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High Frequency PCB

High Frequency PCB

What is High Frequency PCB?

A high-frequency PCB is a particular circuit board with a high electromagnetic frequency that is utilized for high frequency applications (frequency greater than 300MHz or wavelength). In general, a high-frequency board is a circuit board having a frequency greater than 1GHz. The substrate material must have strong electrical performance as well as chemical stability. The loss on the substrate decreases as the power signal frequency increases, emphasizing the significance of high-frequency circuit boards.

high frequency PCB application

High-frequency electronic equipment is the current development trend, especially today when wireless networks are popular. Satellite communications are developing rapidly, and information products are moving toward high speed and high frequency.

Therefore, based on satellite systems and cellular base stations, the development of electronic products requires the integration of special signal requirements into electronic components and products, which requires the use of high-frequency circuit boards.

HF PCB offers a frequency range of 500MHz-2GHz, making it ideal for high-speed designs as well as radio frequency (RF), microwave, and mobile applications. These higher transmission frequencies can also provide faster signal flow rates, which are required for today’s increasingly complex electronic switches and other components.

The Features of High-Frequency PCB

1.DK should be small and stable enough, normally a high DK can lead to a signal transmission delay, the smaller the better.

2.DF should be small, which mainly affects the quality of the signal transmission. The smaller DF, the less signal waste can be.

high frequency board

3.The thermal expansion of copper foil should be the same as much as possible since the difference means that copper foil separates when the heat and cold change.

4.The water absorption capacity must below. A high water absorption capacity affects DK and DF in a damp environment.

5.Heat resistance, chemical resistance, impact resistance, peel strength must be good.

High-Frequency PCB Materials

High-frequency boards for wireless applications and data rates in the upper GHz range place special demands on the material used:

  • Adjusted permittivity.
  • Low attenuation for efficient signal transmission.
  • Homogeneous structure with low tolerances in the insulation thickness and the dielectric constant.

In general, radio frequency can be defined as a frequency above 1 GHz. PTFE material is currently widely used in high-frequency circuit board manufacture, it is also called Teflon, whose frequency is usually above 5 GHz. In addition, an FR4 or PPO substrate can be used for the product frequency between 1 GHz and 10 GHz. These three high-frequency substrates have the following differences:

  • In terms of FR4, PPO and Teflon laminate costs, FR4 is the cheapest, while Teflon is the most expensive.
  • In terms of DK, DF, water absorption and frequency, Teflon is the best.
  • If the product application requires a frequency above 10 GHz, we can only choose Teflon PCB substrates for manufacturing.

Obviously, the performance of Teflon is far better than that of any other substrate. However, the Teflon substrate has the disadvantage of high cost and high heat resistance. In order to improve the PTFE rigidity and the heat resistance property, a large number of SiO 2 or glass fibers are used as the filling material.

On the other hand, due to the molecular inertia of PTFE material, which cannot be easily combined with copper foil, the special surface treatment must be carried out on the combination side. Regarding the combined surface treatment, chemical etching on the PTFE surface or plasma etching is normally used to increase the surface roughness, or an adhesive film is added between the PTFE and copper foil. However, these can affect dielectric performance.

Tips for High-Frequency PCB Design

  1. Multilayer board wiring: High-frequency circuits frequently have a high integration and wiring density. Multilayer boards are not only required for wiring, but they are also an excellent way to prevent interference. A reasonable selection of the size of a certain number of layers of printed board during the PCB layout stage can make full use of the middle layer to set the shielding, better realize the nearby grounding, effectively reduce the parasitic inductance and shorten the signal transmission length, and greatly reduce signal cross interference. All of these strategies improve the reliability of high-frequency circuits.
  2. Avoid routing loops: Try not to generate a loop when routing multiple high-frequency signals. Make the loop region as minimal as possible if it is unavoidable.
  3. The less bending in the lead, the better: the lead of a high-frequency circuit wiring is ideal to use a full straight line, which requires turning, and a 45 degree broken line or arc turning can be employed. This criterion is only utilized to improve the fixing strength of copper foil in low-frequency circuits, although achieving this need can reduce external emission and mutual coupling of high-frequency signals in high-frequency circuits.

PCB design rules for high frequency

  1. The less lead interlayer alternation, the better: The phrase “the less the interlayer alternation of leads, the better” refers to the number of vias (vias) employed in the component connecting procedure. One through can bring roughly 0.5pf dispersed capacitance, according to measurements. Reducing the number of vias can enhance performance and lessen the chance of data errors.

high frequency pcb design

  1. The shorter the lead, the better: signal radiation intensity is proportional to signal line length. The greater the length of the high-frequency signal lead, the easier it is to couple to the components nearby. As a result, the shorter the lead, the better for high-frequency signal lines such as signal clock, crystal oscillator, DDR data, LVDS line, USB line, HDMI line, and so on.
  2. The ground wire of a high-frequency digital signal must be isolated from the ground wire of an analog signal: when the analog and digital ground wires are connected to the public ground wire, they must be connected with high-frequency choke beads or directly isolated, and a suitable location for single point interconnection must be chosen. The ground potential of a high-frequency digital signal’s ground wire is often inconsistent, and there is frequently a voltage differential between the two. Furthermore, the high-frequency digital transmission’s ground cable frequently carries a highly rich harmonic component of the high-frequency signal. When the ground wires of the digital signal and the analog signal are directly coupled, the harmonic of the high-frequency signal will interfere with the analog signal via ground wire coupling. As a result, in general, the ground wires of high-frequency digital and analog signals must be isolated, which can be accomplished by connecting a single point at a suitable position or by high-frequency choke beads.
  3. Connect a high-frequency decoupling capacitor to the integrated circuit block’s power pin: Connect a high-frequency decoupling capacitor to the power pin of each integrated circuit block. Increasing the power pin’s high-frequency decoupling capacitance substantially suppresses interference generated by high-frequency harmonics.

Application for High-Frequency PCB

  • High frequency PCB is used for the following applications:
  • Automotive radar system
  • Global positioning satellite antenna
  • Cellular telecommunications systems – power amplifiers and antennas
  • Live satellite
  • E-band point-to-point microwave link
  • Radio frequency identification (RFID) tag
  • Airborne and ground radar systems
  • Millimeter wave applications
  • Missile guidance system
  • Space satellite transceiver
high frequncy pcb application

High Frequency PCB Fabraction Guidelines

  1. The transmission line corner should be at a 45-degree angle to reduce back loss;
  2. This method is conducive to the effective simulation of the electromagnetic field between insulating materials and adjacent wiring because the dielectric constant values are strictly controlled by the number of layers.
  3. It is manufactured in accordance with the PCB design standards for high-precision etching. The given linewidth has a total inaccuracy of +/-0.0007 inches. The entire management of the wiring (wire) shape and coating surface is critical for resolving the skin effect problem associated with microwave frequency and achieving these parameters.
  4. In a high-frequency environment, surface-mounted SMD components are preferable to components with leads.
  5. For signal vias, avoid utilizing the via machining (PTH) procedure on the sensitive board, as this will result in lead inductance at the via; instead, use buried blind holes or back drills.
  6. To prevent the influence of three-dimensional electromagnetic fields on the circuit board, abundant grounding layers must be provided.
  7. Use a non-electrolytic nickel plating or gold dipping process rather than the HASL method for electroplating; this type of electroplating can give a superior skin effect for high-frequency currents while also helping to prevent environmental contamination.
  8. The solder barrier layer can prevent solder paste from flowing. The solder dam is commonly employed as the solder barrier layer.

Reliable High Frequency PCB Manufacturer

GESP  is one of the top manufacturers of HF PCBs.
We create high-layer count circuit boards.
13 years high frequency PCB manufacturing experience.

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