How to Clean Printed Circuit Boards(PCB)?

Printed Circuit Board is becoming more popular, and contaminants will be generated in the manufacturing process. These contaminants include flux residues and adhesives as well as dust and other debris. PCB boards that are not able to maintain a clean surface will fail due to resistance and leakage, which can affect the life expectancy of the product. Cleaning the PCB board during manufacturing is a crucial step.

1. Why Clean Up the PCB?

The three main types of printed circuit boards residues are:

Particulate contaminants: They include dust, lint, and solder balls. Solder balls can be a soldering defect. They can cause an electric short if they are collected in one spot by the equipment oscillation. Solder balls are easily cleaned and removed.

Non-polar contaminants: The appearance of PCB boards can be affected by non-polar contaminants, such as rosin, white wax, and antioxidant oils that are used in wave soldering. Cosmetics, hand sanitizers, or cosmetics used by the operator, may also have an impact.

Polar contaminants: halide, acids and salts – can have a serious impact on the effectiveness of PCB.

2. PCB Cleaning Principle

Cleaning flux residues begins with a dissolving action. The residues are removed from the circuit boards by transporting them to the cleaning agent. Controlling the temperature of detergents or adding ultrasonic rinses to the process will accelerate the dissolution and cleaning. Ultrasonic cleaning is the safer method.

3. PCB Cleaning Method

There are several methods of cleaning PCB surfaces, including the use of compressed air, soda water, pure water, detergents, ultrasonic, and automatic PCBA cleaning machines and so on.

Compressed Air Method

The first PCB cleaner to mention is compressed air. It removes dirt and dust from printed circuit boards. Before using compressed air to remove dust and dirt from a printed board, make sure you turn off your device and unplug any cables. If you spray compressed air onto plugged-in or energized devices, it can cause permanent damage. Electrocution can also occur. After disconnecting and switching off the appliance, continue spraying compressed air into the vents to give your PCB an immediate makeover. A short spray may suffice; its duration will depend on how much dirt and dust exist on its surface.

The Soda Method

Baking soda (also known as sodium bicarbonate) is an efficient PCB cleaner that can remove dirt and corrosion without harming the board itself. Baking soda’s mild alkaline nature and mildly abrasive properties help dislodge any hard-to-remove substances such as corrosion from its surfaces. Its mild alkaline nature helps with dislodging stubborn substances such as tough mold spores that brushes cannot reach.

Pure Water Cleaning Technique

Clean PCB boards using pure water alone for best results. This technique works best when dealing with PCB boards that aren’t too dirty, or contain no harmful chemicals. After soaking the PCB board in purified water and gently scrubbing off dirt off its surface, rinse it clean water to finish up.

Detergent Cleaning Method

If there are more serious dirt marks on the PCB surface, detergent cleaning solutions may be used to clean it. Dilute them until you reach an acceptable concentration before submerging your PCB for several minutes in it before thoroughly rinsing with water.

Ultrasonic Cleaning Method

Ultrasonic cleaners are another popular way of using ultrasonic waves for PCB board cleaning; their vibrations quickly remove dirt and other impurities by placing it inside their cleaner. Even better is to use a cleaning solution that suits your PCB.

Automatic Cleaning Machine

In SMT automatic production lines, the automatic cleaning machine is installed between board loader machine and solder paste printer machine. It is important to clean the PCB before it leaves the factory. This is because it is very easy to create static electricity, which can lead to electrostatic damage, or adsorption of dust, in the SMT. Also, dust and chips may remain on the PCB surface, at the edges, through-holes, and other areas. Dusty chips can also cause poor printing, poor soldering (such as virtual soldering), component warping and skewing. Before printing solder paste, remove fine plate chips, dust, metal particles and other foreign materials from the surface before the PCB pad. This will also eliminate static electricity on the PCB, prevent virtual soldering defects and improve the product’s quality.

PCB Surface Cleaning machine

The PCB Surface Cleaning Machine is used to remove fine foreign particles from the PCB pads on the SMT production lines or coating lines online, before solder paste is printed or adhesive coated. This is to ensure the PCB is clean and eliminate soldering problems such as virtual soldering and empty soldering in advance.

There are some things you should keep in mind regardless of the method you use to clean the PCB:

√ Choose the right cleaning agent and method for cleaning different types of PCB boards and contaminants.

√ It is important to clean the PCB carefully to prevent damage.

√ Dry the PCB completely after cleaning to ensure there is no liquid left.

4. PCB Cleaner

Board washing water is a chemical cleaning agent that is used in the industry to remove the residue of flux and rosin on the surface after the circuit board has been connected. Traditional methods of cleaning printed circuit board used organic solvents. However, these have been banned because of the harmful effects of CFC-113 organic solvent on the atmosphere oxygen layer. What is the difference between PCB board cleaning products? Are there any precautions we need to take when using PCB board circuit board cleaners?

Types of PCB Cleaners:

1）Chlorinated Solvent Wash Water

The solvent is a mixture of chlorinated and other solvents. It removes the flux and dissolves the rosin quickly. It leaves no residue and is volatile.

2) Hydrocarbon Solvent Washing Water

It is also possible to use hydrocarbon-based washing water as part of PCB board cleaning process, with two distinct kinds: quick-drying and slow-drying options available.

3) Water-Based Plate Washing Water

There is water-based plate washing solution which is non-toxic, safe, and does not cause gas volatilization during cleaning process. However, since circuit boards contain metal pins, caution should be exercised when using the water based board cleaner water because it lacks an anti-rust feature.

Composition of PCB Cleaner:

Except for cleaners based on water, most detergents are made of a mix of solvents which evaporate quickly. Freon is a very useful material for detergents. It is a great material for cleaning because it’s fast and effective. It has gradually been discontinued from an environmental perspective. The majority of environmentally friendly detergents contain small molecules such as alcohols, hydrocarbons and ketones. They also include ether, ester solvents (such as butyl-acetate), acetone, ethylene glycol, butyl-ethers, butyl-acetates, solvent oils, etc. The detergents made by different manufacturers may differ, but they all contain a combination of these solvents as well as corrosion inhibitors (rust inhibitors), penetrating agents, and corrosion inhibitors.

Features of PCB Cleaners:

Cleaners have similar properties to fluxes:

1) Keep flammable products away from open flames.

2) Simple evaporation must be stored in an airtight container.

3) Steam is not toxic for the body but can be harmful if swallowed.

4) It is not harmful to touch your skin. However, repeatedly doing this may cause skin to become dry over time.

5) If it accidentally gets into the eyes, rinse eyes with water immediately and apply an eye ointment immediately to avoid infection.

5. PCB Board Cleaning Steps

Preparation before cleaning:

All connectors including jumper plug and card boards must be carefully removed one by one. The potentiometer, transformers, and solenoid (inductance) coils must also be removed. Check if the electrolytic cap on the circuit is bulging or leaking at the top. If so, remove it and make a note of its value. Checking the circuit board of the computer power supply is very important. This includes checking if there are any cracks between the printed circuit pads and the components.

1) Use a soft, clean paintbrush (a brush with a width of 1 inch is best) and compressed air at a pressure around 0.1Mpa to remove dust from the circuit board. To remove dust from the circuit board, apply a pressure of about 0.1Mpa. This liquid is available in special stores.

2) Clean the circuit board with a special washing water. This liquid is available in special stores. If you don’t have washing water, then rinse the board with tap water. The water flow should not be too strong. Use a soft brush to brush the circuit boards while flushing.

3) Use a soft, neutral-colored brush dipped into soap to gently and carefully clean all parts of the circuit board. This includes the jumper plugs, the south and north bridge chips, BI0S and the bottoms of every other IC chip. Also, clean the bottoms of the large capacitors, the bottoms of each IC chip.

4) Then, rinse the circuit board with clean water. Note: The soapy water must also be thoroughly rinsed.

5) After washing the PCB, use dry compressed air at a pressure of 0.1Mpa to remove the water. Pay attention to the jumper plug and other parts of the socket such as the CPU socket AGP, PCI, memory slots, north and south bridge chips, BIOS, the bottoms of all IC chips, the bottoms of large capacitors, etc. If you do not have compressed air, try a rubber pump which can be used to repair clock or camera.

6) Wash the circuit board with secondary distilled alcohol or anhydrous water (place the board in an oblique position, let the soldered side face up, then dip a 10~12 oil brush into anhydrous ethanol and clean the board from top to bottom). Carbontetrachloride has a higher effectiveness, but is toxic. Only use when absolutely necessary.

The cleaning process is now complete. It is clean, thorough, and environmentally friendly.

6. PCB Cleaning Technology

Semi-aqueous cleaning: This cleaning is a mixture of organic solvents and deionized waters, with a small amount of additives, cleaning agents. This type of cleaning falls somewhere in between water and solvent cleaning. These cleaners have low toxicity and are low-flashpoint organic solvents. These products are safe to use, but they must be washed and dried using water.

Water cleaning technology: This is the future of clean technology. It is important to set up a workshop for the purification and treatment of discharge water. Water is used as a cleaning medium. Additives, corrosion inhibitors, chelating agents and surfactant are then added to create a water-based series of cleaning agents that can remove non-polar contaminants and water solvents.

Water cleaning skills will be the direction in which cleaning skills are developed in the future. Let’s look at its benefits first.

√ No incineration and nontoxic;

√ The detergent formula has a high degree of freedom and a broad cleaning scale. It is also easy to remove both polar and a non-polar pollutant;

√ It is a cost-effective natural solvent and easy to get.

Let’s talk about its disadvantages:

• In areas with limited water resources, the clean method is bound to be restricted by the natural conditions in the area, since it uses a large amount of water;

• Metal parts can rust easily, and some components cannot be cleaned by water;

• It is hard to dry, and it takes a lot more energy;

• The equipment costs are high. The demand for wastewater treatment is also high. And the equipment covers a wide area.

No-clean technology: Used for soldering without clean flux or clean solder paste. Directly into the next step after soldering.

Solvent cleaning: It is mainly used to dissolve contaminants using solvents. Solvent cleaning is simple due to its fast volatilization characteristics and strong solubility.

Ultrasonic cleaning: Use of ultra-high frequencies to create thousands of tiny bubbles, and then to hit the surface of an item to remove dirt. It is possible to clean in place because it uses liquid. The cleaning process can be carried out as long as the surface of an object is touched. It works on multiple surfaces at once. It is an effective method of washing that takes only 15 minutes. Ultrasonic cleaning has the advantage that it reduces electromagnetic interference, and improves the performance of components and pads.

Ultrasonic cleaning machines are used for most of the current cleaning equipment. They can be divided roughly into liquid phase cleaning or vapor phase cleaning.

The PCB boards to be cleaned are soaked in detergent liquid. The detergent temperature in the ultrasonic cleaner is usually 35 °C to 85 °C. (There are two ways to heat the detergent, but it is best to use a heat plate.) Cleaning time is between 2 and 5 minutes. General cleaning agents can be used with liquid phase cleaning.

The vapor phase cleaning machine is composed of three tanks. One tank is for hot cleaning. A second tank is immersed in ice and frozen. And the third tank is steaming. After the third tank is heated, steam is produced, and then the low temperature parts are cooled down in the liquid drip tank. The parts are cleaned properly. The PCB boards will look cleaner after being cleaned in a cleaning solution. Cleaning such equipment requires nonflammable liquids like trichloroethylene.

7. Summary

When selecting an appropriate cleaning method for any PCB boards, local conditions must always be taken into account. The original cleaning process equipment, production conditions, safety and environmental requirements, (non-combustible, non-explosive and harmless to human body, will not adversely impact the environment), and cleaning costs are all factors to consider. What’s more, the choice of cleaning agent and cleaning method should be complied with the future development direction of the company. All choices should be forward-looking.