Circuit boards play an important role in optimizing the layout of electrical appliances for fixed circuits. What about high-frequency circuits and how are the advantages of high-frequency circuit boards made?
The circuit board is mainly composed of pads, Vias, mounting holes, wires, components, connectors, filling, electrical boundaries, etc. The main functions of each component are as follows: Pads: metal holes for soldering component pins.
Vias: There are metal vias and non-metal vias, wherein the metal vias are used to connect the component pins between the layers.
Mounting hole: used to fix the circuit board.
Wire: Electrical network copper film used to connect component pins.
Connector: components used for connection between circuit boards.
Filling: copper coating for ground wire network can effectively reduce impedance.
Electrical boundary: used to determine the size of the circuit board. All components on the circuit board cannot exceed this boundary.
In the design of high frequency circuits, the power supply is designed in the form of layers, which is much better in most cases than in the form of buses, so that the circuit can always follow the path with the least impedance.
In addition, the Power board has to provide a signal loop for all generated and received signals on the PCB, which can minimize the signal loop and thus reduce noise, which is often ignored by low-frequency circuit designers.
In the design of high frequency PCB, we should follow the following principles: the unification and stability of power supply and ground.
Careful consideration of wiring and proper termination can eliminate reflection.
Carefully considered wiring and appropriate terminations can reduce capacitive and inductive crosstalk.
Noise suppression is required to meet EMC requirements. 1. Dielectric loss (Df)
It must be small, which mainly affects the quality of signal transmission. The smaller the dielectric loss, the smaller the signal loss. 2.
Low water absorption and high water absorption will affect the dielectric constant and dielectric loss when affected with damp. 3. Dielectric constant (DK)
It must be small and stable. Usually, the smaller 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 is easy to cause signal transmission delay. 4.
The thermal expansion coefficient with copper foil is as consistent as possible, because inconsistency will cause copper foil separation in cold and hot changes. 5.
Other heat resistance, chemical resistance, impact strength, peel strength, etc. must also be good.
In general, high frequency can be defined as a frequency above 1 GHz.
At present, the high frequency commonly used is fluorine medium substrate, such as PTFE (PTFE)Usually called Teflon.
1. Impedance control requirements are relatively strict, and relative line width control is very strict, with a general tolerance of about 2%.
2. Due to the special plate, the adhesion of PTH during copper deposition is not high. It is usually necessary to roughen the vias and surfaces with the help of plasma treatment equipment, in order to increase the adhesion of PTH hole copper and solder resist ink.
3. The plate cannot be grinded before solder resist, otherwise the adhesion will be very poor, and only micro-etching liquid medicine can be used for roughening.
4. Most of the plates are polytetrafluoroethylene materials. There will be many burrs when forming with ordinary milling cutters, and special milling cutters are required.
5. High frequency circuit board is a special circuit board with high electromagnetic frequency. Generally speaking, high frequency can be defined as a frequency above 1 GHz.
Its physical properties, precision and technical parameters are very high, and are commonly used in the fields of automobile anti-collision systems, satellite systems, radio systems, etc.
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