PCB Cleaner: Things You Need to Know - PCBasic

Even PCBs that have been manufactured with high precision may cause short circuits, corrosion, or even product failure due to residual flux, dust, fingerprints, or moisture if they are not effectively cleaned. For this reason, PCB cleaning is necessary, to ensure the stability of electronic products and extend electronic devices’ service life. Whether you are an electronic DIY enthusiast, a product engineer, or a technician, understanding how to clean PCBs, mastering different types of circuit board cleaning methods, and choosing the appropriate PCB cleaner are all the basis for ensuring the long-term reliable operation of the equipment.

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Next, we will delve into various PCB cleaning techniques. It covers a variety of solutions ranging from manual cleaning to the use of automated equipment such as ultrasonic PCB cleaners and deionized water cleaning machines.

Overview of PCB Cleaning

PCB cleaning is not only about appearance, but also directly affects electrical performance and service life. After soldering, contaminants such as flux residue, dust, moisture or fingerprints usually remain on the PCB surface. These impurities may cause corrosion, short circuits or performance degradation of the circuit board. Therefore, it is necessary to clean the circuit board. Common cleaning scenarios include: post-soldering treatment, maintenance/rework process, treatment before applying protective coating, and treatment before long-term storage. The so-called PCB cleaner refers to the chemicals, tools or equipment used to remove these contaminants. Choosing the appropriate circuit board cleaner can effectively ensure the long-term stable operation of the circuit board.

Types of PCB Cleaners

Different types of PCB board cleaners are suitable for different contaminants and cleaning requirements. Choosing the right cleaning agent can not only effectively remove contaminants, but also prevent damage to circuit boards or affect the performance of electronic components. The following are several common PCB cleaners:

Solvent-based PCB Cleaner

This type of cleaner is based on highly volatile organic solvents and can quickly dissolve stubborn flux residues, grease, welding fumes and other contaminants. Common types of cleaners include isopropyl alcohol (IPA) or commercial flux cleaners. They are suitable for cleaning rosin and no-cleaning fluxes and are very commonly used in manual soldering and maintenance scenarios.

Water-based PCB Cleaning Solution

This kind of PCB cleaner focuses on environmental protection and low toxicity. It adopts deionized water or water-based chemical formulas, which are more friendly to the human body and the environment. It is usually used in conjunction with a spray cleaning system or a batch cleaning machine to remove water-soluble flux. This type of PCB cleaner is widely used in mass manufacturing and green electronic production.

Dedicated PCB Flux Cleaner

Dedicated solvents developed based on the type of flux (rosin, no-rinse, water-soluble) are more targeted. An excellent PCB flux cleaner can effectively remove the active residues around the solder joints and avoid leaving white deposits. It is suitable for military and medical PCB cleaning applications with high-reliability requirements.

PCB Cleaner Spray

PCB cleaner spray penetrates quickly and removes surface contamination by spraying. This cleaner is suitable for cleaning small areas or hard-to-reach parts. It is very convenient for on-site maintenance or repair personnel to use at will and is suitable for various scenarios of cleaning circuit boards.

Electronic Board Cleaner

This type of cleaner is specially designed for sensitive circuits and features anti-static, anti-corrosion and residue-free properties. This type of cleaner is suitable for high-precision equipment, such as communication base stations, industrial control systems, medical instruments, etc. It can safely clean the surface of the PCB without damaging the components, improving the overall system stability.

When choosing the most suitable PCB cleaner, it is not only necessary to consider the type of contaminants, but also to make a comprehensive judgment by taking into account the circuit board structure, component sensitivity, environmental protection requirements and cleaning methods. Next, we will introduce several common cleaning methods to you, mainly from the aspects of manual and machine cleaning.

Manual PCB Cleaning Methods

In sample making, rework or small-batch DIY projects, manual cleaning of PCBs is a common and practical method. Compared with automated equipment, manual methods have lower costs and are more flexible to operate. This way is suitable for cleaning local solder joint residues, flux contamination or slightly oxidized areas. So, how to clean the PCB manually?

First of all, it is necessary to prepare the required tools and materials. The basic tools and cleaning supplies required include: lint-free cloths/wiping paper, anti-static brushes, cotton swabs, compressed air cans, isopropyl alcohol (IPA) or flux remover, anti-static gloves, etc. Sure, if what you pursue is convenience, you can also use PCB cleaner spray. This type of circuit board cleaner spray has good solubility and rapid evaporation characteristics, and is an ideal choice for removing flux and oil stains.

Then, the formal cleaning process can begin:

Step 1: Evenly spray the PCB cleaner spray or isopropyl alcohol on the solder joints, pins or contaminated surfaces that need cleaning, and wait for a few seconds to allow it to penetrate and soften the flux residue. This step is the initial treatment of the contaminated area.

Step 2: Use an anti-static brush or cotton swab to gently scrub the contaminated area to help separate flux residues, dust or stains. This process requires patience and avoiding vigorous scratching to prevent damage to the solder pads.

Step 3: Use a lint-free cloth or wiping paper to remove the dissolved flux and dirt to prevent it from adhering to the surface of the circuit board again after drying.

Step 4: Use a compressed air tank or a hot air gun in the low-temperature setting to dry the PCB to ensure there is no liquid residue and avoid the risk of short circuits or corrosion.

Step 5: Use a magnifying glass or microscope to carefully observe the cleaning area again: checking if there is still flux residue or white powder, and whether there are problems caused by improper cleaning such as scratches, pad damage, burrs, etc.

If there are still residues, steps 1 to 4 can be repeated, or a more powerful PCB flux cleaner can be considered. Although manual cleaning is simple, only when the operation is standardized and the materials are properly selected can the goal of electrical safety and long-term stable operation be truly achieved. For complex or large-scale applications, it is still necessary to use the best PCB cleaner, such as automatic spray cleaning, ultrasonic or deionized water systems. Only in this way can higher consistency and efficiency be achieved, as well as more professional PCB cleaning.

Machine-Assisted PCB Cleaning Methods

For large quantities or complex circuit boards, equipment cleaning is required to achieve consistent and efficient results. Common cleaning equipment includes:

Ultrasonic PCB Cleaner

The PCB ultrasonic cleaner cleans by generating microbubble vibrations in the liquid through high-frequency sound waves. This machine can penetrate deep into cracks and crevices, effectively removing flux residues and particles. And it can be deeply cleaned without touching the circuit board, making it highly suitable for cleaning multi-layer boards and high-density components.

Vapour Phase Cleaning

The vapour phase cleaning machine dissolves contaminants by heating solvent vapor and is suitable for removing no-cleaning fluxes. It has the advantages of high efficiency and suitability for industrial-grade dense circuits. However, good ventilation is required and attention should be paid to operational safety.

Spray-in-Air Systems

This type of system applies the cleaning solution to the PCB surface through a high-pressure nozzle and then dries it with an air knife. The Spray-in-air systems are suitable for large-scale cleaning and are widely used in SMT assembly lines.

Dishwasher-Type Batch Cleaners

This device is similar to an industrial dishwasher and is often used for batch PCB cleaning. It has high consistency and the cleaning, rinsing and drying process is fully automatic.

Deionized Water Cleaning Machine

The deionized water cleaning machine can effectively remove particles, oxides and organic residues by combining surface activation and ultrapure water to rinse PCBs. This type of cleaning machine is an ideal choice for aerospace, medical and other applications that require ultra-clean surfaces. Its environmentally friendly and non-corrosive process is conducive to improving the reliability of subsequent adhesion, coating and welding. Moreover, this device has zero residue, no scale or metal ions, and is highly safe.

How to Choose the Suitable PCB Cleaning Method?

How can we clean circuit boards efficiently and safely in the face of various cleaning devices and methods? Here are some common scenarios and frequently used methods. Hope they can be of some help to you:

Application Scenario / Need

Recommended Cleaning Method

Small batch soldering, prototyping, or repair

Manual cleaning

Post-solder flux removal

Solvent-based localized cleaning

High-volume production

Automated cleaning systems

High-density or complex PCBs (e.g., BGA, QFN)

Ultrasonic cleaning

Water-soluble flux or ionic contamination

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Additional reading:
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Deionized water cleaning (eco-friendly)

Spot cleaning or field repair

Spray-type cleaner

Eco-friendly and non-corrosive requirements

Water-based or plasma cleaning

Conclusion

Learning how to clean circuit boards is a basic skill that every electronics professional must master. Whether it is sample boards, repair parts or batch products on the production line, choosing the appropriate PCB cleaning methods and tools can greatly enhance the reliability of the products. Selecting the best PCB cleaner is the key to ensuring the stable operation of electronic products. After reading this article, you must have gained more understanding of PCB cleaning. Of course, if you need clean high-volume PCBs, you can also contact PCBasic!

About PCBasic

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.

Corrosion from PCB fabrication contamination (photo courtesy of Foresite)

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

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, 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. 

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.

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:

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, 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.

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.

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