General principles in PCB design

- Aug 11, 2016-

To get the best performance of electronic circuits, components and wire cloth and deployment is very important. In order to design good quality,

Low cost PCB. We should follow the following general principles:

1. Layout

First of all, to consider the PCB size. PCB size is too large, the printing of lines long, resistance increases, noise immunity

Decreased cost increases; too small, the heat is not good, and adjacent lines susceptible to interference. In determining the size of the PCB. Then indeed

Given special element position. Finally, the circuit according to the function unit, all the components of the circuit layout.

In determining the location of specific components To comply with the following principles:

(1) as short as possible connection between high-frequency components, try to reduce electromagnetic interference parameters and their distribution between each other.

Susceptible to interference components can not suffer too close to each other, the input and output components should be kept away.

(2) may have a higher potential difference between certain components or wires, should increase the distance between them, so as not to discharge lead

An accidental short circuit. With high voltage components should be arranged at the time of commissioning the reach of the hand.

(3) components weighing more than 15g should be secured by the bracket, and then welded. Those big, heavy, heat

Many components, not mounted on the PCB, and should be installed in the machine chassis backplane, and should consider the heat problem. Thermal yuan

Member away from the heating element.

Layout (4) for the potentiometer, adjustable inductors, variable capacitors, micro-switches and other adjustable components of the machine should be considered

Structural requirements. If the machine within the regulation, should be placed on top of the printed circuit board for easy adjustment of the place; if outside the machine to adjust its position to

And the position of the knob on the panel of the chassis to adapt.

(5) should stay out of the printing position of the positioning hole and pull the mounting bracket occupied.

According functional unit circuit. When all the components of the circuit layout, subject to the following principles:

(1) in accordance with the flow circuit arrangement positions of the respective functional circuit elements which enable easy layout of the flow of the signal, and the signal do

Possible to maintain the same direction.

(2) the core elements of each functional circuit as the center around which to lay. Component should be uniform, neat, tight

Minato arranged on the PCB. Minimize and shorten the lead and the connection between the various components.

(3) In the high frequency circuit, to consider the distribution parameter between components. General circuit components should as far as possible

Parallel. Thus, not only beautiful. And easy assembly and welding. Easy to mass production.

(4) located on the edge of the circuit board components, from the edge of the board is generally not less than 2mm. Best rectangular board shape

shape. Aspect ratio of 3: 2 to 4: 3. Circuit board size is larger than 200x150mm when. The board should consider suffered mechanical


2. wiring

Wiring principles are as follows;

(1) with input and output wire should be avoided adjacent parallel. Plus the best line between the ground, in order to avoid feedback coupling.

The minimum width (2) consists of a printed photo conductor adhesion strength between the wire and pull insulating substrate and a current value flowing through their decisions


When the foil thickness of 0.05mm, a width of 1 ~ 15mm when. 2A through current, temperature is not higher than 3 ℃, because

This wire width of 1.5mm can meet the requirements. For integrated circuits, especially digital circuits, generally 0.02 ~ 0.3mm derivative selected from

Line width. Of course, as long as the permit, or as much as possible with a wide line. Especially the power and ground.

The minimum spacing between wires is mainly determined by the worst-case line insulation resistance and breakdown voltage. For integrated circuits, in particular

Which is a digital circuit, as long as the process allows, can small spacing to 5 ~ 8mm.

(3) printed conductors and generally arc-shaped corner, and right-angle or angle in high-frequency circuits can affect electrical performance. In addition,

Try to avoid using a large area of copper foil, otherwise. When heated for a long time, easy expansion of the copper foil and shedding phenomenon. Must Omo

When the copper foil, preferably with a grid-like. This is conducive to exclude the volatile gas between the copper foil and the substrate adhesive heat generated.

3. Pad

Pad center hole diameter slightly larger than the device lead. Weld pad too easy to form. Pad diameter D is generally not small

In (d + 1.2) mm, where d is the pore diameter of the lead. High density digital circuits, the smallest diameter of the pad preferably (d + 1.0) mm

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