General principles of PCB design (layout)

General principles of PCB design

In order to obtain the best performance of electronic circuits, the layout of components and wires is very important. In order to design PCB with good quality and low cost, the following general principles shall be followed:

1. Layout

First, consider the PCB size. When the PCB 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 poor, and the adjacent lines are easy to be disturbed. After determining the PCB size, determine the position of special components. Finally, all components of the circuit are arranged according to the functional units of the circuit.

The following principles shall be observed when determining the position of special elements:

(1) Shorten the wiring between high-frequency components as much as possible, and try to reduce their distribution parameters and mutual electromagnetic interference. Components susceptible to interference shall not be too close to each other, and input and output components shall be as far away 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. Components with high voltage shall be arranged in places not easy to touch during commissioning.

(3) Components weighing more than 15g shall be fixed with brackets and then welded. Those large, heavy and heat generating components should not be installed on the printed board, but on the chassis bottom plate of the whole machine, and the heat dissipation should be considered. The thermal element shall be far away from the heating element.

(4) For the layout of potentiometer, adjustable inductance coil, variable capacitor, microswitch and other adjustable elements, the structural requirements of the whole machine shall be considered. If it is adjusted in the machine, it should be placed above the printed board for easy adjustment; If it is adjusted outside the machine, its position shall adapt to the position of the adjustment knob on the chassis panel.

(5) The position occupied by the positioning hole of the printed plate and the fixed support 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) Arrange the position of each functional circuit unit according to the circuit flow, make the layout convenient for signal flow, and keep the signal in the same direction as far as possible.

(2) Take the core components of each functional circuit as the center and layout around it. The components shall be evenly, neatly and compactly arranged on the PCB. The leads and connections between components shall be reduced and shortened as far as possible.

(3) For the circuit working at high frequency, the distribution parameters between components should be considered. For general circuits, components shall 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) Components located at the edge of the circuit board are generally not less than 2mm away from the edge of the circuit board. The best shape of the circuit board is rectangle. The aspect ratio is 3:2 to 4:3. When the surface size of the circuit board is greater than 200x150mm, the mechanical strength of the circuit board shall be considered.

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