PCB de alta frequência
PCB de alta frequência

PCB de alta frequência

High Frequency Circuit: First choice for processing special signals

The division of circuit boards can take various approaches, and a PCB de alta frequência is categorized by its functionality. This term distinguishes it from traditional circuit types, representing a circuit board used in environments where the operating frequency exceeds 100GHz. This board is suitable for handling RF (Radio Frequency) and microwave circuits. While circuits often meet data transmission requirements in low-frequency environments, as the frequency increases, maintaining circuit characteristics becomes more complex. This complexity can lead to signal distortion and interference. Hence, special wiring, high-quality substrate materials, and a reliable manufacturer are all essential aspects for project reliability.

Best High Frequency PCB Manufacturer - FS Tech

As an industry-experienced Fabricante de PCB, FS Technology understands customers’ expectations and demands for high-frequency projects. We take specific measures to address these pain points and assist you in transitioning from concept to PCBA.

High Frequency PCB Substrate Material Selection Guide

The choice of substrate material in high-frequency circuits is crucial, as it imparts various properties and characteristics to the PCB. Therefore, understanding the application environment and selecting from different high-frequency PCB materials’ features before commencing circuit design is essential to ensure the project’s flawless execution.

Key Aspects of High-Frequency Materials

In digital communication, high-speed 10Gb/s square wave signals are, in fact, composed of multiple sinusoidal wave signals at different frequencies superimposed. This square wave signal includes a fundamental frequency signal at 5GHz, along with its third-order (15GHz), fifth-order (25GHz), and seventh-order (35GHz) harmonic signals. In high-frequency circuits, ensuring signal integrity and sharp transitions in rising and falling edges of signals is crucial, much like in RF and microwave circuits where low loss and transmission distortion are imperative.

In project planning, two critical parameters are the DK (dielectric constant) and DF (dissipation factor). When selecting the substrate material, the variation in the DK value is typically the primary consideration. For projects that prioritize signal transmission quality and characteristic impedance control, the performance of the DF value under different conditions, such as frequencies, temperatures, and humidity, also needs to be considered.

Different substrate materials exhibit noticeable variations in DK and DF values at different frequencies, especially when frequencies span from 1MHz to 1GHz. Taking FR-4 as an example, its DK value is 4.7 at 1MHz, and it decreases to 4.19 at 1GHz. However, as the frequency surpasses 1GHz, the change in the DK value tends to stabilize, showing a negative correlation, meaning that as the frequency increases, the change in the DK value becomes less pronounced.

When we consider high-frequency circuit design, particularly within the 10GHz frequency range, the impact of frequency variations on the DK value of high-frequency PCB is minimal. In the 1MHz to 1GHz range, the fluctuation in DK value is usually around +/- 0.02. At this point, the trend of DK value changes at different frequencies tends to gradually diminish.

In contrast, the variation curve of the DF value at different frequencies is usually more pronounced and tends to increase. Therefore, when evaluating the high-frequency performance of materials, we pay closer attention to changes in the DF value. High-quality high-frequency PCB substrate materials typically possess two key characteristics: firstly, minimal impact of frequency variations on the DF value, and secondly, a lower baseline DF value compared to general materials.

Recommendations for High-Frequency PCB Substrate Materials

Rogers

Taconic High Frequency PCB

Rogers is an American PCB material company, and in comparison to traditional materials like FR4, their developed Rogers laminates are relatively expensive. Nevertheless, they are still widely used, which confirms Rogers PCB’s position in the high-frequency domain.

Rogers offers numerous material series, among which RO3000 and RO4000 are considered the most efficient high-frequency materials. Both are high-performance, low dielectric loss materials designed for high-frequency and RF (Radio Frequency) applications. They are suitable for microstrip lines, antennas, power amplifiers, filters, and other high-frequency circuits. The RO3000 series is ceramic-filled PTFE composite materials for high-frequency circuits, while the RO4000 series comprises prepreg and hydrocarbon ceramic laminates, with the latter offering better performance at a higher cost.

Tacónico

Taconic High Frequency PCB

Taconic is one of the world’s largest PTFE CCL (Copper-Clad Laminate) manufacturers, renowned for its dominant position in the high-frequency PCB and antenna market, with a market share exceeding 80%. They offer a range of high-performance materials, particularly suitable for high-frequency applications. Below are two materials recommended by FS Technology for PCB de alta frequência projects:

Taconic RF-35 Ceramic: Cost is often a key consideration in high-frequency PCB manufacturing. RF-35, as an economical choice, is made from PTFE filled with ceramics and woven glass. Its processo de fabrico is relatively straightforward, while it offers excellent electrical performance and lower signal loss. Hence, it’s particularly well-suited for cost-sensitive projects.

Taconic TLX: High-frequency projects may need to address challenges related to high power and high temperatures. TLX is made from PTFE and glass fiber, offering outstanding dimensional stability, heat resistance, and mechanical performance, which aids in resolving high-power and high-temperature issues. However, it’s important to note that due to its higher performance requirements, the processo de fabrico may be relatively complex, resulting in higher costs.

High Frequency PCB FAQ

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Gestão térmica

Generating heat on a placa PCBA is normal, and it may result from environmental factors, component heat generation, or current flow, typically dissipating on its own. However, in high-frequency circuits, heat generation is more prominent. This can be due to their use in high-power projects, In addition, high-frequency signal transmission requires more current. For this reason, your high-frequency PCB project may require additional heat management techniques to aid in heat dissipation:

Thermal Via Arrays: Strategically placed vias can help dissipate heat into the surrounding air, such as arranging them around high-heat components. However, more vias do not necessarily mean better heat dissipation. To maximize their effectiveness, it’s advisable to set the via diameter at around 0.1 mm.

Wide Traces: Traces, or copper conductors carrying the current, don’t directly reduce heat so often overlooked by designers. Optimizing trace widths can influence current-carrying capacity and the overall heat distribution across the PCB. This can reduce heat generated due to self-resistance and alleviate high current density in local areas. However, it’s important to maintain an optimal trace width as overly wide traces can lead to crosstalk issues in high frequency PCB.

Heat Sinks/Cooling Fans: These are physical mechanisms for accelerating airflow across the PCB surface to enhance heat dissipation. The challenge here is accommodating these in the limited space that high frequency PCB typically have, thanks to their densely packed traces and component layout. 

Colocação de componentes: High frequency PCB may contain heat-emitting components, and it’s essential to maintain adequate distances between them and separate them from heat-sensitive materials. If vertically mounted, heat-emitting components should be placed nearer the top. Employing analysis software to identify potential hotspots and optimizing component layout is an effective strategy.

Manufacturing Challenges and Solutions

A common issue in high-frequency PCB manufacturing is the low bond strength between the laminate layers and the resin, which can lead to delamination. To avoid this problem, it is recommended to use laminates and resins with similar coefficients of thermal expansion. In the stacking process, it is essential to closely monitor parameters like pressing temperature, duration, pressure, and the resin curing process.

As mentioned earlier, addressing thermal management issues in high-frequency PCBs involves mitigating the heat generated during processes like CNC or laser drilling, as these can lead to material hardening around the drilled holes. To tackle this, it is advisable to use resin fills, often applied as filler resins, to alleviate this concern. Resin fills can help absorb some of the heat generated during drilling and improve the quality of drilled holes.

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