First, consider the size of the PCB. If the PCB size is too large, the printed lines will be long, the impedance will increase, the anti-noise capability will decrease, and the cost will also increase; if the PCB size is too small, the heat dissipation will be poor, and the adjacent lines will be easily interfered. After determining the size of the PCB, determine the location of special components. Finally, according to the functional units of the circuit, all components of the circuit are laid out.

Observe the following guidelines when locating special components:

① Shorten the connection between high-frequency components as much as possible, and try to reduce their distribution parameters and mutual electromagnetic interference. Components that are susceptible to interference should not be too close to each other, and input and output components should be kept as far apart as possible.

②There may be a high potential difference between some components or wires, and the distance between them should be increased to avoid accidental short circuit caused by discharge. Components with high voltage should be arranged as far as possible in places that are not easily accessible by hand during debugging.

③ Components weighing more than 15 g should be fixed with brackets and then welded. Those components that are large, heavy and generate a lot of heat should not be installed on the printed board, but should be installed on the chassis bottom plate of the whole machine, and the heat dissipation problem should be considered. Thermal elements should be kept away from heating elements.

④ For the layout of adjustable components such as potentiometers, adjustable inductance coils, variable capacitors, and micro switches, 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 where it is convenient for adjustment; if it is adjusted outside the machine, its position should be adapted to the position of the adjustment knob on the chassis panel.

According to the functional unit of the circuit, when laying out all the components of the circuit, the following principles should be followed:

① Arrange the positions of each functional circuit unit according to the circuit flow, so that the layout is convenient for signal circulation, and the signals are kept in the same direction as possible.

②The core component of each functional circuit is the center, and the layout is carried out around it. Components should be evenly, neatly and compactly pulled on the PCB to minimize and shorten the leads and connections between components.

③ For circuits that work at high frequencies, the distribution parameters between components should be considered. In general circuits, the components should be arranged in parallel as much as possible. In this way, it is not only beautiful, but also easy to install and weld, and easy to mass produce.

④ Components located at the edge of the circuit board are generally not less than 2 mm away from the edge of the circuit board. The optimal shape of the circuit board is a rectangle. The aspect ratio is 3:2 or 4:3. When the size of the circuit board surface is larger than 200 mm✖150 mm, the mechanical strength of the circuit board should be considered.