The Use of FR4 Material in PCB Fabrication

FR4 is a common substrate material in PCBs that can be either uncoated or coated. It is one of the most-used materials in the industry due to reliability and cost-effectiveness.

FR-4 is a laminate made from glass cloth, epoxy resin and mineral filler. The glass cloth provides electrical insulation and mechanical strength while the epoxy resin provides chemical resistance and good thermal properties.

The glass-reinforced epoxy laminate is the most common substrate material for printed wiring boards because of its mechanical properties and cost-effectiveness. In addition, the epoxy has excellent dielectric properties, making it an ideal top coating for printed circuit boards.

Understand the PCB Industry

FR4 has a resin content of 20%, while other materials like epoxy glass or polyimide have a resin content of 30%. The lower resin content of FR-4 means that it has less dielectric constant, which means that it has better signal transmission properties than other materials.

Many engineers prefer FR4 to other substrates because of its higher signal transmission properties. As a result, FR-4 sheet is a very common, low-cost material in constructing electronic equipment cabinets, like computer racks. It is also often applicable in constructing metal enclosures for electric devices such as motor controllers and power supplies for industrial motors or actuators.

Is FR4 the way to go?

FR4 has many advantages. It is inexpensive, lightweight, and offers relative electrical and mechanical stability. It also has a wide range of the FR4 thicknesses. But it is not the best board material for all applications. For example, you may consider high-frequency laminates if you’re building a radio. Therefore, you should compare the Df (dissipation factor) values of different laminates. It will help you decide which one is right for your design.

What is FR4 Substrate Material?

FR4 Material

If you’re unfamiliar with what FR4 stands for in PCB, it stands for flame-retardant. An FR4 PCB is a fiberglass-reinforced epoxy laminated sheet complying with the UL94 V-0 standard. National Electrical Manufacturers Association (NEMA) created this designation in 1968. The flame-retardant properties of FR-4 are an advantage because it offers excellent electrical insulation. As a result, FR4 printed circuit boards are ideal for many applications, including electronic contract manufacturing.

FR4 is a popular substrate choice for many applications despite varying thermal and electrical properties. The low cost and mechanical properties make it an excellent choice for various electronics applications. Altium Designer supports advanced high-speed applications and specialized laminates. With its rules-driven environment, Altium Designer on Altium 365 delivers unprecedented integration and efficiency to the electronics industry. Regardless of your industry, you can confidently design a circuit using Altium Designer on FR4 substrates.

Choosing the Right PCB Design Software

PCB design software is available in many forms. Some of them are free, while others require a fee. Both types of software provide a very user-friendly interface, but most are limited in their component sets. Freeware programs are the best option for those with no experience in the field. However, they are also limited to producing only single or double-sided PCB boards, and lack a 3D viewing component. Therefore, a bit of research is essential before making a purchase.

Whether or not your design software supports the FR4 thickness standard will depend on several factors. A thin FR4 board is preferable for small devices such as USB connectors. However, FR4 boards are also less flexible, making them a poor choice for larger projects. Thick FR4 boards, on the other hand, are more durable and can support flex lines and V-grooves.

The dielectric constant for FR4 materials makes them good for high-frequency circuit boards without losing their electrical properties. However, this makes them less compatible with other materials for high-frequency applications, such as RF and microwave devices. Therefore, PCB designers need to use PCB design software that supports the FR4 thickness standard to avoid redesigning the board to use a new material.

The Copper Foil and Glass Substrate

Generally, FR4 is the primary insulating backbone of a printed circuit board (PCB). Copper foil is then laminated to it to create the circuits that make up the finished product. In complex PCB designs, we use FR4 on more than one side. These circuit boards may include multiple solder mask layers, which prepare for the final silkscreen layer and lead free soldering process.

FR4 is a type of glass substrate from a fiberglass cloth with an epoxy resin binder. FR1 and FR2 are composite materials made of cellulose paper impregnated with phenolic resin. CEM-1, on the other hand, is a composite of cellulose paper and fiberglass that is fused together. FR4 is applicable in consumer electronics such as televisions and stereos.

Should you consider weight?

FR4 substrates can be thin or thick. A thin one will reduce the overall weight of the board and the components it supports. Thinner FR4 boards will not accommodate grooves or large sizes. Despite its low weight and flexibility, FR-4 is not good for high-temperature environments, aerospace applications, or boards that need to flex regularly. Further, it can become damaged during shipping.

FR4 Dielectric Constant and Material Properties

The dielectric constant of PCB materials varies from manufacturer to manufacturer. For example, FR4 has a high dielectric constant, but this depends on its thickness and resin content.

The dielectric constant of FR4 is a vital determinant of mechanical and thermal reliability. As a result, FR4 dielectric constants are a critical component of circuit boards used in high-temperature environments, such as engine compartments. Luckily, modern PCB designers can perform FR4 simulations using Altium Designer. The software’s layer stack manager makes generating impedance profiles for each PCB laminate easy.

FR4 is an insulator with favorable mechanical and electrical properties. It isolates adjacent copper planes and offers overall flexural and bending strength. The material is available in various forms and strengths, depending on the manufacturer’s specifications and requirements. It also has favorable water resistance and strength. Nevertheless, FR4 is not the only PCB material on the market. Alternative materials are also available that offer similar benefits.

The dielectric constant of PCB materials depends on the glass weaving style and the resin content. Depending on these properties, FR4 dielectric constant ranges from 3.8 to 4.8. The dielectric constant is also affected by moisture absorption, the ability of a circuit board to resist water. Therefore, if you subject the material to high-frequency exposure, it will lose its dielectric property and be useless.

You should design high-frequency PCBs with accuracy. In addition, the dielectric constant of FR4 varies across its area, requiring accurate dispersion and propagation delay calculations. High-frequency boards require a high-frequency material with a lower thermal coefficient. A high-frequency board will handle the added heat that comes with high-frequency operation. The thermal coefficient of FR-4 is around 40 ppm/degree Celsius.

General Properties of FR4 Substrate

Unlike other materials, FR4 substrate exhibits a wide range of properties, including impedance matching, thermal conductivity, and a low specific heat capacity. We use FR4 as the basis of most PCBs in a wide range of environments.

Board Thickness

The thickness of your PCB is an important factor to consider in PCB design. Several factors can impact its thickness, including the size and functionality of the board. Thinner boards are ideal for small devices, USB connectors, and many Bluetooth accessories. However, if you are working on a larger project, you should consider thicker boards. This is due to the limitations of thinner FR4 boards.

Moisture Absorption

This is another important property to consider when designing your circuit board.

Moisture absorption refers to the capacity of a material to resist water. It measures how much moisture the board material can hold without degrading. We measure it as a percentage of the circuit board material. In case of FR4, the moisture absorption is very low – it is only 0.10% when immersed in water for 24 hours. It is therefore the ideal choice for use in electronics manufacturing.

Glass Transition Temperature

The glass transition temperature of FR-4 is between 115 and 200 degrees Celsius. The exact temperature depends on the manufacturing process and resins used in FR-4. Typical FR-4 PCBs will contain a layer of FR-4 between two thin layers of copper laminated together. FR-4 is fire resistant, thanks to the bromine it contains. This material has replaced G-10 composite, which most use in electronic circuitry. The advantages of FR-4 over G-10 include its low cost, high mechanical strength, and excellent insulating capacity in both humid and dry environments.

The NEMA LI 1-1998 standard defines the FR-4 category and identifies this material’s electrical and physical properties. In addition, each FR-4 material has a unique structure and composition. For example, the basic fiberglass layer gives FR4 its structural stability, and the epoxy flame-resistant resin gives it its rigidity. In addition, FR4 has an excellent mechanical and insulating capacity in both dry and humid environments.

FR4 is also commonly used as the primary insulating backbone of a PCB. A manufacturing company will build the circuit on the FR4 board, and then laminate it with copper foil to form the finished product. Many PCBs use more than one side, with multiple solder mask layers. The solder mask layers are necessary to prepare the circuit board for the final silkscreen layer. Further, these layers allow for the V-grooves.

Why FR4 Material is in Common Use in PCB Manufacturing

FR4 is a versatile and inexpensive material used for PCB manufacturing. It is best suited for high density multi-layer boards and is applicable for PCMCIA and automotive applications. Moreover, it is known for its electrical characteristics and ease of processing.

FR4 offers a uniform dielectric constant even when exposed to extreme temperatures, such as at high frequencies. In contrast, other thin PCB materials may have grooves that increase the likelihood of board damage due to high frequency signals transmission.

Moreover, FR4 boards are less likely to suffer from signal integrity issues than those made of other materials. However, there are some disadvantages of using FR4 material for PCB manufacturing.

FR4 is not a single PCB material but a category of materials designated by the NEMA (National Electrical Manufacturers Association). It is composed of a tera-function epoxy resin and woven fiberglass cloth with filler. FR4 boards typically have good electrical insulation properties and mechanical strength. Moreover, FR4 PCBs are among the most common circuitry boards in various fields.

In addition to its insulating properties, FR4 provides a perfect conductive backbone for PCBs. You layer copper foil layers on FR4 board and heat to form circuitry. In this way, FR4 is ideal in PCB manufacturing process, but is not always the best choice for harsh and high-frequency situations. In the end, FR4 is the best choice for low-frequency applications and in general.

Is FR4 the Best Board Material for Your Design?

Read on to discover some of the benefits of FR4 PCBs, a versatile board material. First, they can save you space. Thinner FR4 PCBs save more space than thicker ones. And when it comes to high-frequency designs, the more capacitance, the better. Then, you can add features like grooves or enlarge the board’s surface.

Fire resistance and economic considerations

FR4 PCBs are highly fire-resistant and feature an epoxy resin layer to increase rigidity. This combination of fiberglass and epoxy resin offers printed circuit boards a wide range of benefits. The advantages include cost-effectiveness, excellent mechanical and electrical properties, and high strength-to-weight ratios. If you’re interested in designing a PCB, FR4 is an excellent choice.

FR4 operates as the insulating backbone for circuitry, which is then laminated using layers of copper foil. Once the board is complete, it is ready for soldering.

Signal loss measures

Signal loss is an important consideration in PCB design. FR4 will suffer from greater electrical signal losses compared to the most high frequency laminates. To solve this problem, choose high frequency materials. Its high dielectric constant will allow you to design a smaller circuit board. We can also use this material for RF-based PCBs. However, you should be aware that FR4 PCBs are not the best choice for high-frequency designs.

Standard Thickness

The thickness of FR4 PCBs depends on your needs. Its standard thickness is 0.78mm. Double thickness is 1.57mm. And triple thickness is 2.36mm. The copper thickness in FR4 boards can be as thin as 18um. FR4 has a lower thermal coefficient than other materials in terms of thickness, making it more flexible in hotter environments. Therefore, thin FR4 PCB can be extremely useful for developing a circuitry board for hot environments.

Takeaway Applications

Typical applications for thin FR4 material include medical and automotive PCBs, which need to bend and flex frequently. However, thinner materials are not suitable for PCBs that have grooves, as they are more prone to breakage.

Thinner boards are better for smaller electronic projects and devices, while thicker boards are better for large and complex ones. Having a thicker FR4 PCB also allows you to make deeper grooves and enlarge the surface area.


If you’re looking for an extremely stable impedance, FR4 is the best board material for your design. Its stable dielectric constant means better predictability of performance and reliability, especially in high-frequency designs and larger electronic circuits. In contrast, RF4 is not suitable for high-frequency applications because it has a fluctuating dielectric constant. FR4 is more stable than any other high frequency laminate and has better stability in impedance.

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