Printed circuit boards (PCBs) are the backbone of electronic devices. They provide a platform for connecting various electronic components that make up the device. The quality of the PCB substrate material has a significant impact on the reliability and performance of the electronic device. FR4 and FR2 are two common types of PCB substrates that are widely used in electronic devices. In this blog post, we will discuss the differences between FR4 and FR2, their characteristics, advantages, and disadvantages, and how to choose the right substrate for your project.
What is FR4?
FR4 is a flame-retardant glass-reinforced epoxy laminate. It is the most commonly used substrate material for PCBs. FR4 is composed of a woven fiberglass core that is impregnated with epoxy resin, which is then cured under heat and pressure to form a rigid, durable substrate. The material is named after its flame-retardant properties, which allow it to withstand high temperatures without catching fire.
FR4 has a standard thickness range of 0.1 mm to 3.2 mm, with a typical thickness of 1.6 mm. It is available in various grades, which differ in their electrical, mechanical, and thermal properties. The most common grades are FR4 Standard, FR4 High-Tg, and Glass Epoxy Halogen-Free.The most widely used grade of Glass Epoxy is FR4 Standard, whereas Glass Epoxy High-Tg offers a higher glass transition temperature, making it suitable for high-temperature applications. Glass Epoxy Halogen-Free is an environmentally friendly grade that is free of halogens, which are harmful to the environment.
Advantages of FR4
Excellent electrical properties: FR4 has a high dielectric constant and low dissipation factor, which make it an ideal substrate for high-frequency circuits.
High mechanical strength: Glass Epoxyhas excellent mechanical properties, including high tensile strength, flexural strength, and impact resistance. The suitability of Glass Epoxy for high-reliability applications arises from its ability to withstand mechanical stress or vibration that the board may be subjected to.
Good dimensional stability: Glass Epoxy has a low coefficient of thermal expansion, which means that it does not expand or contract significantly with changes in temperature. This makes it suitable for applications where dimensional stability is critical.
Glass Epoxy, the most commonly used PCB substrate material, is widely available from many suppliers due to its popularity.
Disadvantages of FR4
Cost: Glass Epoxy is more expensive than some other PCB substrate materials, which can make it less attractive for low-cost applications.
Limited thermal conductivity: FR4 has a relatively low thermal conductivity, which can lead to thermal management issues in high-power applications.
What is FR2?
Manufacturers make FR2 as a laminate of flame-retardant phenolic cotton paper.
Although some applications exist, FR2 is not a common substrate material for PCBs.
Manufacturers make the core of FR2 by impregnating paper with phenolic resin.
They then cure this core under heat and pressure to create a rigid substrate.The material gets its name from its flame-retardant properties, which enable it to withstand high temperatures without catching fire.
Its low cost and good mechanical properties are what FR2 is known for. However, it has inferior electrical properties compared to FR4. It has a lower dielectric constant, higher dissipation factor, and lower insulation resistance. Low-cost, low-frequency applications typically use FR2 where high-performance is not critical.
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