First, consider the PCB size. When the PCB size is too large, the printed lines are long, the impedance is increased, the anti-noise ability is lowered, and the cost is also increased; if the size is too small, the heat dissipation is not good, and adjacent lines are susceptible to interference. After determining the PCB size, determine the location of the particular component. Finally, according to the functional unit of the circuit, all the components of the circuit are laid out.
Observe the following principles when determining the location of a particular component:
1. Minimize the wiring between high-frequency components and try to reduce their distribution parameters and mutual electromagnetic interference. Components that are susceptible to interference cannot be placed too close together, and input and output components should be kept as far away as possible.
2. Some components or wires may have a high potential difference, and the distance between them should be increased to avoid accidental short circuit caused by discharge. Components with high voltage should be placed as far as possible in the hands of the hand when debugging.
3. Components weighing more than 15g should be fixed with brackets and then soldered. Those components that are large, heavy, and have a lot of heat should not be mounted on the printed board, but should be installed on the chassis of the whole machine, and heat dissipation should be considered. The thermal element should be kept away from the heating element.
4. For the layout of adjustable components such as potentiometers, adjustable inductors, variable capacitors, microswitches, etc., the structural requirements of the whole machine should be considered. If it is adjusted inside the machine, it should be placed on the printed board for easy adjustment; if it is adjusted outside the machine, its position should be adapted to the position of the adjustment knob on the chassis panel.
5. Should leave the position occupied by the positioning holes of the printed board and the fixed bracket.
When PCB layout of circuit components, it must meet the requirements of anti-interference design:
1. Arrange the position of each functional circuit unit according to the flow of the circuit, so that the layout facilitates signal circulation and keeps the signal as consistent as possible.
2. Center around the core components of each functional circuit and arrange it around it. Components should be arranged evenly, neatly and compactly on the PCB. Minimize and shorten leads and connections between components.
3. Circuits operating at high frequencies should consider the distribution parameters between components. In general, the circuit should be arranged in parallel as much as possible. In this way, it is not only beautiful, but also easy to load and weld, and easy to mass produce.
4. Components located at the edge of the board are generally not less than 2mm from the edge of the board. The optimal shape of the board is a rectangle. The length and width are 3:2 or 4:3. When the board surface size is larger than 200×150mm, the mechanical strength of the board should be considered.
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