FR-4 (or FR4) is a grade designation assigned to glass-reinforced epoxy laminate sheets, tubes, rods and printed circuit boards (PCB). FR-4 is a composite material composed of woven fiberglass cloth with an epoxy resin binder that is flame resistant (self-extinguishing).
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.
NEMA is the regulating authority for FR-4 and other insulating laminate grades. Grade designations for glass epoxy laminates are: G10, G11, FR4 and FR5. Of these, FR4 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.
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.
Typical physical and electrical properties of FR-4 are as follows. LW (length wise, warp yarn direction) and CW (cross wise, fill yarn direction) refer to the fiber orientations in the plane of the board (in-plane) that are perpendicular to one another. The through-plane direction is also referred to as the z-axis.
|Speciﬁc gravity/density||1850 kg/m³||3118 lbs/yd³|
|Water absorption||-.125" < .10 %|
|Temperature index||140 °C||284 °F|
|Thermal conductivity, through-plane||0.29 W/(m-K), 0.343 W/(m-K)|
|Thermal conductivity, in-plane||0.81 W/(m-K), 1.059 W/(m-K)|
|Rockwell hardness||110 M scale|
|Bond strength||> 1000 kg||2200 lbs|
|Flexural strength-LW-A-.125"||> 440 MPa||65,000 psi|
|Flexural strength-CW-A-.125"||> 345 MPa||50,000 psi|
|Tensile strength (.125") LW||> 310 MPa||45,000 psi|
|Izod impact strength-LW||> 54 Nm/m|
|Izod impact strength-CW||> 44 Nm/m||8 ft-lbs/in|
|Compressive strength-flatwise||> 415 MPa||60,000 psi|
|Dielectric breakdown-A||> 50 kV|
|Dielectric breakdown-D48/50||> 50 kV|
|Dielectric strength||20 kV/mm|
|Dielectric constant permittivity||4.70 max, 4.35 @ 500 MHz, 4.34 @ 1 GHz|
|Glass Transition Temperature||Can vary, but is over 120 °C|
|Young's modulus - LW||3.5x10^6 psi|
|Young's modulus - CW||3.0x10^6 psi|
|CTE x-axis||14 ppm/°C|
|CTE y-axis||13 ppm/°C|
|CTE z-axis||175 ppm/°C|
|Poisson's ratio - LW||0.136|
|Poisson's ratio - CW||0.118|
Printed circuit boards
FR-4 is the primary insulating backbone upon which the vast majority of rigid printed circuit boards (PCBs) are produced. 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."
FR-4 copper-clad sheets are fabricated with circuitry etched into copper layers to produce printed circuit boards. More sophisticated and complex FR-4 printed circuit boards are produced in multiple layers, also known as "multilayer circuitry".
When ordering a copper clad laminate board, both the FR-4 thickness and the copper foil thickness must be specified separately.
In the USA, FR-4 thickness is specified in mils or inches, and common thicknesses range from 10 mils (0.010 in, 254 µm) to 3 in (76.2mm).
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 ounce, 2 ounce, and 3 ounce. These work out to thicknesses of 34.1 µm (1.34 mils), 68.2 µm (2.68 mils), and 102.3 µm (4.02 mils), respectively. Some PCB manufacturers refer to 1 ounce copper foil as having a thickness of 35 µm; this may also be referred to as 35μ, 35 micron, or 35 mic.
1/0 - denotes 1 ounce (28.3 gram) copper one side / with no copper on the other side.
1/1 - denotes 1 ounce copper on both sides.
H/0 or H/H - denotes half ounce copper on one or both sides, respectively.
2/0 or 2/2 - denotes 2 ounce copper on one or both sides, respectively.
- 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.
- 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.