Effective application of multilayer circuit board for PCB routing
In the whole process of PCB design, most of the technical engineers choose to use multi-layer circuit board to route high-speed signal board. Such multi-layer circuit board is an indispensable component and a reasonable way to help the technical engineers reduce the impact of power circuit. When using multilayer circuit board to design high speed signal circuit of PCB, the technical engineer must effectively select the number of layers to reduce the size of circuit board, make full use of the inner layer to set the shielding off, keep the nearest grounding device, reasonably reduce the internal parasitic inductor, reduce the length of signal transmission, and reduce the cross influence between signals. All of these methods have an impact on high speed power circuit The credibility of the work is very useful.In addition to the above mentioned ways to improve the reliability of PCB signal transmission by using multi-layer circuit board, there are also some authoritative data to display information. For the same raw material, the noise of four-layer board is 20 dB lower than that of double-sided circuit board. The lower the bending of the conductor, the higher it is. It is better to select the full parallel line. The turning point must be 45 degree curve or arc turning point, which can reduce the coupling between the high-speed signal open to the outside world and the radiation source and reflection surface of the signal.
The less wires between pins of components in high speed power supply circuit, the higher.
In the whole process of PCB high-speed signal power circuit design and wiring, the technical engineer must try to reduce the lead in the middle of the pin of high-speed power circuit components. It is believed that the longer the lead, the greater the value of all over inductors and contact resistance, which will cause reflection surface and vibration of high-speed electric control system.In addition to minimizing the wires in the middle of the pins of high-speed power circuit components, in the whole process of PCB wiring, the lower the virtual beam replacement between the pins of each high-speed power circuit component, the higher, that is to say, the lower the commonly used pad in the whole process of component connection, the higher. Generally speaking, a pad can produce a contact resistance of about 0.5pf, which will cause the tinning time of the power circuit to rise continuously. In addition, attention should be paid to the "cross influence" introduced by the short distance parallel plane wiring of the signal line in the high-speed power circuit routing. If the parallel plane cannot be prevented from spreading, large-scale "ground" can be arranged on the back of the parallel plane signal line to reduce the influence. In the two adjacent layers, the direction of wiring shall be named as mutually vertical.
For very critical signal wires, some modules shall be surrounded by ground wires.
In the whole process of PCB routing design, technical engineers can select the way surrounded by ground wires for some very critical signal wires. In addition to the signal wiring that is not easily affected, such as clock signal and high-speed simulation analog signal, the ground wire that is maintained in the field can be added, that is, the signal wire to be maintained is clamped in the middle. Because in the whole process of the design, all kinds of signal wiring can not generate loop, the same ground wire can not generate current loop. If the loop power circuit is caused, it will have a great impact on the system software. Selecting the way that the ground wire surrounds the signal line can reasonably prevent the loop from occurring during the line routing. One or more high frequency decoupling capacitors should be set around each IC chip. High frequency choke is used to connect analog ground wire and large digital ground wire to common ground wire. Some high-speed signal lines should be solved in a unique way: the differential signal signal is specified to be wired on the same layer and close to the parallel plane as much as possible, and it is not allowed to insert all signals in the middle of the differential signal line, and the same length is specified.In addition to several design schemes mentioned above, when developing PCB signal line routing design scheme, technical engineers should also try to reduce the branch or stump of high-speed signal line routing. High frequency signal line is very easy to cause large electromagnetic wave radiation on the surface. If the high frequency signal line is placed between the switching power supply and the grounding wire, the radiation source will be reduced a lot according to the digestion and absorption of the radio wave by the switching power supply and the bottom layer.
