10 Questions You Should to Know about Electronic Board Scrubbing Machine

What Is Ionic Contamination?

What is Polar Contamination?

With competitive price and timely delivery, JYN sincerely hope to be your supplier and partner.

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 molecule; these molecules never split apart. Water, Isopropanol (or IPA) is an examples of a polar molecule.

When populating the board with components, the components themselves also 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 lays the foundation for conductive mishaps (dendritic growth, ECM, etc).  It is common practice to “bake” the boards to remove extraneous moisture.

Corrosion from PCB fabrication contamination (photo courtesy of Foresite)

Etching Chemicals

These 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

Heavy no-clean flux residue with visible copper corrosion (photo courtesy of Foresite)

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

Dendritic grown between solder pads, caused by ionic contamination (photo courtesy of Foresite)

In addition to these widely seen residues, 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/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 from PCB fabrication, to the soldering and component population, to the 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, as well during initial high humidity validation testing at the beginning of the project. 

Strict quality control and standard operating procedures during the PCB assembly and the stages of assembly manufacturing 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, 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.

White flux residue with visible copper corrosion (photo courtesy of Foresite)

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:

The company is the world’s best Electronic Board Scrubbing Machine supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

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.

Flux-Off® Rosin with a brush attachment

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. 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, which ensures fresh solvent every time, 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 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, like used for aerospace and medical electronics. PCBs can be submerged in a sump of boiling solvent, in a rinse sump with ultrasonics, and 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– 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 finally dry cycle.
• 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 more a more aggressive solvent flux remover, addition 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. 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, and changing variable like cleaning time, agitation, and additional heat can make up the difference.

For water-based cleaners run in a batch or inline cleaning system, cleaner concentration can be adjusted, cycle time increased, and temperature increased to improve performance.

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 variable 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.

Flux residues don't evaporate along with the solvent.

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.

Aerosol with straw good for cleaning under 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.

Aerosol brush attachment over a wiper dissolves and absorbs flux residues at the same time.

There are a variety of methods that can be used to clean PCB circuit boards depending on the type of board, the type of grime, and experience level and available tools of the person doing the cleaning.

You must ask yourself one important question before cleaning a circuit board: "Is having the PCB board clean worth the risk of breaking it in the process?" This is particularly true if the board is working, but just dirty. Cleaning a PCB circuit board always involves a risk of damaging the board or the components on it. (If the board is already broken and you need to clean it to attempt repairs, the decision is obviously much easier.)
To remove dust or other light debris from a printed circuit board it is generally advisable to simply brush the substance with either an old (dry) toothbrush, a dry (clean) paint brush, or the "upholstery" brush from a vacuum cleaner. Once the dirt is loose, the brush can be used to directly whisk the dust away, or a compressed air source can be used to blow the PCB board clean. It is generally not advisable to use an operating vacuum cleaner to try to remove dirt from a circuit board unless it is a specially designed vacuum cleaner for electronics work. (A household vacuum cleaner can generate thousands of volts of static electricity at the head of the hose which can cause damage to some electronics.)

Grime (dust/dirt mixed with something tacky - oil, Pepsi, wax, etc.)
Grime is particularly common on monitor chassis PCB boards where high temperatures cause outgassing of components coated with wax. The wax forms a sticky film on the board which traps dirt easily-- and since the high-voltage potential of the monitor anode will attract airborne particles, monitor boards can become particularly filthy. Other boards will sometimes become encrusted with dirt and gunk that simply won't brush away, so more aggressive cleaning can be become necessary.
Grime that appears to be mixed with some form of oil or wax (or spilled Coke, or Pepsi, or God-knows-what else) will need some form of detergent applied followed by mild scrubbing to expunge the offending contaminants.
Your first step should be to remove any socketed components (chips, cables,etc.). These PCB parts can be cleaned separately using the technique described below-- and removing them now will let the cleaning process get under the sockets and clean much more completely than if you left the parts in place.(Of course, you will need to make note of where the socketed components go to make sure you get them replaced in the correct locations and with the proper orientation.)
Certain components may not react well to liquid-based cleaning. Old open-frame/carbon film potentiometers, any components contained in cardboard, and older non-watertight crystals may be damaged by contact with PCB liquids. You may wish to desolder these components to be safe if you have them on the board to be cleaned. Also note that many types of stickers will be destroyed by this process, so EPROMs may need to be recovered, etc.
The actual cleaning of the board can usually be safely accomplished by spraying the surface with a generous amount of a PCB household, non-phosphate based cleaner. "Simple Green" and "409" seem to work quite well. Let the cleaner sit for 10-15 seconds to loosen the dirt and then scrub lightly with an old toothbrush or clean paint brush. (A 2.5" wide nylon paintbrush will make short work of grunge on a monitor chassis with a liberal spray of '409' applied!). Once the board is scrubbed down, you will need to rinse it *very* well with water. Technically speaking, a PCB demineralized/purified water should be used, but tap water is probably fine for 99% of applications. A spray attachment from a kitchen sink works well for rinsing and for monitor chassis' a garden hose with a spray-head is quite effective.(Random semi-related warning-- do NOT clean the silver/grey PCB coating off of the back of a monitor CRT! It is a required coating for proper operation PCB of the monitor!)
After rinsing, carefully blot the circuit board dry with a clean terry-cloth towel (and shake it to get hidden water out). Compressed air (either from a can or a compressor) can also be used to blow off excess water.

Thorough drying of the circuit board is critical. While hand-drying the board, preheat a household oven to about 170 degrees F. Once the oven is up to temperature, turn the oven OFF, and place the cleaned PCB inside the oven and close the door. Allow then board to dry for 2-3 hours. (Overnight is fine.) It's a good idea to warn roommates/spouse when you do this. (Having someone preheat the oven the 500 degrees to broil a roast while you board is still in the oven is *bad*.)
After the drying cycle is complete you can remove your board from the oven and perform a visual inspection for any damage. If unsealed PCB potentiometers are on the board (like a monitor chassis) they may need to be turned back and forth several times to remove any residue from the wiper area to regain smooth operation.
An alternate method for cleaning this type of grime is to use the clean/rinse cycles of a household dish-washer. Make sure the dishwasher is free of any food particles and place the board inside like you would a large plate. A small amount of dish-washing detergent can be added to help the cleaning process, and if possible the water temperature should be set to the lowest setting. You will want to remove the board from the dish washer at the end of the rinse cycle (do not use the dish-washer's dry cycle as it is not well temperature-regulated-- use the oven technique listed above).
Solder Flux (brownish crusted material on the solder-side of the PCB)
Many solder fluxes used in PCB repair and some types of manufacturing are water resistant. They will leave a yellow-to-brownish "crust" on the pins of chips on the circuit board's solder-side. This is usually the result of a previous repair that was not properly cleaned.
Solder flux can usually be removed with household rubbing alcohol and a toothbrush. Wet the toothbrush with the alcohol, and gently scrub.Repeated applications may be necessary. If available, anhydrous alcohol (used for electronics cleaning) works much faster. Blot the cleaned area with a non-linting tissue (like Kimwipes EX-L) or a clean towel.
There are also commercial cleaners used for flux and grease removal. Some types of cleaners are available from Radio Shack, but are generally overpriced and of marginal quality. A professional grade cleaner like Tech Spray's "Envi-Ro-Tech " will perform best but can be more difficult for a hobbyist to obtain.

Paint (spray point, latex, etc.)
Paint in and of itself is usually not harmful to the operation of a game PCB. Since paint can be difficult to remove, unless you need to clean the board for repair work it may be best to leave it alone.
If you have to clean the paint off, try to determine what type it is. Spray paints will generally come off with standard mineral spirits or paint thinners. Follow up use of any thinners or paint removers with the cleaning procedure for "Grime". Latex paints can be removed with latex cleaners, or sometimes soap and water. Your mileage may vary.
Before selecting a cleaner to try, remember that many old chips have their numbers painted or silk-screened on (modern chips are usually laser etched).Paint removal techniques can often strip transistors or chips of their markings making identification very difficult.
Also note that most PCB silk-screening and printed circuit boards themselves are epoxy based-- an aggressive paint removal product that works against epoxy (MEK, JASCO, etc.) may damage the PCB or silkscreen.

Corrosion (acid damage, salt water spray, etc.)
Corrosion should be neutralized and cleaned as soon as possible. The most common forms of corrosion on game PCB's will usually be salt-air exposure and battery acid (from Lithium or NiCad batteries).
In the case of battery acid leakage, the board should be neutralized with a mixture of baking soda and water forming a thin paste. Gently scrub the paste into the PCB with a toothbrush and let it sit for 20-30 minutes. Note that acids can often get under the protective solder-mask coating of a PCB and travel along the traces to areas quite far from where the visible battery damage has occurred. A neutralizing "soak" with the base mixture will help mitigate any further ingress of the acid.
After soaking/scrubbing, rinse the board thoroughly and follow-up with the "Grime" cleaning procedure listed above.
For boards suffering from salt-air or water-based corrosion, the cleaning procedure for "Grime" is usually all that is required.
Salt and acid damaged boards will often form hard oxides on metal surfaces that won't yield to gentle scrubbing. Media blasting (glass or plastic beads or crush walnut shells or corn cobs) will often help remove more stubborn oxides and tarnish.

Specialty Techniques ('other')
Depending on the equipment you PCB have available, other cleaning methods can be beneficial.
Ultrasonic cleaning such as with a Bransonic cleaner can get rid of 'hidden' contaminants and reach areas direct scrubbing can't. It will also remove fluxes and oils if used in conjunction with appropriate detergents.

Media blasting ("bead blasting") is a dry cleaning method which is particularly good for removing oxidation build-up and some types of paint/coatings.
Media tumbling is most often used for cleaning small parts or spent ammunition casings ('brass'). It is also useful for removing oxidation or polishing of small parts for arcade games.
Metal cleaners/polishes ("Brasso", etc.) can be used to remove some types of metal oxidation/tarnished from chips and connectors.

Want more information on PCB Brush Cleaning Machine? Feel free to contact us.