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  • Precision Cleaning for Advanced Multi-Material PCBs

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    BY ELIZABETH NORWOOD, SENIOR CHEMIST, MICROCARE, LLC.

    As electronic devices continue to advance, Printed Circuit Boards (PCBs) have evolved to incorporate a diverse range of materials to meet demands for higher performance, smaller size, and improved reliability. However, this variety of materials presents a significant challenge – finding cleaning solutions that can effectively remove contaminants without damaging these delicate components.

    The Importance of Contaminant Removal
    The pursuit of higher performance, smaller sizes, and enhanced reliability has driven the adoption of new PCB materials, each with unique properties. However, all contaminants, whether flux residues, fingerprint oils, dust, or uncured solder paste, should be removed. If left, they can lead to problems like short circuits, corrosion, and complete failure, affecting product quality and reliability. Contaminated PCBs may also result in customer dissatisfaction, decreased brand reputation, and potential financial losses due to returns, repairs, or recalls.
    Modern PCBs’ intricate geometries and densely packed components, including features like bottom termination or tight standoff components, worsen this cleaning challenge, making precision cleaning vital to ensure best PCB functionality and longevity.

    Emerging PCB Materials
    The evolution of materials within PCB manufacturing has changed electronic product design, providing manufacturers with increased options. While traditional fiberglass-reinforced epoxy laminates maintain a substantial market share, there has been a notable increase in the adoption of advanced materials.

    These innovative materials are being driven by the demand for higher performance, miniaturization, and improved reliability in electronic devices. For instance, high-frequency laminates such Precision Cleaning for Advanced Multi-Material PCBs

    ■ PCB Production: Multi-material PCBs and components make thorough PCB cleaning a challenge.
    ■ Vapor Degreaser: Vapor degreasing is a well-established and effective method for precision cleaning of complex multi-material boards.

    as PolyTetraFluorEthylene (PTFE) and ceramic-filled hydrocarbon-based materials enable unprecedented data transmission rates and other high-frequency applications, exhibiting low signal loss and enhanced signal integrity.
    Moreover, the emergence of wearable electronics and flexible displays has caused the development of PCBs capable of bending, twisting, and conforming to various shapes without compromising functionality. Materials like polyimide have eased this transformation, offering flexibility and stretchability that traditional rigid PCBs could not achieve.
    Effective heat dissipation has also become a critical concern as electronic devices become increasingly compact and powerful. For example, Metal-Core PCBs (MCPCBs) offer enhanced thermal conductivity, ensuring reliable performance and an extended operational lifespan for these high-density components.

    Furthermore, the electronics industry has embraced sustainability initiatives, adopting eco-friendly materials such as bio-based resins, recycled substrates, and lead-free solder alternatives, reflecting a commitment to reducing environmental impact.

    Nanocomposites have also appeared as game-changers, incorporating nanoparticles such as carbon nanotubes and nanoceramics into the base material. These materials offer improvements in mechanical strength, thermal conductivity, and electrical properties, making them important in the aerospace and medical sectors, where performance, reduced size, and increased reliability are integral.

    As the diversity of materials in PCB manufacturing expands, the challenges of effective cleaning have multiplied. Traditional cleaning methods may fall short when confronted with the unique properties of these advanced substrates. Aggressive cleaning agents can potentially damage delicate materials, while ineffective cleaning can leave contaminants that compromise performance and reliability.

    Vapor Degreasing: A Reliable Cleaning Solution for Advanced PCBs With PCB materials consistently evolving, vapor degreasing stands out as a well-established and effective method for precision cleaning of complex multi-material boards. This closed-loop system uses specifically formulated low-boiling point, non-flammable cleaning fluids. These fluids efficiently remove contaminants from densely populated PCBs without compromising the integrity of sensitive materials.

    This meticulous approach guarantees an elevated level of cleanliness. Plus, the advantage of vapor degreasing is the ability to customize the cleaning fluid to work with a broad spectrum of materials and match specific contaminants encountered.

    Types of Contamination
    Contaminants can infiltrate PCBs during manufacturing, storage, shipping, and handling, ranging from uncured solder paste to oils, inks, and coatings. To ensure optimal performance, thorough cleaning to micron or submicron levels is imperative.

    Organics: These encompass rosin solder pastes and fluxes, creating robust solder joints. They consist of solvents, resins, and additives, including polar or non-polar White Residue: Inorganic contamination left by lead-free or no-clean fluxes and pastes, require more aggressive cleaning fluids to remove.

    The electronics industry has embraced sustainability initiatives, adopting eco-friendly materials such as bio-based resins, recycled substrates, and lead-free solder alternatives, reflecting a commitment to reducing environmental impact.

    compounds. Specialty cleaning fluids or flux removers are effective against organic contaminants, with mild to medium strength solutions usually preferred.

    Inorganics: Flux and solder paste activators like acids, bases, and halogens constitute inorganic contamination. Often stemming from lead-free or no-clean fluxes and pastes, these residues, especially white residues, can be stubborn to remove. Aggressive cleaning fluids are necessary, but careful evaluation is crucial to prevent damage to delicate PCB components.

    Water: Water, considered a subset of inorganic contamination, poses unique challenges for PCB cleaning. To address water contamination effectively, batch drying in a vapor degreaser equipped with a water separator is recommended.

    Two drying fluid methods are available, depending on the water quantity:
    Absorption drying is suitable for small water quantities. Using a solvent and alcohol mix, this method is hydrophilic, absorbing water from the PCBs to prevent water spots.

    For heavily wet conditions, displacement drying is preferable. This method employs fluids with surfactants to displace water droplets from PCBs. The dense, hydrophobic solvent displaces water, allowing it to float to the surface of the drying fluid for removal, ensuring thorough drying of the PCBs.

    Particulate: Commonly found on PCBs, particulate contamination varies in size from sub-microscopic to visible debris like dust, dirt, fibers, and metal chips. Electrostatically bonded to PCB surfaces, particulates require an electrostatic polar cleaning fluid to break the bond and displace them. Additional agitation, such as vibrating ultrasonic energy or boiling action, aids in enhancing the cleaning fluid’s efficacy in removing insoluble contamination.

    The Importance of Testing
    Rigorous testing and gradual adjustments are essential to ensure best cleaning results and material compatibility. Careful testing ensures thorough cleaning and evaluates the compatibility of cleaning fluids with the advanced materials used in today’s PCB manufacturing. This process typically involves cleaning trials on sacrificial or test boards, starting with a mild cleaner and progressively moving to stronger options until the desired level of cleanliness is achieved.

    Comprehensive testing across multiple areas of the PCB is crucial to ensure the safety of all materials that may meet the cleaning fluid, either directly or indirectly. By partnering with critical cleaning experts, manufacturers can gain the knowledge needed to select the right cleaning fluid and process improvements, leading to best cleaning results while supporting material integrity.

    Manufacturers must prioritize material compatibility assessments alongside cleaning method choice, recognizing the potential risks of solvent-induced damage or degradation. By integrating comprehensive testing protocols early into the cleaning process, manufacturers can confidently navigate the complexities of PCB cleaning, achieving best results while minimising risks to material integrity.

    A Forward-Thinking Strategy
    As the electronics industry continues to push the boundaries of innovation, the challenges of precision cleaning for advanced multi-material PCBs will only intensify. Vapor degreasing, with its ability to accommodate a wide range of materials and customizable cleaning solutions, is a forward-thinking strategy for supporting the reliability and longevity of these sophisticated electronic components.

    By using advanced cleaning methods like vapor degreasing and collaborating with critical cleaning experts, electronics manufacturers can ensure that their products meet the highest performance and durability standards, even as the complexity of PCB materials continues to evolve. This approach not only safeguards the functionality of modern electronics but also paves the way for the innovations of tomorrow.

    Elizabeth Norwood is a Senior Chemist at MicroCare, LLC, which offers precision cleaning solutions. She has been in the industry more than 25 years and holds a BS in Chemistry from the University of St. Joseph. Norwood researches, develops, and tests cleaning-related products. She currently has one patent issued and two pending for her work. For more information, visit www.microcare.com.

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