As vantagens da placa de alta frequência e dicas de designPostado em 15/07/2020
Sobre as vantagens e dicas de design da placa de alta frequência
O que é uma placa de alta frequência?
High-frequency board refers to a special circuit board with high electromagnetic frequency, which is used for PCB in the field of high frequency (frequency greater than 300MHZ or wavelength less than 1 meter) and microwave (frequency greater than 3GHZ or wavelength less than 0.1 meter). It is a circuit board produced on the microwave substrate copper-clad board using part of the process of the ordinary rigid circuit board manufacturing method or using a special processing method. Generally speaking, high-frequency boards can be defined as circuit boards with frequencies above 1 GHz.
With the rapid development of science and technology, more and more device designs are applied in the microwave frequency band (>1GHZ) and even in the field of millimeter wave (30GHZ). This also means that the frequency is getting higher and higher, and the requirements for the substrate of the circuit board are also getting higher and higher. For example, the substrate material needs to have excellent electrical properties and good chemical stability. With the increase of the power signal frequency, the loss on the substrate is very small, so the importance of high-frequency plates is highlighted.
- Mobile communication products.
- Power amplifier, low noise amplifier, etc.
- Passive devices such as power dividers, couplers, duplexers, filters, etc.
- Automotive anti-collision system, satellite system, radio system and other fields.
Advantages of high-frequency boards
The high-frequency board with induction heating technology has been widely used in the communication industry, network technology, and high-speed information processing systems to meet the requirements of many high-precision parameter instruments. The reliable high-frequency circuit board provides great help in actual production. So, what are the advantages of such a powerful high-frequency board?
- High efficiency
And the advanced induction heating technology can achieve the target heating demand, and the efficiency is very high. Of course, while paying attention to efficiency, it also has environmental protection characteristics, which is very suitable for the development direction of today’s society.
- High speed
The transmission speed is inversely proportional to the square root of the dielectric constant. This means that the smaller the dielectric constant, the faster the transmission speed. This is the advantage of high-frequency circuit boards. It uses special materials, which not only guarantees a small dielectric constant, but also maintains stable operation, which is very important for signal conduction.
- Great controllability
It is widely used in high-frequency circuit boards that require heat treatment of precision metal materials in various industries. In the process of its field, not only can the heating of parts of different depths be realized, but also the heating of the local characteristics can be focused on. Whether it is surface or deep, concentrated or decentralized heating, it can be easily done.
- Strong tolerance
The dielectric constant and medium have certain requirements on the environment. Especially in the south, wet weather will seriously affect the use of circuit boards. High-frequency circuit boards made of materials with extremely low water absorption can challenge such environments. At the same time, it also has the advantages of resistance to chemical corrosion, moisture resistance, high temperature resistance and great peel strength, so that high-frequency circuit boards play a powerful performance.
High-frequency board circuit board features
- Impedance control requirements are relatively strict, and relative line width control is very strict, with a general tolerance of about 2%.
- Due to the special plate, the adhesion of PTH when sinking copper is not high. Usually need to use plasma processing equipment, etc. to roughen the via and surface first, in order to increase the adhesion of PTH hole copper and solder resist ink.
- The board cannot be ground before solder masking, otherwise the adhesion will be very poor, and it can only be roughened with a micro-etching solution.
- Most of the plates are made of Teflon-like materials. There are many burrs formed by ordinary milling cutters, and special milling cutters are needed.
- High-frequency circuit boards are special circuit boards with high electromagnetic frequencies. Generally speaking, high-frequency circuit boards can be defined as frequencies above 1 GHz.
- Its physical performance, accuracy, and technical parameters are very high, and it is often used in automotive anti-collision systems, satellite systems, radio systems, and other fields.
High-frequency board design tips
- The corner of the transmission line should adopt a 45° angle to reduce the return loss.
- A high-performance dielectric circuit board with a strictly controlled dielectric layer value and a number of layers shall be used. This method is beneficial to the effective simulation calculation of the electromagnetic field between the insulating material and the adjacent wiring.
- O PCB design specifications related to high-precision etching shall be specified. The total error of line width should be considered as +/-0.0007 inches. Manage the undercut and cross section of the wiring shape and specify the wiring side plating conditions. Overall management of wiring (wire) geometry and coating surface. It is very important to solve the problem of skin effect related to microwave frequency and realize these specifications.
- Protruding pin leads have tapped inductance and parasitic effects. Avoid using leaded components. In high-frequency environments, it is best to use surface mount SMD components.
- For signal vias, avoid using via processing (pth) on sensitive boards. Because this process will cause lead inductance at the via. For example, when a through hole on a 20-layer board is used to connect 1 to 3 layers, there are 4 to 19 layers of lead inductance, and buried blind holes or back drilling should be used.
- Provide a rich ground plane. Use molded holes to connect these ground layers to prevent the influence of 3D electromagnetic fields on the circuit board.
- To choose electroless nickel plating or immersion gold plating process, do not use HASL method for electroplating. This plated surface can provide better effects for high-frequency currents. In addition, this highly solderable coating requires fewer leads, which helps reduce environmental pollution.
- The solder mask prevents the solder paste from flowing. However, due to the thickness uncertainty and the unknown dielectric constant performance, covering the entire board surface with solder resist material will cause circuit performance changes in the microstrip design. Solder dams are generally used as solder masks.
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