Physical Properties of FR4
Composition and Structure
FR4 is a composite material made from woven fiberglass cloth impregnated with an epoxy resin binder. The fiberglass reinforcement provides strength and stability, while the epoxy resin offers insulation and resistance to various environmental factors. The combination of these materials results in a laminate with excellent physical properties.
Density and Weight
One of the key physical properties of FR4 is its density. The typical density of FR4 ranges from 1.7 to 1.9 g/cm³, depending on the specific grade and manufacturer. This relatively low density makes FR4 lightweight compared to other materials with similar strength and stiffness.
Dimensional Stability
FR4 exhibits excellent dimensional stability, meaning it maintains its shape and size under various environmental conditions. This property is crucial for PCB applications, where precise and consistent dimensions are required. The dimensional stability of FR4 is attributed to its low moisture absorption and low coefficient of thermal expansion (CTE).
Mechanical Properties of FR4
Tensile Strength
FR4 possesses high tensile strength, which is the maximum stress the material can withstand before breaking when subjected to a stretching load. The typical tensile strength of FR4 ranges from 310 to 380 MPa (45,000 to 55,000 psi), depending on the specific grade and thickness.
Flexural Strength
Flexural strength is another important mechanical property of FR4. It represents the material’s ability to resist bending under load. FR4 has a flexural strength ranging from 415 to 585 MPa (60,000 to 85,000 psi), making it suitable for applications that require resistance to bending and deformation.
Impact Resistance
FR4 exhibits good impact resistance, which is the ability to withstand sudden and intense forces without breaking or cracking. The impact strength of FR4 is typically measured using the Izod impact test, and values range from 6.4 to 8.0 kJ/m² (0.3 to 0.38 ft-lbs/in).
| Property | Value Range |
|---|---|
| Density | 1.7 – 1.9 g/cm³ |
| Tensile Strength | 310 – 380 MPa (45,000 – 55,000 psi) |
| Flexural Strength | 415 – 585 MPa (60,000 – 85,000 psi) |
| Izod Impact Strength | 6.4 – 8.0 kJ/m² (0.3 – 0.38 ft-lbs/in) |
Electrical Properties of FR4
Dielectric Constant
The dielectric constant, also known as relative permittivity, is a measure of a material’s ability to store electrical energy in an electric field. FR4 has a dielectric constant that typically ranges from 4.2 to 4.9 at 1 MHz, depending on the specific grade and manufacturer. This relatively low dielectric constant makes FR4 suitable for high-frequency applications.
Dielectric Strength
Dielectric strength is the maximum electric field strength that a material can withstand before electrical breakdown occurs. FR4 has a high dielectric strength, typically ranging from 20 to 28 kV/mm (500 to 700 V/mil), making it an excellent insulator for electrical applications.
Dissipation Factor
The dissipation factor, also known as loss tangent, is a measure of a material’s power loss in an alternating electric field. FR4 has a low dissipation factor, typically ranging from 0.02 to 0.03 at 1 MHz, which indicates low power loss and good insulation properties.
| Property | Value Range |
|---|---|
| Dielectric Constant (1 MHz) | 4.2 – 4.9 |
| Dielectric Strength | 20 – 28 kV/mm (500 – 700 V/mil) |
| Dissipation Factor (1 MHz) | 0.02 – 0.03 |
Thermal Properties of FR4
Glass Transition Temperature
The glass transition temperature (Tg) is the temperature at which a polymer material transitions from a hard, glassy state to a soft, rubbery state. For FR4, the glass transition temperature typically ranges from 125°C to 135°C (257°F to 275°F), depending on the specific grade and manufacturer. This relatively high Tg makes FR4 suitable for applications that require stability at elevated temperatures.
Thermal Conductivity
Thermal conductivity is a measure of a material’s ability to conduct heat. FR4 has a relatively low thermal conductivity, typically ranging from 0.3 to 0.4 W/mK, which means it is a good thermal insulator. This property is beneficial for PCB applications, as it helps to minimize heat transfer between components.
Coefficient of Thermal Expansion (CTE)
The coefficient of thermal expansion (CTE) is a measure of a material’s dimensional change in response to a change in temperature. FR4 has a relatively low CTE, typically ranging from 12 to 16 ppm/°C (7 to 9 ppm/°F) in the X and Y directions, and 50 to 70 ppm/°C (28 to 39 ppm/°F) in the Z direction. This low CTE contributes to the dimensional stability of FR4 under varying temperature conditions.
| Property | Value Range |
|---|---|
| Glass Transition Temperature (Tg) | 125°C – 135°C (257°F – 275°F) |
| Thermal Conductivity | 0.3 – 0.4 W/mK |
| CTE (X and Y directions) | 12 – 16 ppm/°C (7 – 9 ppm/°F) |
| CTE (Z direction) | 50 – 70 ppm/°C (28 – 39 ppm/°F) |
Frequently Asked Questions (FAQ)
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What is FR4 material used for?
FR4 is primarily used in the manufacturing of printed circuit boards (PCBs) for electronic devices. Its excellent mechanical, electrical, and thermal properties make it an ideal choice for this application. FR4 is also used in other industries, such as automotive, aerospace, and construction, where its strength, stability, and insulation properties are valuable. -
Is FR4 flame retardant?
Yes, FR4 is flame retardant. The “FR” in its name stands for “Flame Retardant,” indicating that it has been treated with flame-retardant chemicals to improve its resistance to fire. This property is essential for many applications, particularly in the electronics industry, where fire safety is a critical concern. -
What is the difference between FR4 and G10?
FR4 and G10 are both composite materials made from woven fiberglass and epoxy resin. The main difference between the two is that FR4 is specifically designed to be flame retardant, while G10 is not. G10 is often used in applications where flame retardancy is not a primary concern, such as in the manufacture of high-stress mechanical parts. -
Can FR4 be used for high-frequency applications?
Yes, FR4 can be used for high-frequency applications. Its relatively low dielectric constant and dissipation factor make it suitable for use in applications involving high-frequency signals, such as in radio frequency (RF) circuits. However, for extremely high-frequency applications, specialized materials like Rogers laminates may be more appropriate. -
Is FR4 resistant to chemicals?
FR4 exhibits good resistance to many chemicals, including acids, alkalis, and solvents. This property makes it suitable for use in environments where exposure to these substances is likely. However, it is essential to consult the manufacturer’s data sheets and conduct appropriate testing to ensure compatibility with specific chemicals and application requirements.
Conclusion
FR4 is a versatile composite material with a unique combination of physical, mechanical, electrical, and thermal properties. Its excellent strength, stability, insulation, and flame retardancy make it an ideal choice for a wide range of applications, particularly in the electronics industry for the manufacturing of printed circuit boards.
By understanding the various properties of FR4, engineers and designers can make informed decisions when selecting materials for their projects. Whether it’s for PCBs, high-stress mechanical parts, or other applications requiring a strong, stable, and insulating material, FR4 offers a reliable and cost-effective solution.
As technology continues to advance, the demand for high-performance materials like FR4 will likely continue to grow. By staying informed about the latest developments in material science and engineering, we can continue to push the boundaries of what is possible and create innovative solutions to meet the challenges of the future.
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