What is FR4 material?

What is FR4 material?

Selecting the right PCB material is critical for the performance, reliability, and cost of your electronic project. FR4 PCB material is the most widely used substrate in the printed circuit board industry. In this comprehensive guide, we’ll examine why FR4 is the standard, its key properties, benefits, and limitations, tips for selecting the right FR4 material, and how it compares with other PCB material choices.

What is FR4?

FR4 stands for Flame Retardant 4, a glass fiber–reinforced epoxy laminate. This composite structure gives FR4 exceptional mechanical strength, good electrical insulation, and crucial flame resistance, making it the default choice for PCB fabrication.

Defining FR4: More Than Just a Name

FR4 stands for "Flame Retardant 4," and it refers to a specific grade of glass-reinforced epoxy laminate material that is used as the base for PCBs. The “FR” signifies its flame-retardant capabilities, crucial for electronic safety compliance, while the “4” is a designation among various flame-retardant materials (like FR1, FR2, FR3, and FR5).

FR4 is engineered from woven fiberglass cloth bonded with a high glass transition epoxy resin. This composite construction creates a mechanically robust, electrically insulating, and flame-resistant material—making it ideal as the backbone for a wide range of PCB applications, from single-layer prototypes to complex multi-layer high-speed designs.

Key Points:

• FR: Flame retardant, critical for safety
• 4: Indicates glass-reinforced epoxy composition

Properties of FR4 Material

• Flame Retardance: Self-extinguishing, preventing fire spread.
• Electrical Insulation: High electrical resistance, insulating PCB traces.
• Mechanical Strength: Durable, lightweight, and impact-resistant.
• Dielectric Constant (Dk): 4.2–4.8 (varies by manufacturer and thickness); impacts impedance and signal integrity.
• Dissipation Factor (Df): Typically 0.02; affects signal loss, especially at RF frequencies.
• Moisture Absorption: Less than 0.2%; maintains properties in humid environments.
• Glass Transition Temperature (TG): Typically 135–180°C.

Property Comparison by Manufacturer

Types of FR4 PCB Material

• Standard FR4: For general applications (TG 135–150°C).
• High TG FR4: Withstands higher temperatures (up to 180°C); ideal for lead-free soldering & automotive.
• High CTI FR4: High Comparative Tracking Index; improved resistance to electrical tracking.
• FR4 Without Copper Laminate: Used for insulation, non-conductive applications.

Benefits of FR4 in PCBs

• Affordable: Ideal for prototyping, small and medium production runs.
• Lightweight & Strong: Excellent strength-to-weight ratio.
• Low Water Absorption: Reliable in humid or moisture-prone uses.
• Good Insulator: Maintains circuit isolation and signal integrity.

Drawbacks and Limitations of FR4 PCBs

• Not for High-Heat Applications: Max TG is ~180°C; not suitable for aerospace or harsh power electronics.
• Lead-Free Soldering: Difficulty withstanding > 250°C without thermal degradation.
• High-Frequency Limits: Variable Dk and higher Df can impact high-speed, RF, and microwave circuits.
• Manufacturing Issues: Potential for weave exposure, crazing, measling, and delamination if not processed properly.

FR4 vs Other FR Ratings

FR4 PCB Applications

• Consumer Electronics: Smartphones, wearables, home appliances.
• Industrial Controls: Automation, instrumentation.
• LED Lighting: PCBs for LED arrays.
• Automotive Circuits: Standard modules.
• Prototyping: Due to affordability and easy processing.

IMS vs FR4: IMS (Insulated Metal Substrate) PCBs use metal base for heat dissipation, while FR4 is best for signal integrity and general-purpose use.

How FR4 is Used in PCB Fabrication

• Insulating Backbone: Core material between copper layers in single/double/multi-layer PCBs.
• Copper Lamination: Layers of copper foil are bonded to FR4, etched to form circuit patterns.

How to Select the Right FR4 Thickness

• Thin FR4 (0.2–0.6 mm): Small, lightweight, flexible circuit assemblies.
• Standard FR4 (1.0–1.6 mm): Most consumer and industrial PCBs.
• Thick FR4 (up to 3.2 mm): Power circuits, connectors, high mechanical stress.

Factors to Consider:

• Size & Weight Constraints
• Component Height
• Electrical Impedance
• Required Flexibility or Rigidity

Tips for Selecting the Right FR4 Material

• Match TG value to peak soldering temperature.
• Ensure consistent Dk for signal-sensitive designs.
• For high frequency or voltage, consider High CTI or High TG types.
• For humid or outdoor use, choose low moisture absorption variants.

FR4 PCB Cost Factors

• Cost per Square Inch: Varies by thickness, copper weight, TG type, order quantity, and finish.
• Bulk Ordering: Lower per-unit cost for higher quantities.

Industry Standards: IPC-A-600 and FR4

IPC-A-600 sets quality standards for FR4 PCB materials, covering:

• Weave Exposure Acceptability
• Allowed texture and subsurface conditions
• Measling, crazing, and delamination thresholds for PCB reliability

Why Learn About FR4 PCB Material?

Whether you’re a design engineer or a decision-maker in electronics procurement, understanding FR4 material properties helps in:

• Selecting the best PCB substrate material for your budget and technical requirements.
• Ensuring long-term PCB reliability and product safety.
• Avoiding issues with signal loss, impedance matching, or mechanical failure in finished products.
• Navigating compliance with industry standards, such as UL, IPC, and RoHS

Anatomy of FR4 Material

Let’s break down what makes FR4 material so effective and versatile:

• Fiberglass (Woven Fabric Layer): This core provides impressive mechanical strength, dimensional stability, and rigidity, ensuring that the PCB keeps its shape even when subjected to stress, vibration, or thermal cycling.
• Epoxy Resin (Binder/Matrix): The epoxy resin is the “glue” that encapsulates the fiberglass, resulting in excellent electrical insulation and impressive chemical resistance. Its glass transition temperature (Tg) determines the maximum operational temperature.

Together, these components create a substrate with superb electrical properties, low moisture absorption, and strong flame retardance.

Structure of FR4 PCB Material

*Note: Copper foil and solder mask are part of the whole PCB manufacturing process, not the FR4 sheet itself, but they interact closely with FR4’s properties.

Key Characteristics of FR4

• Flame-Retardant: Passes UL94-V0, self-extinguishing within 10 seconds after flame removal.
• High Dielectric Strength: Maintains electrical isolation between copper traces.
• Mechanical Strength: Excellent dimensional stability and resistance to warping.
• Moisture Resistance: Low water absorption (<0.2%); performance is not significantly degraded by humidity.
• Glass Transition Temperature (Tg): Ranges from 130°C (standard) up to 200°C (High-TG FR4).
• Cost-Effective: Offers one of the best price-performance ratios in the industry.

Quick Fact Table: FR4 at a Glance

FR4 in Circuit Board Manufacturing

FR4 PCB substrate is pivotal not only for consumer electronics but also for industrial, automotive, military, and aerospace PCBs. Its balanced material properties allow for the integration of through-hole components, edge connectors, solder mask applications, multi-layer PCB architectures, and more.

Quote: “Without the innovation of flame-retardant glass-reinforced epoxy like FR4, the reliability and accessibility of modern electronics would simply not be possible.” — Senior Materials Scientist, Global PCB Manufacturer

How to Determine FR4 Thickness for PCB Design

Why FR4 Thickness Matters

FR4 PCB thickness directly affects several aspects of PCB reliability and function:

• Signal Integrity: Thicker or thinner substrates influence controlled impedance and transmission line widths, especially important in high-frequency and RF circuit board designs.
• Mechanical Strength: Thicker FR4 offers enhanced mechanical stability for supporting heavy components, connectors, and resisting flex or vibration.
• Space Efficiency: Devices like smartphones, wearables, and medical gadgets may require thinner PCBs for compact form factors.
• Thermal Management: Thicker boards can disperse heat more efficiently in power electronics, but may also trap heat if not properly designed.
• Cost: Thicker boards typically require more material and may cost more to manufacture and process through drilling, plating, and lamination.

Common FR4 Thickness Options

While custom thicknesses are possible, standard sizes help streamline the PCB manufacturing process and ensure compatibility with common assembly and design practices. Here’s a quick reference:

Fun fact: The most common industry standard thickness for an FR4 PCB is 1.6 mm (0.063 inch)—a perfect blend of durability, manufacturability, and compatibility for most component and edge connector profiles.

How to Select the Right FR4 Thickness for Your PCB

Key Considerations for FR4 Thickness Selection

Here are the most important factors to evaluate when deciding on FR4 material thickness for your printed circuit board design:

1. Application and End-Use Environment

• Wearables and multi-functional IoT devices often demand ultra-thin PCBs (0.2-0.8 mm) for light weight and compactness.
• Automotive, industrial control, and military/aerospace PCBs benefit from thicker FR4 (1.6 mm and above) for added mechanical strength and resistance to vibration, shock, and environmental damage.
• High-frequency and RF circuit boards may require precise stackup configurations and customized thicknesses for controlled impedance.

2. Electrical Performance: Signal Integrity & Impedance

• The distance between layers (set by core and prepreg thickness) directly impacts signal propagation, impedance matching, and signal integrity.
• High-speed design uses field solvers to calculate exact trace width and spacing—a process where changing the FR4 thickness, even slightly, can shift impedance targets.

3. Component Profile and Mounting

• Tall, through-hole, or edge connector components demand a thicker substrate for robust mechanical anchoring.
• SMT (surface mount technology) boards, especially those with fine-pitch components, can often use thinner PCBs for precise assembly.

4. Thermal and Mechanical Stresses

• Power PCBs and boards exposed to rapid temperature cycling may require increased thickness for better thermal coefficient performance and dissipation.
• Flexibility is needed for certain interconnects and dynamic parts (as in flex-rigid PCBs), while rigidity is important for load-bearing or mobile applications.

5. Manufacturing and Assembly Constraints

• Manufacturer capabilities and tooling may limit your choices; not all PCB factories support custom thicknesses or ultra-thin substrates.

Quick Reference Table: FR4 Thicknesses & Use Cases

Benefits of using FR4 as PCB material

Choosing the right substrate is foundational to any successful printed circuit board (PCB) design, and FR4 material stands apart as the industry standard for exceptional reasons. Whether you’re constructing a basic consumer device, a multilayer control system for industrial machinery, or the next innovation in the IoT space, FR4 offers a set of properties that reliably align with stringent electrical, thermal, and mechanical demands—at a price point accessible to both large manufacturers and small prototyping shops.

At a Glance: Key Benefits of FR4 PCB Material

Applications of FR4 PCB

FR4 PCB Application Table

Why is Rogers Better Than FR4 Material?

When designing high-performance printed circuit boards, the choice of substrate material is crucial. Rogers and FR4 are two of the most common PCB materials—but when do you choose Rogers, and why is Rogers often considered better than FR4, especially for advanced applications?

Key Differences Between Rogers and FR4 PCB Materials

Top Reasons Rogers is Better Than FR4

1. Superior High-Frequency Performance Rogers PCBs have a much lower and more stable dielectric constant, which ensures minimal signal loss and distortion—even at high frequencies. This is vital for applications such as RF, microwave, 5G, and aerospace.

2. Lower Signal Loss (Low Dissipation Factor) Thanks to their low loss tangent, Rogers laminates allow cleaner and faster signal transmission. FR4, on the other hand, tends to absorb more signal, resulting in greater loss—especially as frequencies increase.

3. Exceptional Thermal Management Rogers materials withstand higher temperatures and offer better thermal stability than FR4, making them reliable for demanding environments (e.g., automotive radar, satellite communications).

4. Consistent Electrical Properties Rogers provides uniform signal behavior across the board, which is critical in precision designs. FR4’s electrical properties can vary with temperature and frequency.

When Should You Use Rogers Instead of FR4?

• RF, microwave, and millimeter wave PCBs
• High-speed digital circuits (data centers, telecom, aerospace)
• Advanced automotive radar and sensors
• Any application where signal integrity and low signal loss are priorities

When is FR4 Still a Good Choice?

• Consumer electronics and general-purpose boards with moderate speed requirements
• Cost-sensitive applications without strict high-frequency standards