Flame retardant FR-4 insulation sheet

FR-4 is a common composite material that is widely used in the manufacture of electronic circuit boards. It consists of fiber glass cloth and imported epoxy resin. And it has high mechanical properties, dielectric properties, electrical insulation properties. The insulation class is F, and the main colors are white (primary), light green, black and yellow.The FR in FR-4 stands for “flame retardant,” while the 4 signifies that it’s a glass epoxy.

Why is FR4 insulation sheet flame retardant?

Due to its special chemical composition, FR-4 insulation sheets are effective in slowing down the spread of fire during combustion and protecting electronic equipment from damage. Specifically, FR-4 material releases flame retardant substances during the combustion process that interrupt the combustion chain reaction, thereby reducing the rate of combustion and even causing the flame to extinguish itself. In addition, FR-4’s flame retardant rating typically achieves a 94V-0 rating. It means it produces virtually no harmful gases during combustion testing, making it friendlier to the environment and human health. Specifically:

Thermal decomposition and heat absorption: FR-4 materials will undergo thermal decomposition at high temperatures, absorbing a large amount of heat, thus lowering the temperature of the burning area and slowing down the burning speed.

Release of flame-retardant gases: During thermal decomposition, FR-4 releases flame-retardant gases such as water vapor and carbon dioxide, which can dilute the oxygen concentration in the combustion area and thus inhibit combustion.

Formation of charcoal layer: During the combustion process, a layer of charcoal will be formed on the surface of FR-4, which can isolate the heat and oxygen transmission, further slowing down the combustion speed.

Flame retardancy test methods for FR-4 insulation sheets

In order to ensure that the flame retardancy of FR-4 insulation sheets meets the relevant standards and requirements, a series of flame retardancy tests are usually required. These test methods include, but are not limited to, the following:

Vertical burning test: In accordance with UL 94, the sample is placed vertically and one end is ignited to observe the flame propagation speed, burning time, and the production of drips.

Horizontal Combustion Test: In accordance with IEC 60695-11-10, the sample is placed horizontally and one end is ignited to evaluate the burning performance of the sample under the action of the flame and the nature of the drippings.

Limiting Oxygen Index Test: Evaluates the flame retardancy of a sample by measuring the minimum concentration of oxygen required to maintain combustion under specified conditions.

Application areas of FR-4 insulation sheets

Thanks to its excellent flame-retardant properties, FR-4 insulation sheets are widely used in many fields. The following are its main application areas:

Electronics industry: FR-4 insulation sheet is one of the main materials for making PCB boards (printed circuit boards). In electronic equipment, PCB boards carry a variety of electronic components and circuit connections, so their flame retardant properties are critical to the safety and stability of the equipment.

Aerospace: In the aerospace field, FR-4 insulation sheets are used to make aircraft instrument panels, navigation systems, communication systems and other key components. These components need to withstand extreme environments such as high temperatures and high pressures, so the material is required to have excellent flame retardant properties and stability.

Automotive industry: In the automotive industry, FR-4 insulation sheets are used to make automotive circuit boards, engine control systems, in-car entertainment systems and other components. The flame retardant properties of these components are important for ensuring the safety and reliability of automobiles.