High-frequency printed circuit board Substrate

High-frequency printed circuit board Substrate

The high frequency of electronic equipment is a development trend, especially in the growing development of wireless networks and satellite communications, information products are moving towards high speed and high frequency, and communication products are moving toward the standardization of voice, video, and data for wireless transmissions with high capacity and speed. The development of a new generation of products requires high-frequency substrates, and satellite systems, mobile phone receiving base stations and other communication products must use high-frequency circuit boards. In the next few years, they will inevitably develop rapidly, and high-frequency substrates will be in great demand.

Basic characteristics of high-frequency substrate materials require the following:

(1) The dielectric constant (Dk) must be small and stable. Usually the smaller the signal, the better the transmission rate of the signal is inversely proportional to the square root of the dielectric constant of the material. High dielectric constant can easily cause signal transmission delay.

(2) The dielectric loss (Df) must be small, which mainly affects the quality of signal transmission. The smaller the dielectric loss, the smaller the signal loss.

(3) The coefficient of thermal expansion of the copper foil is as consistent as possible, because the inconsistency will cause copper foil separation in the cold and hot changes.

(4) Low water absorption and high water absorption will affect the dielectric constant and dielectric loss in the presence of moisture.

(5) Other heat resistance, chemical resistance, impact strength, peel strength, etc. must also be good.

In general, high frequency can be defined as frequency above 1GHz. Currently used high frequency circuit board substrate is fluorine germanium dielectric substrate, such as polytetrafluoroethylene (PTFE), usually known as Teflon, usually used in Above 5GHz. There are also FR-4 or PPO substrates that can be used between 1GHz and 10GHz. The physical properties of these three high-frequency substrates are compared as follows. At the present stage, three types of high-frequency substrate materials such as epoxy resin, PPO resin, and fluorine-based resin are used, and the epoxy resin is the cheapest, and the fluorine-based resin is the most expensive; and the dielectric constant, dielectric loss, and water absorption are used. Considering the frequency characteristics, the fluorine resin is the best and the epoxy resin is poor. When the frequency of product application is higher than 10 GHz, only the fluorocarbon resin printed board can be applied.

Obviously, the high-frequency performance of fluorine-based resin is much higher than that of other substrates, but its disadvantages are poor rigidity and high coefficient of thermal expansion, in addition to high cost. For polytetrafluoroethylene (PTFE), a large amount of inorganic material (such as silica SiO2) or a glass cloth is used as a reinforcing filler material to improve the rigidity of the substrate and reduce the thermal expansion thereof for the purpose of improving the performance. In addition, due to the molecular inertness of the PTFE resin itself, it is not easy to combine with the copper foil. Therefore, special surface treatment with the copper foil is required. Treatment methods include chemical etching or plasma etching on the surface of Teflon to increase the surface roughness or to increase the adhesion between the copper foil and Teflon resin to increase the bonding force, but may have a dielectric property. Influencing the development of the entire fluorine-based high-frequency circuit substrate requires the cooperation of raw material suppliers, research institutes, equipment suppliers, PCB manufacturers, and communication product manufacturers to keep up with the rapid development of high-frequency circuit boards.