PCB is one of the essential components and devices in electronics due to its wide availability and simplicity. Among the various types and forms of PCB, high-frequency PCB is widely used due to its general purpose.

What is High-Frequency PCB?

A high-frequency PCB is very similar to any other form of PCB (printed circuit board). It is compatible with microwave radio frequency communications, ranging from five hundred megahertz to two thousand gigahertz. Due to its ability to transmit signals to greater distances, it is widely used in a variety of devices, including radar, industrial, military, and medical equipment.

HF PCB is a form of PCB that is generally used in applications that require a specific signal to be transmitted between two objects. It can operate between 500 MHz and 2 GHz, making it an excellent choice for mobile, microwave, radio frequency, and other high-speed design applications. Proteus Ares PCB design software is suitable for embedded systems.

HF PCB Uses

Here are some of the most common uses of high-frequency printed circuit boards (HF PCBs) to go a step further.

It is used to make a variety of military-related equipment.

It is used to make a variety of medical equipment PCB instruments.
Hf frequencies are used in various machinery and equipment in the industrial sector.
Radar devices created using HF PCBs can communicate.

PCB Design for High Frequency Applications
Since building this board is a time-consuming and expensive undertaking, several basic factors must be considered when building this board. These criteria can vary depending on various factors, including product volume, budget, high-frequency PCB materials, design layout, and industry standards.

Once these parameters are determined, you can start designing a high-frequency PCB. These procedures also apply to buildings.

The first step is to monitor the frequency of the PCB board
To improve the performance of the circuits that use it, higher-frequency printed circuit boards are usually built with a frequency of 50 Hz.

If you are dealing with a high-frequency circuit board, you can measure the diameter of the traces on the PCB. If the rise time of your device switching speed is more than three times the length of the trace found, your operating board is likely a high-frequency printed circuit board.

High-frequency PCB Design

Accurate measurements of the substrate, conductors, and impedance are required.
The most commonly used substrate material is PRFE, which has low losses.
Therefore, multiple layers are needed to manage impedance.
The size of microvias can range up to 75 microns.
Layout Design and Its Importance

The most critical step in high-speed product production is improving the layout design.

If you are not an expert in layout design, you need to talk to the person responsible for designing the layout before paying for it. Taking a few simple steps early on will save you a lot of effort if you need to re-do the layout design.

Make sure the layout designer has all the information they need to integrate your suggestions immediately.

When looking for a layout designer, you should have all the information you need, including the following:

Layout sketch
Number of layers
Signal layers
Board thickness
Location of critical components
Location of bypass components
Nature of basic traces
Material for high-frequency printed circuit boards
High-frequency wireless applications have specific requirements for high-frequency PCB materials, so high-frequency boards must be used.

The dielectric constant of the material used has been customized according to the application needs.
Signal transmission is achieved by reducing attenuation.
When it comes to creating homogeneity, dielectric constant tolerance is not that important.
With the right material layering, FR4 can be used in a variety of applications. This approach helps improve by using the same dielectric material. These properties are provided by lower loss factor, lower dielectric constant, and are not dependent on the temperature or frequency of the system.

Factors that Decide High-Frequency PCB Material

When choosing a high-frequency PCB and the right material for your project, you should consider the following aspects:

The axis of the material determines how it behaves; therefore, when the axis moves, the behavior also changes. It must be small enough to provide a stable input for signal transmission.
Likewise, the dissipation factor (DF) must also be low, as a larger DF degrades the quality of the transmitted signal. Therefore, there is less signal waste.

Another molecular structure-based component that can affect high-frequency RF materials is called loss tangent. On the other hand, low-frequency transmission is not affected.
Careful spacing can reduce crosstalk and skin effect. When the board starts to communicate with itself, it is called “crosstalk” when unwanted coupling occurs between the board and the components. The gap between the traces and the planes must be as small as possible to prevent crosstalk.
The resistance of the trace is directly related to the skin effect. When the resistance of the board increases, the temperature also increases. When designing the circuit, you must ensure that the length and width of the traces do not affect the board at high frequencies.

The smaller the via diameter, the lower the conductivity and is more suitable for high frequencies. High-frequency PCB materials preferably have high resistance to peeling, impact, and heat.
Its thermal expansion coefficient describes the effect of temperature on the dimensions of the material. Due to the material’s sensitivity to temperature, even slight changes can have a significant impact on PCB drilling and assembly. The copper foil must have the same thermal expansion coefficient as the rest of the board, because if the temperature changes, the change in thermal expansion may cause the copper foil to separate.

The working environment of the equipment is very important. Using the equipment in a laboratory or indoor environment will not cause any moisture problems. When your equipment is exposed to a humid environment, problems may arise.
Therefore, the water absorption of high-frequency PCB materials should be moderate, because significant absorption factors may change the DF and DK values ​​of moisture.

Suitable Material Selection for HF PCB
Materials that can withstand high frequencies include:

Rogers 4350B High Frequency
Rogers RO3001
Rogers RO3003
Taconic’s RF-35 Ceramic.
Taconic’s TLX
E Fiberglass ISOLA IS620
ARLON 85N is a good example.
At this point, engineers begin to establish production processes, keeping in mind key process factors such as line width and dielectric spacing to guarantee that the design meets user needs and operates consistently and reliably under all conditions.

Controlled Impedance Transmission Lines

Developing controlled impedance transmission lines is critical to avoiding signal degradation.

Microstrip and Stripline Stripline is the two most common technologies for creating controlled impedance transmission lines. To be considered a microstrip line, you must have a trace on the top layer and a ground plane underneath it.

You can calculate the impedance of a microstrip line by considering several variables, such as the relative dielectric constant of the board material, the thickness and width of the trace, and the height of the trace above the plane. If you want to get better results, you must place the ground plane closer to the top layer.

Stripline, often referred to as RF PCB or HFPCB, is a controlled impedance addition similar to microstrip, but with an additional set of planes at the top left corner of the trace.

A trace must be inserted between the two surface layers. The ability to confine EMI radiation to two planes makes stripline superior to microstrip in signal transmission.

Why are high frequency circuit boards important?

Transmitting signals at high speeds becomes more challenging due to the complexity of electronic components and switching circuits.
Due to the short pulse rise time, high-frequency PCB methods must pay attention to the conductor diameter in electronic components.
In other words, when high-frequency signals are present on the board, the impedance changes according to the transmission elements.

Advanced process control functions and implementations are required to prevent this from happening.
Conductor trace structure, layer formation, and dielectric constant are important causes of impedance in high-frequency printed circuit boards (HF PCBs).

Frequently Asked Questions or FAQs

What kind of substrate is usually used to construct PCBs for high-frequency circuits?
Polytetrafluoroethylene (PTFE) material, commonly known as Teflon, is currently widely used as a high-frequency PCB material.

Which PCB laminate is best for high-frequency use?
With high-frequency technology, polytetrafluoroethylene (PTFE) has become a common laminate material for PCBs. Despite its high cost, PTFE, a synthetic thermoplastic fluoropolymer, has good dielectric properties in microwave applications.

KKPCB conducts research on special processing technologies such as ordinary double-sided boards, thick copper circuit boards, high-frequency circuit boards, HDI circuit boards, rigid-flexible circuit boards, FPC flexible boards, buried blind hole circuit boards, and IC carrier boards. Provides PCB design, PCB layout, PCB prototyping and PCB assembly services.