A: After Surface Mount Technology (SMT) assembly, the printed circuit boards (PCBs) often need to undergo a cleaning process to remove any flux residues, soldering paste, and other contaminants that might be present on the board’s surface. Cleaning the PCBs is crucial to ensure their reliability and functionality. There are several methods and techniques used for PCB cleaning after SMT assembly:

  1. Water-Based Cleaning: Water-based cleaning is one of the most common methods used in PCB cleaning. It involves using water-based cleaning agents, usually mixed with detergents or surfactants, to remove contaminants from the PCB surface. The boards are typically immersed in a cleaning solution, and various cleaning mechanisms, such as spraying, agitation, or ultrasonic vibrations, can be employed to enhance the cleaning process.
  2. Solvent Cleaning: Solvent-based cleaning involves using organic solvents (such as isopropyl alcohol or acetone) to dissolve and remove flux residues and other contaminants from the PCB surface. Solvent cleaning is effective, but it may require proper ventilation due to the volatile nature of the solvents.
  3. Aqueous Cleaning: Aqueous cleaning combines water-based cleaning agents with mechanical agitation to remove contaminants from the PCBs. This method is particularly effective for removing water-soluble flux residues. Aqueous cleaning can be performed using batch or inline systems.
  4. Ultrasonic Cleaning: Ultrasonic cleaning involves using high-frequency sound waves to create tiny bubbles in the cleaning solution. These bubbles collapse near the PCB surface, creating tiny shock waves that help dislodge and remove contaminants. Ultrasonic cleaning is often combined with water-based or solvent-based cleaning methods.
  5. Vapor Phase Cleaning: Vapor phase cleaning utilizes a vaporized cleaning agent that condenses onto the PCB, effectively dissolving and removing contaminants. This method is less common but can be helpful for specific applications.
  6. Saponification Cleaning: Saponification cleaning is used for removing rosin-based flux residues. It involves using alkaline cleaning agents that chemically react with the flux residues, converting them into water-soluble substances that can be rinsed away.
  7. Ionized Air Cleaning: Ionized air blowers can remove loose particles and contaminants from the PCB surface. While this method is not as thorough as liquid-based cleaning, it can help remove loose debris.

It’s important to note that the choice of cleaning method depends on factors such as the type of contaminants, the type of components on the PCB, and the desired level of cleanliness. Also, proper care should be taken to ensure the cleaning process does not damage sensitive components, such as integrated circuits or connectors.

After PCB cleaning, it’s essential to thoroughly rinse the PCBs to remove any traces of cleaning agents, as these residues could cause issues if left on the board. Proper drying and inspection should follow the cleaning process to ensure that the PCBs are ready for the next stages of assembly and testing.

PCB Cleaning Machine
Example of a PCB Cleaning Machine