The most widely and extensively used material for manufacturing printed circuit boards is FR-4 material, with excellent electrical and mechanical properties. It is regarded as a general printed circuit board material FR4. The abbreviation FR stands for flame-retardant or flame-resistant material. It is self-extinguishable. The number 4 in FR-4 is the code for the flame-retardant material. FR-4 belongs to the class of epoxy FR4 laminated fiberglass. FR-4 is composed of fiberglass cloth bonded by epoxy as an adhesive. FR4 PCB material is available in many colors: blue, green, white, black, etc. Normally, the thickness used is 1.6 mm and 1.2 mm. There are five grades for FR material. They are FR-1, FR-2, FR-3, FR-4, and FR-5.
High Mechanical Strength: It displays excellent mechanical strength. It can withstand mechanical stress, which occurs during manufacturing processes, assembly operations, and other handling operations. It exhibits great dimensional stability when exposed to high temperatures and other environmental factors.
Excellent Electrical Insulation: While FR4 displays excellent electrical insulation properties, it does not allow an electric current to flow between conductors on a PCB. This prevents short circuits, other electrical damage, and fire.
Excellent Thermal Stability: Another FR4 material property is excellent thermal management properties.
Low Moisture Absorption Rate: The moisture absorption rate of FR4 material is low. If immersed in water for twenty-four hours, the moisture absorption is 0.01%
Flame Retardant: FR4 is a self-extinguishable flame-retardant material. Fire will not spread in the event of accidents.
Lower Cost: FR-4 costs less than its counterparts, which makes it a very good choice for all manufacturers.
Reinforcement: Woven glass Fiber cloth is normally the reinforcement laminate for FR-4, which provides mechanical support and electrical properties. The typical constituents of E-grade glass used in FR-4 are shown in the below table.
Resin: The FR4 laminated fiberglass resin structure normally consists of bi-, tetra-, and multi-functional epoxy groups. Curing agents, flame retardants, fillers, etc. are added to the resin system to accelerate the performance of the laminate.
Curing Agents: Curing agents are used to harden the PCB. Curing agents known as dicyandiamide, commonly known as DICY, and phenol novolac are widely used in the PCB industry.
Flame Retardants: They are added to reduce the flammability of the laminate. They suppress combustion by forming gas barriers against oxygen. Nowadays halogen-free flame retardants are used
Fillers: Fillers are added to resins to achieve a lower coefficient of thermal expansion and to avoid cracks in the plated through holes. Fillers also help to retard the flammability of the material and reduce the cost. Fillers used for FR-4 are silica and aluminum silicate.
Accelerators: They are added to the resin system to speed up the curing rate. Imidazole is one of the widely used accelerators used for the FR-4 PCB.
A PCB’s most basic building blocks are resin and reinforcement composites. FR4 PCB material is a composite of woven fiberglass reinforcement. The steps to fabricate FR-4 are listed below.
