① Dielectric constant: Dk needs to be small and stable. Generally, the smaller Dk, the faster the signal transmission speed, which is inversely proportional to the square root of the dielectric constant of the substrate. The larger Dk, the more likely it is to cause signal transmission delay.

　　② Dielectric loss: At the same time, the smaller the Dk, the better the signal transmission quality, and the smaller the dielectric loss, the smaller the signal loss.

　　③ The thermal expansion coefficient of copper foil should be consistent as much as possible, with low water absorption, other heat resistance, chemical resistance, impact strength, peel strength, and other aspects that must be well protected.

　　Normally, high-frequency boards are defined as above 1GHz. Currently, most of the high-frequency circuit board substrates produced are fluorine based dielectric substrates, such as Teflon, which are mostly used for frequencies above 5GHz. Other FR4 substrates are used between 1GHz and 10GHz. Currently, there are mostly three types of substrates for high-frequency PCB production in the market: epoxy resin, Teflon, and PPO resin. Among them, epoxy resin is the most cost-effective for production, while Teflon is the most expensive for production, and PPO resin is medium in terms of dielectric constant Water absorption and frequency characteristics of Teflon are the best choices. If the product frequency is really higher than 10GHz, only Teflon can meet the requirements. Of course, not all PCB high-frequency boards must choose Teflon materials, and the specific situation depends on the customer's demand for the product.