Abstract:

The cleaning process following PCB soldering is crucial for the electrical performance, lifespan, and reliability of the product. It is also a vital step in PCB manufacturing.

The Necessity of the Cleaning Process:

Various flux types are used in PCB assembly. Flux generally consists of active agents, film agents, additives, and solvents. Active agents often include organic acids or halogens, while additives may include acidity regulators, corrosion inhibitors, and flame retardants. Residue from these substances after soldering can negatively impact electronic performance.

For precision circuits, the presence of salt or alkali residues, combined with moisture or gases, can create electrolyte solutions, leading to galvanic cell reactions, electrochemical corrosion, leakage, and short circuits. Additionally, dust particles can create undesirable contact points, causing discharge, poor heat dissipation, and potential fire hazards. The acids and gases may also directly corrode the circuits through redox reactions, while electrostatic accumulations can damage components through breakdowns.

Thus, the effectiveness of cleaning after PCB soldering is critical for the electrical performance, longevity, and reliability of the product. Moreover, selecting the appropriate cleaning method is essential, as it influences product lifespan, environmental impact, and human health.

Common PCB Cleaning Methods:

Currently, PCB cleaning methods are divided into manual cleaning, gas-phase cleaning, ultrasonic cleaning, centrifugal cleaning, and semi-water cleaning. Each method requires specific cleaning agents, and the cleanliness of the PCB must be verified to meet the standards for the corresponding product grade, as specified in the “Cleaning Requirements After Soldering for Military PCB Assemblies”.

1. Manual Cleaning

Manual cleaning is commonly used in military product manufacturing. Its main advantages include flexibility, simplicity, and not requiring specialized equipment. This method is typically used for small batch production or multi-variety PCB assemblies. However, it has drawbacks such as inconsistent quality, low efficiency, and difficulty cleaning beneath components like BGAs.

Initially, 1,1,2-Trichlorotrifluoroethane was the preferred solvent due to its excellent cleaning performance, compatibility, and safety. However, it was later banned due to its ozone-depleting properties. Alcohol-based solvents became the alternative, offering affordability and ease of access. Despite this, alcohol cleaning caused issues such as deliquescence or extraction of flux residues, which left white spots around solder joints, affecting the reliability of military-grade electronics.

To address these issues, alcohol-based solvents are now being phased out, and various modified alcohol cleaning agents are used instead. These are tailored to specific flux types to enhance cleaning efficiency.

2. Ultrasonic Cleaning Machine:

Ultrasonic cleaning provides excellent cleaning results, but the ultrasonic vibrations may cause internal damage to components (such as crystal vibration), making it unsuitable for PCB cleaning in the electronics industry.

3. Gas-phase Cleaning:

Gas-phase cleaning is a CFC-based cleaning technology that offers good cleaning performance. However, scientists have found that CFCs damage the atmospheric ozone layer, meaning it no longer meets environmental requirements.

4. Water Cleaning:

Currently, two types of water cleaning technologies exist. The first involves using an aqueous solution with saponifiers at temperatures between 60°C and 70°C. The saponifiers react with rosin-type flux residues to form water-soluble fatty acid salts, which are then rinsed off with continuous water flow. The second method is a water cleaning process for non-rosin, water-soluble fluxes.

5. Semi-water Cleaning:

Semi-water cleaning is a process that uses solvents followed by a rinse with hot water and drying. It is widely used because it does not require changes to the solder resist used in existing processes, does not disrupt the production process, and provides excellent cleaning results. Most electronics manufacturers in the United States use this technology, and Japan accounts for 20% to 30% of their electronic cleaning processes using semi-water cleaning. When combined with the appropriate cleaning agents, it effectively removes both organic and inorganic contaminants such as rosin, water-soluble flux residues, and non-cleaning flux solder paste from PCB surfaces.


The advantages of this method include consistency, reliability, and high efficiency. It is particularly effective for post-soldering cleaning of large-scale PCB assemblies. However, it is not suitable for certain components like potentiometers, adjustable resistors, and non-sealed devices, and can be sensitive to moisture on PCBs.

If you have any questions about PCBs or PCBA, please feel free to contact us at info@wellcircuits.com.