In high-speed PCB design, layout is more important. Its rationality is directly related to subsequent wiring, signal transmission quality, EMI, EMC, ESD and other issues, which are related to the success or failure of product design. The specific steps can be done according to the initial layout and the detailed layout.
The work to be done in the initial layout is mainly to divide the principle into a reasonable area on the PCB board according to the function. First, the main component is placed in the corresponding area, and the heat dissipation problem should be considered in the process of placement. Gap, fan should pay attention to the direction of the wind, as much as possible let the wind blow to the heat-generating components and a larger range; and the weight of the entire PCB board should be balanced to avoid the PCB after the component Distorted deformation brings great hidden dangers to product quality; for structural restrictions, it is necessary to pay attention to the placement of fixed-position components, as well as the requirements of height-limiting areas and prohibited areas.
The detailed layout can be done as follows.
1. After the initial layout, the remaining components are placed in the area defined by the initial layout according to the function of each part of the circuit. The position of the components cannot be determined simply by the mouse line between the components on the PCB. Bypass capacitors, decoupling capacitors, storage capacitors, impedance matching resistors, and ESD components are required to make these components fully function.
2. Directional component can only be in two directions at most, and the non-directional component should be center-aligned in one row, which is convenient for production and aesthetics.
3. In addition to the height limit area, components with a certain height must also consider the insertion and removal of other connectors and the use of other peripherals.
4. Component should be placed at a certain distance, maintaining a distance of 120 mils from the edge of the board (this spacing can be adjusted according to the processing level of the processing plant; if the PCB itself has a process side, the spacing can be ignored), and the reverse side also has a patch. The PCB of the component, the chip component should be 80 mils away from the DIP component foot (this spacing can be adjusted according to the processing level of the processing plant), which is convenient for debugging, production and heat dissipation.
5. For high-sensitivity circuits and components to maintain a certain distance from other circuits, to avoid mutual interference, such as clock chips and related components, crystals, switching power supplies, inductors, etc.; and there should be enough between the components with large heat Space, easy to air circulation and can be covered with a large area of copper foil to dissipate heat.
6. Analog circuit and the digital circuit should be placed separately from each other and kept at a certain distance to avoid mutual interference; the relevant circuit of the I/O part should be placed close to the edge of the PCB to facilitate interference to leave the internal circuit of the PCB as soon as possible, and Filter and anti-ESD devices are placed around the I/O section circuitry to filter out interference from the interface and protect the circuitry within the PCB from electrostatic discharge.