What is FR 4 PCB?

An FR 4 PCB refers to a printed circuit board constructed using FR4 material, which is the standard base laminate for most PCBs.

Understanding FR4

As the reference states, FR4, also written as FR-4, is both a name and a standard rating.

• Material Name: FR4 is the name applied to the fiberglass-reinforced epoxy-laminated sheets used in printed circuit board manufacturing. This composite material forms the rigid core of the vast majority of PCBs.
• Standard Grade Rating: The name FR4 also functions as a grade used to rate epoxy laminate sheets based on their flammability rating. "FR" stands for flame retardant, and the '4' indicates that it meets a specific standard (defined by NEMA - National Electrical Manufacturers Association) for its fire resistance properties.

Essentially, when you talk about an "FR4 PCB," you are referring to a circuit board built on a substrate made from this specific type of flame-retardant fiberglass and epoxy resin composite.

Why is FR4 So Common?

FR4 is the most widely used material for printed circuit boards due to a balance of cost, performance, and manufacturing ease.

Here are some key characteristics and advantages:

• Cost-Effective: It's relatively inexpensive compared to higher-performance PCB materials.
• Good Mechanical Strength: The fiberglass reinforcement provides rigidity and durability.
• Adequate Electrical Properties: It offers sufficient insulation and dielectric properties for many electronic applications.
• Thermal Resistance: It can withstand typical soldering temperatures without degrading significantly.
• Flame Retardant: Meets safety standards (UL 94V-0 rating is typical) due to its flame-retardant additives.
• Ease of Manufacturing: FR4 is easy to drill, etch, and process using standard PCB fabrication techniques.

Structure of an FR4 PCB

A typical FR4 PCB is a layered structure:

1. FR4 Core: The central, rigid layer made of fiberglass cloth impregnated with epoxy resin.
2. Copper Layers: Thin layers of copper foil laminated onto one or both sides of the FR4 core (for single or double-sided boards). Multi-layer boards have additional FR4 prepreg (partially cured epoxy-impregnated fiberglass) and copper layers stacked and pressed together.
3. Solder Mask: A protective layer (usually green, but other colors are common) applied over the copper traces to prevent short circuits during soldering and protect against environmental factors.
4. Silkscreen: A layer printed on top of the solder mask (typically white or black) to add component designators, logos, and other markings.

Applications

FR4 PCBs are ubiquitous, found in a vast array of electronic devices, from consumer electronics (televisions, computers, smartphones) to industrial equipment, automotive electronics, and simple hobbyist projects. Its versatility makes it suitable for most general-purpose electronic circuits that don't require extreme performance characteristics (like very high frequencies or temperatures).