What is FR4 PCB?

What is FR4 PCB?
Definition and Core Components of FR4 PCB

Basic Concept

FR4 is an abbreviation for Flame Retardant 4 (flame-retardant rating 4) and complies with the UL94V-0 standard. It refers to a composite material composed of epoxy resin and glass fiber cloth.
An FR4 PCB is a printed circuit board (PCB) that uses FR4 as its base material. It accounts for over 70% of the global PCB market and serves as the "universal substrate" in the electronics industry.

Typical Structure

• Copper Foil Layer: The conductive layer with a thickness ranging from 1 oz to 3 oz (approximately 35 μm to 105 μm).
• Base Material: Epoxy resin (adhesive) + glass fiber (reinforcing material that provides mechanical strength).
• Solder Mask Layer: An insulating protective layer that is green or available in other colors.
• Silkscreen Layer: Used to mark component positions and parameters.

Core Characteristics of FR4 Material

Physical and Chemical Properties

• Flame Retardancy: Self-extinguishing under the UL94V-0 standard, suitable for high-safety scenarios.
• Mechanical Strength: Glass fiber imparts high rigidity and flexural strength (typical value: flexural strength > 400 MPa).
• Temperature Resistance: The glass transition temperature (Tg) of conventional FR4 ranges from 130°C to 180°C, offering excellent stability at high temperatures.

Electrical Properties

• Dielectric Constant (Dk): Ranges from 4.2 to 4.8 at 1 GHz, suitable for low- to medium-frequency circuits. It has a volume resistivity of 10^8 Ω·cm, meeting the requirements of most low-voltage circuits.

Application Scenarios of FR4 PCB

General Electronic Devices

• Consumer Electronics: Mobile phone motherboards, computer motherboards, and home appliance control boards.
• Industrial Control: Programmable logic controllers (PLCs), sensors, and power modules.

Special Requirement Scenarios

• Multilayer Boards: Complex wiring with 4 to 16 layers is achieved through lamination processes (e.g., server motherboards).
• Thick Copper Boards: With a copper thickness of ≥ 3 oz, they are used in high-current power modules (e.g., electric vehicle charging stations).

Comparison Between FR4 and Other PCB Materials

Design and Manufacturing Considerations

Moisture Absorption Management
FR4 is prone to moisture absorption (with an absorption rate of approximately 0.1%–0.3%). It needs to be baked before soldering (e.g., at 120°C for 2 hours) to prevent "board popping."

Coefficient of Thermal Expansion (CTE) Matching
FR4 has a relatively high Z-axis CTE (50–70 ppm/°C). Direct soldering with components having a high CTE (such as ball grid arrays (BGAs)) should be avoided.

High-Frequency Alternatives
For high-frequency performance requirements, hybrid PCBs (combining FR4 with localized layers of high-frequency materials) can be used.

Summary

FR4 PCBs remain the preferred substrate material in electronic design due to their low cost, high reliability, and ease of processing. However, in high-frequency and high-heat-dissipation scenarios, targeted material substitutions are necessary. During the design process, performance and cost must be balanced based on specific requirements.

• FR4PCB.TECH, Specialized Production: FP4, High TG, halogen-free, aluminum/copper/ceramic-based, and Rogers material printed circuit boards (PCBs).

  Offerings: Double-sided boards, multilayer boards, HDI (High-Density Interconnect) boards, rigid-flex boards, high-frequency boards, etc., to cater to diverse requirements.

  Surface Finish Processes: OSP (Organic Solderability Preservative), HASL (Hot Air Solder Leveling), ENIG (Electroless Nickel/Immersion Gold), immersion silver, immersion tin, electroplated nickel-gold, and electroless palladium, etc.

  Product Application Areas: Industrial control, telecommunications equipment, consumer electronics, automotive electronics, medical devices, aerospace, computers and data centers, energy and power, IoT (Internet of Things) and smart home, military and defense, marine electronics, AI (Artificial Intelligence) terminals.
  Contact us immediately at info@fr4pcb.tech to obtain preferential quotations.