FR4 epoxy boards：What are the fire resistance and flame retardant ratings?

If you work in electronics, PCB design, or electrical insulation materials, FR4 epoxy boards are materials you frequently encounter. What does the abbreviation "FR" specifically mean? What standards do the fire resistance and flame retardant ratings of FR4 epoxy boards adhere to? These questions directly relate to product safety compliance and the scientific selection of materials. This article will explain these aspects one by one, from definition and ratings to principles and applications.

What is an FR4 epoxy board?

FR4 epoxy board is a composite insulation material with fiberglass cloth as reinforcement and epoxy resin as the matrix. "FR" is an abbreviation for "Flame Retardant," and "4" represents a specific material category for epoxy fiberglass cloth laminates. Its naming directly indicates the product's flame retardant properties.

Core characteristics of FR4 epoxy boards:

High mechanical strength: It can withstand significant pressure and impact.

Stable insulation performance: Ensures the safe operation of electrical equipment.

Meets heat resistance standards: Glass transition temperature not lower than 130℃.

Flame-retardant and self-extinguishing: All indicators meet international fire protection standards.

FR4 Fire Rating: UL94 V-0 is the core indicator

The fire rating of FR4 epoxy boards is mainly determined according to the UL 94 international standard, which is a universal testing standard for the flame retardant performance of plastics. It classifies the flame retardant rating of materials into the following four categories:

♦ V-0: The material self-extinguishes within 10 seconds of combustion, with no burning particles dripping.

♦ V-1: The material self-extinguishes within 30 seconds of combustion, allowing a small amount of burning particles to drip.

♦ V-2: The material self-extinguishes within 30 seconds of combustion, allowing burning particles to drip.

♦ HB: The material burns horizontally, and a burning rate does not exceed 75mm/min.

Currently, most mainstream FR4 epoxy boards meet the UL94 V-0 rating requirements. This type of board can quickly self-extinguish after being exposed to fire, effectively preventing the spread of fire and providing direct safety protection for electronic equipment and power systems.

FR4 Epoxy Board Flame Retardant Rating

Flame retardancy is the core attribute of FR4 epoxy boards. It is defined as: the material can burn in the presence of an ignition source, but the combustion cannot be sustained or will self-extinguish after the ignition source is removed.

The flame retardant properties of FR4 epoxy boards are achieved as follows: The epoxy resin matrix itself is flammable. Manufacturers add brominated epoxy resin, phosphorus-based flame retardants, and other components to the epoxy resin to give the board flame retardant properties. These flame retardants decompose when heated, interrupting the combustion process in the following three ways:

♦ Absorb the heat generated during combustion and reduce the surface temperature of the material.

♦ Release inert gases to dilute the oxygen concentration in the combustion zone.

♦ Form an insulating char layer that blocks heat transfer into the material.

Application Scenarios of FR4 Epoxy Board

With its stable fire-resistant and flame-retardant properties, FR4 epoxy board is widely used in the following fields:

Printed Circuit Boards (PCB): Ensures operational safety of circuits under short-circuit or high-temperature conditions.

Electrical Equipment Insulation: Used in insulation components such as circuit breakers, transformers, and motor slots.

Mechanical Structural Parts: Suitable for manufacturing support frames, mounting plates, and other components that require both flame retardancy and mechanical strength.

Industrial Automation Equipment: Maintains stable performance in high-temperature and humid environments.

FR4-Related International Standards and Environmental Requirements

In addition to the UL94 standard, the flame-retardant performance of FR4 epoxy boards must also comply with the following international regulations:

IEC 61249-2-2: This standard specifies the performance requirements for halogen-free copper-clad laminates used in PCBs. FR4 epoxy boards that meet this standard possess qualified flame-retardant properties.

RoHS Directive: This directive restricts the use of hazardous substances such as PBBs and PBDEs. Currently, mainstream eco-friendly FR4 epoxy boards adopt RoHS-certified reactive brominated epoxy resins or halogen-free flame-retardant systems. This ensures compliance with UL94 V-0 flame-retardant level while also meeting environmental protection requirements.

With its excellent flame-retardant properties and fire-resistance rating, FR4 epoxy board is widely used in the electronics, electrical, and industrial sectors. Understanding its fire rating and flame-retardant classification not only helps enhance equipment safety but also enables more informed decisions during design and material selection. Choosing high-quality FR4 boards that meet the UL94 V-0 standard is essential for ensuring long-term reliability in electrical systems.