What Is FR-4?
FR-4, short for Flame Retardant 4, is a widely-used flame-retardant epoxy composite material which provides robust mechanical strength and superior electrical, thermal and fire-resistant properties.
FR-4 is fabricated by combining epoxy resin with woven fiberglass reinforcement and flame-retardant additives. The material is produced by impregnating layers of glass cloth with epoxy resin and subjecting them to heat and pressure.
FR4 is commonly utilized as a substrate material in electronics due to its:
- Excellent flame retardancy
- High thermal stability
- Superior electrical insulation properties among others
What are the properties of FR-4 Material?
Flame Retardancy
FR4 has a UL94 V-0 rating, indicating superior flame retardancy.Further fire resistance can be achieved by incorporating additional additives without compromising electrical properties.
Mechanical properties
Hardness – FR4 maintains a hardness value between 110 and 130 on the Rockwell M scale. It is notably resistant to surface deformation.
High Flexural Strength – FR4 has a high strength that makes it resistant to bending and warping. It provides stability and reliability in applications that require dimensional accuracy and structural integrity. The material has a flexural strength of 450-650 MPa.
Physical properties
FR4 is a composite material consisting of woven fiberglass cloth and epoxy resin.
FR4 exhibits low moisture absorption, high mechanical strength, and good thermal stability.
FR4 laminates can withstand high temperatures and maintain their properties in various environmental conditions.
Electrical Insulation
FR4 provides excellent insulation for printed circuit boards and electronic components. It offers high dielectric strength and low dielectric constant. It also protects against electrical breakdown and signal loss in high-frequency applications.
Chemical resistance
- Excellent resistance to dilute and concentrated acids, alcohols, and bases
- Good resistance to aldehydes, esters, aliphatic hydrocarbons, ketones
- Limited resistance to aromatic and halogenated hydrocarbons and oxidizing agents
What are the benefits of FR4 over other circuit board materials?
When compared to other materials, FR4 has:
- Higher heat resistance FR4: (Tg of 130-140°C [266-284°F])
- Standard epoxy: (Tg of 90-110°C [194-230°F])
- Better electrical insulation properties
- Greater mechanical strength
- Excellent dimensional stability
FR4 is often preferred over standard epoxy laminates. It has superior flame retardancy combined with its high glass transition temperature. This benefit makes it more suitable for high-performance electronic applications.
In many areas, FR4 is replacing other circuit board materials. These include phenolic and polyimide for improved reliability. FR4 can compete with many high-end substrates such as ceramic and polytetrafluoroethylene (PTFE) in certain applications.
What are the Limitations of FR-4 pcb circuit board materials
FR4 has greatly contributed to the electronics industry, but there still exist some drawbacks with this composite material.
The standard grade of FR4 has:
- lower thermal conductivity
- lower frequency performance
These properties are inferior compared to more advanced substrates, due to its glass-reinforced epoxy composition.
Moreover, FR4 in its basic form is susceptible to moisture absorption and thermal degradation. At high frequencies (>1 GHz), it can experience significant signal loss, increased dielectric constant, and reduced insulation resistance.
Many high-performance circuit boards are manufactured using modified FR4 to make it capable of handling:
higher operating temperatures as well as
improved electrical characteristics
Additionally, enhanced FR4 often requires additives such as ceramic fillers and flame retardants. This makes it suitable for applications beyond standard printed circuit boards.
Applications for FR-4 Material
FR4 has extensive applications in the PCB industry. FR4 boards are strong and durable. They allow for high-density circuit designs and multilayer constructions. FR4 substrates are cost-effective, heat-resistant, and more resistant to warping. FR4 laminates are mainly used for making circuit boards for:
- computers, smartphones, and other consumer electronics,
- industrial control systems and automation equipment,
- aerospace and defense applications,
- medical devices and diagnostic equipment.
FR4 has good dimensional stability, low moisture absorption, and high chemical resistance. These benefits allow its use in the CNC machining industry. It is an effective material to replace metals and plastics in applications like:
- electrical enclosures,
- insulators,
- switch plates,
- custom electronic housings,
- prototype components, etc.
Its excellent machinability enables precise fabrication and complex geometries to produce high-performance parts.
FR4 is employed to manufacture components in various industries such as:
- telecommunications equipment,
- automotive electronics,
- robotics and automation,
- renewable energy systems.
