FR4 Guidelines: When You Can Use It and When You Can't

FR4 Guidelines: When You Can Use It and When You Can't

Most electrical engineers and individuals involved with printed circuit boards are familiar with FR4 material. Fr4 Fiber Glass Epoxy Sheet is the main material used to make most rigid circuit boards. However, many people do not know what FR4 is, let alone why it is the most popular PCB basis.

Read on to learn more about FR4 printed circuit boards, such as what they are, why they are so popular, and how the FR4 PCB specification compares to other options in the industry.


What is FR4 material Epoxy Fiber Glass Sheet?

G10 Fr4 Insulate Sheet is also written as FR-4, which is both a name and a rating. This designation applies to glass fiber reinforced epoxy resin laminates used in the manufacture of printed circuit boards. However, the designation is also used as a grade for rating epoxy laminates. The designation basically indicates the basic quality of the laminate, which means that various boards and designs fall under the FR4 rating. The "FR" in the name stands for flame retardant, while the "4" means the material is different from others in the same class.

The material broadly known as FR4 is a composite structure. The most basic layer of the material is fiberglass woven into a thin cloth-like sheet. Fiberglass provides the necessary structural stability to FR4. This innermost fiberglass layer is then surrounded and bonded with flame retardant epoxy. This resin imparts rigidity to the material, among other physical properties.


FR4 sheet is widely popular among electrical engineers and designers as a PCB substrate. The material's low cost and versatility, along with its wealth of beneficial physical properties, illustrate this popularity. FR4 sheet is an electrical insulator with high dielectric strength. They also have a high strength to weight ratio, are lightweight and resistant to moisture. Add this to their relative temperature resistance, and FR4s can perform well in most environmental conditions.


FR4-PCB connection

These qualities make FR4 an ideal substrate for quality PCB manufacturing processes. When used properly, these properties can also form the basis of high-quality and low-cost PCBs.

In a PCB, FR4 forms the main insulating backbone. This is the basis upon which manufacturing companies build circuits. Once ready, FR4 boards are laminated with one or more layers of copper foil using heat and adhesives. This copper forms the circuit in the finished product and may cover one or both sides, depending on the board design.


Complex PCBs may use more than one side, and the board may even be layered to produce more complex circuits. From here, the circuit is drawn and etched away, then covered with solder mask, preparing the board for the final silkscreen layer and subsequent soldering process.


How to choose FR4 thickness

When ordering laminates for a PCB project, the designer or electrical engineer must specify the FR4 PCB thickness. This is measured in inches, such as thousandths of an inch, or u or millimeters, depending on which setting works best. FR4 sheets come in a wide range of thicknesses, depending on the needs of the project, but tend to range from 10 to 3 inches.

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