Here’s everything you need to know about PCB cleaning standards and the steps to meet them, including performing cleanliness tests.
PCB cleanliness standards define acceptable contamination levels for printed circuit boards and assemblies. We explain the standards below, including how they help prevent defects and improve PCB quality and durability.
What is a Clean PCB?
A clean PCB is a printed circuit board that has been thoroughly cleaned to remove contaminants. PCB contaminants can be ionic, non-ionic, or particulate matter. They include salts, acids, and moisture.
Contamination sources also vary. They can be chemicals from etching and plating, drilling, debris, or assembly flux residuals. The board may also pick up dust, cloth fibers, and other materials from the environment.
Sometimes, workers contaminate circuit PCBs if they handle them with their bare hands. The hands pass perspiration oils and other dirt to the boards, causing them to need cleaning.
A clean circuit board should not harbor the contaminants mentioned above. If they do, the levels must be within set limits or safe by electronics industry standards.
PCB Cleanliness Standards
Various standards guide manufacturers on PCB cleanliness requirements. They are IPC, ROSE, and application-based versions. Let’s examine each standard and what it entails.
IPC Standards
Various IPC (Association Connecting Electronics Industries) standards specify PCB cleanliness acceptability levels. They generally concern bare and populated boards.
- IPC 5704 — provides guidance on how to clean bare (unpopulated) circuit boards before assembly
- IPC 610 — this standard outlines PCBA cleanliness requirements by outlining their acceptability requirements
- IPC J STD 001 — the IPC J STD 001 standard applies to soldered assemblies, defining their ionic contamination limits
Other Standards
Some PCB cleaning standards are application-specific. That’s because some industries are stricter regarding long-term durability and reliability than others. Examples include military, aerospace, and medical device PCBs.
These have higher cleanliness requirements than consumer electronics boards. Manufacturers often use in-house rules for these boards, alongside external standards.
How are PCBs Cleaned?
PCB cleaning is either a manual or automated process. The preferred choice depends on whether you’re cleaning a few boards or involved in large-scale production processes. Here’s what you need to know about each procedure.
Manual Cleaning
Workers manually remove contaminants from the board using handheld tools like brushes. Manual cleaning is cost-effective for smaller volumes, including prototypes. Automation is a better option for higher volumes.
Automated Cleaning
Specialized machines clean the circuit boards with minimal human intervention. Automated cleaning is fast, with the option for cleaning many pieces simultaneously. PCB manufacturers use this method for high production runs.
PCB Cleaning Methods
PCB cleaning methods include dry cleaning, using liquids, and ultrasonic cleaning. Each method has its benefits and best application. They include the need to target specific materials and other cleaning requirements.
Dry Cleaning
Dry cleaning requires no chemicals or solvents. Instead, it uses compressed air or a vacuum to remove materials from the PCB surface. It also includes brushing off particulates and other pollutants.
Wet Cleaning
Wet cleaning requires a liquid. The liquid is usually water, an organic solvent, or an aqueous solution. De-ionized water removes ionic residuals, such as sodium chloride.
On the other hand, specialized chemicals, such as isopropyl alcohol, remove organic materials. These include rosin and no-clean flux residuals.
Ultrasonic Cleaning
Ultrasonic cleaning uses high-frequency sound waves (up to 40 kHz) to loosen stubborn contaminants or difficult-to-clean boards. The waves create microscopic implosions that agitate contaminants and aid their removal.
Plasma Cleaning
This cleaning method utilizes ionized air to remove impurities. The high-energy electrons interact with impurities, breaking them down. The technique is highly effective, making it a preferred option for high-reliability boards.
PCB Cleanliness Tests
Manufacturers determine the cleanliness of printed circuit boards by conducting various tests. The tests mainly measure the presence and amounts of residuals, providing a basis for evaluation. They include the following.
Visual Examination
You examine the circuit board using your eyes, looking for signs of contaminants, such as chemical residuals and corrosion. Visual inspection is fast and cost-effective. However, it may not pick up some contaminants.
ROSE Test
The ROSE, or Resistivity of Solvent Extract, test determines the amount of ionic components on a circuit board. It involves immersing the board in a solvent (isopropyl alcohol and de-ionized water) of known resistivity.
The solvent dissolves ionic pollutants. Measuring the resulting solution’s resistivity indicates the concentration of ionic contaminants. ROSE test results are highly reliable and used for PCBs with stringent requirements.
IC Test
IC stands for Ion Chromatography, an advanced testing method for ionic contamination. A solvent dissolves the residuals. The eluent undergoes an ion separation process (chromatography), indicating the types of contaminants.
SIR Testing
Surface Insulation Resistance (SIR) testing assesses the presence of ionic residuals by measuring their conductivity level. A low SIR indicates a high amount, while a high value means a comparatively clean board.
PCB Cleanliness for Defect Prevention
Contamination harms printed circuit boards, especially if the materials are electrically conductive. Besides improving a board’s appearance, removing them helps prevent the following problems.
- Corrosion — ionic contaminants corrode the circuit board and its components, which may affect the performance and durability of electronic devices
- Dendritic Growth — they also cause electrochemical migration and the growth of dendrites. These can lead to short-circuits
- Adhesion Challenges — dirt affects the adhesion of coatings, leading to peeling and exposing the board to the elements
- Soldering Problems — residuals interfere with the soldering process and may cause weak joints and premature board failure.
How Manufacturers Meet PCB Cleanliness Standards
Depending on the application, the manufacturer determines the applicable PCB and PCBA cleanliness standards. They then ensure the board meets them. While measures may vary, the following are key steps.
- PCB Design Considerations — avoiding creating layouts that encourage entrapment by ensuring proper component placement and spacing
- Material Selection — choosing materials that are less likely to cause contamination or attract pollutants, such as no-clean flux
- Optimized Cleaning — ensuring the cleaning process, method, and agent suit the type of residuals present on the board
- Regular Monitoring — implementing procedures that ensure high levels of cleanliness throughout the board’s production process
- Controlled Environment — controlling manufacturing conditions to prevent dust, debris, moisture, etc., from reaching the boards
- Staff Training — educating workers on PCB cleanliness requirements and best practices when handling bare and assembled circuit boards
- Safe Storage — ensuring clean storage conditions to prevent dust and other dirt from setting on cleaned circuit boards.
Conclusion
PCB cleanliness standards provide essential guidelines on how to prevent and remove contaminants. That includes suggested cleaners and cleaning methods. Manufacturers must implement strict cleanliness guidelines, ensuring products meet application requirements. It makes electronic products dependable. It also extends their lifespan.
