What is the difference between FR4 and fr5 PCB?

Introduction to FR4 and FR5 PCB

Printed Circuit Boards (PCBs) are essential components in modern electronics, providing a reliable and efficient means of connecting electronic components. Two of the most common materials used in PCB fabrication are FR4 and FR5. These materials are both glass-reinforced epoxy laminates, but they have distinct properties that make them suitable for different applications. In this article, we will explore the differences between FR4 and FR5 PCBs, their characteristics, and their respective use cases.

What is FR4 PCB?

FR4 (Flame Retardant 4) is a widely used PCB material that consists of a woven fiberglass cloth impregnated with an epoxy resin binder. The “4” in FR4 refers to the woven glass reinforcement used in the material. FR4 is known for its excellent mechanical and electrical properties, making it a popular choice for a wide range of electronic applications.

Characteristics of FR4 PCB

  1. High strength and stiffness
  2. Good electrical insulation properties
  3. Excellent moisture resistance
  4. Flame retardant
  5. Suitable for multilayer PCBs
  6. Cost-effective

What is FR5 PCB?

FR5 (Flame Retardant 5) is another glass-reinforced epoxy laminate used in PCB fabrication. The main difference between FR4 and FR5 lies in the type of glass reinforcement used. While FR4 uses a woven glass cloth, FR5 employs a non-woven glass mat. This difference in reinforcement results in distinct properties that make FR5 suitable for specific applications.

Characteristics of FR5 PCB

  1. Higher thermal resistance compared to FR4
  2. Better dimensional stability at elevated temperatures
  3. Improved mechanical strength
  4. Enhanced electrical properties
  5. Suitable for high-temperature applications
  6. More expensive than FR4

Differences Between FR4 and FR5 PCB

Composition and Structure

The primary difference between FR4 and FR5 PCBs lies in their composition and structure. FR4 uses a woven glass cloth as its reinforcement, which is impregnated with an epoxy resin binder. The woven structure of the glass cloth provides excellent mechanical strength and stability to the PCB.

On the other hand, FR5 uses a non-woven glass mat as its reinforcement. The non-woven structure of the glass mat allows for better resin flow during the lamination process, resulting in a more homogeneous distribution of the resin throughout the PCB. This homogeneous distribution contributes to FR5’s improved thermal and mechanical properties.

Thermal Properties

FR5 PCBs exhibit better thermal properties compared to FR4. The non-woven glass mat used in FR5 allows for better heat dissipation, making it more suitable for high-temperature applications. FR5 has a higher glass transition temperature (Tg) than FR4, which means it can maintain its mechanical and electrical properties at higher temperatures.

Property FR4 FR5
Glass Transition Temperature (Tg) 130°C – 140°C 170°C – 180°C
Thermal Conductivity 0.3 W/mK 0.4 W/mK
Thermal Expansion Coefficient (CTE) 14-16 ppm/°C 12-14 ppm/°C

The higher glass transition temperature and better thermal conductivity of FR5 make it a preferred choice for applications that involve exposure to high temperatures, such as automotive and aerospace electronics.

Mechanical Properties

Both FR4 and FR5 PCBs exhibit good mechanical strength and stability. However, FR5 has slightly better mechanical properties due to its non-woven glass mat reinforcement. The homogeneous distribution of the resin in FR5 results in improved strength and dimensional stability.

Property FR4 FR5
Flexural Strength 415 MPa 480 MPa
Tensile Strength 310 MPa 345 MPa
Compressive Strength 415 MPa 480 MPa

The enhanced mechanical properties of FR5 make it more suitable for applications that require higher structural integrity and resistance to mechanical stresses.

Electrical Properties

FR4 and FR5 PCBs have similar electrical properties, as both materials use glass reinforcement and epoxy resin. However, FR5 exhibits slightly better electrical properties due to its non-woven glass mat structure.

Property FR4 FR5
Dielectric Constant (at 1 MHz) 4.5 4.3
Dissipation Factor (at 1 MHz) 0.02 0.018
Surface Resistivity 10^6 – 10^9 MΩ 10^6 – 10^9 MΩ
Volume Resistivity 10^8 – 10^10 MΩ·cm 10^8 – 10^10 MΩ·cm

The lower dielectric constant and dissipation factor of FR5 make it slightly better suited for high-frequency applications compared to FR4.

Cost Comparison

FR4 PCBs are generally more cost-effective than FR5 PCBs. The woven glass cloth used in FR4 is less expensive and more readily available than the non-woven glass mat used in FR5. Additionally, the manufacturing process for FR4 PCBs is more standardized and widely adopted, contributing to its lower cost.

However, the cost difference between FR4 and FR5 PCBs may be justified in applications that require the enhanced thermal, mechanical, or electrical properties offered by FR5.

Applications of FR4 and FR5 PCB

FR4 PCB Applications

FR4 PCBs are widely used in various electronic applications due to their excellent balance of mechanical, electrical, and thermal properties. Some common applications of FR4 PCBs include:

  1. Consumer electronics (smartphones, laptops, televisions)
  2. Industrial control systems
  3. Telecommunications equipment
  4. Medical devices
  5. Automotive electronics (non-critical applications)

FR5 PCB Applications

FR5 PCBs are primarily used in applications that require higher thermal resistance, improved mechanical strength, and enhanced electrical properties. Some common applications of FR5 PCBs include:

  1. Automotive electronics (critical applications)
  2. Aerospace and defense systems
  3. High-temperature industrial equipment
  4. Power electronics
  5. LED lighting systems

Frequently Asked Questions (FAQ)

  1. Q: Can FR4 PCBs be used in high-temperature applications?
    A: While FR4 PCBs can withstand temperatures up to 130°C – 140°C, they may not be the best choice for high-temperature applications. FR5 PCBs, with their higher glass transition temperature, are better suited for such applications.

  2. Q: Are FR5 PCBs more expensive than FR4 PCBs?
    A: Yes, FR5 PCBs are generally more expensive than FR4 PCBs due to the higher cost of the non-woven glass mat and the more specialized manufacturing process.

  3. Q: Can FR5 PCBs be used for multilayer boards?
    A: Yes, FR5 PCBs can be used for multilayer boards. However, due to their higher cost, they are typically used only when the enhanced properties of FR5 are required.

  4. Q: Are FR4 and FR5 PCBs both flame retardant?
    A: Yes, both FR4 and FR5 PCBs are flame retardant. The “FR” in their names stands for “Flame Retardant.”

  5. Q: Which PCB material is better for high-frequency applications?
    A: FR5 PCBs are slightly better suited for high-frequency applications due to their lower dielectric constant and dissipation factor compared to FR4 PCBs.

Conclusion

FR4 and FR5 PCBs are both glass-reinforced epoxy laminates used in the fabrication of printed circuit boards. While they share many similarities, the key difference lies in the type of glass reinforcement used. FR4 PCBs use a woven glass cloth, while FR5 PCBs employ a non-woven glass mat.

This difference in reinforcement results in distinct properties that make each material suitable for specific applications. FR4 PCBs are more cost-effective and widely used in consumer electronics, industrial control systems, and telecommunications equipment. On the other hand, FR5 PCBs offer better thermal resistance, improved mechanical strength, and enhanced electrical properties, making them ideal for high-temperature applications, automotive electronics, and aerospace systems.

When choosing between FR4 and FR5 PCBs, it is essential to consider the specific requirements of the application, such as operating temperature, mechanical stresses, and electrical performance. By understanding the differences between these two materials, designers and engineers can make informed decisions to ensure the optimal performance and reliability of their electronic devices.