FR4 vs Rogers: Which PCB Material Should You Choose?

Traditionally, manufacturers have been making PCBs or printed circuit boards of materials that offer resistance to heat and are, therefore, less expensive to produce. As the electronics industry is increasing in terms of high frequency application, only FR4 is not enough. Some equipment, while not being subject to extreme temperatures, may have to work at RF or radio frequencies. According to the extreme performance conditions demanded by RF, specialized materials such as Rogers are necessary to deliver the best functionality from PCBs. See our recent article on different types of via's in pcb design. Rogers extensive PCB material portfolio enables its use in diverse applications, including:

• 5G NR mmWave antennas
• Satellite communications
• Radar systems
• Automotive sensors
• Aerospace Avionics
• High-speed datacom
• Test instrumentation

Let's explore what makes Rogers PCB materials such superior solutions for these cutting-edge electronics domains.

What is FR4:

FR4 is a thermoset glass fabric reinforced epoxy resin composite. It is the traditional material that is the basis for most PCBs and is an acronym for Flame Retardant Level 4. Being a composite material made of epoxy and glass fiber, manufacturers shape it in the form of sheets and laminate it with copper foil on one or both sides.

Key properties and characteristics of FR4:

Low cost - FR4 is one of the most economical PCB substrate materials

Moderate dielectric constant - Around 4.5 at 1 MHz

Moderate loss tangent - Around 0.02 at 1 MHz

However, FR4 suffers from performance limitations at higher frequencies due to dielectric losses, making it unsuitable for many RF applications. The relatively high and inconsistent dielectric constant and loss tangent also make FR4 a poor choice for precision analog and high-speed digital circuits.

What is Rogers:

Unlike FR-4, the Rogers substrate materials offer different compositions. Some of them use a ceramic base rather than glass. Various compositions are available, such as woven glass reinforced with hydrocarbons, and they offer electrical performance very close to that of PTFE.

Some key properties of Rogers materials:

Stable dielectric constant - Tightly controlled, varies by material in the 2.9 - 10.2 range

Low loss tangent - Around 0.0009 - 0.002 at 10 GHz

Excellent high frequency performance - Low signal loss up to mmWave frequencies

Low thermal expansion - Matching the coefficient of copper for reliability

The precise dielectric properties, close matching to copper, and low losses make Rogers an ideal choice for performance-driven microwave, telecom, aerospace and defense applications. However, the exotic material compositions result in Rogers costing 5-10x more compared to FR4 on a per area basis.

Types of Rogers PCB Material:

Rogers makes various types of PCB material for different applications. These include:

7 Main Difference Between FR-4 and Rogers Material:

1. Frequency of Operations

The major difference between regular boards made of FR-4 and those with Rogers material is in their application. PCBs made of FR-4 can operate properly only when the frequency of operations is within a certain range. On the other hand, PCBs made of the Rogers material can perform over a much larger range of frequencies. For instance, while FR-4 PCBs can hardly reach 10 MHz, Rogers PCBs can operate very well in applications extending well beyond 500 MHz.

2. Material Hardness

There is a substantial difference in material hardness between FR-4 and Rogers material. FR-4 is mainly epoxy resin and quite hard. On the other hand, Roger’s material, being hydrocarbon, is comparatively softer.

3. Processing Technology

Although Rogers materials are meant for high-frequency operation, they are different from PTFE microwave PCB materials. Roger’s series of materials does not require any special treatment, such as special treatment for through-hole processing, and no extra technological processes are necessary.

The FR-4 material is epoxy glass cloth laminate, which offers stable electrical insulation, a smooth surface, good flatness, and no pitting. It is suitable for products requiring good electrical insulation. This material is also suitable for use as backing boards for PCB drilling, FPC stiffeners, planetary gears, test plates, motor insulators, and many more.

4. Cost

Cost is an important factor for electronic equipment. Customers look for manufacturers offering PCBs with the best and most economical performance. Although making boards with FR-4 can save costs, this material is suitable for products operating at low frequencies and moderate temperature settings. On the other hand, for applications requiring high-speed operation or high temperatures, using Rogers material would be more suitable, even if it is more expensive.

5. Impedance Stability

The maximum dielectric constant of FR-4 material is 4.5. In comparison, Roger’s material has a dielectric constant of about 2.2-12.85. The higher dielectric constant of Rogers material contributes to high impedance stability.

6. Thermal Capability

For applications operating at high speeds, the PCB must also have better thermal capacity to prevent it from overheating and causing operational problems. Rogers PCBs, with their higher thermal capabilities, perform better than FR-4 at high temperatures and for high-speed applications.

7. Signal Integrity

Rogers PCB material has a dissipation factor of 0.004%. In comparison, the dissipation factor for FR-4 material is 0.02%. The significantly lower dissipation factor of the Rogers PCB material contributes to a substantially lower signal loss, thereby improving the signal integrity.

Conclusion:

We have presented a comprehensive comparison between regular FR-4 and Rogers PCB materials, and how to select the most optimum material for an application. The Rogers PCB materials have the advantage of not requiring any special process for fabricating PCBs. In suitable cases, designers can offset the higher cost of Rogers material by using it only for layers that handle high frequencies and using FR-4 for others.

For printed circuit board fabrication involving radio and microwave frequencies, mobile networking, and space technology, Rogers PCB materials offer uncompromising performance compared to any other types of PCB materials, including FR4. While being more expensive in comparison to other materials, Rogers PCB materials are worth the extra cost when printed circuit boards must work in unfavorable environmental conditions, at high frequencies, and with very high reliability.