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FR4 Material: What Are Its Properties and Use?

FR4 material is a glass-reinforced epoxy laminate commonly used in applications requiring high stiffness and rigidity, such as printed circuit boards (PCBs). It is generally available in two forms: as a solid core laminate or as a multilayer laminate. In either form, it’s a fire-resistant material used to create high-quality PCBs.

This post will discuss FR-4 material, its properties, and more detail.

What Is FR4 Material?

FR-4 is a high-strength, high-resistant, glass-reinforced epoxy laminate material used to fabricate printed circuit boards (PCBs). The National Electrical Manufacturers Association (NEMA) defines it as a standard for glass-reinforced epoxy laminates. 

The FR stands for flame retardant, and the number 4 differentiates this type of laminate from other similar materials. This particular laminate has woven glass-reinforced epoxy resin. 

FR-4 PCB refers to the board manufactured with adjacent laminate material. This material is incorporated in double-sided, single-sided, and multi-layered boards.

NEMA originally developed FR4 substrates in the 1960s, and many other companies now produce them.

Why Is FR4 Used in PCBs?

Macro close-up of the printed circuit board

Macro close-up of the printed circuit board

In addition to being robust and stable, FR4 boards have good thermal properties and won’t warp or crack when you apply heat.

FR4 comprises two primary materials: epoxy resin and fr4 fiberglass. Fiberglass is a thin sheet, which gives it its structure, while an epoxy resin laminate provides rigidity and other physical characteristics.

Combining these two materials results in a high-density board with good electrical properties, making FR-4 ideal for an insulator on printed circuit boards (PCBs).

FR4 Material Types

FR-4 has many different variations depending on the thickness of the material and chemical properties, such as the standard FR-4 and G10. The following list shows some common designations for FR4 PCB materials.

  • Standard FR4:  This is the most common type of FR4. It provides good mechanical and moisture resistance, with heat resistance of about 140℃ to 150℃.
  • FR4 With High Tg: FR4 with high Tg is suitable for applications requiring high thermal cycling and temperatures greater than 150℃. Standard FR4 is limited to around 150℃, while FR4 with high Tg can withstand much higher temperatures.
  • FR4 With High CTI: FR4 with high CTI (Chemical Thermal Interaction) has better thermal conductivity than regular FR4 material. It has a comparative tracking index higher than 600 Volts.
  • FR4 without copper laminate: FR4 without copper laminate is a non-conductive material with excellent mechanical strength. It is mainly suitable for insulating boards and board supports.
  • FR4 G10: FR-4 G10 is a solid core material with excellent mechanical properties, high thermal shock resistance, excellent dielectric properties, and good electrical insulation properties.
Printed circuit boards

Printed circuit boards

Fr4 circuit board material consists of two layers: an inner layer of fiberglass and an outer layer of epoxy resin. Several fr4 properties, including:

Flame Retardant

Flame retardants are mixed with FR4 materials to make them more fire-resistant. The flame retardant treatments can be either organic or inorganic. 

Organic treatments include halogen compounds such as bromine, chlorine, fluorine, and iodine, while inorganic treatments include aluminum trihydrate (ATH). 

FR4 materials are treated with these compounds to make them more fire-resistant.

Good Electrical Properties

FR-4 has a glass-reinforced epoxy laminate. This material has good electrical properties, strength, stiffness, and high thermal resistance.

Low Moisture Absorption

FR4 material has a low moisture absorption rate, so it does not change shape when exposed to high humidity levels. This makes it ideal for applications where exposure to moisture is likely, such as electronic devices and other electrical components.

FR4 Material Thickness

The thickness of FR4 material is an essential factor when choosing a circuit board fabricator. However, there are limitations on how thin or thick you can go with your design. The standard FR4 PCB thickness is about 0.2 to 3.2mm and varies from product to product.

Application of FR4 PCB

3D Rendering of MCUs and circuit traces

3D Rendering of MCUs and circuit traces

Some common uses for FR4 include:

  • Industrial Wear Applications
  • Screw Terminal Strips
  • Electrical Insulation
  • Arc Shields
  • Transformers
  • Busbars
  • Washers
  • Standoffs
  • Switches
  • Relays

IPC-A-600 Standard for FR4 Materials

IPC-A-600 is a standard that covers the requirements for fabricating printed circuit boards (PCBs) using rigid and flexible FR4 materials. The standards relate to the base material’s surface and subsurface. The standards apply to all sites involved in the manufacturing, testing, and inspecting FR4 materials.

FR4 Materials Benefits

FR4 is a general-purpose laminate material with excellent mechanical and electrical properties. High mechanical strength, good dielectric properties, and thermal stability make it suitable for many applications. This material is resistant to heat, chemicals, moisture, and most solvents.

Other benefits of FR4 materials include:

  • FR4 is a low-cost alternative to other similar materials
  • It has a high dielectric strength which helps its electrical insulation properties.
  • The material is lightweight and has a high strength-to-weight ratio.
  • It is moisture resistant and has relative temperature resistance as well.
  • FR4 is water resistant and is suitable for various PCB applications.
  • Standard Fr4 PCB thickness is only about 0.2 to 3.2 mm

All these properties make it ideal in a variety of environments.

Limitations of FR4 Circuit Board Materials

Many products and industries use FR4 circuit boards. However, when using them in your projects, you need to be aware of some limitations to FR4 circuit boards.

Insulating Stability

FR-4 Boards are excellent insulators, but they can be damaged if overstressed. The same occurs in case of high temperature or excessive electric current passing through the circuit board. This can make the circuit boards fail and stop working correctly.

Controlled Impedance

The dielectric constant of FR4 is not uniform like those of high-speed board materials. Dk varies as frequency increases. High-speed materials have dielectric constant tolerances of less than 2%, whereas FR4 has tolerances of up to 10%. This challenges impedance values for controlled impedance boards.

Signal Losses

Signal loss is an essential aspect of PCB design, particularly in high-frequency applications. FR4 isn’t the best material for these applications since it has a more wondrous Df (dissipation factor) than high-frequency materials.

Temperature Stability

The main limitation of FR4 circuit boards is that they cannot withstand extreme temperatures. The surface temperature of FR4 can reach a specific limit, but if the temperature increases above this level, there is a risk of damage to the circuit board material.

Alternative PCB Materials

FR4 is not the only material used for PCB manufacture; there are also other materials such as:

  • FR5 (High Tg FR4)
  • Teflon
  • Polymide

When is FR4 Not the Best Material For Your Board?

FR4 is a good choice for your circuit board because it’s relatively cheap, easy to work with, and versatile. However, there are some cases where you should consider an alternative material, including:

  • If lead-free soldering is required: an fr4 copper clad board is a better option as it doesn’t contain lead.

If you need high dielectric strength or thermal stability:  you may want to use a glass reinforced panel instead of FR4.

Factors to Consider When Choosing FR4 PCB

The electronic circuit board 

The electronic circuit board 

It would help if you considered many factors when choosing an FR4 PCB. The most crucial factor is the quality and durability of the product. Many manufacturers sell their products at an affordable price, but they do not guarantee the quality of their products. 

You should always check as many reviews as possible before buying an FR4 PCB board from any manufacturer. Here are other factors to consider:

The Thickness of Sheet

The thickness of the sheet determines how many layers you can have on your board. For higher-layer boards, thicker sheets will last longer.

Impedance Matching

Impedance matching is essential for any electrical circuit because it ensures that all parts of your course work together correctly without interference.

Spacing

The spacing between the copper traces on a board is crucial regarding how much current can flow through each copper trace. The more closely spaced they are, the lower will be the current carrying capacity of your board.

FR-4 Material vs. Rogers Material 

  • There is a significant cost difference between Rogers and FR-4 materials.
  • Compared with FR-4 material, Rogers material is excellent at handling high frequencies.
  • The signal loss caused by FR-4 is higher than that caused by Rogers material due to its higher Df or dissipation factor.
  • Regarding impedance stability, Rogers material has a broader range of Dk values than FR-4.
  • Rogers material has a dielectric constant between 6.15 and 11, while FR-4 has a dielectric constant of about 4.5.
  • Rogers material has less variation in temperature than FR-4 material.

Summary

FR4 is a material with many benefits and advantages. With its low weight, high strength, and resistance to fire and chemicals, it’s no wonder that FR4 has become so popular in the manufacturing world. 

If you’re looking for an FR4 manufacturer of printed circuit boards or boards of any other material, WellPCB can help. We supply high-quality boards and circuits in any quantity while maintaining quality and on-time delivery.

Finally, if you’ve got any questions about your PCB projects and whether the fr4 material is the right fit for your needs, feel free to contact us or leave a comment below.

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Hommer Zhao
Hi, I am Hommer, the founder of WellPCB. So far, we have more than 4,000 customers worldwide. If you have any questions, you can feel free to contact me. I really appreciate any help you can provide.

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