FR4 and FR5 are designations for different types of fiberglass-reinforced epoxy laminate materials used in the construction of printed circuit boards (PCBs). These materials provide the substrate for the PCB, offering electrical insulation and mechanical support for the electronic components mounted on the board. Here are the main differences between FR4 and FR5: 

1. Composition:

• FR4: FR4 (Flame Retardant 4) is a type of glass epoxy laminate. It is composed of woven fiberglass cloth impregnated with an epoxy resin. The "4" in FR4 refers to the Tg (glass transition temperature) rating of the material.

• FR5: FR5 is also a flame-retardant glass epoxy laminate material. Like FR4, it is composed of woven fiberglass cloth and epoxy resin. The primary difference is in the Tg rating, as FR5 typically has a higher glass transition temperature.

2. Glass Transition Temperature (Tg):

• FR4: FR4 materials generally have a Tg rating around 130-140°C (degrees Celsius). Tg is the temperature at which the material transitions from a rigid to a more flexible state.

• FR5: FR5 materials have a higher Tg rating, often around 150-170°C or even higher. The higher Tg makes FR5 suitable for applications where higher-temperature operation or processing is required.

3. Temperature Resistance:

• FR4: FR4 is suitable for standard electronic applications with moderate operating temperatures. It is widely used in a variety of PCBs.

• FR5: FR5 is chosen for applications where a higher temperature resistance is necessary, making it suitable for more demanding or specialized electronic devices.

4. Applications:

• FR4: FR4 is the most common and widely used PCB material. It is suitable for a broad range of applications, including consumer electronics, industrial electronics, and general-purpose PCBs.

• FR5: FR5 is often chosen for applications where higher thermal performance is required, such as in high-frequency and high-speed communication devices, military applications, and other specialized electronics.

When selecting between FR4 and FR5 for a specific application, factors such as operating temperature, mechanical strength, and cost considerations should be taken into account. The choice of material depends on the requirements and specifications of the electronic device being designed.