How to draw a good multi-layer high-frequency board, the editor of Zhongke Circuit will share with you the wiring skills of the multi-layer high-frequency board, and I hope it will be helpful to you.

　　Multi-layer high-frequency boards often have high integration and high wiring density. The use of multi-layer circuit boards is not only necessary for wiring, but also an effective means to reduce interference. In the PCB Layout stage, the size of the printed board with a certain number of layers is reasonably selected, and the intermediate layer can be fully used to set the shielding, which can better achieve the nearest grounding, and effectively reduce the parasitic inductance and shorten the transmission length of the signal. All of these methods are beneficial to the reliability of high-frequency circuits.

　　When the same material is used, the noise of the four-layer circuit board is 20dB lower than that of the double-sided circuit board. However, at the same time, there is also a problem. The higher the number of layers of the PCB high-frequency board (multi-layer high-frequency board), the more complex the manufacturing process and the higher the unit cost. It is also necessary to carry out reasonable component layout planning and use correct wiring rules to complete the design.

　　1. The less the alternation between the lead layers between the pins of the high-frequency circuit device, the better

　　The so-called "the less the interlayer alternation of the leads, the better" means that the fewer vias used in the component connection process, the better. A via can bring about 0.5pF of distributed capacitance, and reducing the number of vias can significantly improve speed and reduce the possibility of data errors.

　　2. The shorter the lead between the pins of the high-frequency circuit device, the better

　　The radiation intensity of the signal is proportional to the trace length of the signal line. The longer the high-frequency signal lead is, the easier it is to couple to the components close to it. Therefore, for signals such as clocks, crystal oscillators, DDR data, High-frequency signal lines such as LVDS lines, USB lines, and HDMI lines are required to be as short as possible.

　　3. The less the leads are bent between the pins of high-speed electronic devices, the better

　　The leads of the high-frequency circuit wiring are preferably all straight lines, which need to be turned, and can be turned with a 45-degree folded line or an arc. This requirement is only used to improve the fixing strength of the copper foil in the low-frequency circuit, while in the high-frequency circuit, this requirement is met. A requirement can reduce the external emission and mutual coupling of high-frequency signals.

　　4. Pay attention to the "crosstalk" introduced by the parallel traces of the signal lines

　　In high-frequency circuit wiring, attention should be paid to the "crosstalk" introduced by the parallel wiring of signal lines in close proximity. Crosstalk refers to the coupling phenomenon between signal lines that are not directly connected. Since the high-frequency signal is transmitted along the transmission line in the form of electromagnetic waves, the signal line will act as an antenna, and the energy of the electromagnetic field will be emitted around the transmission line. called crosstalk. The parameters of the PCB board (multi-layer high-frequency board) layer, the spacing of the signal lines, the electrical characteristics of the driving end and the receiving end, and the termination method of the signal lines all have a certain influence on the crosstalk. Therefore, in order to reduce the crosstalk of high-frequency signals, it is required to do the following as much as possible when wiring:

　　①For the high-frequency signal clock, try to use the low-voltage differential clock signal and wrap the ground, and pay attention to the integrity of the ground punching;

　　②If parallel traces in the same layer are almost unavoidable, in two adjacent layers, the trace directions must be perpendicular to each other;

　　③ Under the condition that the wiring space allows, insert a ground wire or ground plane between the two lines with more serious crosstalk, which can play the role of isolation and reduce crosstalk;

　　④ Under the premise of the wiring space permit, increase the spacing between adjacent signal lines, reduce the parallel length of the signal lines, and try to make the clock line perpendicular to the key signal lines instead of parallel;

　　⑤ When there is a time-varying electromagnetic field in the space around the signal line, if parallel distribution cannot be avoided, a large area of "ground" can be arranged on the opposite side of the parallel signal line to greatly reduce the interference;

　　⑥In digital circuits, the usual clock signals are signals with fast edge changes, and the external crosstalk is large. Therefore, in the design, the clock line should be surrounded by ground wires and more ground wire holes should be made to reduce distributed capacitance and thus reduce crosstalk;

　　⑦ Do not suspend the unused input terminal, but ground it or connect it to the power supply (the power supply is also grounded in the high-frequency signal loop), because the dangling line may be equivalent to the transmitting antenna, and the grounding can suppress the emission. Practice has proved that eliminating crosstalk in this way can sometimes be effective immediately.

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