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Knowledge For PCB What is FR4 of PCB material?

What is FR4 of PCB material?

August 25, 2022     Knowledge For PCB

What is FR4 in PCB fabrication?

FR4 is the most common material grade used for fabricated circuit boards. ‘FR’ indicates the material is flame retardant and the ‘4’ indicates woven glass reinforced epoxy resin

CEM-1 is a low-cost, flame-retardant, cellulose-paper-based laminate with only one layer of woven glass fabric.

CEM-2 has a cellulose paper core and woven glass fabric surface.

CEM-3 is very similar to the most commonly used PCB material, FR-4.


FR-4 epoxy glass fiber cloth substrate is a type of substrate with epoxy resin as the binder and electronic grade glass fiber cloth as the reinforcing material. It is an important substrate for making multilayer printed circuit boards with bonded sheets and thin copper laminates with inner cores. It is the most widely used product type. Due to the development of electronic product mounting technology and PCB technology, there are FR-4 products with high Tg.

FR-4 is a kind of flame-resistant material grade code, which means that the resin material must be able to extinguish itself after the burning state, it is not a material name, but a material grade, so there are very many kinds of FR-4 grade materials used in general circuit boards, but most of them are made of the so-called four-function (Tera-Function) epoxy resin, However, most of them are composite materials made of so-called Tera-Function epoxy resin with filler and glass fiber.

Industry Associations

NEMA American Electrical Manufacturers Association provides a material standard, with which the corresponding IEC International Electrotechnical Commission standard is EPGC202, and there is no domestic standard that corresponds to it.
The closest domestic standard is 3240 epoxy laminated glass cloth sheet, and the corresponding IEC standard for 3240 is EPGC201, and the only difference between EPGC201 and EPGC202 is the flame retardant property. Therefore, it can be simply considered that FR-4 is an improved product of 3240 with enhanced flame retardant properties.


FR-4 epoxy glass cloth laminate surface colors are.
Yellow FR-4, White FR-4, Black FR-4, Blue FR-4, etc.
FR-4 is a substrate used in PCB, which is a category of board material. The board material is classified into four main categories according to different reinforcement materials as follows.
1) FR-4: glass cloth substrate
(2) FR-1, FR-2, etc.: paper substrate
(3) CEM series: composite substrate
(4) Special material substrate (ceramic, metal base, etc.) FR-4 is a plate laminated product made of special electronic cloth dipped in epoxy phenolic resin and other materials by high temperature and high pressure hot pressing.
Features: high mechanical and dielectric properties, good heat and moisture resistance and good machinability.
Uses: Electric motors, electrical equipment for insulation structure parts, including various types of switch FPC reinforcement electrical insulation carbon film printed circuit boards, computer drilling pad mold jig (PCB test stand) and can be used in humid environmental conditions and transformer oil

Basic characteristics

Vertical laminar bending strength A: Normal: E-1/150, 150±5℃≥340Mpa
Parallel laminar impact strength (simple beam method): ≥ 230KJ/m
Insulation resistance after water immersion (D-24/23): ≥ 5.0×108Ω
Vertical layer to electrical strength (in 90 ± 2 ℃ transformer oil, plate thickness of 1mm): ≥ 14.2MV / m
Parallel layer breakdown voltage (in 90 ± 2 ℃ transformer oil): ≥ 40KV
Relative dielectric constant (50Hz): ≤5.5
Relative permittivity (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

Process characteristics

(1)Melting point of FR-4 process press board (203℃)
(2)High chemical resistance
(3)Low loss factor (Df 0.0025)
(4)Stable and low dielectric constant (Dk 2.35)
(5)Thermoplastic material

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    WDXPCB is a professional PCB manufacturer and exporter located in Shenzhen, China. providing PCB manufacturing services including HDI,FPC,Rigid-Flex PCB,High Multi-layer PCB,and MCPCB


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