Microwave Tech - Talking about the parameters of high-frequency board and high-frequency circuit board

Talking about the parameters of high-frequency board and high-frequency circuit board

The high frequency of electronic equipment is a development trend, especially with 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 speed. Therefore. The development of new generation products all require 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 inevitably develop rapidly, and high-frequency substrates will be in large demand.

The basic characteristics of the substrate material of the high-frequency circuit board require the following points:

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 damp.

3. Try to be consistent with the thermal expansion coefficient of the copper foil, because the inconsistency will cause the copper foil to separate in the cold and heat 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 stable, usually the smaller the better. The signal transmission rate is inversely proportional to the square root of the material's dielectric constant. High dielectric constant is likely to cause signal transmission delay.

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

At the present stage, the three types of high-frequency substrate materials: epoxy resin, PPO resin and fluorine-based resin, epoxy resin is the cheapest, and fluorine-based resin is the most expensive; and it is based on dielectric constant, dielectric loss, and water absorption. Considering the frequency characteristics, fluorine resin is the best and epoxy resin is inferior. When the frequency of the product application is higher than 10GHz, only the fluorine-based resin printed board can be applied. Obviously, the performance of fluorine-based resin high-frequency substrates is much higher than other substrates, but its shortcomings are low rigidity and large thermal expansion coefficient in addition to high cost. For polytetrafluoroethylene (PTFE), in order to improve performance, a large amount of inorganic substances (such as silica SiO2) or glass cloth are used as reinforcing fillers to increase the rigidity of the substrate and reduce its thermal expansion. In addition, due to the molecular inertness of the PTFE resin itself, it is not easy to bond with the copper foil, so special surface treatment on the bonding surface of the copper foil is required. The treatment method includes chemical etching or plasma etching on the surface of PTFE to increase the surface roughness or add a layer of adhesive film between the copper foil and the PTFE resin to improve the bonding force, but it may affect the performance of the medium. The development of the entire fluorine-based high-frequency circuit board 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.