The basic characteristics and development prospects of FR4 pcb material

FR4 glass epoxy resin is currently the most used substrate in the pcb market. more than 80% of the pcb is manufactured with FR4, what is FR4, what are its characteristics, this article will focus on giving you an introduction.

FR4 is a glass fiber epoxy resin copper cladding board, it is based on chlorite, quartz sand, limestone, dolomite, boron calcium stone, boron magnesium stone six kinds of minerals as raw materials by high temperature melting, drawing, winding, weaving and other processes manufactured. The diameter of its monofilament for a few microns to more than two dozen microns, equivalent to a hair strand of 1/20 ~ 1/5, each bunch of fiber raw silk is composed of hundreds or even thousands of monofilaments.
The FR prefix refers to the flammability rating of the resin system used in the laminated composites that make up the substrate of a printed circuit board. The addition of bromine compounds to the resin produces flame retardant properties that are self-extinguishing and combustible.

FR4 Basic Characteristics

●Vertical laminar bending strength A: normal: E-1/150, 150±5℃≥340Mpa

●Parallel laminar impact strength (simply supported beam method): ≥230KJ/m

●Insulation resistance after water immersion (D-24/23): ≥5.0×108Ω

●Vertical laminar electrical strength (in 90±2℃ transformer oil, plate thickness 1mm): ≥14.2MV/m

●Parallel layer to the breakdown voltage (in 90 ± 2 ℃ transformer oil): ≥ 40KV

●Relative dielectric constant (50Hz): ≤5.5

●Relative dielectric constant (1MHz): ≤5.5

●Dielectric loss factor (50Hz): ≤0.04

●Dielectric loss factor (1MHz): ≤0.04

●Water absorption (D-24/23, plate thickness 1.6mm): ≤19mg

●Density: 1.70-1.90g/cm³.

●Flammability: FV0

What are the properties of FR4 substrates?

Flame Retardant

Chemicals used on materials to prevent or retard the spread of fire are known as flame retardants.FR4 substrates have excellent thermal, mechanical and electrical properties, making them perfect for a wide range of electronic applications. Flame retardant laminates and prepregs are very versatile, suitable for a variety of manufacturing procedures and produce predictable results.

Good Electrical Properties

The electrical properties of PCB materials are critical to signal integrity and impedance considerations. They determine how quickly an electrical signal can propagate through the material and how much charge it can retain in a given volume.

Low Moisture Absorption

Moisture absorption is the ability of a PCB material to resist absorbing water when immersed in water. It is given by the percentage increase in weight of the circuit board material due to water absorption under controlled conditions.FR4 material has a low moisture absorption of 0.10% after 24 hours of immersion in water.


Limitations of FR4 circuit board materials

FR4 has been used in printed circuit boards for many years. It is inexpensive and provides adequate electrical insulation. However, when FR4 is used in high-speed applications, the following problems may occur:

Insulation Stability
Although FR4 is a good insulator, it has its limitations when subjected to high power, high voltage or high heat. If certain limits are exceeded, the insulating properties of the material will deteriorate and they will begin to conduct electricity. This can lead to board failure.

Controlled Impedance
FR4 does not provide a uniform dielectric constant like high speed circuit board materials. As frequency increases, Dk changes. While high-speed materials have a dielectric constant tolerance of less than 2%, FR4 has a tolerance of up to 10%. the change in Dk in FR4 poses a challenge while maintaining the impedance value. Therefore, this material is not a preferred choice for controlling impedance boards.

Signal Loss
Signal loss is an important aspect of PCB design, especially in high-frequency applications.FR4 is not the best material for these applications because it has a larger Df (dissipation factor) than high-frequency materials.

FR4 Performance Classification

Standard F4
Baseline electric grade F4 epoxy glass provides the most economical, general purpose substrate for typical consumer electronics and digital circuit boards without pushing extreme frequency limits.

High Frequency F4
Multi-glass bodies like rf-35 control dielectric values below +/-0.05 across the microwave region. These tightly aligned low loss materials become critical to RF device integrity.

High Temperature F4
Through resin modification or bismaleimide-triazine blends, some FF4 formulations withstand temperatures above 230°C to meet the needs of aerospace and automotive electronics equipment.

Highly reliable F4
Isola’s “HR” family and Allen family 85N laminates utilize high resin content and glass weaving to punch holes in multilayers and are elastically rigid designed to resist crack propagation.

Development Prospect of FR-4 Copper Clad Laminate

FR-4 copper clad laminate is the core material of printed circuit boards, which is widely used in electronics, communications, computers, automotive, aerospace and other fields. With the development of 5G, Internet of Things, intelligent manufacturing and other emerging industries, FR-4 laminates have a very broad market outlook.

First of all, the development of 5G will promote the demand for FR-4 laminates, 5G communication technology requires superior high-frequency transmission performance, so the performance of FR-4 laminates also need to be improved. For example, the dielectric constant of the sheet needs to be increased and the dielectric loss of the sheet needs to be reduced. In addition, the miniaturization and lightweight of 5G equipment also put forward higher requirements for the performance of FR-4 boards, such as the need to optimize the thickness of the board. Therefore, with the rapid development of 5G in the future, FR-4 copper cladding board market demand growth prospects.

Secondly, the widespread application of the Internet of Things (IoT) will also drive the growth of FR-4 copper-clad laminates market demand. The Internet of Things requires higher performance indicators (such as high-frequency transmission, high-speed transmission, etc.), in addition to the miniaturization of the Internet of Things terminal equipment requires thinner and lighter FR-4 copper cladding boards, which will promote the FR-4 cladding board market demand continues to increase.

Again, the rapid development of intelligent manufacturing will have a positive impact on FR-4 laminate market demand. Intelligent manufacturing has become a national strategy, the transformation and upgrading of the manufacturing industry requires more intelligent equipment. These devices require high-speed transmission of high-frequency transmission and other performance indicators such as stringent FR-4 copper cladding boards, the market demand will also continue to increase.

FR4 has been widely used in electronic equipment for its high reliability, good processability, heat resistance and excellent electrical properties. Its dielectric constant and dielectric loss angle tangent and other electrical performance parameters are controlled with high precision, which can ensure stable signal transmission. In addition, FR4 sheet has good thermal stability and can remain stable in high-temperature environments, making it suitable for applications under various environmental conditions. Therefore, FR4PCB is an excellent electronic material, providing a strong guarantee for the performance and reliability of electronic equipment.