1. As the world continues to witness the miniaturization of circuits and electronic products, the demand for conformal coating PCBs has surged more than ever. To protect PCBs from factors such as moisture, extreme temperatures, and dust, manufacturers have increasingly adopted conformal coatings. Choosing the right type of coating is crucial.
2. However, sifting through the vast amount of information available online can be a daunting task. Fortunately, this article aims to simplify the process by providing 12 guidelines for selecting the ideal conformal coating for your PCB.
3. The role of PCB conformal coating is multifaceted. Beyond protecting electronic components from corrosion and environmental factors, conformal coatings serve several other important functions.
4. These include acting as an insulating material for printed circuit boards and minimizing environmental stress during the assembly of PCBs. Additionally, conformal coatings can reduce the need for complex enclosures.
5. Conformal coatings also protect printed circuit boards from fungi, heat, moisture, and air pollutants such as dust and dirt, thereby enhancing the longevity of the PCB.
6. Classification and attributes of conformal coatings vary widely, and the best choice depends on the specific protection required. Factors such as ease of rework and the method of application are also important considerations. Here are some typical classifications of conformal coatings:
7. • Acrylic resins: These coatings offer excellent general protection and moderate flexibility. They are also known for their reasonable moisture resistance and dielectric strength.
• Epoxy resins—besides creating hard coatings, they are categorized into two types. They offer excellent moisture, chemical, and abrasion resistance.
• Silicone—this silicone provides average anti-fungal and moisture resistance. It performs well in high-temperature ranges and is suitable for high-vibration tools.
• Polyurethane—this coating excels in chemical and moisture resistance. Additionally, polyurethane has abrasion and solvent resistance.
• Parylene—this unique coating, applied via vapor deposition, offers high dielectric strength. It is also suitable for high-temperature applications.
• UV-curing coatings—these coatings are known for their rapid production but are difficult to repair or rework once cured.
Three anti-paint selection principles
To ensure your PCB receives the optimal conformal coating, consider the following principles:
Single component ease of use
When selecting a conformal coating, prioritize single-component options. Single-component coatings do not require mixing before application and provide excellent chemical and moisture resistance, making them highly preferred. They are easy to apply and have a long pot life, though they require extended curing times for the best results.
Material curing mechanism
While not the primary criterion, the curing mechanism affects application methods and long-term reliability. Reliable mechanisms include:
• UV curing—uses UV light for fast curing but can be challenging to rework.
• Thermal curing—suitable for secondary UV curing or when other mechanisms fail.
• Moisture curing—used with evaporation curing.
• Evaporative curing—where the liquid carrier evaporates first, sometimes requiring multiple dips for adequate coverage.
Long shelf life
The shelf life indicates how long the product maintains its quality on the shelf under proper conditions. Products with short shelf lives are problematic, especially for those preferring long-term usability. Silicone Conformal Coating 433B is notable for its fast curing and extended shelf life.
Wide operating temperature range
As PCB designs push for higher performance, materials that withstand varying temperatures become crucial. Conformal coatings should protect without impacting the PCB’s function. Silicone, for example, offers protection across a wide temperature range.
Engineering or performance characteristics
The coating’s engineering and performance features are critical. Check for chemical resistance and durability against dust and humidity. Ensure it doesn’t stress components, especially under extreme thermal conditions, and can handle hot spots.
Protection from temperature and mechanical shock
PCBs in high-temperature environments, like military applications, need coatings that protect against extreme temperatures and mechanical stress. Ensure the conformal coating resists abrasion and remains effective despite frequent handling.
Rapid curing without by-products
The conformal coating should cure quickly after application, ideally at room temperature. Rapid curing is crucial for high production rates and avoiding by-products that could affect the PCB’s function.
Low toxicity and cost
Opt for conformal coatings that are both non-toxic and cost-effective. Avoid materials that could negatively impact health or increase costs significantly.
Repairability
The chosen conformal coating should be easy to repair or rework. Ensure the repair material matches the initial coating for consistent performance and reliability.
Verification methods and techniques
Verify the coating with inspection, testing, and analysis methods. This ensures the coating meets requirements before mass production and performs as expected.
Generalization
When selecting a conformal coating, balance functional requirements with the appropriate material choice to ensure optimal protection for your PCB.
2. However, sifting through the vast amount of information available online can be a daunting task. Fortunately, this article aims to simplify the process by providing 12 guidelines for selecting the ideal conformal coating for your PCB.
3. The role of PCB conformal coating is multifaceted. Beyond protecting electronic components from corrosion and environmental factors, conformal coatings serve several other important functions.
4. These include acting as an insulating material for printed circuit boards and minimizing environmental stress during the assembly of PCBs. Additionally, conformal coatings can reduce the need for complex enclosures.
5. Conformal coatings also protect printed circuit boards from fungi, heat, moisture, and air pollutants such as dust and dirt, thereby enhancing the longevity of the PCB.
6. Classification and attributes of conformal coatings vary widely, and the best choice depends on the specific protection required. Factors such as ease of rework and the method of application are also important considerations. Here are some typical classifications of conformal coatings:
7. • Acrylic resins: These coatings offer excellent general protection and moderate flexibility. They are also known for their reasonable moisture resistance and dielectric strength.
• Epoxy resins—besides creating hard coatings, they are categorized into two types. They offer excellent moisture, chemical, and abrasion resistance.
• Silicone—this silicone provides average anti-fungal and moisture resistance. It performs well in high-temperature ranges and is suitable for high-vibration tools.
• Polyurethane—this coating excels in chemical and moisture resistance. Additionally, polyurethane has abrasion and solvent resistance.
• Parylene—this unique coating, applied via vapor deposition, offers high dielectric strength. It is also suitable for high-temperature applications.
• UV-curing coatings—these coatings are known for their rapid production but are difficult to repair or rework once cured.
Three anti-paint selection principles
To ensure your PCB receives the optimal conformal coating, consider the following principles:
Single component ease of use
When selecting a conformal coating, prioritize single-component options. Single-component coatings do not require mixing before application and provide excellent chemical and moisture resistance, making them highly preferred. They are easy to apply and have a long pot life, though they require extended curing times for the best results.
Material curing mechanism
While not the primary criterion, the curing mechanism affects application methods and long-term reliability. Reliable mechanisms include:
• UV curing—uses UV light for fast curing but can be challenging to rework.
• Thermal curing—suitable for secondary UV curing or when other mechanisms fail.
• Moisture curing—used with evaporation curing.
• Evaporative curing—where the liquid carrier evaporates first, sometimes requiring multiple dips for adequate coverage.
Long shelf life
The shelf life indicates how long the product maintains its quality on the shelf under proper conditions. Products with short shelf lives are problematic, especially for those preferring long-term usability. Silicone Conformal Coating 433B is notable for its fast curing and extended shelf life.
Wide operating temperature range
As PCB designs push for higher performance, materials that withstand varying temperatures become crucial. Conformal coatings should protect without impacting the PCB’s function. Silicone, for example, offers protection across a wide temperature range.
Engineering or performance characteristics
The coating’s engineering and performance features are critical. Check for chemical resistance and durability against dust and humidity. Ensure it doesn’t stress components, especially under extreme thermal conditions, and can handle hot spots.
Protection from temperature and mechanical shock
PCBs in high-temperature environments, like military applications, need coatings that protect against extreme temperatures and mechanical stress. Ensure the conformal coating resists abrasion and remains effective despite frequent handling.
Rapid curing without by-products
The conformal coating should cure quickly after application, ideally at room temperature. Rapid curing is crucial for high production rates and avoiding by-products that could affect the PCB’s function.
Low toxicity and cost
Opt for conformal coatings that are both non-toxic and cost-effective. Avoid materials that could negatively impact health or increase costs significantly.
Repairability
The chosen conformal coating should be easy to repair or rework. Ensure the repair material matches the initial coating for consistent performance and reliability.
Verification methods and techniques
Verify the coating with inspection, testing, and analysis methods. This ensures the coating meets requirements before mass production and performs as expected.
Generalization
When selecting a conformal coating, balance functional requirements with the appropriate material choice to ensure optimal protection for your PCB.
