High Frequency PCB

What is High Frequency PCB?

A high frequency printed circuit board (PCB) is specifically designed to handle and transmit high-frequency signals efficiently. These PCBs typically operate above 1 GHz, making them suitable for both high-frequency applications (frequencies above 300 MHz, wavelengths shorter than 1 m) and microwave applications (frequencies above 3 GHz, wavelengths shorter than 0.1 m). As technology advances, engineers increasingly design devices to operate not only in the microwave range but also at millimeter-wave frequencies above 77 GHz. QFPCB has extensive experience in the mass production of 77GHz millimeter-wave circuit boards, highlighting the increasing demand for higher-frequency applications.

Manufacturers typically produce high frequency PCB using specialized materials such as Rogers, Taconic, Arlon, Isola, and F4B. Engineers select these materials because they provide stable dielectric constants (Dk) and low dissipation factors (Df), which support reliable signal transmission in high-frequency and microwave applications.

As operating frequencies continue to increase, designers impose stricter performance requirements on PCB substrates. The materials must maintain signal integrity, minimize transmission loss, and deliver consistent electrical performance in high-frequency and microwave environments.

How to Select High Frequency Microwave Circuit Materials?

When selecting materials for High Frequency Microwave Circuit, it’s important to consider not only the dielectric constant (Dk) and loss tangent (Df), but also the mechanical properties, thickness, size, and type of copper foil.

Key Considerations:

• Small RF Circuit: For compact RF circuits, choose materials with a higher dielectric constant (Dk) to reduce the signal wavelength.
• Low Loss Circuit: For low signal loss, select materials with a low Df value to maintain signal integrity during transmission.
• Long-Distance Interconnections: If the circuit requires long interconnections, materials with lower Df should be chosen to minimize signal loss over distance.
• Harsh Environments: If the PCB will be exposed to high temperatures, vibrations, or shocks, ensure the material’s reliability by evaluating characteristics like Tg, Td, and water absorption.

Difference Between High-Frequency and High-Speed PCBs

High-frequency and high-speed PCBs (Printed Circuit Boards) may sound similar, but they address different application needs. They differ significantly in terms of electrical performance, material selection, and design focus. At QFPCB, we have extensive experience in manufacturing both types of PCBs. Here are the key differences:

1. Main Concepts:

• High Frequency PCB
  Refers to PCBs designed to handle high-frequency signals (typically >1GHz). These are commonly used in RF (Radio Frequency), microwave, and millimeter-wave communication devices like radars, antennas, and wireless communication modules. The focus is on signal transmission efficiency, phase stability, and low loss at high frequencies.
• High-Speed PCB
  Refers to PCBs designed for high-speed digital signals (fast signal rise times or data transmission rates). The primary concern is signal integrity (SI) and electromagnetic interference (EMI). High-speed typically refers to systems with data rates exceeding 1Gbps, such as servers, routers, and high-speed data buses.

2. Material:

1）. High Frequency PCB Material Selection

• Low Dielectric Constant (Dk):

Selecting the right PCB material is a critical challenge that must be addressed at the very beginning of circuit design. For high frequency circuits, Therefore, it is essential to choose materials that offer a stable dielectric constant and extremely low loss at high frequencies.The Dk of a material can also change with operating frequency, and it fluctuates with temperature variations. As a result, when selecting High Frequency Circuit Board materials, designers must consider the operating frequency of the circuit and the environmental conditions, such as temperature and humidity, to ensure Dk stability.

Different high frequency Circuit Board materials have varying dielectric constants (Dk). For example, PTFE materials Dk2~10（QFPCB has DK2~25 high frequency board in stock）, making them commonly used in microwave and high-frequency applications. The dielectric constant and loss tangent of the material directly influence signal transmission characteristics and attenuation levels.

Designers generally prefer materials with low dielectric constants and low loss tangents to reduce signal loss and improve high-frequency performance. However, they may also select high-frequency materials with higher Dk values when they need to reduce the overall size of the finished circuit board.

When choosing a dielectric material, engineers should avoid excessively high Dk values, as they can negatively affect signal propagation characteristics and impedance control.

A higher dielectric constant results in narrower conductor widths in the design, which not only increases conductor losses but also adds complexity to the PCB manufacturing process.

• Low Dissipation Factor (Df):

  For high frequency Circuit Board transmission line circuits, insertion loss consists of several components: dielectric loss, conductor loss, radiation loss, and leakage loss. These components collectively contribute to the total insertion loss. Leakage loss occurs when energy dissipates due to leakage current flowing between the signal trace and ground. However, high-frequency PCB materials typically exhibit high bulk resistivity, which significantly limits leakage current. As a result, designers generally consider leakage loss negligible in high-frequency applications.

  Conductor loss occurs when the signal traveling along a transmission line dissipates energy due to the inherent resistance and surface impedance of the conductor. As frequency increases, effects such as skin effect further contribute to this loss.

  Dielectric loss, in contrast, results from the intrinsic dissipation characteristics of the substrate material and directly depends on its dissipation factor (Df). By selecting materials with a relatively low Df, designers can effectively reduce overall insertion loss and improve high-frequency signal performance.

  For circuits operating in the mid-to-low-frequency range, insertion loss is mainly determined by conductor loss and dielectric loss. As the operating frequency increases, especially in the millimeter-wave range, the wavelength of the signal shortens. In this frequency range, the non-closed structure of the transmission line, as well as the unchanged cross-sectional area and trace width, makes radiation loss more significant and no longer negligible.

  Although microstrip transmission lines are more prone to radiation loss and spurious modes at millimeter-wave frequencies compared to the other three types of losses, their many advantages—such as ease of fabrication, simple design, small physical size, and easy integration—make them widely used in millimeter-wave circuits.

                                                               Loss of microstrip line with different thickness of the same material

• Skin effect of copper foil roughness：

The surface roughness of the copper foil used in high frequency materials can affect the dielectric constant of microstrip line circuits. The presence of surface roughness on the copper foil slows down the propagation speed of electromagnetic waves in the circuit. Compared to a very smooth copper surface, the rougher copper foil creates a “slow wave” effect, which leads to an increase in the apparent dielectric constant of the circuit.

The rougher the copper foil surface, the higher the dielectric constant presented by the circuit, while a smoother copper foil surface results in a lower dielectric constant. Therefore, using smoother copper foil leads to smaller variations in the final circuit’s dielectric constant (Dk), improving the consistency of the circuit’s performance.

Surface roughness significantly influences the effective dielectric constant, particularly in thin substrates. When the dielectric thickness decreases, the relative impact of copper surface profile increases, leading to more noticeable variations in Dk. In contrast, thicker substrates mitigate this effect, resulting in more stable dielectric behavior.

Changes in Dk values ​​of circuits with different copper foils of 5mil RO3003 material

In general, choosing a copper foil with less RMS roughness reduce signal loss and interference. QFPCB can provide you with different types of copper foils to meet your different needs.

If you need to evaluate the conductor loss of High Frequency Microwave Circuit materials, QFPCB advise you to use trace’s DC resistance, skin effect, and copper roughness factor to estimate the conductor loss:

In addition to copper foil roughness, the plating material used for the copper layer also needs to be considered, as it can introduce rough surfaces and result in higher losses. If your equipment operates with high-frequency signals above 1 GHz, QFPCB recommends using OSP (Organic Solderability Preservative) or ImAg (Immersion Silver) plating, as they introduce minimal additional losses.

• Dielectric constant with temperature (TCDk)：

The dielectric constant (Dk) of circuit materials changes with temperature, and this parameter, known as TCDk (Temperature Coefficient of Dielectric Constant), helps engineers assess how material performance might shift under varying conditions. The smaller the TCDk value, the more thermally stable the material’s performance. Ideally, circuit materials would have a TCDk value of 0 ppm/°C, maintaining a fixed Dk regardless of temperature fluctuations. However, in reality, Dk values do vary with temperature, and only materials with very low TCDk values can be considered thermally stable. Typically, a TCDk absolute value of less than 50 ppm/°C is desirable for stable high-performance materials.

When a circuit must operate across a wide temperature range while maintaining consistent performance—such as in automotive radar sensors, which require precise measurements under varying thermal conditions—the TCDk parameter becomes a critical consideration.

Materials based on the same resin system can exhibit differing TCDk characteristics. For instance, PTFE is known for its exceptional performance and low-loss properties in high-frequency circuits. However, the TCDk characteristics of PTFE-based materials can vary significantly. Some PTFE-based materials show substantial Dk variations with temperature, with TCDk values reaching 200 ppm/°C or higher. Conversely, other PTFE-based materials achieve near-ideal TCDk stability.

The attached graph illustrates the TCDk curves of various circuit materials. It is evident that epoxy resin-based materials exhibit poor TCDk performance, while certain PTFE materials filled with special ceramics show excellent TCDk stability. For example, the widely used RO3003™ material for 77 GHz automotive millimeter-wave radar features a TCDk value of -3 ppm/°C, making it highly suitable for such demanding applications.

• Water Absorption：

When selecting circuit materials, design engineers often overlook moisture absorption, even though it plays a critical role in circuit performance and system consistency. Materials with low moisture absorption help minimize changes in dielectric constant (Dk) and loss, ensuring that the circuit maintains nearly identical performance under various environmental conditions.

High Frequency Microwave Circuit Material

Rogers RT/duroid series:

The Rogers RT/duroid series offers a wide range of high-frequency laminate materials designed for demanding RF, microwave, and millimeter-wave applications. Key models include RT/duroid 5880, known for its ultra-low dielectric constant (Dk) of 2.20 and exceptionally low loss, ideal for aerospace and satellite systems, and RT/duroid 5870, which shares similar low Dk properties with enhanced thermal stability. For higher dielectric constant needs, RT/duroid 6006 and RT/duroid 6010.2LM offer Dk values of 6.15 and 10.2, respectively, catering to compact circuit designs and phased-array antennas. RT/duroid 6002 and RT/duroid 6202 and 6202PR provide stable Dk (2.94) and low loss for stripline and microstrip applications. Meanwhile, RT/duroid 6035HTC delivers excellent thermal conductivity, making it suitable for high-power RF and heat-sensitive applications. The RT/duroid series is trusted for its versatility, reliability, and performance in challenging environments.

Rogers RO3000 series:

The Rogers RO3000 series provides a range of high-performance laminates specifically engineered for RF, microwave, and millimeter-wave applications. These materials deliver low insertion loss and excellent dielectric stability across a wide frequency range.

Key grades include RO3003 (Dk 3.00) and its enhanced version, RO3003G2. RO3003G2 improves mechanical robustness while maintaining the low dissipation characteristics required for high-frequency circuit designs. For compact and high-density applications, RO3010 (Dk 10.20) and RO3210 (Dk 10.20) offer higher dielectric constants, enabling designers to reduce circuit size in applications such as antennas and RF filters. RO3035 (Dk 3.50) provides a balanced solution for designs that require moderate dielectric constant values with stable electrical performance.

Engineers widely adopt the RO3000 series in telecommunications systems, automotive radar modules, and aerospace electronics because the materials combine electrical reliability, good processability, and stable thermal performance under demanding operating conditions.

Rogers RO4000 series:

The Rogers RO4000 series includes a diverse selection of high-performance laminates designed for RF, microwave, and mixed-signal applications, offering an excellent balance of performance, reliability, and cost-effectiveness.

RO4003C (Dk 3.38) is a popular choice for general high-frequency applications, while RO4350B (Dk 3.48) provides improved thermal stability and ease of processing for more demanding designs. For higher dielectric constant needs, RO4360G2 (Dk 6.15) supports compact circuit designs.

The RO4500 series, including RO4533, RO4534, and RO4535, offers cost-effective solutions with tailored Dk values for broadband and millimeter-wave applications. RO4725JXR and RO4730G3 are optimized for antenna designs, with a focus on stability and low PIM (Passive Intermodulation). For advanced, low-loss systems, RO4830 and RO4835 (Dk 3.48, with enhanced oxidation resistance) deliver reliable performance in high-power RF and automotive radar applications, making the RO4000 series versatile across wireless infrastructure, IoT, and telecommunication systems.

Taconic series:

Taconic provides a broad portfolio of PCB materials tailored for a wide range of applications. Its low-loss, high-frequency laminates—such as TLY-5, TLY-3, TLY-5A, TLX-0, TLX-8, and TLP-5—are well suited for antennas, filters, and radar systems. For compact circuits and microwave filters requiring superior thermal stability, engineers can choose ceramic-filled PTFE options, including CER-10, CER-3, CER-2.5, and CER-6.

For RF and microwave applications, materials such as RF-35, RF-35TC, RF-30, and RF-60A provide cost-effective solutions while maintaining stable electrical performance. Taconic’s hybrid and multilayer offerings—including TacPreg, TacLam, and EZ-IO—support high-reliability, multilayer structures. Automotive and millimeter-wave applications benefit from materials like TT-6000, TLC-30, and TLY-5A, which reliably support 24 GHz and 77 GHz systems.

High-temperature and specialty laminates, including TacPreg, TacLam-1000, and ThermalClad, ensure consistent performance under extreme conditions. This comprehensive material portfolio makes Taconic a versatile choice for engineers designing high-frequency, high-performance, and high-reliability PCB solutions.

Isola series:

Isola offers a range of high-frequency laminates engineered for RF, microwave, and millimeter-wave applications, delivering low loss and excellent thermal reliability. The IS680 series—including IS680-247, IS680-260, and IS680-280—provides stable dielectric properties and low dissipation factors, making these laminates well suited for antennas, filters, and other RF components.

The IS620 and IS620i grades are designed for hybrid constructions, combining superior electrical performance with strong mechanical properties. I-Tera MT40 features an ultra-low loss profile and high thermal stability, making it ideal for 5G infrastructure, aerospace systems, and high-speed digital circuits. For even higher-performance applications, I-Tera MT77 offers low insertion loss and excellent dielectric constant stability, optimized for automotive radar and other high-frequency systems.

Engineers widely use these materials in telecommunications, data centers, and advanced wireless technologies due to their reliable performance, thermal stability, and processing versatility.

WANGLING：

WANGLING produces F4BM-1/2 through a precisely controlled lamination process, combining non-alkali fiberglass fabric, bonding film, Teflon resin, and PTFE film in accordance with optimized material formulations and strict manufacturing standards.This product takes some advantages over F4B series in the electrical performance（wider range of dielectric constant、lower dielectric loss angle tangent increased resistance、and more reliable performance）

F4BM employs forward rotating ED copper foil for cladding, making it ideal for applications that do not require PIM indicators. With precise adjustments to the ratio between polytetrafluoroethylene and glass fiber cloth, the F4BM series achieves a low loss and enhances dimensional stability. As the dielectric constant increases, the proportion of glass fiber also increases, resulting in improved dimensional stability, reduced coefficient of thermal expansion, enhanced temperature fluctuation performance, and decreased dielectric loss.

F4BM-2 &F4BTMS Radio frequency PCB material:

F4BM217(DK2.17), F4BM220(DK2.20), F4BM233(DK2.33), F4BM245(DK2.45), F4BM255(DK2.55), F4BM265(DK2.65), F4BM275(DK2.75), F4BM294(DK2.94), F4BM300(DK3.00);

F4BTMS220(DK2.20), F4BTMS233(DK2.33), F4BTMS255(DK2.55), F4BTMS265(DK2.65), F4BTMS294(DK2.94), F4BTMS300(DK3.00), F4BTMS350(DK3.50), F4BTMS430(DK4.30), F4BTMS450(DK4.50), F4BTMS615(DK6.15), F4BTMS1000(DK10.2);

High Speed PCB Material Selection

High speed PCBs handle fast digital signals with steep rise times and require materials that maintain signal integrity and minimize noise. Key requirements include:

• Controlled Impedance:
  Materials with consistent Dk values ensure precise impedance matching for high-speed signals.
• Low Loss:
  While not as critical as high frequency PCBs, lower Df values help reduce signal attenuation at high data rates.
• Mechanical Compatibility with FR4:
  Many high-speed applications use enhanced FR4 materials or hybrid stacks for cost-effectiveness and compatibility with standard PCB fabrication processes.
• Examples of Materials:
  • High-performance FR4 (e.g., Isola FR408HR, Panasonic Megtron series)
  • Rogers RO4350B, RO4003C (for hybrid designs)
  • Nelco N4000-13 series
  • TUC (Thermoset materials) for low-cost designs
• Applications:
  High-speed data buses, network routers, 5G base stations, and server boards with data rates >1Gbps.

Design Considerations:

High Frequency PCB Design Focus:

1. Impedance Control: Transmission line impedance must be precisely matched to prevent reflection and loss.
2. Signal Loss: Use low-loss materials and optimize trace width and thickness.
3. Phase Stability: Ensure consistent signal behavior at high frequencies.
4. Parasitic Effects: Minimize parasitic capacitance and inductance at high frequencies.

High-Speed PCB Design Focus:

1. Signal Integrity: Reduce reflections, crosstalk, and signal distortion.
2. Timing Control: Strict timing matching is essential for high-speed signals.
3. Electromagnetic Compatibility (EMC): Minimize electromagnetic radiation and interference.
4. Multilayer Design: Typically requires multilayer stacking to handle complex routing and robust power distribution.

Noteworthy Issues in High Frequency PCB Design

To avoid common issues and improve the design-to-manufacturing transition, the following considerations should be kept in mind:

1. Minimize High-Frequency Interference: Increase the distance between high-speed and analog signals to reduce crosstalk. Also, pay attention to grounding to minimize noise interference.
2. Differential Distribution Lines: For differential signals, ensure that the two lines are of the same length and that the spacing remains constant to maintain differential impedance.
3. Transmission Line Design: Proper design of controlled impedance transmission lines is crucial to avoid signal loss. Microstrip lines and ribbon lines are commonly used methods.
4. Designers should use surface-mount components in high-frequency applications instead of leaded components. Surface-mount devices (SMDs) minimize parasitic (lead) inductance and reduce signal distortion, which helps maintain signal integrity at high frequencies.
5. Designers should provide sufficient and continuous ground planes to ensure effective grounding throughout the PCB. Proper ground connectivity reduces electromagnetic interference (EMI), improves return current paths, and enhances overall signal integrity in high-frequency designs.

Why Are High Frequency PCBs More Expensive?

High Frequency Microwave Circuit are typically more costly than standard PCBs because they require specialized materials, precise designs, and advanced manufacturing techniques:

• Material Cost: High Frequency PCBs use premium materials like PTFE ceramics and ceramic-filled PTFE, which are expensive but necessary for minimizing signal loss and ensuring high-quality signal transmission.
• Design Complexity: Designing high frequency PCBs requires precise impedance calculations and thermal management, driving up design costs.
• Manufacturing Precision: High Frequency PCBs demand higher manufacturing accuracy and advanced equipment, which increases production costs.

Manufacturing High Frequency PCBs

The manufacturing process for High Frequency Microwave Circuit Board requires high precision and specialized techniques such as Laser Direct Imaging (LDI) and Controlled Impedance Drilling (CID). Key factors include:

1. Transmission Line Accuracy: High-frequency transmission lines require precise manufacturing tolerances, typically within ±0.02 mm. At QFPCB, we ensure accuracy with tolerances as tight as ±0.01 mm.
2. Plating Thickness Control: Uniform plating thickness is critical for maintaining consistent characteristic impedance and signal quality.
3. Drilling Precision: Using high-precision drilling equipment, we avoid rough edges that could distort signals and ensure good electrical performance.
4. Mechanical Processes: Different high-frequency dielectric materials require specialized forming processes. Our team uses advanced milling and cutting techniques to ensure the material is not deformed, ensuring precise shape tolerance and material consistency.

Why Choose QFPCB?

With more than 15 years of expertise in high-frequency PCB manufacturing, QFPCB leverages advanced laser systems and highly automated production lines to deliver precise fabrication, tight tolerance control, and reliable performance for demanding RF and microwave applications. We are experts in producing high frequency PCBs with cutting-edge technologies like Laser Direct Imaging (LDI) and Controlled Impedance Drilling (CID). Our extensive inventory includes premium materials such as Rogers, PTFE, and ceramic-filled PTFE, ensuring we can meet the diverse needs of our customers.

At QFPCB, we are dedicated to providing exceptional customer support, ensuring your project runs smoothly from design to production. Contact us today to learn more about how we can assist with your High Frequency PCB needs.