The circuit board is the support part of the circuit elements and devices in the electronic product. Even if the circuit schematic design is correct and the printed circuit board is not designed properly, the reliability of electronic products will have an adverse effect. In the design of printed circuit board, we should pay attention to the correct method, comply with the general principles of PCB design, and should meet the requirements of anti-interference design.
The general principles of PCB design
To make the electronic circuit get the best performance, the layout of the components and the layout of the wire is very important. In order to design PCB with good quality and low cost, the following general principles should be followed:
First, the size of the PCB should be considered. When the size of PCB is too large, the printing line is long, the impedance increases, the noise reduction ability is reduced, and the cost is increased. Too small is not good enough for heat dissipation, and the adjacent lines are easily disturbed. After determining the size of the PCB, the position of the special element is determined. Finally, according to the function unit of the circuit, all the components of the circuit are laid out.
The following principles should be observed in determining the position of a special element:
As far as possible, the connection between high frequency components is reduced, and their distribution parameters and mutual electromagnetic interference can be reduced. The interfered components cannot be too close to each other, and the input and output components should be as far away as possible.
There may be a high potential difference between some components or wires, and the distance between them should be increased so as not to lead to an accidental short circuit. High voltage components should be arranged as far as the hand is not easy to touch.
The components weighing more than 15g should be fixed with the support and then welded. The large, heavy, and more calorific components, should not be installed on the printed board, but should be installed on the chassis of the whole machine, and the heat dissipation should be considered. The thermosensitive element should be far away from the heating element.
The layout of adjustable components, such as potentiometers, adjustable inductor coils, variable capacitors and microswitches, should be considered. If the machine is adjusted, it should be placed on the PCB to adjust conveniently. If it is adjusted outside the machine, its position should be adjusted to the position of the adjusting knob on the chassis panel.
The position of the positioning hole of the printed board and the fixed support should be left out.
The PCB layout of the components of the circuit should meet the requirements of anti-interference design.
The position of each functional circuit unit is arranged according to the flow of the circuit, so that the layout is convenient for the circulation of the signal and the signal is kept in the same direction as far as possible.
The core of each functional circuit is centered around it and is arranged around it. The components should be evenly, neatly and compactly arranged on the PCB. As far as possible to reduce and shorten the lead and connection between the components.
In the circuit working at high frequency, the distribution parameters between the components should be considered. The general circuit should be arranged in parallel as far as possible. In this way, it is not only beautiful, but also easy to install and welding, and easy to produce in batch.
The components on the edge of the circuit board are generally not less than 2mm on the edge of the circuit board. The best shape of a circuit board is a rectangle. The length and width of both are 3:2 or 4:3. When the size of the circuit board is larger than 200 * 150mm, the mechanical strength of the circuit board should be considered.