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

　　The basic characteristics of the substrate material of the high-frequency circuit board are as follows:

　　1. Other heat resistance, chemical resistance, impact strength, peel strength, etc. must also be good.

　　2. Low water absorption and high water absorption will affect the dielectric constant and dielectric loss when wet.

　　3. The thermal expansion coefficient of the copper foil should be as consistent as possible, because the inconsistency will cause the copper foil to separate in the hot and cold changes.

　　4. 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.

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

　　Generally speaking, the high frequency of a high frequency circuit board can be defined as a frequency above 1GHz. At present, the most commonly used high-frequency circuit board substrates are fluorine dielectric substrates, such as polytetrafluoroethylene (PTFE), usually called Teflon, which is usually used above 5GHz. In addition, FR-4 glass fiber board or PPO substrate can be used for products between 1GHz and 10GHz. The physical properties of these three high-frequency substrates are compared as follows:

　　Eight-layer high-frequency circuit board

　　The three types of high-frequency substrate materials used at this stage are epoxy resin, PPO resin and fluorine-based resin. Epoxy resin is the cheapest, while fluorine-based resin is the most expensive. Considering the frequency characteristics, fluorine-based resins are the best, and epoxy resins are poor. When the frequency of product application is higher than 10GHz, only fluorine resin printed board can be applied. Obviously, the performance of fluorine-based resin high-frequency substrates is much higher than other substrates, but its disadvantages are poor rigidity and high thermal expansion coefficient in addition to high cost. For polytetrafluoroethylene (PTFE), in order to improve performance, a large number of inorganic substances (such as silica SiO2) or glass cloth are used as reinforcing filler materials to improve the rigidity of the substrate and reduce its thermal expansion. In addition, due to the molecular inertness of polytetrafluoroethylene resin itself, it is not easy to bond with copper foil, so special surface treatment of the bonding surface with copper foil is required. The treatment method includes chemical etching or plasma etching on the PTFE surface, increasing the surface roughness or adding an adhesive film layer between the copper foil and the PTFE resin to improve the bonding force, but it may affect the performance of the medium. Influence, the development of the entire fluorine-based high-frequency circuit substrate requires the cooperation of raw material suppliers, research units, equipment suppliers, PCB manufacturers and communication product manufacturers to keep up with the rapid development of high-frequency circuit boards. needs.

Read recommendations:

Single copper base PCB

Six-layer Immersion Gold Board (BGA)

DIP plugin

Six-layer Immersion Gold Board (BGA)

Where is the quality assurance of chip processing factories in PCBA processing and production?