Harnessing Aluminum PCBs: Optimal Heat Dissipation Solutions

aluminum pcb substrate

Printed Circuit Board (PCB) substrates play a pivotal role in electronic design, serving as the foundation for circuitry and components. Their selection significantly impacts the performance, reliability, and longevity of electronic devices. Amidst the array of substrate materials available, aluminum PCB substrates have been steadily gaining traction across diverse industries. Renowned for their exceptional thermal conductivity, mechanical strength, and electrical insulation properties, aluminum PCBs offer a compelling solution for applications demanding efficient heat dissipation and robust performance. As industries continue to prioritize compact, high-performance electronics, the popularity of aluminum PCB substrates continues to soar, driving innovation and enabling advancements in fields ranging from automotive and aerospace to telecommunications and LED lighting.

Understanding PCB Substrates

Printed Circuit Board (PCB) substrates serve as the foundation upon which electronic components are mounted and interconnected, forming the backbone of electronic circuits. These substrates provide mechanical support to components while facilitating electrical connections through conductive pathways etched or printed onto their surfaces.

PCB substrates play a crucial role in electronic circuits for several reasons:

Mechanical Support: PCB substrates provide a sturdy platform for mounting electronic components, ensuring proper alignment and structural integrity within the device.

Electrical Insulation: The substrate material acts as an insulator, preventing unintended electrical contact between conductive elements on the board. This insulation is essential for maintaining circuit integrity and preventing short circuits.

Signal Transmission: The properties of the substrate material influence the transmission of electrical signals through the circuit. Factors such as dielectric constant and loss tangent affect signal integrity, speed, and attenuation.

Thermal Management: PCB substrates also play a vital role in managing thermal dissipation within electronic devices. Some materials offer better thermal conductivity, helping to dissipate heat generated by components and ensuring reliable operation.

Selecting the right substrate material is critical for optimizing the performance, reliability, and cost-effectiveness of electronic circuits. Different applications require substrates with specific properties tailored to their unique requirements:

High-Frequency Applications: For applications involving high-frequency signals, substrates with low dielectric constants and minimal signal loss are preferred to maintain signal integrity and minimize attenuation.

High-Temperature Environments: In environments with elevated temperatures, substrates with high glass transition temperatures (Tg) and excellent thermal conductivity are necessary to ensure the reliability and longevity of the circuitry.

Mechanical Durability: Applications subject to mechanical stress or vibration require substrates with high mechanical strength and durability to withstand harsh operating conditions without compromising performance.

Cost Considerations: Cost-effective substrates that meet the performance requirements of the application without unnecessary overspecification are essential for maximizing the value proposition of the electronic device.

In summary, selecting the right PCB substrate material is crucial for achieving optimal performance, reliability, and cost-effectiveness in electronic circuits. By understanding the role of substrates and evaluating their properties in alignment with application requirements, designers can ensure the successful development of electronic devices across a wide range of industries and applications.

Aluminum PCBs

Aluminum PCBs, also known as metal-core PCBs or insulated metal substrate (IMS) PCBs, are a specialized type of printed circuit board that features a base layer of aluminum or aluminum alloy instead of the traditional FR4 or epoxy substrate. This aluminum layer provides several unique characteristics and advantages:

Definition and Features

Aluminum PCBs consist of a layer of thermally conductive dielectric material bonded to a metal base, typically aluminum.

The dielectric layer serves as an insulating barrier between the metal base and the circuitry, providing electrical isolation while facilitating efficient heat transfer.

Circuit traces are typically etched onto the dielectric layer, allowing for the integration of electronic components.

Advantages of Aluminum Substrates

Enhanced Thermal Management: One of the most significant advantages of aluminum PCBs is their exceptional thermal conductivity. Aluminum’s high thermal conductivity allows for efficient dissipation of heat generated by electronic components, reducing operating temperatures and enhancing overall reliability.

Improved Performance: The superior thermal management capabilities of aluminum substrates enable electronic components to operate at their optimal performance levels, minimizing the risk of overheating and performance degradation.

Mechanical Stability: Aluminum PCBs offer excellent mechanical stability and rigidity, making them suitable for applications subject to mechanical stress or vibration. This stability ensures the integrity of the circuitry, even in demanding operating conditions.

Lightweight Design: Compared to traditional substrates, aluminum PCBs offer a lightweight design, making them ideal for applications where weight reduction is a priority, such as aerospace and automotive electronics.

Cost-Efficiency: Despite their advanced thermal properties, aluminum PCBs can be cost-effective solutions for thermal management, offering a balance between performance and affordability.

Applications Where Aluminum PCBs Excel

LED Lighting: Aluminum PCBs are widely used in LED lighting applications due to their ability to efficiently dissipate heat generated by high-power LEDs. They help extend the lifespan of LED fixtures while maintaining consistent performance.

Power Electronics: In power electronics applications, such as motor drives, inverters, and power supplies, aluminum PCBs are preferred for their ability to handle high currents and dissipate heat effectively, ensuring reliable operation.

Automotive Electronics: Aluminum PCBs are increasingly used in automotive electronics, including engine control units (ECUs), LED headlights, and power converters, where thermal management and reliability are critical.

Telecommunications: Telecommunication infrastructure equipment, such as base station antennas and power amplifiers, often utilizes aluminum PCBs to maintain stable performance in high-temperature environments and harsh operating conditions.

In summary, aluminum PCBs offer numerous advantages over traditional substrates, including superior thermal management, mechanical stability, and lightweight design. Their versatility and reliability make them well-suited for a wide range of applications across various industries where efficient heat dissipation and high-performance electronics are essential.

Properties of Aluminum PCB Substrates

Aluminum PCB substrates possess several key properties that make them advantageous for various electronic applications. Understanding these properties is essential for optimizing the performance and reliability of electronic devices:

Thermal Conductivity: 

Aluminum PCB substrates are renowned for their high thermal conductivity, typically ranging from 1 to 3 W/mK. This property allows them to efficiently dissipate heat generated by electronic components, preventing overheating and ensuring reliable operation.

The superior thermal conductivity of aluminum substrates enables them to act as efficient heat sinks, transferring heat away from critical components and dispersing it across the board’s surface and into the surrounding environment.

Dielectric Constant (εr):

The dielectric constant of aluminum PCB substrates refers to the material’s ability to store electrical energy when subjected to an electric field. It influences the speed at which electrical signals propagate through the substrate.

Aluminum substrates typically have low dielectric constants, ranging from 3 to 5, which minimize signal loss and distortion. This property is particularly crucial for high-frequency applications where signal integrity is paramount.

Glass Transition Temperature (Tg):

The glass transition temperature (Tg) of aluminum PCB substrates denotes the temperature at which the material transitions from a rigid to a more flexible state. It is a critical parameter that affects the mechanical and thermal stability of the substrate.

Aluminum substrates exhibit relatively high Tg values, typically ranging from 100°C to 150°C. This high Tg ensures that the substrate maintains its structural integrity and dimensional stability under elevated temperatures, preventing warping or delamination of the circuitry.

Contributions to Performance and Reliability:

Enhanced Thermal Management: The high thermal conductivity of aluminum substrates enables efficient heat dissipation, minimizing temperature gradients and hotspots within the electronic device. This ensures that components operate within their specified temperature ranges, thereby enhancing performance and reliability.

Signal Integrity: The low dielectric constant of aluminum substrates helps preserve the integrity of electrical signals by minimizing signal attenuation and distortion. This is critical for maintaining the accuracy and reliability of high-speed digital and analog circuits.

Mechanical Stability: The combination of high Tg and mechanical rigidity ensures that aluminum PCB substrates remain structurally stable under varying thermal and mechanical stresses. This stability prevents dimensional changes and mechanical failures, contributing to the long-term reliability of the electronic device.

In summary, the properties of aluminum PCB substrates, including high thermal conductivity, low dielectric constant, and high glass transition temperature, play crucial roles in enhancing the performance and reliability of electronic devices. By efficiently dissipating heat, preserving signal integrity, and maintaining mechanical stability, aluminum substrates enable the development of high-performance electronics across a wide range of applications.

See Also: Tg of PCB Material

Explanation of Tg (Glass Transition Temperature)

The Glass Transition Temperature (Tg) of a PCB material refers to the temperature at which the material transitions from a glassy, rigid state to a rubbery, flexible state. It is a critical parameter in PCB design as it determines the maximum temperature at which the material can maintain its dimensional stability and mechanical integrity.

Below the Tg, the material behaves in a glassy manner, with high rigidity and low flexibility, making it suitable for structural support and precise component placement. Beyond the Tg, the material becomes more flexible and prone to deformation, potentially leading to solder joint failures, delamination, and other reliability issues.

Significance in PCB Design

Tg plays a crucial role in determining the thermal and mechanical properties of PCBs, particularly in applications where elevated temperatures are present, such as high-power electronics or environments subject to temperature fluctuations.

Selecting a PCB material with an appropriate Tg is essential to ensure the reliability and longevity of the electronic device. Failure to consider Tg can result in performance degradation, mechanical failures, and premature device failure, especially under thermal stress.

Importance of Selecting a Suitable Tg for Aluminum PCBs

In the case of aluminum PCBs, selecting the right Tg is paramount due to their unique thermal characteristics and applications. The high thermal conductivity of aluminum substrates makes them particularly effective in dissipating heat generated by electronic components.

A suitable Tg ensures that the aluminum substrate maintains its structural integrity and dimensional stability under the high temperatures encountered during operation. This prevents warping, delamination, and other mechanical failures that could compromise the reliability of the PCB.

The choice of Tg for aluminum PCBs should be based on the specific application requirements, including the operating temperature range, thermal cycling conditions, and mechanical stress levels. For example, applications subjected to extreme temperatures or rapid temperature changes may require a higher Tg to ensure long-term reliability.

By carefully considering the Tg of the PCB material, designers can optimize the thermal and mechanical performance of aluminum PCBs, ensuring that they meet the stringent requirements of their intended applications while maximizing reliability and longevity.

In summary, understanding the significance of Tg in PCB design is crucial for ensuring the reliability and performance of electronic devices, particularly in applications involving aluminum substrates. By selecting a suitable Tg based on application requirements, designers can mitigate the risks associated with thermal and mechanical stresses, ensuring the long-term reliability of aluminum PCBs in various demanding environments.

Aluminum PCB Dielectric Material

Overview of Dielectric Materials Used in Aluminum PCBs

Dielectric materials play a crucial role in aluminum PCBs by providing insulation between conductive layers and facilitating the transmission of electrical signals. These materials are selected based on their dielectric properties, thermal performance, mechanical stability, and compatibility with manufacturing processes. Dielectric materials used in aluminum PCBs must exhibit high thermal conductivity to efficiently dissipate heat generated by electronic components while maintaining excellent electrical insulation properties.

Role of Dielectric Materials in Insulation and Signal Transmission

Dielectric materials serve two primary functions in aluminum PCBs:

1. Electrical Insulation: Dielectric materials act as insulators between conductive layers, preventing electrical short circuits and ensuring the integrity of the circuit. They must exhibit high breakdown voltage and low dielectric loss to minimize signal attenuation and distortion.

2. Signal Transmission: Dielectric materials influence the speed and quality of signal transmission through the PCB. Low-loss dielectrics are preferred to minimize signal degradation and maintain signal integrity, particularly in high-frequency applications.

Common Dielectric Materials Used in Aluminum PCB Manufacturing

Several dielectric materials are commonly used in aluminum PCB manufacturing, each offering unique properties suited to different applications:

1. Polyimide (PI): Polyimide is a popular choice for dielectric material in aluminum PCBs due to its excellent thermal stability, flexibility, and resistance to high temperatures. It is well-suited for applications requiring reliable performance under harsh operating conditions, such as aerospace and automotive electronics.

2. Epoxy Resin: Epoxy resin-based materials are widely used in aluminum PCBs for their cost-effectiveness, ease of processing, and good electrical insulation properties. They offer adequate thermal performance and mechanical stability for many electronic applications.

3. FR4: While primarily associated with traditional PCBs, FR4 can also be used as a dielectric material in aluminum PCBs. FR4 offers good electrical insulation and mechanical strength, making it suitable for applications where cost is a significant consideration and moderate thermal performance is acceptable.

4. Ceramic-filled Polymers: Some advanced dielectric materials feature a combination of polymers and ceramic fillers to enhance thermal conductivity while maintaining good electrical insulation. These materials offer improved thermal performance compared to traditional polymer-based dielectrics and are often used in high-power electronic applications.

In summary, the dielectric material used in aluminum PCBs is critical for ensuring reliable insulation and signal transmission while effectively dissipating heat generated by electronic components. By selecting the appropriate dielectric material based on the specific requirements of the application, designers can optimize the performance, reliability, and thermal management of aluminum PCBs in various electronic devices and systems.

Design Guidelines for Aluminum PCBs

Designing aluminum PCB layouts requires careful consideration of various factors to ensure optimal thermal management, component placement, routing, and manufacturability. Here are some detailed guidelines:

Guidelines for Designing Aluminum PCB Layouts

1. Thermal Management:

    Incorporate large copper pours and vias to maximize thermal conductivity and heat dissipation.

    Ensure sufficient spacing between components to allow for adequate airflow and heat distribution.

    Place high-power components near the center of the board to minimize thermal gradients.

    Use thermal vias to transfer heat away from critical components to the aluminum substrate efficiently.

2. Component Placement:

    Place components strategically to minimize signal interference and optimize signal integrity.

    Group components with similar thermal profiles together to facilitate uniform heat dissipation.

    Keep sensitive components away from high-temperature areas and heat sources to prevent performance degradation.

    Follow recommended placement guidelines provided by component datasheets and manufacturers.

3. Routing:

    Use wide traces and vias for power and ground connections to reduce resistance and impedance.

    Optimize signal traces to minimize signal loss, reflections, and crosstalk.

    Maintain consistent trace widths and spacing to ensure uniform impedance and signal integrity.

    Avoid sharp bends and right-angle traces to minimize signal distortion and improve manufacturability.

Considerations for Thermal Management, Component Placement, and Routing

1. Thermal Management:

    Consider the operating temperature range and thermal requirements of the application when selecting substrate materials and thicknesses.

    Implement thermal relief pads for through-hole components to minimize heat transfer to the solder joints.

    Design the PCB layout to facilitate efficient heat dissipation from high-power components to the aluminum substrate.

2. Component Placement:

    Place critical components, such as power devices and voltage regulators, in areas with direct access to the aluminum substrate for optimal heat dissipation.

    Avoid placing components in areas with poor airflow or limited heat dissipation to prevent overheating and thermal stress.

    Ensure adequate clearance between components to facilitate assembly, testing, and maintenance.

3. Routing:

    Route power and ground traces as wide as possible to minimize resistance and voltage drops.

    Keep signal traces short and direct to reduce signal degradation and propagation delays.

    Use differential routing for high-speed signals to minimize electromagnetic interference (EMI) and signal integrity issues.

    Consider signal integrity simulations and impedance matching techniques to ensure reliable signal transmission.

Tips for Optimizing Designs for Manufacturability and Reliability

1. Design for Assembly (DFA):

    Minimize the number of components and assembly steps to reduce manufacturing costs and assembly time.

    Design the PCB layout with standard component sizes and footprints to facilitate automated assembly processes.

2. Design for Test (DFT):

    Include test points and access points for debugging, testing, and programming during the manufacturing process.

    Ensure adequate clearance and accessibility for test probes and equipment.

3. Design for Reliability:

    Use high-quality materials and finishes to enhance PCB reliability and longevity.

    Implement design features such as proper solder mask coverage, annular rings, and controlled impedance to prevent solder defects, pad lifting, and signal integrity issues.

    Perform thorough design reviews and simulations to identify and mitigate potential reliability risks before manufacturing.

By following these guidelines and considerations, designers can develop aluminum PCB layouts optimized for efficient thermal management, reliable performance, and ease of manufacturing. Attention to detail in layout design and adherence to best practices contribute to the overall success and quality of aluminum PCB-based electronic devices.

PCBWay and Aluminum PCB Services

Introduction to PCBWay:

PCBWay stands out as a prominent provider of comprehensive PCB manufacturing and assembly services, catering to the needs of electronics designers, engineers, and manufacturers worldwide. With a commitment to quality, reliability, and innovation, PCBWay has established itself as a trusted partner for delivering high-quality PCB solutions tailored to diverse industry requirements.

Overview of PCBWay’s Aluminum PCB Services:

PCBWay offers a comprehensive range of services specifically tailored to meet the demands of aluminum PCB fabrication and assembly. With state-of-the-art facilities, advanced technologies, and a team of experienced professionals, PCBWay provides customers with unparalleled expertise and support throughout the entire manufacturing process.

Capabilities and Expertise in Aluminum PCB Fabrication:

1. Advanced Manufacturing Technologies: PCBWay employs cutting-edge manufacturing technologies and processes to produce aluminum PCBs with precision and efficiency. From CNC drilling and routing to thermal management solutions, PCBWay utilizes the latest equipment and techniques to ensure the highest quality standards.

2. Customized Solutions: PCBWay offers customizable solutions to accommodate a wide range of design specifications and requirements. Whether it’s single-sided, double-sided, or multilayer aluminum PCBs, PCBWay can tailor the manufacturing process to meet the unique needs of each project.

3. High-Quality Materials: PCBWay utilizes high-quality aluminum substrates and dielectric materials to ensure the reliability and performance of aluminum PCBs. By sourcing materials from reputable suppliers and conducting rigorous quality control checks, PCBWay guarantees the consistency and durability of its products.

4. Expertise in Thermal Management: With extensive experience in thermal management solutions, PCBWay specializes in designing and fabricating aluminum PCBs optimized for efficient heat dissipation. By leveraging advanced thermal simulation tools and techniques, PCBWay ensures that aluminum PCBs can withstand high temperatures and maintain optimal performance in demanding applications.

5. Comprehensive Assembly Services: In addition to aluminum PCB fabrication, PCBWay offers comprehensive assembly services to streamline the manufacturing process and provide customers with a one-stop solution for their PCB needs. With automated assembly lines, experienced technicians, and strict quality control measures, PCBWay ensures the reliability and consistency of assembled aluminum PCBs.

In summary, PCBWay stands as a leading provider of aluminum PCB manufacturing and assembly services, offering customers unmatched expertise, quality, and support throughout the entire production process. With a commitment to innovation and customer satisfaction, PCBWay continues to set the standard for excellence in the PCB industry.

Applications of Aluminum PCB Substrates

Aluminum PCB substrates find widespread use across various industries and applications due to their exceptional thermal management capabilities, mechanical stability, and reliability. Below are some detailed examples of industries and products where aluminum PCBs are commonly employed:

1. LED Lighting:

    Aluminum PCBs are extensively used in LED lighting applications, including streetlights, automotive headlights, and household bulbs.

    The superior thermal conductivity of aluminum substrates helps dissipate heat generated by high-power LEDs, ensuring optimal performance and longevity.

    Aluminum PCBs enable the design of compact, lightweight LED fixtures while maintaining efficient heat dissipation and reliability.

2. Automotive Electronics:

    In the automotive industry, aluminum PCBs are employed in various electronic components, including engine control units (ECUs), LED headlights, and power converters.

    Aluminum substrates offer excellent thermal management properties, making them ideal for automotive applications where temperature fluctuations and heat dissipation are critical considerations.

    Aluminum PCBs help improve the performance and reliability of automotive electronics while withstanding the harsh operating conditions encountered in vehicles.

3. Power Electronics:

    Aluminum PCBs are widely used in power electronics applications, such as motor drives, inverters, and power supplies.

    The high thermal conductivity of aluminum substrates allows for efficient heat dissipation, enabling power devices to operate at optimal temperatures and maximizing system reliability.

    Aluminum PCBs help enhance the efficiency, power density, and reliability of power electronics systems, making them suitable for industrial, commercial, and renewable energy applications.

4. Telecommunications:

    In the telecommunications industry, aluminum PCBs are employed in base station antennas, power amplifiers, and RF/microwave components.

    Aluminum substrates offer excellent thermal stability and mechanical strength, making them well-suited for telecommunications equipment operating in outdoor environments and high-temperature conditions.

    Aluminum PCBs enable the design of compact, lightweight telecommunications devices with improved thermal performance and reliability.

5. Consumer Electronics:

    Aluminum PCBs are increasingly used in consumer electronics products, such as smartphones, tablets, and wearable devices.

    The thermal management capabilities of aluminum substrates help dissipate heat generated by high-performance components, such as processors and batteries, improving device performance and longevity.

    Aluminum PCBs enable the design of sleek, compact consumer electronics devices with enhanced thermal efficiency and reliability.

In summary, aluminum PCB substrates are integral to a wide range of industries and applications, including LED lighting, automotive electronics, power electronics, telecommunications, and consumer electronics. Their ability to efficiently dissipate heat, provide mechanical stability, and ensure reliability makes them indispensable components in modern electronic devices and systems.

Future Trends in Aluminum PCB Technolog

Emerging Trends and Advancements

1. Advanced Thermal Management Solutions: Future aluminum PCB technology is expected to focus on further improving thermal management capabilities to address the increasing power densities and thermal challenges in electronic devices. This may involve the development of novel materials with enhanced thermal conductivity or the integration of advanced heat dissipation structures, such as embedded heat pipes or microfluidic channels.

2. Miniaturization and High-Density Integration: With the ongoing trend towards miniaturization and high-density integration of electronic components, aluminum PCB technology is likely to evolve to accommodate smaller form factors and higher component densities. This may involve the development of advanced fabrication processes, such as laser drilling and microvia technology, to enable the fabrication of more compact and densely packed aluminum PCBs.

3. Enhanced Reliability and Durability: Future aluminum PCBs are expected to feature improved reliability and durability to meet the demanding requirements of various applications, including automotive, aerospace, and industrial electronics. This may involve advancements in materials science and manufacturing processes to enhance the mechanical strength, thermal stability, and long-term performance of aluminum substrates.

4. Integration of Functional Components: There is a growing interest in integrating functional components directly onto aluminum PCB substrates to simplify assembly, reduce system complexity, and improve overall performance. This may involve the integration of power devices, sensors, and passive components directly onto the PCB substrate, enabling more compact and efficient electronic systems.

Predictions for the Future Direction

1. Increased Adoption in High-Power Applications: As electronic devices continue to demand higher power densities and more efficient thermal management solutions, aluminum PCBs are expected to see increased adoption in high-power applications, such as automotive power electronics, renewable energy systems, and data center infrastructure.

2. Expansion into New Industries: The versatility and performance advantages of aluminum PCBs are likely to drive their expansion into new industries and applications beyond their traditional domains. This may include emerging technologies such as electric vehicles, 5G telecommunications, and advanced medical devices, where efficient heat dissipation and reliable performance are critical requirements.

3. Continued Innovation in Manufacturing Processes: Future advancements in aluminum PCB technology will be driven by continuous innovation in manufacturing processes, materials science, and design methodologies. This may involve the development of new fabrication techniques, such as additive manufacturing and advanced surface treatments, to enable the production of next-generation aluminum PCBs with enhanced performance and functionality.

4. Integration with IoT and Smart Systems: Aluminum PCBs are expected to play a vital role in the development of IoT (Internet of Things) devices and smart systems, where compact size, high reliability, and efficient thermal management are essential requirements. This may involve the integration of aluminum PCBs into smart sensors, wearable devices, and connected appliances to enable seamless connectivity and intelligent functionality.

In summary, the future of aluminum PCB technology is poised for significant advancements, driven by emerging trends such as advanced thermal management solutions, miniaturization, enhanced reliability, and integration with functional components. As electronic devices continue to evolve and demand higher performance, aluminum PCBs will play an increasingly important role in enabling the development of innovative and efficient electronic systems across a wide range of industries and applications.

FAQs about aluminum pcb substrate

What is the best substrate for PCB?

The best substrate for PCBs depends on the specific requirements of the application. Common substrates include FR4 (fiberglass-reinforced epoxy), aluminum, ceramic, and flexible materials like polyimide. Each substrate offers unique properties such as thermal conductivity, dielectric constant, and mechanical strength, making them suitable for different applications.

What is aluminum PCB dielectric material?

The dielectric material used in aluminum PCBs is typically a layer of thermally conductive dielectric material bonded to an aluminum base. This dielectric material serves as an insulating barrier between the metal base and the circuitry, providing electrical isolation while facilitating efficient heat transfer.

What is aluminum PCB material?

Aluminum PCB material refers to the base material of a printed circuit board, which consists of a layer of aluminum or aluminum alloy. Aluminum PCBs are also known as metal-core PCBs (MCPCBs) or insulated metal substrate (IMS) PCBs. They offer exceptional thermal conductivity, mechanical stability, and electrical insulation properties, making them ideal for applications requiring efficient heat dissipation.

What is the substrate layer of a PCB board?

The substrate layer of a PCB board refers to the base material upon which the circuitry is constructed. It provides mechanical support to the components and facilitates electrical connections through conductive pathways. The substrate layer is typically made of a non-conductive material such as FR4, aluminum, ceramic, or flexible materials like polyimide.