Overview
FR4 is a flame-retardant glass-reinforced epoxy laminate material widely used as the standard substrate for printed circuit boards (PCBs) and electrical insulation components. The designation “FR” stands for Flame Retardant, while the number “4” identifies the specific grade within the NEMA classification system.
FR4 combines woven fiberglass cloth reinforcement with epoxy resin, providing an exceptional balance of mechanical strength, electrical insulation, dimensional stability, flame resistance, and chemical resistance.
FR4 is widely used in:
- Printed Circuit Boards (PCBs)
- Electrical Insulation Components
- Electronic Equipment
- Aerospace Electronics
- Industrial Automation Systems
- Telecommunications Equipment
- Medical Electronics
- High-Voltage Applications
Due to its excellent performance and cost-effectiveness, FR4 remains the most commonly used PCB substrate material worldwide.
Material Specification
| Property | Value |
|---|---|
| Material Designation | FR4 |
| Full Name | Flame Retardant Glass Epoxy Laminate |
| Material Family | Thermoset Composite |
| Reinforcement | Woven Glass Fiber |
| Matrix Material | Epoxy Resin |
| Density | 1.80–2.00 g/cm³ |
| Appearance | Green, Yellow, Natural, Black |
| Typical Manufacturing Methods | Lamination, CNC Machining, PCB Fabrication |
| Standard Forms | Sheets, Panels, PCB Laminates |
Chemical Composition
FR4 consists of fiberglass reinforcement embedded within a flame-retardant epoxy resin system.
| Component | Function |
|---|---|
| Woven Glass Fiber | Structural Reinforcement |
| Epoxy Resin | Matrix Material |
| Flame Retardant Additives | Fire Resistance |
| Coupling Agents | Fiber-Resin Bonding |
| Fillers | Performance Optimization |
The glass fiber content typically ranges from 50–70% by weight.
Common FR4 Grades
| Grade | Characteristics |
|---|---|
| Standard FR4 | General PCB Applications |
| High Tg FR4 | Enhanced Thermal Stability |
| Lead-Free FR4 | RoHS-Compliant Electronics |
| High CTI FR4 | Improved Electrical Tracking Resistance |
| Halogen-Free FR4 | Environmentally Friendly Electronics |
| High-Speed FR4 | Signal Integrity Applications |
Mechanical Properties
Typical Values
| Property | Value |
|---|---|
| Tensile Strength | 300–500 MPa |
| Flexural Strength | 400–700 MPa |
| Compressive Strength | 400–600 MPa |
| Elastic Modulus | 18–24 GPa |
| Hardness | Rockwell M110–120 |
| Impact Strength | Moderate |
Typical Mechanical Performance
| Property | Performance |
|---|---|
| Strength | Excellent |
| Rigidity | Outstanding |
| Dimensional Stability | Outstanding |
| Wear Resistance | Good |
FR4 provides significantly higher stiffness than most engineering plastics.
Physical Properties
| Property | Value |
|---|---|
| Density | 1.80–2.00 g/cm³ |
| Water Absorption | <0.15% |
| Thermal Conductivity | 0.25–0.40 W/m·K |
| Moisture Resistance | Excellent |
| Dimensional Stability | Outstanding |
Low moisture absorption contributes to excellent electrical performance.
Thermal Properties
| Property | Value |
|---|---|
| Glass Transition Temperature (Tg) | 130–180°C |
| High Tg Grades | Up to 200°C |
| Continuous Service Temperature | 120–140°C |
| Decomposition Temperature | >300°C |
| Coefficient of Thermal Expansion | 10–18 ppm/°C (X-Y) |
FR4 maintains stability across a broad range of electronic operating conditions.
Strength-to-Weight Ratio
| Material | Density (g/cm³) | Tensile Strength |
|---|---|---|
| FR4 | 1.90 | 400 MPa |
| Aluminum 6061 | 2.70 | 310 MPa |
| G10 | 1.85 | 450 MPa |
| PEEK | 1.32 | 100 MPa |
FR4 offers an excellent strength-to-weight ratio for structural electronic applications.
Electrical Properties
Typical Values
| Property | Value |
|---|---|
| Volume Resistivity | >10¹⁴ Ω·cm |
| Surface Resistivity | >10¹³ Ω |
| Dielectric Strength | 18–25 kV/mm |
| Dielectric Constant (1 MHz) | 4.2–4.8 |
| Dissipation Factor | 0.01–0.03 |
Electrical Performance
| Property | Performance |
|---|---|
| Electrical Insulation | Outstanding |
| Arc Resistance | Excellent |
| Dielectric Stability | Excellent |
| High Voltage Performance | Excellent |
FR4 is specifically engineered for electrical insulation applications.
Flame Resistance
| Property | Performance |
|---|---|
| UL94 Rating | V-0 |
| Self-Extinguishing | Yes |
| Flame Spread | Very Low |
| Smoke Generation | Low |
The V-0 flame rating is one of FR4’s defining characteristics.
Moisture Resistance
| Property | Performance |
|---|---|
| Water Absorption | Very Low |
| Humidity Resistance | Excellent |
| Electrical Stability in Moisture | Excellent |
| Environmental Durability | Excellent |
FR4 maintains performance even in humid operating environments.
Chemical Resistance
| Chemical Environment | Performance |
|---|---|
| Water | Excellent |
| Oils & Greases | Excellent |
| Dilute Acids | Good |
| Dilute Alkalis | Good |
| Solvents | Good |
| Fuels | Good |
| Strong Oxidizers | Moderate |
FR4 performs well in most industrial electronic environments.
Machinability
| Process | Rating |
|---|---|
| CNC Milling | Excellent |
| CNC Drilling | Excellent |
| Routing | Outstanding |
| Laser Processing | Good |
| Precision Machining | Excellent |
Machinability Comparison
| Material | Machinability |
|---|---|
| FR4 | Excellent |
| G10 | Excellent |
| Aluminum | Excellent |
| PEEK | Excellent |
Carbide tooling is recommended due to fiberglass reinforcement.
Manufacturing Characteristics
| Manufacturing Process | Rating |
|---|---|
| PCB Fabrication | Outstanding |
| CNC Machining | Excellent |
| Lamination | Outstanding |
| Electrical Component Manufacturing | Outstanding |
FR4 is the industry-standard material for PCB production.
International Equivalent Standards
| Standard | Equivalent Grade |
|---|---|
| NEMA | FR4 |
| IEC | Glass Epoxy Laminate |
| UL | FR4 V-0 |
| IPC | FR4 PCB Material |
| DIN | Epoxy Glass Laminate |
| GB/T (China) | 环氧玻璃布层压板 |
Available Forms
| Product Type | Availability |
|---|---|
| PCB Laminates | Yes |
| Sheets | Yes |
| Panels | Yes |
| Insulation Components | Yes |
| CNC Machined Parts | Yes |
Typical Applications
Electronics Industry
- Printed Circuit Boards
- Multilayer PCBs
- Electronic Housings
- Insulation Structures
Electrical Industry
- Switchgear Components
- Transformer Insulation
- Bus Bar Supports
- High-Voltage Insulators
Industrial Automation
- Control Panels
- PLC Systems
- Sensor Mounts
- Electrical Assemblies
Aerospace Industry
- Avionics Systems
- Electronic Modules
- Insulation Components
Medical Electronics
- Diagnostic Equipment
- Medical Control Systems
- Instrumentation Boards
Telecommunications
- Network Equipment
- Communication Devices
- Signal Processing Systems
Advantages
Excellent Electrical Insulation
Outstanding dielectric performance for electronic applications.
High Mechanical Strength
Provides structural support and durability.
Flame Retardant
UL94 V-0 rated for fire safety.
Excellent Dimensional Stability
Maintains tight tolerances under varying conditions.
Low Moisture Absorption
Ensures reliable electrical performance.
Cost-Effective
Provides excellent performance at moderate cost.
Limitations
Brittle Compared to Plastics
Less impact resistant than engineering thermoplastics.
Difficult to Recycle
Thermoset structure limits recyclability.
Tool Wear During Machining
Glass fibers accelerate cutting tool wear.
Limited High-Frequency Performance
Not ideal for very high-speed RF applications compared with advanced laminates.
Comparison with Common PCB Materials
| Property | FR4 | G10 | Rogers 4350B | CEM-1 |
|---|---|---|---|---|
| Flame Resistance | Outstanding | Moderate | Excellent | Good |
| Electrical Performance | Excellent | Excellent | Outstanding | Good |
| Cost | Low | Low | High | Very Low |
| Mechanical Strength | Excellent | Excellent | Good | Moderate |
| PCB Applications | Outstanding | Limited | High Frequency | Entry-Level |
Comparison with G10
| Property | FR4 | G10 |
|---|---|---|
| Flame Resistance | Better | |
| Electrical Properties | Similar | |
| Mechanical Strength | Similar | |
| Cost | Similar | |
| Safety Compliance | Better |
FR4 is essentially a flame-retardant version of G10.
Available Surface Finishes
Standard Finishes
- Copper Clad Finish
- Natural Laminate Finish
- Matte Finish
Functional Finishes
- Electrical Insulation Finish
- High Voltage Finish
- PCB Grade Surface
Specialty Grades
- Standard FR4
- High Tg FR4
- Halogen-Free FR4
- Lead-Free FR4
- High-Speed FR4
Frequently Asked Questions (FAQ)
What is FR4?
FR4 is a flame-retardant glass fiber reinforced epoxy laminate used primarily for PCB manufacturing and electrical insulation applications.
What is FR4 used for?
Typical applications include:
- Printed Circuit Boards
- Electrical Insulators
- Industrial Control Systems
- Electronic Equipment
Is FR4 electrically insulating?
Yes. FR4 provides excellent dielectric and insulation properties.
Is FR4 flame resistant?
Yes. Standard FR4 carries a UL94 V-0 flame-retardant rating.
Is FR4 machinable?
Yes. FR4 can be CNC machined, drilled, routed, and fabricated into precision components.
Why choose FR4?
Because it combines:
- Excellent Electrical Insulation
- High Strength
- Flame Resistance
- Dimensional Stability
- Cost Efficiency
What is the difference between FR4 and G10?
FR4 is flame-retardant and UL-rated, while G10 offers similar mechanical and electrical properties but without mandatory flame-retardant characteristics.
Does GCNOV provide FR4 manufacturing services?
Yes. GCNOV provides:
- FR4 CNC Machining
- PCB Manufacturing Support
- Electrical Insulation Components
- Precision FR4 Fabrication
- Prototype Development
- Low-Volume Production
- Mass Production