Reliable FR4 PCBs, Made Affordable

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Introduction

Thickness & Performance

Applications

What is an FR4 PCB?

Flame Retardant 4, or FR4, is a material grade used in PCB manufacturing. It is made of fibreglass and "4" represents the UL94 V-0 flammability standard (it must self-extinguish after being ignited). Fiberglass reinforced woven glass fibre and epoxy resin with makes it excellent for electrically insulated applications. FR4 is a widely used material due to its low cost and high reliability.

FR4 Material Overview

FR4 represents flame-retardant grade 4 glass-reinforced epoxy laminate. The material's dielectric constant and dissipation factor (loss tangent) are moderate. FR4 can be used in low-speed and high-power applications, making it the first choice for many hobbyists. This makes it suitable for general-purpose electronic designs.

Dielectric constant: around 4.5 at 1MHz (moderate). Loss tangent: around 0.02 at 1MHz (moderate). The glass transition temperature (Tg) determines how the material behaves under heat. It is one of the most important thermal properties in the classification of FR4 materials.

Structure and Properties of FR4

FR-4 is a composite material used as the substrate in PCBs. Its structure is made from:

1. Woven Fiberglass Cloth (E-glass fibers): — Fibreglass provides higher mechanical strength and appears as a fine woven fabric inside the laminate.
2. Epoxy Resin (flame-retardant, brominated): — Epoxy acts as the matrix, binding the fiberglass together and providing excellent electrical insulation and thermal resistance.
3. Copper Foil (in PCBs): — Copper foil layers are used to make tracks and are laminated onto FR-4 using heat and pressure.

Benefits of FR4 PCB Material

Cost-Effective and Widely Available

FR-4 is affordable compared to advanced laminates like Rogers. Its low cost makes it popular and the industry standard for most applications. It is globally available, making it easy to source for large production volumes.

Good Mechanical Strength

The woven fiberglass provides higher tensile strength, making it more resistant to warping, bending, and mechanical stress.

Reliable Electrical Insulation

Due to a moderate dielectric constant, it is excellent for low-frequency and higher-power applications. Additionally, the epoxy-fiberglass structure offers higher signal isolation.