FR-4

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FR-4, an abbreviation for Flame Resistant 4, is a type of material used for making a printed circuit board (PCB). It describes the board itself with no copper covering. The FR-4 used in PCBs is typically UV stabilized with a tetrafunctional resin system. It is typically a yellowish color. FR-4 manufactured strictly as an insulator (without copper cladding) is typically a difunctional resin system and a greenish color. FR-4 is similar to an older material called G-10. G-10 lacked FR-4's self extinguishing flammability characteristics. FR-4 has widely replaced G-10 in most applications. Some military appications where destruction of the circuitboard is a desirable trait will still utilize G-10.

1 Explanation
2 Description and specifications
3 Applications
4 See also

[edit] Explanation

A PCB needs to be an insulator to avoid shorting the circuit, physically strong to protect the copper tracks placed upon it, and to have certain other physical electrical qualities (see below). FR-4 is preferred over cheaper alternatives such as synthetic resin bonded paper (SRBP) due to several mechanical and electrical properties; it is less lossy at high frequencies, absorbs less moisture, has greater strength and stiffness and is highly flame resistant compared to its less costly counterpart. FR-4 is widely used to build high-end consumer, industrial, and military electronic equipment.

[edit] Description and specifications

FR-4 is a composite of a resin epoxy reinforced with a woven fiberglass mat. It is a material from the class of epoxy resin bonded glass fabric (ERBGF).

Property	Value
Dielectric constant (Permittivity)	4.70 Max, 4.35 @ 500 MHz, 4.34 @ 1 GHz
Dissipation Factor (Loss tangent)	0.020 @1 MHz
Dielectric strength	20 MV/m (500 V/mil )
Surface Resistivity (min)	2x10^5 MΩ
Volume Resistivity (min)	8x10^7 MΩ*cm
Typical Thickness	0.049-0.100 inches
Typical stiffness (Young's modulus)	2.5 x 10^6 PSI (for use in PCBs)