What is High Frequency (HF) PCB

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.
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.
   

HF Circuit Board Material

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

1. Adjusted permittivity.
2. Low attenuation for efficient signal transmission.
3. 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.

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