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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).

"FR" stands for "flame retardant", and does not denote that the material complies with the standard UL94V-0 unless testing is performed to UL 94, Vertical Flame testing in Section 8 at a compliant lab. The designation FR-4 was created by NEMA in 1968.

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.

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^{[citation needed]} will still use G-10 non flame resistant.

Properties

Which materials fall into the "FR-4" category is defined in the NEMA LI 1-1998 standard. 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. The values shown below are an example of a certain manufacturer's material. Another manufacturer's material will usually have slightly different values. Checking the actual values, for any particular material, from the manufacturer's datasheet, can be very important, for example in high frequency applications.

Parameter	Value
Specific gravity/density	1.850 g/cm³ (0.0668 lb/cu in)
Water absorption	−0.125 in < 0.10%
Temperature index	140 °C (284 °F)
Thermal conductivity, through-plane	0.29 W/(m·K),^[1] 0.343 W/(m·K)^[2]
Thermal conductivity, in-plane	0.81 W/(m·K),^[1] 1.059 W/(m·K)^[2]
Rockwell hardness	110 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 (ε_r)	3.9 – 4.7,^[3] 4.4 @ 1 GHz (Supplier Isola) ^[4]
Loss Tangent (tanδ)	0.02 – 0.03,^[3] 0.030 @ 1 GHz^[5]^[4]
Glass transition temperature	Can vary, but is over 120 °C
Young's modulus – LW	3.5×10^⁶ psi (24 GPa)
Young's modulus – CW	3.0×10^⁶ psi (21 GPa)
Coefficient of thermal expansion – x-axis	1.4×10⁻⁵ K⁻¹
Coefficient of thermal expansion – y-axis	1.2×10⁻⁵ K⁻¹
Coefficient of thermal expansion – z-axis	7.0×10⁻⁵ K⁻¹
Poisson's ratio – LW	0.136
Poisson's ratio – CW	0.118
LW sound speed	3602 m/s
CW sound speed	3369 m/s
LW acoustic impedance	6.64 MRayl

where:

LW: Lengthwise
CW: Crosswise
PF: Perpendicular to laminate face

Applications

FR-4 is a common material for printed circuit boards (PCBs). A thin layer of copper foil is typically laminated to one or both sides of an FR-4 glass epoxy panel. These are commonly referred to as copper clad laminates. The copper thickness or copper weight can vary and so is specified separately.

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

References

^ ^a ^b Azar, Kaveh; Graebner, John E. (1996). "Experimental determination of thermal conductivity of printed wiring boards". Twelfth Annual IEEE Semiconductor Thermal Measurement and Management Symposium. Proceedings. pp. 169–182. doi:10.1109/STHERM.1996.545107. ISBN 0-7803-3139-7. S2CID 110285100.
^ ^a ^b Sarvar, F.; Poole, N. J.; Witting, P. A. (1990). "PCB glass-fibre laminates: Thermal conductivity measurements and their effect on simulation". Journal of Electronic Materials. 19 (12): 1345–1350. Bibcode:1990JEMat..19.1345S. doi:10.1007/bf02662823. S2CID 95273262.
^ ^a ^b "Using Pre-Emphasis and Equalization with Stratix GX" (PDF). ALTERA Datasheet. Altera Corporation: 3. 2003.
^ ^a ^b "HF Transmission" (PDF). Atmel Corporation: 7. 2003.
^ "PCB Layout Guidelines for Designing with Avago SFP+Transceivers" (PDF). Avago Technologies: 2. 2005.

@@ Line 1: / Line 1: @@
+{{Short description|NEMA grade designation for glass-reinforced epoxy laminate material}}
 {{more citations needed|date=September 2014}}
+{{use dmy dates|date=March 2021|cs1-dates=y}}
 '''FR-4''' (or '''FR4''') is a [[National Electrical Manufacturers Association|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'').
-"FR" stands for '''flame retardant''', and does not denotes that the material complies  with the standard [[UL 94|UL94V-0]] unless testing is performed to UL 94, Vertical Flame testing in Section 8 at a compliant lab. The designation FR-4 was created by NEMA in 1968.
+"FR" stands for "flame retardant", and does not denote that the material complies  with the standard [[UL 94|UL94V-0]] unless testing is performed to UL 94, Vertical Flame testing in Section 8 at a compliant lab. The designation FR-4 was created by NEMA in 1968.
 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: [[G10_(material)|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|date=August 2012}} replaced G-10 in most applications.
+Grade designations for glass epoxy laminates are: [[G10 (material)|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|date=August 2012}} 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''.
+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{{Citation needed|date=December 2020}} will still use G-10 ''non flame resistant''.
 == Properties ==
-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.
+Which materials fall into the "FR-4" category is defined in the NEMA LI 1-1998 standard. 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. The values shown below are an example of a certain manufacturer's material. Another manufacturer's material will usually have slightly  different values. Checking the actual values, for any particular material, from the manufacturer's datasheet, can be very important, for example in [[high frequency]] applications.
 {| class="wikitable"
@@ Line 18: / Line 19: @@
 ! Parameter                                 !! Value
 |-
-| [[Density|Specific gravity/density]]      || {{convert|1.850|g/cm3|lb/in3|abbr=on}} <!-- 1.85&nbsp;g/cm³ -->
+| [[Density|Specific gravity/density]]      || {{convert|1.850|g/cm3|lb/in3|abbr=on}} <!-- 1.85&nbsp;g/cm<sup>3</sup> -->
 |-
 | Water absorption                          || −0.125&nbsp;in < 0.10%
@@ Line 24: / Line 25: @@
 | Temperature index                         || {{convert|140|°C|°F|abbr=on}}
 |-
+| [[Thermal conductivity]], through-plane   || 0.29 W/(m·K),<ref name="IEEE_1996"/> 0.343 W/(m·K)<ref name="Savar-Poole-Witting_1990"/>
-| [[Thermal conductivity]], through-plane   || 0.29 W/(m·K),<ref name=IEEE>{{cite journal|last=Azar|first=K|author2=Graebner J. E.|title=Experimental Determination of Thermal Conductivity of Printed Wiring Boards|journal=Proceedings of the Twelfth IEEE SEMI-THERM Symposium|year=1996|pages=169–182|doi=10.1109/STHERM.1996.545107}}</ref> 0.343 W/(m·K)<ref name=JEM>{{cite journal|last=Sarvar|first=F.|author2=N. J. Poole |author3=P. A. Witting |title=PCB glass-fibre laminates: Thermal conductivity measurements and their effect on simulation|journal=Journal of Electronic Materials|year=1990|volume=19|issue=12|pages=1345–1350|doi=10.1007/bf02662823}}</ref>
 |-
-| Thermal conductivity, in-plane            || 0.81 W/(m·K),<ref name=IEEE /> 1.059 W/(m·K)<ref name=JEM />
+| Thermal conductivity, in-plane            || 0.81 W/(m·K),<ref name="IEEE_1996"/> 1.059 W/(m·K)<ref name="Savar-Poole-Witting_1990"/>
 |-
 | Rockwell hardness                         || 110 M scale
@@ Line 50: / Line 51: @@
 | Dissipation factor (D24/23)               || 0.018
 |-
-| Dielectric constant permittivity          || 4.70 max., {{nowrap|4.35 @ 500 MHz}}, {{nowrap|4.34 @ 1 GHz}}
+| Dielectric Constant (ε<sub>r</sub>) || {{Nowrap|3.9 – 4.7}},<ref name="Altera_2003"/> {{nowrap|4.4 @ 1 GHz (Supplier Isola)  }}<ref name="Atmel_2003"/>
+|-
+|Loss Tangent (tanδ)
+|0.02 – 0.03,<ref name="Altera_2003"/> 0.030 @ 1 GHz<ref name="Avago_2005"/><ref name="Atmel_2003"/>
 |-
 | Glass transition temperature              || Can vary, but is over 120&nbsp;°C
@@ Line 81: / Line 85: @@
 == Applications ==
-FR-4 is a common material for [[printed circuit board]]s (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.
+FR-4 is a common material for [[printed circuit board]]s (PCBs). A thin layer of [[copper foil]] is typically laminated to one or both sides of an FR-4 glass epoxy panel. These are commonly referred to as copper clad laminates. The [[copper thickness]] or [[copper weight]] can vary and so is specified separately.
+FR-4 is also used in the construction of [[relay]]s, [[switch]]es, [[standoff (separator)|standoff]]s, [[busbar]]s, [[washer (hardware)|washer]]s, [[electric arc|arc]] shields, [[transformer]]s and [[screw terminal]] strips.
-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 [[ounce]]s per square foot (oz/ft<sup>2</sup>), commonly referred to simply as ''ounce''. Common thicknesses are 1&nbsp;oz/ft<sup>2</sup> (300&nbsp;g/m{{sup|2}}), 2&nbsp;oz/ft<sup>2</sup> (600&nbsp;g/m{{sup|2}}), and 3&nbsp;oz/ft<sup>2</sup> (900&nbsp;g/m{{sup|2}}). These work out to thicknesses of 34.1&nbsp;μm (1.34 [[thou (length)|thou]]), 68.2&nbsp;μm (2.68 thou), and 102.3&nbsp;μm (4.02 thou), respectively. Some PCB manufacturers refer to 1&nbsp;oz/ft<sup>2</sup> copper foil as having a thickness of 35&nbsp;μm (may also be referred to as 35&nbsp;μ, 35 [[micron]], or 35 mic).
-* 1/0 – denotes 1&nbsp;oz/ft<sup>2</sup> copper one side, with no copper on the other side.
-* 1/1 – denotes 1&nbsp;oz/ft<sup>2</sup> copper on both sides.
-* H/0 or H/H – denotes 0.5&nbsp;oz/ft<sup>2</sup> copper on one or both sides, respectively.
-* 2/0 or 2/2 – denotes 2&nbsp;oz/ft<sup>2</sup> copper on one or both sides, respectively.
-FR-4 is also used in the construction of [[relay]]s, [[switch]]es, [[Standoff (separator)|standoffs]], [[busbar]]s, [[Washer (hardware)|washers]], [[Electric arc|arc]] shields, [[transformer]]s and [[screw terminal]] strips.
 ==See also==
 *[[FR-2]]
 *[[Polyimide]]
-*[[G10 (material)]]
+*[[G-10 (material)]]
 ==References==
-{{Reflist}}
+{{Reflist|refs=
+<ref name="IEEE_1996">{{cite book |author-last1=Azar |author-first1=Kaveh |author-last2=Graebner |author-first2=John E. |title=Twelfth Annual IEEE Semiconductor Thermal Measurement and Management Symposium. Proceedings |chapter=Experimental determination of thermal conductivity of printed wiring boards |date=1996 |pages=169–182 |doi=10.1109/STHERM.1996.545107|isbn=0-7803-3139-7 |s2cid=110285100 }}</ref>
-* [http://www.nema.org/Standards/Pages/Industrial-Laminated-Thermosetting-Products.aspx Industrial Laminated Thermosetting Products NEMA LI 1-1998]
+<ref name="Savar-Poole-Witting_1990">{{cite journal |author-last1=Sarvar |author-first1=F. |author-first2=N. J. |author-last2=Poole |author-first3=P. A. |author-last3=Witting |title=PCB glass-fibre laminates: Thermal conductivity measurements and their effect on simulation |journal=[[Journal of Electronic Materials]] |date=1990 |volume=19 |issue=12 |pages=1345–1350 |doi=10.1007/bf02662823|bibcode=1990JEMat..19.1345S |s2cid=95273262 }}</ref>
+<ref name="Altera_2003">{{cite journal |publisher=[[Altera Corporation]] |date=2003 |title=Using Pre-Emphasis and Equalization with Stratix GX |url=https://datasheet.datasheetarchive.com/originals/library/Datasheets-SW6/DSASW00108149.pdf |journal=ALTERA Datasheet |pages=3}}</ref>
+<ref name="Atmel_2003">{{cite journal |journal=[[Atmel Corporation]] |date=2003 |title=HF Transmission |url=https://datasheet.datasheetarchive.com/originals/library/Datasheet-02/DSA0019066.pdf |pages=7}}</ref>
+<ref name="Avago_2005">{{cite journal |journal=[[Avago Technologies]] |date=2005 |title=PCB Layout Guidelines for Designing with Avago SFP+Transceivers |url=https://datasheet.datasheetarchive.com/originals/library/Datasheet-080/DASF001217.pdf |pages=2}}</ref>
+}}
+==Further reading==
+* {{cite book |title=Industrial Laminated Thermosetting Products |publisher=[[National Electrical Manufacturers Association]] (NEMA) |id=NEMA LI 1-1998 (R2011) |date=2012-02-01 |orig-date=2011, 1998 |url=http://www.nema.org/Standards/Pages/Industrial-Laminated-Thermosetting-Products.aspx}}
 [[Category:Printed circuit board manufacturing]]