Last updated

FR-4 (or FR4) is a NEMA grade designation for glass-reinforced epoxy laminate material. FR-4 is a composite material composed of woven fiberglass cloth with an epoxy resin binder that is flame resistant (self-extinguishing).

National Electrical Manufacturers Association association of electrical equipment and medical imaging manufacturers in the United States

The National Electrical Manufacturers Association (NEMA) is the largest trade association of electrical equipment manufacturers in the United States. It was founded in 1926 and maintains its headquarters in Rosslyn, Virginia, in the Washington metropolitan area. Its approximately 350 member companies manufacture products used in the generation, transmission, distribution, control, and end use of electricity. These products are used in utility, industrial, commercial, institutional, and residential applications. The association’s Medical Imaging & Technology Alliance (MITA) division represents manufacturers of cutting-edge medical diagnostic imaging equipment including MRI, CT, x-ray, and ultrasound products. Other major end markets include building systems, electrical infrastructure, industrial systems, lighting systems and utility systems. Their combined industries account for 360,000 American jobs in more than 7,000 facilities in every state. Their industry produces $106 billion shipments of electrical equipment and medical imaging technologies per year with $36 billion exports. NEMA also has offices in Mexico City.

Composite material material made from a combination of two or more dislike substances

A composite material is a material made from two or more constituent materials with significantly different physical or chemical properties that, when combined, produce a material with characteristics different from the individual components. The individual components remain separate and distinct within the finished structure, differentiating composites from mixtures and solid solutions.

Fiberglass (US) or fibreglass (UK) is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet, or woven into a fabric. The plastic matrix may be a thermoset polymer matrix—most often based on thermosetting polymers such as epoxy, polyester resin, or vinylester—or a thermoplastic.


"FR" stands for flame retardant, and denotes that the material complies with the standard UL94V-0. The designation FR-4 was created by NEMA in 1968.

UL 94 Standard for Safety of Flammability of Plastic Materials for Parts in Devices and Appliances testing

UL 94, the Standard for Safety of Flammability of Plastic Materials for Parts in Devices and Appliances testing, is a plastics flammability standard released by Underwriters Laboratories of the United States. The standard determines the material’s tendency to either extinguish or spread the flame once the specimen has been ignited. UL-94 is now harmonized with IEC 60707, 60695-11-10 and 60695-11-20 and ISO 9772 and 9773.

FR-4 glass epoxy is a popular and versatile high-pressure thermoset plastic laminate grade with good strength to weight ratios. With near zero water absorption, FR-4 is most commonly used as an electrical insulator possessing considerable mechanical strength. The material is known to retain its high mechanical values and electrical insulating qualities in both dry and humid conditions. These attributes, along with good fabrication characteristics, lend utility to this grade for a wide variety of electrical and mechanical applications.

Grade designations for glass epoxy laminates are: G-10, G-11, FR-4, FR-5 and FR-6. Of these, FR-4 is the grade most widely in use today. G-10, the predecessor to FR-4, lacks FR-4's self-extinguishing flammability characteristics. Hence, FR-4 has since[ when? ] replaced G-10 in most applications.

G-10 is a high-pressure fiberglass laminate, a type of composite material. It is created by stacking multiple layers of glass cloth, soaking in epoxy resin, and compressing the resulting material under heat until the epoxy cures. It is manufactured in flat sheets, most often a few millimeters thick.

FR-4 epoxy resin systems typically employ bromine, a halogen, to facilitate flame-resistant properties in FR-4 glass epoxy laminates. Some applications where thermal destruction of the material is a desirable trait will still use G-10 non flame resistant.

Bromine Chemical element with atomic number 35

Bromine is a chemical element with symbol Br and atomic number 35. It is the third-lightest halogen, and is a fuming red-brown liquid at room temperature that evaporates readily to form a similarly coloured gas. Its properties are thus intermediate between those of chlorine and iodine. Isolated independently by two chemists, Carl Jacob Löwig and Antoine Jérôme Balard, its name was derived from the Ancient Greek βρῶμος ("stench"), referencing its sharp and disagreeable smell.


FR-4 does not specify specific material, but instead a grade of material, as defined by NEMA LI 1-1998 specification. Typical physical and electrical properties of FR-4 are as follows. The abbreviations LW (lengthwise, warp yarn direction) and CW (crosswise, fill yarn direction) refer to the conventional perpendicular fiber orientations in the XY plane of the board (in-plane). In terms of Cartesian coordinates, lengthwise is along the x-axis, crosswise is along the y-axis, and the z-axis is referred to as the through-plane direction. Keep in mind that the values for the parameters listed below are an example for a certain manufacturer's material. Each manufacturer will have slightly different values for the parameters listed below. It's better to check the datasheet of the specific material being used. Verifying the actual values is very important for high frequency designs.

Specific gravity/density 1.850 g/cm3 (0.0668 lb/cuin)
Water absorption−0.125 in < 0.10%
Temperature index140 °C (284 °F)
Thermal conductivity, through-plane0.29 W/(m·K), [1] 0.343 W/(m·K) [2]
Thermal conductivity, in-plane0.81 W/(m·K), [1] 1.059 W/(m·K) [2]
Rockwell hardness110 M scale
Bond strength> 1,000 kg (2,200 lb)
Flexural strength (A; 0.125 in) - LW> 415 MPa (60,200 psi)
Flexural strength (A; 0.125 in) - CW> 345 MPa (50,000 psi)
Dielectric breakdown (A)> 50 kV
Dielectric breakdown (D48/50)> 50 kV
Dielectric strength 20 MV/m
Relative permittivity (A)4.4
Relative permittivity (D24/23)4.4
Dissipation factor (A)0.017
Dissipation factor (D24/23)0.018
Dielectric constant permittivity4.70 max., 4.35 @ 500 MHz, 4.34 @ 1 GHz
Glass transition temperatureCan vary, but is over 120 °C
Young's modulus - LW3.5×10^6 psi (24 GPa)
Young's modulus - CW3.0×10^6 psi (21 GPa)
Coefficient of thermal expansion - x-axis1.4×105 K−1
Coefficient of thermal expansion - y-axis1.2×105 K−1
Coefficient of thermal expansion - z-axis7.0×105 K−1
Poisson's ratio - LW0.136
Poisson's ratio - CW0.118
LW sound speed3602 m/s
CW sound speed3369 m/s
LW acoustic impedance6.64 MRayl


Perpendicular to laminate face


FR-4 is a common material for printed circuit boards (PCBs). A thin layer of copper foil is laminated to one or both sides of an FR-4 glass epoxy panel. These are commonly referred to as copperclad laminates.

Printed circuit board Board to support and connect electronic components

A printed circuit board (PCB) mechanically supports and electrically connects electronic components or electrical components using conductive tracks, pads and other features etched from one or more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive substrate. Components are generally soldered onto the PCB to both electrically connect and mechanically fasten them to it.

When ordering a copper clad laminate board, the FR-4 and copper thickness can both vary and so are specified separately. In the USA, copper foil thickness is specified in units of ounces per square foot (oz/ft2), commonly referred to simply as ounce. Common thicknesses are 1 oz/ft2 (300 g/m2), 2 oz/ft2 (600 g/m2), and 3 oz/ft2 (900 g/m2). These work out to thicknesses of 34.1 μm (1.34 thou), 68.2 μm (2.68 thou), and 102.3 μm (4.02 thou), respectively. Some PCB manufacturers refer to 1 oz/ft2 copper foil as having a thickness of 35 μm (may also be referred to as 35 μ, 35 micron, or 35 mic).

FR-4 is also used in the construction of relays, switches, standoffs, busbars, washers, arc shields, transformers and screw terminal strips.

See also

Related Research Articles

Epoxy family of polymer

Epoxy is either any of the basic components or the cured end products of epoxy resins, as well as a colloquial name for the epoxide functional group. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups.

Flexible electronics technology for assembling electronic circuits by mounting electronic devices on flexible plastic substrates, such as polyimide, PEEK or transparent conductive polyester film

Flexible electronics, also known as flex circuits, is a technology for assembling electronic circuits by mounting electronic devices on flexible plastic substrates, such as polyimide, PEEK or transparent conductive polyester film. Additionally, flex circuits can be screen printed silver circuits on polyester. Flexible electronic assemblies may be manufactured using identical components used for rigid printed circuit boards, allowing the board to conform to a desired shape, or to flex during its use. An alternative approach to flexible electronics suggests various etching techniques to thin down the traditional silicon substrate to few tens of micrometers to gain reasonable flexibility, referred to as flexible silicon.

Aluminium foil thin, flexible sheets of aluminium, used for wrapping food, and other purposes

Aluminium foil, often referred to with the misnomer tin foil, is aluminium prepared in thin metal leaves with a thickness less than 0.2 mm ; thinner gauges down to 6 micrometres are also commonly used. In the United States, foils are commonly gauged in thousandths of an inch or mils. Standard household foil is typically 0.016 mm thick, and heavy duty household foil is typically 0.024 mm. The foil is pliable, and can be readily bent or wrapped around objects. Thin foils are fragile and are sometimes laminated to other materials such as plastics or paper to make them more useful. Aluminium foil supplanted tin foil in the mid 20th century.

Substrate is used in a converting process such as printing or coating to generally describe the base material onto which, e.g. images, will be printed. Base materials may include:

FR-2 is a NEMA designation for synthetic resin bonded paper, a composite material made of paper impregnated with a plasticized phenol formaldehyde resin, used in the manufacture of printed circuit boards. Its main properties are similar to NEMA grade XXXP (MIL-P-3115) material, and can be substituted for the latter in many applications.

FR4 may refer to:

Micarta is a brand name for composites of linen, canvas, paper, fiberglass, carbon fiber or other fabric in a thermosetting plastic. It was originally used in electrical and decorative applications. Micarta was developed by George Westinghouse at least as early as 1910 using phenolic resins invented by Leo Baekeland. These resins were used to impregnate paper and cotton fabric which were cured under pressure and high temperature to produce laminates. In later years this manufacturing method included the use of fiberglass fabric and other resin types were also used. Today Micarta high pressure industrial laminates are produced with a wide variety of resins and fibers. The term has been used generically for most resin impregnated fibre compounds. Common uses of modern high pressure laminates are as electrical insulators, printed circuit board substrates, and knife handles.

Electrical steel

Electrical steel is an iron alloy tailored to produce specific magnetic properties: small hysteresis area resulting in low power loss per cycle, low core loss, and high permeability.

SU-8 photoresist

SU-8 is a commonly used epoxy-based negative photoresist. Negative refers to a photoresist whereby the parts exposed to UV become cross-linked, while the remainder of the film remains soluble and can be washed away during development.

The role of the substrate in power electronics is to provide the interconnections to form an electric circuit, and to cool the components. Compared to materials and techniques used in lower power microelectronics, these substrates must carry higher currents and provide a higher voltage isolation. They also must operate over a wide temperature range.

Thiolyte is a brand name for electrical insulating thermoset phenolic laminate materials.


Perfboard is a material for prototyping electronic circuits. It is a thin, rigid sheet with holes pre-drilled at standard intervals across a grid, usually a square grid of 0.1 inches (2.54 mm) spacing. These holes are ringed by round or square copper pads, though bare boards are also available. Inexpensive perfboard may have pads on only one side of the board, while better quality perfboard can have pads on both sides. Since each pad is electrically isolated, the builder makes all connections with either wire wrap or miniature point to point wiring techniques. Discrete components are soldered to the prototype board such as resistors, capacitors, and integrated circuits. The substrate is typically made of paper laminated with phenolic resin or a fiberglass-reinforced epoxy laminate (FR-4).

A thousandth of an inch is a derived unit of length in a system of units using inches. Equal to ​11000 of an inch, it is normally referred to as a thou, a thousandth, or a mil.

Composite epoxy materials (CEM) are a group of composite materials typically made from woven glass fabric surfaces and non-woven glass core combined with epoxy synthetic resin. They are typically used in printed circuit boards.

Microvias are used as the interconnects between layers in high density interconnect (HDI) substrates and printed circuit boards (PCBs) to accommodate the high input/output (I/O) density of advanced packages. Driven by portability and wireless communications, the electronics industry strives to produce affordable, light, and reliable products with increased functionality. At the electronic component level, this translates to components with increased I/Os with smaller footprint areas, and on the printed circuit board and package substrate level, to the use of high density interconnects (HDIs).

A stamped circuit board (SCB) is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or traces etched from copper sheets laminated onto a non-conductive substrate. This technology is used for small circuits, for instance in the production of LEDs.

Pad cratering is a mechanically induced fracture in the resin between copper foil and outermost layer of fiberglass of a printed circuit board (PCB). It may be within the resin or at the resin to fiberglass interface.

Conductive anodic filament, also called CAF, is a metallic filament that forms from an electrochemical migration process and is known to cause printed circuit board (PCB) failures.


  1. 1 2 Azar, K; Graebner J. E. (1996). "Experimental Determination of Thermal Conductivity of Printed Wiring Boards". Proceedings of the Twelfth IEEE SEMI-THERM Symposium: 169–182. doi:10.1109/STHERM.1996.545107.
  2. 1 2 Sarvar, F.; N. J. Poole; P. A. Witting (1990). "PCB glass-fibre laminates: Thermal conductivity measurements and their effect on simulation". Journal of Electronic Materials. 19 (12): 1345–1350. doi:10.1007/bf02662823.