< img src="https://mc.yandex.ru/watch/96881261" style="position:absolute; left:-9999px;" alt="" />
April 26, 2024

What is FR-4: The Preferred Material for Printed Circuit Boards


Hey there! If you've ever wondered about the materials that power your electronic devices, let's explore the world of FR-4. This material isn't just another component; it's a cornerstone of modern electronics, pivotal in everything from smartphones to car control systems.

In this article, we'll unpack everything you need about FR-4. From its unique properties and benefits to its diverse applications, we're here to provide a comprehensive understanding of why FR-4 is a vital player in electronics manufacturing.

Whether you're a hobbyist, an engineer, or just curious, there's something here for everyone. Let's get started and explore the world of this fascinating material!

What is FR-4 Material?

What Exactly is FR-4?

Have you ever heard of FR-4 but need clarification on what it stands for?

Let's clear that up! FR-4 is a widely recognized grade of epoxy laminate essential in producing printed circuit boards (PCBs). But it's not just any material—it's the backbone that supports and insulates the electronic components that make your gadgets work.

Breaking Down the Components

FR-4 is made up of two primary components:

  • Fiberglass: This provides the structural framework, offering rigidity and durability to the laminate.
  • Epoxy Resin: This binds the fiberglass, adding to its strength and making it flame retardant.

Why is it Called FR-4?

The "FR" in FR-4 stands for "Flame Retardant," highlighting one of its vital safety features. The number "4" distinguishes this material from other flame-retardant materials.

FR-4's ability to resist burning makes it a safe choice for various electronic applications, ensuring devices function well and adhere to safety standards. This characteristic is particularly crucial because it helps prevent electronic failures that could lead to fire hazards.

Critical Properties of FR-4 Materials

Robust Mechanical Strength

One of the standout features of FR-4 is its impressive mechanical strength. This material is built to withstand significant stress and strain without compromising its shape or integrity. 

This robustness makes FR-4 the go-to choice for securely supporting and mounting delicate electronic components. Whether in your home computer or a high-tech drone, FR-4 ensures that all parts stay firmly in place, even under challenging conditions.

Superior Electrical Insulation

FR-4 isn't just tough; it's also an excellent insulator. This property is crucial in preventing electrical currents from straying where they shouldn't, thereby protecting the integrity of the circuit and reducing the risk of short circuits and other electrical failures. 

Its high dielectric strength means that FR-4 can effectively separate conductive layers even at relatively thin thicknesses, which is essential for the multilayer PCBs in advanced electronic devices.

Thermal Resistance

Electronics generate heat, and managing that heat is vital for maintaining performance and longevity. That's where FR-4's thermal resistance comes into play. This material can withstand high temperatures without degrading, making it suitable for devices that operate under intense heat conditions.

Whether inside a bustling server room or in the engine compartment of a car, FR-4 keeps cool and performs reliably.

Flame Retardancy

Safety is paramount in electronics, and FR-4 addresses this by being inherently flame retardant. This means it can halt or slow the spread of fire, providing crucial seconds to prevent damage or disaster in the event of a malfunction.

This property is particularly valued in consumer electronics and aerospace applications, where fire risk must be minimized.

Moisture Resistance

Lastly, FR-4's resistance to moisture adds yet another layer of durability and reliability. This feature ensures that the material does not absorb water, which could otherwise lead to swelling, warping, or a breakdown of its electrical insulating properties. In humid environments or devices exposed to weather, FR-4 maintains its performance without compromise.

These properties make FR-4 an incredibly versatile and dependable material in the electronics industry, supporting everything from everyday gadgets to critical aerospace components.

FR-4's ability to perform under pressure, resist environmental challenges, and ensure safety sets it apart as a foundational material in modern electronics.

How FR-4 is Manufactured and Processed

Overview of FR-4 Manufacturing

The manufacturing process of the FR-4 sheets and boards is meticulous, ensuring high quality and performance in the final products. 

The process begins with creating fiberglass cloth, the foundational layer for strength and durability. This cloth is then impregnated with an epoxy resin mixture, providing flame-retardant properties and additional structural integrity.

Laminating and Curing

Once the fiberglass is prepared, the next step is the lamination process. The impregnated fiberglass cloth is layered as needed and sandwiched between copper foils if the PCB design requires it. 

This assembly is then placed under heat and pressure in a lamination press, which causes the epoxy resin to flow and fill the gaps in the fiberglass cloth.

After lamination, the material undergoes a curing process where it is hardened under controlled heat to set the resin, enhancing the mechanical and electrical properties of the board.

Drilling and Etching

Post-curing FR-4 boards are drilled and milled to create the necessary holes and slots for component placement and assembly. These holes are typically plated with copper to form conductive vias that electrically connect different layers of the PCB.

Following drilling, the boards undergo an etching process where unwanted copper is removed to define the circuit patterns. This step is crucial for ensuring the pathways for electrical currents are accurately mapped according to the PCB design.

Versatility in PCB Manufacturing

FR-4's versatility shines in its adaptability to various PCB designs:

  • Single-Sided Boards: FR-4 is used to manufacture single-sided PCBs for simpler electronic devices where the circuit elements and components are only placed on one side of the board.
  • Double-Sided Boards: More complex devices require double-sided PCBs, with components mounted on both sides of the FR-4 board. This setup allows for more intricate circuits and greater functionality within a compact space.
  • Multilayer PCBs: For advanced electronic applications, FR-4 can be used to create multilayer PCBs, which consist of three or more layers of circuitry embedded within the material. These are essential for modern, high-density devices where space and performance are at a premium.

Finishing Touches

The final steps in the manufacturing process include applying a solder mask over the copper traces to protect against oxidation and prevent solder bridges during component soldering. This is followed by silkscreening, where component labels and other markings are printed on the PCB surface to aid in assembly and maintenance.

Where is FR-4 Used?

Pivotal Role in PCBs

FR-4 is most famously used as the primary material for printed circuit boards (PCBs) in virtually all electronic devices. This includes everything from daily gadgets like smartphones and laptops to critical telecommunications and computing infrastructure equipment. 

The material's electrical insulation properties and mechanical strength make it ideal for supporting and protecting electronic components against physical and thermal stress.

Beyond Electronics: Industrial Applications

FR-4's attributes extend its usefulness beyond typical consumer electronics into more demanding fields:

  • Aerospace: FR-4 is used for various interior components in the aerospace industry due to its low weight and strong fire retardancy, which are critical in high-altitude environments.
  • Automotive: In automotive manufacturing, FR-4 produces electronic components that control everything from basic vehicle operations to advanced safety systems.
  • Military and Defense: The material's durability and reliability under extreme conditions make it suitable for military hardware, including communication devices and control panels.

Advantages of FR-4 in Electronic Manufacturing


One of FR-4's most compelling benefits is its cost-effectiveness. Despite its high performance and reliability, FR-4 remains an affordable option for PCB manufacturing, which helps keep the overall costs of electronic products down. 

This affordability makes it accessible for various applications, from prototyping to large-scale production.

Versatility Across Different Environmental Conditions

FR-4 is remarkably versatile and capable of performing under various environmental conditions. Its thermal resistance ensures stability in devices that experience significant temperature fluctuations, while its moisture resistance protects against humidity and damp conditions. 

This makes FR-4 ideal for outdoor or harsh environments and everyday consumer electronics.

Comparison with Other Materials

Compared to other materials like G-10, FR-4 offers enhanced flame retardancy, which is crucial for safety in electronic manufacturing. While G-10 is also a glass-epoxy composite, it lacks the flame-retardant properties of FR-4, making FR-4 the preferred choice in applications where fire resistance is necessary.

Furthermore, FR-4's ability to be used in various PCB configurations, from single-layered to complex multilayer setups, showcases its superior adaptability.

Combining these benefits—cost-effectiveness, versatility, and superior material properties compared to alternatives like G-10—establishes FR-4 as a fundamental material in electronic manufacturing, maintaining its status as the backbone of PCB production.

How to Select the Appropriate FR-4 Material for Your Needs

Choosing the suitable FR-4 material for your project can significantly impact the performance and durability of your electronic devices. Here are some crucial factors and tips to help you select the best FR-4 material.

Key Factors to Consider

Thermal Properties

  • Operating Temperature: Consider the operating temperature range of your device. FR-4 materials come with different glass transition temperatures (Tg), which indicate the temperature at which the material begins to soften. If your device operates under high heat conditions, choosing a material with a higher Tg is crucial.
  • Thermal Expansion: Pay attention to the coefficient of thermal expansion (CTE) of the FR-4 material. Materials with lower CTE are preferable for thermal cycling applications, as they reduce the risk of mechanical failure due to repeated heating and cooling.


  • Device Size and Space Constraints: The thickness of the FR-4 material can affect the overall size and weight of your device. Thinner materials benefit compact devices but may offer less mechanical support and heat dissipation than thicker materials.
  • Impedance and Signal Integrity: In high-frequency applications, the thickness of the FR-4 can influence the impedance of the PCB. Proper thickness selection is essential to ensure good signal integrity and to avoid cross-talk between circuits.

Tips on Selecting Between Standard FR-4 and High TG FR-4

Standard FR-4

  • General Applications: Standard FR-4 is suitable for most consumer electronics and other applications where the device does not experience extreme temperatures. It offers excellent mechanical strength, electrical insulation, and flame retardancy at a lower cost.
  • Typical Use Cases: Ideal for household electronics, office equipment, and other environments with standard operating temperatures.

High TG FR-4

  • High-Temperature Applications: High TG FR-4 is designed to perform in environments with higher thermal resistance. It maintains its mechanical and electrical integrity at higher temperatures than standard FR-4.
  • Recommended Use Cases: Best for automotive electronics, industrial machinery, and other applications that involve high power densities or are exposed to high operational temperatures.

Making the Decision

Consider your project's specific requirements when deciding between standard and high TG FR-4. Assess factors like thermal demands, mechanical stresses, and environmental conditions. 

It's also wise to consult with material specialists or PCB fabricators to get insights based on experience with similar applications. This collaborative approach ensures that you choose the most suitable FR-4 material, optimizing your product's performance and reliability.


FR-4 has long been the foundation of electronic manufacturing, mainly due to its remarkable blend of mechanical strength, electrical insulation, thermal resistance, and cost-effectiveness. This material meets various technical specifications and ensures safety and reliability across countless applications, from consumer electronics to critical aerospace components.

Are you planning your next electronic project? Reach out for more about selecting the suitable FR-4 material for your needs.

Whether you need standard FR-4 or High TG FR-4, we're here to help.

Contact us today to ensure your project's success with the best materials available. Let's create something great together!

Article written by Alice Lee

Get a Free Quote Now!