with it, you need to suspend your PCBs in the middle of the cleaner not resting on the bottom.

Very true. For mechanical parts I have a wire basket. The goal is that the parts to be cleaned should be touching only the fluid as much as possible. I made a wire hanger that allowed me to hang a number of PCB's and dip them in the solution where they are suspended right in the middle.

Heat, in my opinion, is critical. The effectiveness of the process diminishes rapidly in cool water. Do not discount the benefit of the de-gas cycle either. It works to get rid of the tiny bubbles that are in suspension. The bubbles are too small to rise to the surface on their own and the de-gas cycle essentially pulses the transducers which causes the small bubbles to combine and rise out of the solution. The 'denser' fluid has a better effectiveness since the bubbles will stick to the surface and isolate that area from any ultrasonic action. Some people think that when you dip the part into the solution, it will get wet. That is not true. If the parts enters quickly, the cavitation will create bubbles that stick to the dirty surfaces and stay there during the cleaning cycle. The areas where the bubbles were will be untouched. Gently place the parts in the tank and gently remove them. Good detergents help this as well.

My thinking was that if all the parameters are optimized, it will reduce the cycle time, improve the end result, and minimize risk of damage to the the PCB/components.

Note on disposal: Even if your detergent is biodegradable, the stuff you cleaned off the PCB is probably not. Factory400 - the worlds smallest factory. https://www.youtube.com/c/Factory400

John_ITIC

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #10 on: October 20, , 11:55:21 pm » Ok, Crest it is. Branson EC seems easiest to find in the U.S. So if I get the below equipment & solution, I would be good to go?

http://www.ebay.com/itm/Crest-0-5-Gal-Benchtop-Ultrasonic-Cleaner-w-Heater-and-Mechanical-Timer-CP200HT-/?hash=item2af60a:m:mdH2iiZCWuvulWDvmfXHKjQ

http://www.all-spec.com/products/635-028.html?gclid=CPfd_bCd0sgCFQiNaQod5V8LrA

Thanks,
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Shock

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #11 on: October 21, , 05:40:14 am » Think about ordering one with the wire tray as well.

Make sure what you're cleaning fits in the tray at least at a 45 degree angle comfortably and will be totally submerged. You need to think of future needs as well. The 45 degrees helps get the agitating action get up around components.

If you buy the gallon of detergent its about 25% cheaper but you need to work it out yourself (if you need that much).


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Spikee

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #12 on: October 21, , 08:53:18 am » When you have something lIke the ti hdc ( with an hole in the bottom) how would you clean that? Freelance electronics design service, Small batch assembly, Firmware / WEB / APP development. In Shenzhen China

Shock

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #13 on: October 21, , 10:59:50 am »

When you have something like the ti hdc ( with an hole in the bottom) how would you clean that?

BGA with an ultrasonic cleaner setup for cleaning electronics as well. If it's sensitive to cleaning then you best read up or contact the manufacturer. You are submerging at temperature and it's a mildly abrasive cleaning method (results depend how long you clean). So writing on labels, adhesives and rubber and that kind of material can be affected especially if you leave it in too long. Some labels may wear straight away, the ones on components are normally hard wearing though.

If you read the Branson EC specs it says it can slightly tarnish polished aluminum. Soldering/Rework: Pace ADS200, Pace MBT350
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jwm_

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #14 on: October 22, , 01:44:19 am »

I use acetone, works better than ipa, and unlike ipa, there is no law prohibiting its use in any concentration.

There are laws prohibiting IPA where you are? I can understand methanol having some restrictions, but IPA is not really more dangerous than a lot of household things.

In any case, you can turn any percentage IPA into 100% IPA just by adding salt. salt water and isopropyl are not miscible, so when you add a bunch of salt to a water IPA mix, it seperates out into a salt water and pure alcohol layer, you then just siphon off the pure alcohol layer. The following users thanked this post: aterren

helius

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #15 on: October 22, , 02:39:08 am » The "air quality" rules in Southern California are imbecilic. Volatile Organic Chemicals are the enemy, and you can't have them! Except for acetone, that doesn't count because... um... because we need it to do our nails. Please don't tell us that watering down cleaners will lead to more waste and pollution, that's somebody else's problem.

Acetone is not great for PCB cleaning. Not only is the smell overpowering, but it attacks ABS resins and destroys switches and capacitor seals.
Asahiklin AK-225 was close to ideal, and you could buy it until last January. Some of us have stockpiles...
Now that it is no longer available, there are new mixtures on the market that claim to dissolve stubborn no-clean fluxes. Reading the MSDS for cleaners can be interesting (remember that ingredients judged non-hazardous do not need to be listed). Many of the "heavy duty" cleaners contain DuPont's Vertrel, a series of decafluoropentanes. Some use even more exotic solvents, like Honeywell's "Solstice", a chlorofluoroalkene that is evidently not yet banned.
http://www.all-spec.com/products/acl.html « Last Edit: October 22, , 02:53:39 am by helius »

rx8pilot

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #16 on: October 22, , 06:24:29 am » Acetone? WTF? Seriously?

That is a horrible solution. Factory400 - the worlds smallest factory. https://www.youtube.com/c/Factory400

KL27x

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #17 on: October 22, , 09:17:27 am » Quote

Acetone? WTF? Seriously?

That is a horrible solution.

I'm surprised at this. I have stored many pulled components in pure acetone to clean them up (no electrolytic caps, to be sure), and I have yet to break/melt anything. I actually came to suspect there was an unspoken rule that board-level electrical component plastics must be resistant to acetone. For a short exposure (not necessarily ultrasonic cleaning), I would have thought acetone would be far from a WTF-level of horrible.

I rarely bother to clean rosin residue, but I have noticed that acetone works much better on it (i.e. great) than alcohol. No cleans, different story. « Last Edit: October 22, , 09:26:34 am by KL27x »

Shock

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #18 on: October 23, , 08:11:56 am » IPA will work with Rosin it just takes a while and it doesn't seem to dissolve off, it's more like it saturates very slowly with alcohol. So unless your scrubbing it, whats not been loosen off or washed away will stay in place, at least that is what I experienced when I tried it. Soldering/Rework: Pace ADS200, Pace MBT350
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John_ITIC

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #19 on: October 24, , 12:15:14 am »

http://www.ebay.com/itm/Crest-0-5-Gal-Benchtop-Ultrasonic-Cleaner-w-Heater-and-Mechanical-Timer-CP200HT-/?hash=item2af60a:m:mdH2iiZCWuvulWDvmfXHKjQ

http://www.all-spec.com/products/635-028.html?gclid=CPfd_bCd0sgCFQiNaQod5V8LrA
/John.

Thanks Everyone, I just placed an order for the above equipment. For a while, I was eying the cheap Ebay clones but eventually figured I'd buy a unit that will last some 10 years. Also, It would be silly to put my $3,000 prototype PCB into the cheap $50 cleaner, trying to save a few bucks... Pocket-Sized USB 2.0 LS/FS/HS Protocol Analyzer Model A with OTG decoding.
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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #20 on: October 08, , 05:16:15 am » Hello,

Saving nature and reusing an old thread.
Paintbrush and IPA work just fine for surface cleaning, but would like to have deeper cleaning using ultrasonic. There are several liquids to choose from, but all the products I have found requires rinsing with water. Anyone using alcoholic based cleaner with ultrasonic? (something that is meant to use use that way and is non-flammable)

A

coppercone2

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #21 on: October 08, , 03:48:33 pm » I would not put solvent into an ultrasonic cleaner without a gas flood box to operate it in, if you have a friend that welds aerospace titanium he might have a chamber you can use

That is considered mad dangerous. What you can do though, that is much less dangerous, so long you work outside, is put the alcohol in a bag (limited amount), then put the board in the bag. Not sure if you can use a ESD bag. It will hold up for a little while and if it leaks the alcohol will immediatly go into the water and so long you have alot of water, the mixture is never flammable, so you only need to manage small possible vapor problems... but if you poured 1/2 a gallon of ipa into a stock ultrasonic I would be real scared of that setup.. I highly recommend investing in a flux cleaning solution that is not flammable for this job.

SteveyG

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #22 on: October 08, , 08:35:03 pm »

Hello,

Saving nature and reusing an old thread.
Paintbrush and IPA work just fine for surface cleaning, but would like to have deeper cleaning using ultrasonic. There are several liquids to choose from, but all the products I have found requires rinsing with water. Anyone using alcoholic based cleaner with ultrasonic? (something that is meant to use use that way and is non-flammable)

A

I use an ultrasonic cleaning solution then afterwards use compressed air on the PCB. If the surface finish is not acceptable, spray down with inexpensive brake cleaner. YouTube Channel: https://www.youtube.com/user/sdgelectronics/
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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #23 on: October 09, , 06:40:19 am » "SteveyG"
The cleaner you are using is meant to be rinsed after ultrasonic processing? All the ultrasonic cleaners I have found are like that. If there is a cleaner that does not require anything but one-step ultrasonic processing I would be appreciated to know what is that product.

A

chronos42

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Re: PCB Ultrasonic Cleaner Recommendation?

« Reply #24 on: October 30, , 06:52:07 pm » Hi,
in this thread was mentioned, that ultrasonic cleaning can destroy electronic components. I did not believe this, until today.
I am currently repairing an Instrument from a seller from Israel, which was extremely dirty inside. (No complain about the seller, I was aware about the state of this instrument)
The dirt (desert sand?) was extremely hard to remove, so I used an ultrasonic cleaner. For some of the modules I needed three cleanings from about 20 minutes to remove all the mess.
Now everything is clean, BUT two modules, that worked before the cleaning, have stopped working now.
The reasons are 9 defective RF Transistors (2N) which have an interrupted collector now.
So, be careful, not every semiconductor likes ultrasonic cleaning.

Ultimate Guide to Cleaning Electronics: Improve PCB Reliability Safely & Effectively

TestEquity is an approved distributor for Chemtronics.

Content Source: https://www.chemtronics.com/ultimate-guide-to-cleaning-electronics

In the process of assembling, reworking or repairing printed circuit boards (PCB) for electronic devices, the discussion inevitably turns to whether or not to clean the PCB. Cleaning adds time and expense to the process and doing it wrong can cause more harm than good. This guide will walk you through the reasons to clean PCBs and the best practices for electronics cleaning.

Why Clean a Printed Circuit Board (PCB)?

Since cleaning PCB’s is not always required and adds time and cost to the production or repair process, some justification may be required.

Improve Aesthetic Appearance of PCB

If you are a contract manufacturer of PCB’s, the visual appearance of the board reflects on your work. A clear, greasy-looking residue around a solder joint may raise flags for your customer’s incoming QC inspectors. If the flux residue chars and forms spots on the solder joints it may look like a true defect like a solder joint void or “blow hole”. If the flux residue is from a rework process, it acts as a fault tag in the rework area calling attention to the work even if there shouldn’t be a concern.

Improve Reliability of PCB

Reliability requirements are generally driven by the nature of the final product. For a disposable product like a computer keyboard, nobody loses their life if it stops working. In that case, an EMS supplier may use no-clean flux and forgo the cleaning process. On the other end of the scale, requirements for pacemaker electronics, where board failure could directly lead to death, are going to be much stricter. In that example, cleaning will be required after assembly and any subsequent rework, and the process will be thoroughly tested for effectiveness and repeatability. Long-life durable goods may fall somewhere in-between, with cleaning a requirement but without the rigid testing and controls.

Prevent Corrosion on Components and PCB

Flux residues left on electronic circuit boards are acidic. If they aren’t removed with a cleaning process, the residues can draw in ambient moisture from the air and lead to corrosion of component leads and PCB contacts.

Avoid Adhesion Problems with Conformal Coating

Most people understand that when painting something the surface must be prepared so it is absolutely clean. Otherwise the paint will quickly peel off. The same logic applies to conformal coating, even when the contamination is from no-clean flux. “No-clean” refers to the amount of ionic material left after soldering; it has nothing to do with whether or not coating can stick to it.

When there are flux residues left on the PCB before the coating process, it is common to see the coating lift or delaminate from the surface of the board. This is evident when the pockets are isolated around solder joints rather than the overall surface (the exception being the bottom of a wave-soldered PCB).

To make matters worse, coatings are generally semi-permeable and “breathe” to a certain extent. Moisture can enter and soak into the flux residue and potentially lead to corrosion.

Prevent Dendritic Growth from Ionic Contamination

Polar or Ionic particles left from flux residue and other sources, when exposed to moisture from the ambient air and when current is applied, can connect into a chain or branch called a dendrite (Fig 1). These dendrites are conductive so form an unintended trace that cause current leakage or, over a longer period of time, even a short circuit.

What Is Ionic Contamination?

What is Polar Contamination?

Ionic contaminants are remains of flux that are left behind during the assembly process. Ionic compounds are held together by electrostatic forces and the compound itself has a zero net charge. These materials will disassociate when exposed to water.  These are composed of positively charged cations and negatively charged anions.  A simple example is table salt (sodium chloride), composed of a single positive sodium cation which lacks one electron, and a negatively charged chloride anion (Cl), which has an extra electron.  Polar compounds, on the other hand, can have a positive charge on one side of the molecule and a negative charge on the other side of the molecule; these molecules never split apart. Water and Isopropanol (or IPA) are examples of polar molecules.

When populating the board with components, the components themselves can carry various ionic/conductive contaminants to your assembly including cutting oils/fluids, biocides, and corrosion preventatives. Be aware of common nonionic materials that can also affect the assembly steps – process oils, mold releases, etc. can be detrimental down the line.

What Are The Most Common Ionic Contaminants From The Bare Board Fabrication?

Common Moisture Trapped in the “Layering” Process

Water is a polar contaminant.  It is conducive for dissociating other ionic materials which then lays the foundation for conductive mishaps (dendritic growth, ECM, etc).  It is common practice to “bake” the boards to remove extraneous moisture.

Etching Chemicals

Etching chemicals are highly conductive and can be corrosive as well. They must be chemically neutralized and removed/rinsed and are well-known as sources for current leakage. 

Flux Residues from Soldering

Everyone is familiar with flux residues. Fluxes, whether in liquid, cored wire, or compounded as a paste, can leave residues that can cause serious reliability defects if not removed. Common conductive flux residues from the soldering process can include various unreacted activators, binders, rheology components, and saponifiers. Among these are numerous iterations of acids (abietic, adipic, succinic among others), highly basic ingredients (amino compounds), and even constituents found in “soaps” such as phosphate and sulfate ions. All of these must be cleaned from the substrate, whether by strict solvent cleaning such as vapor degreasing or by aqueous chemistries in the common batch or inline cleaners seen on the manufacturing floor.

Inter-Layer Residues from Drilling and Via Plating Processes

In addition, residues from the cleaning process chemistry itself must also be removed.  This is noticed more in the aqueous cleaning systems.  Many use saponifiers to neutralize and emulsify the flux residues and make them easier to rinse and remove from the substrate.  These components themselves are highly polar and ionic and can also enhance the dendrite and/or ECM mechanism if not removed.  In addition, corrosion preventatives and surfactants are commonly employed in these products.  This is not a bad thing in itself, but care must be taken to ensure they are removed along with the soils during the cleaning process.

How Do You Perform Ionic Contamination Testing?

Poor quality control in fabrication, poor soldering or component population, and even final cleaning stages are all potential sources of contamination. Many of these can be found by ionic contamination testing and analysis such as ROSE testing, ion extraction, and chromatography. Initial high humidity validation testing at the beginning of the project can also identify potential issues. 

If you are looking for more details, kindly visit JYN.

Further reading:
Questions You Should Know about maize vibro separator

Strict quality control and standard operating procedures during the PCB assembly, manufacturing stages, and validation testing can go a long way in preventing a reliability nightmare. Just think – simple mishandling of a part by an operator not using gloves can transfer salts and oils from skin to the substrate that could potentially be catastrophic for your item!

What is White Residue on an Electronic Circuit Board?

White residue is generally a symptom of ineffective PCB cleaning. Common conductive flux residues from the soldering process can include various unreacted activators, binders, rheology components, and saponifiers. Among these are numerous iterations of acids (abietic, adipic, and succinic among others), highly basic ingredients (amino compounds), and even constituents found in “soaps” such as phosphate and sulfate ions. When a cleaner does not fully dissolve all the constituents, or the cleaner is not allowed to flow off the PCB, the remaining solvent can evaporate off and leave behind residue that is either white or like water spots.

How Do You Remove White Residue From an Electronic Circuit Board?

White residues can generally be cleaned by a flux remover. If the residues are the result of insufficient solvency of the original cleaning process, a stronger solvent cleaner may be required. Often agitation is required to remove the residues, which may include a wipe, swab, brush, or an aerosol with a brush attachment. Follow these steps to remove white residue:

1. Spray the residue with a strong solvent.
2. While the area is still wet, scrub with a clean tool like a wipe, swab, or brush.
3. Spray the cleaned area and surrounding areas with the same solvent, angling the board so the rinse is able to run off.

What are the Different Methods of Cleaning Electronic Circuit Boards?

PCB flux removal can either happen at the benchtop, which generally requires a manual cleaning method, or in automatic or semi-automatic processes. This is common for low volume electronic PCB assembly, rework, and repair. Manual cleaning methods are generally more laborious and less repeatable, so results may vary from operator to operator. For higher volume assembly or reduced variability, more automated cleaning methods are used.

Manual Flux Removal Methods

• Aerosol – Aerosol flux removers have the advantage of a sealed system (ensuring fresh solvent) and agitation (provided by the spray pressure and pattern). A straw attachment is generally included to spray into areas with greater precision.
• Aerosol w/brush attachment – A brush can be added to the aerosol nozzle, so the solvent sprays through the brush as you scrub.
• Trigger spray – Trigger spray bottles are more common for water-based cleaners and isopropyl alcohol (IPA), but not for aggressive solvent cleaners.
• Liquid immersion – The PCB can be immersed into a tray or bucket of solvent cleaner, with cleaning tools like swabs and brushes used as needed for tenacious soils. Cleaning performance can be further improved by heating the solvent but this should only be done with nonflammable flux removers.
• Spot cleaning with a swab – A cotton or foam swab can be saturated with a mild solvent like isopropyl alcohol, often from a pump dispenser or “dauber”.
• Presaturated wipes and swabs – For added convenience, wipes and swabs are available presaturated with a mild solvent like isopropyl alcohol.

Automated or Semi-Automated Flux Removal Methods

• Ultrasonic – Ultrasonic cleaning equipment use sound waves to create implosions within the flux residue, breaking it apart and lifting it off the PCB. Most equipment have the option of heating the solvent to increase cleaning performance. Only use this option with a nonflammable flux remover. Cross-contamination can be a concern so change the solvent regularly. Ultrasonic cleaning might be too rough on sensitive components like ceramic-based resisters.
• Vapor degreaser – Vapor degreasing is the go-to process for the highest precision cleaning, as in aerospace and medical electronics. PCBs can be submerged in a sump of boiling solvent, in a rinse sump with ultrasonics, or rinsed in solvent vapors. Special solvents need to be used that are azeotropes or near-azeotropes, so will not change as the solvents are boiled off and reconstituted in a continuous cycle.
• Batch flux remover – This is basically a dishwasher for electronic circuit boards. PCBs are stationary in a rack, and the flux remover (usually water-based) is sprayed over the assembly. The PCB stays in place as the machine goes through the wash, rinse and dry cycles.
• Inline flux remover – An inline washer is more like a carwash for electronic circuit boards. PCBs travel on a conveyor through wash, rinse and dry zones. Water-based flux removers are used.

Does the Flux Type Affect the Effectiveness of the PCB Cleaning Process?

The type of flux can have a big impact on the cleaning process. R, RA and RMA fluxes are generally easier to remove with standard flux removers and isopropyl alcohol. No-clean fluxes are intended to stay on the PCB, so can be more difficult to remove. They may require a more aggressive solvent flux remover, additional agitation like brushing, or a heated solvent. Aqueous fluxes are generally designed to be removed in a batch or inline cleaning system with straight deionized water or water with a saponifier. Alcohol-based or specially formulated solvents can also be used to clean aqueous fluxes, but the same cleaners may have mixed results on other types of fluxes.

The short answer is to match the flux remover with the flux type. However, this can be challenging for an EMS supplier that may have to use a variety of fluxes as required by their various customers. Flux removers are available that can break down a large variety of fluxes while changing the variables, like cleaning time, agitation, or additional heat, can treat distinctive needs adroitly.

For water-based cleaners in batch or inline cleaning systems, cleaner concentration can be adjusted, cycle time increased, and temperature increased to improve performance against various flux types.

What Factors Cause Difficulty Cleaning Flux Residues from PCBs?

Any process engineer will tell you that the key to designing a repeatable process is to control the variables. When removing flux from electronic circuit boards, there are a number of variables that can drastically change the cleaning performance of a cleaner and process:

• Flux type – The type of flux can have a big impact on the cleaning process. R, RA and RMA fluxes are generally easier to remove with standard flux removers and isopropyl alcohol. No-clean fluxes are intended to stay on the PCB, so can be more difficult to remove. They may require a more aggressive solvent flux remover, additional agitation like brushing, or a heated solvent. Aqueous fluxes are generally designed to be removed in a batch or inline cleaning system with straight deionized water or water with a saponifier. Alcohol-based or specially formulated solvents can also be used to clean aqueous fluxes, but the same cleaners may have mixed results on other types of fluxes.
• Higher solids flux – Cleaning a PCB made with a mix of soldering technologies can be a particular challenge. Tacky fluxes or other types with a high level of solids can be more challenging to clean, require more cleaning time, soak time, or additional agitation.
• Amount of flux – A thicker layer of flux residue is more soil to remove and can create flux dams under low stand-off components. This prevents flux remover from fully penetrating under the component.
• Soldering temperature – Higher temperatures have a greater tendency to bake-on flux residues, making them more difficult to remove. High temperature soldering may require more cleaning time, soak time, or additional agitation.
• Lead-free solder> – Lead-free soldering generally requires higher soldering temperature and more highly activated fluxes. Flux residues left from a lead-free soldering process may require more cleaning time, soak time, or additional agitation, and you may actually have to consider a more aggressive flux remover that is engineered for lead-free processes.
• Time between soldering and cleaning process – It is not unusual to finish the assembly on Friday, come back on Monday to clean and be surprised with white flux residues. As flux residues sit on the PCB, volatiles continue to flash off and it becomes more difficult to remove.

If you are suddenly surprised by white residues or some other clear evidence of a cleaning problem that didn’t exist before, step back and look at your process before calling for help. Has anything changed? That will be the first question a technician will ask, and necessary to know before you can identify and solve the problem.

How do you clean a PCB after soldering?

How do you remove solder flux?

The most common way to clean flux residues from a repair area is to saturate a cotton or foam swab with isopropyl alcohol or another cleaning solvent, and rub it around the repair area. While this may be adequate for no-clean flux, where the goal is a visually clean PCB, this may not be clean enough when more heavily activated fluxes are involved, like RA or aqueous. The dirty little secret is that flux residues will not evaporate along with the solvent. You may dissolve the flux, and some of the residues will soak into the swab, but most of the residues will settle back onto the board surface. Many times these white residues are more difficult to remove than the original flux.

One quick and easy improvement to this process is to rinse the board after swabbing around the repair area. While the solvent is still wet, spray over the entire board with an aerosol flux cleaner. Hold the PCB at an angle to allow the solvent to flow over the board and run off, along with any residues that are picked up.

The straw attachment that comes with aerosol flux removers is a good way to increase the spray force and penetrate under the components.

Chemtronics offers the BrushClean™ system with many of their flux removers. The cleaning solvent sprays through the brush, so agitation can be increased by scrubbing while spraying. To absorb the flux residues, a lint-free poly-cellulose wiper can be placed over the repair area, and the spraying and scrubbing can occur over the material. Then remove the wipe and brush attachment, and spray over the board for the final rinse.

How Do I Use the Straw Attachment On The Aerosol Flux Remover to Improve Cleaning Effectiveness?

The use of the straw attachment allows for a more controlled spray, thus eliminating excessive solvent waste. The straw is also useful in directing exactly where the solvent goes. This allows the user to guide the solvent under the component. Without the straw attachment, the solvent would be sprayed at the target area (for instance, the sides of the component), but would be wasted and not reach beneath the component.

How Do I Clean Under Components With An Aerosol Flux Remover?

Best results are obtained when both the corners and sides of each contaminated component are addressed. Directing solvent directly into the corners helps to break up any flux dams located there. Because the corners were cleared first when the sides of the components are addressed, this allows more channels for the solvent to pass through. The more open channels available, the greater the opportunity for the flux to be exposed to the solvent, and as a result, the higher likelihood that all flux trapped under the component will be able to flow out from beneath it.

The choice to use an oscillating or stationary spray is dependent on the size of the component. For a small component it is sufficient to use a stationary spray on the component sides; however, for larger components, a cleaner board can be achieved when the spray oscillates back and forth across each side of the component. This oscillating spray gives the solvent the opportunity to flow up, under the component from many angles, much as the flux had.

Does the Angle of The Spray Affect Cleaning Effectiveness When Using an Aerosol Flux Remover?

In our testing, an exact straw angle of 30o, 45o, or 60o to the board has no differing impact on the cleanliness of the board.  General downward or upward angles are sufficient. In order to make the most of the straw, think about the direction in which the residues need to travel. When trying to remove residues from under a component, spray close to the board at an angle that guides the solvent under the component. When all of the residues have been removed from underneath the component, spray from on top of the component, angling out along the edges to push any residues out, away from the component.

Are There Right and Wrong Ways To Use Cleaning Tools Like Brushes, Swabs and Wipes?

In our testing, handheld brushes and swabs left the board looking dirtier than it started. They spread partially solvated flux around the components which then dried, leaving a white residue. None of the polyurethane foam swabs performed well in this application. Foam swabs became flimsy when saturated with aggressive solvents and were easily torn. Another problem with handheld tools was that the solvent evaporated too quickly. Best results were achieved when a final rinse was utilized. The key is not to let the board dry out. When the board dries, the partially solvated flux dries leaving behind white residue. A slower evaporating solvent, like IPA, would avoid the evaporation issue but should be followed by a rinse (see more details on rinsing below). In addition, some solvent may travel under the component during scrubbing, but without the force of an aerosol spray the likelihood that the residues beneath the component will be removed is slim.

Some solvent cleaners come with a brush that attaches directly to the spray head, and the solvent flows through the brush at a slow rate. This is particularly common in defluxers available in Europe. Brush attachments produced results that were a step above handheld tools, due to the benefit of a constant supply of virgin solvent. However, they did not produce the same level of cleanliness observed in aerosol-only cleaning. The brush attachment allowed for scrubbing problem areas, which can be beneficial. However, the force of an aerosol through a straw attachment produced similar results.

Brush attachments, like handheld tools, have the potential to introduce new contaminants. In addition, for a brush attachment to reach its full potential, a separate aerosol is required for cleaning under components and for the final rinse. Like handheld tools, without the force of an aerosol spray, some solvent may travel under the component during scrubbing; however, the likelihood that the residues under the component will be pushed out is slim. Because the use of a brush attachment requires that the target area remain saturated, the target area remains in a solvent pool throughout the cleaning period. This increases the likelihood that residues may only be relocated on the board instead of being removed completely. A final rinse, then, is especially important.

One commercially available brush system provides a separate brush mechanism for cleaning, which is continually fed by the aerosol can. No cleaning advantages to this system were observed compared to a brush attachment during our testing. A brush system or attachment is often used to reduce solvent usage, but this advantage is greatly decreased if a proper rinse is applied later.

When Is a Final Rinse Required When Cleaning a PCB?

In our testing, the final rinse was found to be a necessary step. This step ensures that all of the solvated flux residues, which have been removed from under and around components, flow off the board completely and are not simply relocated.

At first glance, what we recommend may seem over-the-top. Why go through all the trouble and expense of thoroughly cleaning under the components when no one can see the difference? It all comes down to the reliability requirements of the electronics. For disposable electronic devices assembled with no-clean flux, an overall rinse may be all that is needed for acceptable results. If higher reliability is required, greater care is needed, with the techniques noted above, to prevent latent failure of the final device from ionic contamination. Spending the time and effort up-front is often money well spent.

What is the most popular electronic cleaner?

Chemicals are found throughout the electronic assembly and repair process, but no solvent is more common than isopropyl alcohol. It is universally used for cleaning and as a main constituent of fluxes, but how much do you really know about isopropyl alcohol?

Isopropyl alcohol (CAS #67-63-0) is also referred to as IPA, isopropanol, 2-propanol, and even rubbing alcohol. It dissolves a wide range of polar and non-polar soils, is it is often used to dissolve and remove light oils, fingerprints, cutting fluids, flux residues, carbon deposits, and mold release. It is also readily miscible in water, so can be used as a drying agent as well.

For electronic printed circuit board (PCB) assembly, you will find isopropyl alcohol being used to clean flux residues from recently soldered circuit boards or in PCB repair and rework. IPA is also used to remove solder paste or adhesive from SMT stencils. Maintenance cleaning with isopropyl alcohol is common for removing caked-on and burnt-on flux from SMT reflow ovens, wave soldering fingers, selective soldering nozzles, pallets, and anywhere else flux tends to collect in automated soldering processes.

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