1、 General principles of design
In order to get the best performance of electronic circuit, the layout of components and wires is very important. In order to design a design with good quality and low cost, the following general principles should be followed:
First, consider the design size. When the design size is too large, the printed line is long, the impedance increases, the anti noise ability decreases, and the cost increases; If it is too small, the heat dissipation is not good, and the adjacent lines are vulnerable to interference. After the size is determined, the position of the special element is determined. Finally, according to the functional units of the circuit, all the components of the circuit are arranged.
When determining the location of special components, the following principles should be observed:
(1) Shorten the connection between high frequency components as much as possible, and try to reduce their distribution parameters and mutual electromagnetic interference. The easily disturbed design components should not be too close to each other, and the input and output components should be far away from each other as far as possible.
(2) There may be high potential difference between some components or wires, so the distance between them should be increased to avoid accidental short circuit caused by discharge. The design components with high voltage should be arranged in the place that is not easy to reach when debugging.
(3) Components weighing more than 15g should be fixed with bracket and then welded. Those large, heavy and calorific components should not be installed on the printed circuit board, but on the chassis of the whole machine, and the problem of heat dissipation should be considered. The thermal element should be far away from the heating element design.
(4) For the layout of potentiometer, adjustable inductance coil, variable capacitor, micro switch and other adjustable elements, the structural requirements of the whole machine should be considered. If it is adjusted in the machine, it should be placed in a place convenient for adjustment on the printed circuit board design; In case of external adjustment, the position of the adjustment knob should match the position of the adjustment knob on the chassis panel.
(5) The design position occupied by PCB positioning hole and fixing bracket shall be reserved.
According to the functional unit of the circuit. The layout of all components of the circuit shall comply with the following principles:
(1) The position of each functional circuit unit is arranged according to the circuit flow, so that the layout is convenient for signal flow, and the signal keeps the same direction as far as possible.
(2) The core component of each functional circuit is taken as the center, and the layout is carried out around it. The components shall be evenly, neatly and compactly arranged on the surface. Minimize and shorten the lead and connection between components.
(3) The distribution parameters between components should be considered when the circuit works at high frequency. In general, components should be arranged in parallel as far as possible. In this way, it is not only beautiful, but also easy to assemble and weld, and easy to mass produce.
(4) The distance between the components located at the edge of the circuit board and the edge of the circuit board is generally not less than 2mm. The best shape of circuit board is rectangle. The ratio of length to width is 3:2 or 4:3. The size of circuit board is larger than 200 × When it is 150 mm, the mechanical strength of the circuit board shall be considered.