Component layout and wiring
3.2.5 layout and wiring of components
It is the first step to design the printed circuit board by placing the electronic device and its connection on a certain panel area, which determines the neat appearance of the board and the length and quantity of the printed wire, and also affects the performance of the whole machine to a certain extent. The size of the PCB must be considered first before considering the layout of the components. When the size of PCB is too large, the length of printed circuit, the increase of resistance, the decrease of noise capacity and the increase of cost, the heat dissipation is not good, and the adjacent lines are liable to be interfered.
After determining the PCB size, determine the location of the special components.
Because of its own characteristics, the printed circuit board, such as the printed wire is plane arrangement, the single side printed board lead can not cross each other, copper box anti-stripping strength is low contact point should not be welded more than once, should not use a point of grounding, etc. The layout and wiring of components on printed circuit board also have many unique features.
1. Irregular arrangement of components
The irregular arrangement of components is shown in Fig. 3.2.7. This arrangement is mainly vertical installation. According to the nearest layout of electrical connection of the circuit, the axis direction of the components is not consistent with each other, and there are no certain rules in the arrangement on the board. It seems disorderly, but the printed wire is convenient to be arranged, the printed wire is short and few. It can reduce the distribution parameter of the circuit board, and the interference between the circuits is less. Especially, it is advantageous to resist the high frequency interference above 30MHz.
2) regular arrangement
The regular arrangement of components is shown in Fig. 3.2.8. This arrangement is mainly horizontal installation. The direction of the axis of the components is perpendicular to or parallel to the four sides of the board, and the arrangement is standard and tidy for mechanized drilling and assembly. However, due to the limitation of direction and position, routing is more complicated. This arrangement is suitable for low frequency circuits and low voltage circuits below 1MHz.
To sum up, the components should be arranged evenly and neatly on the printed circuit board, the printed wires should be as short as possible, and the two arrangement formats of the components can be used separately or simultaneously on the printed circuit board in combination with the actual situation.
2. Layout principle of components
Taking single-sided printed circuit board as an example, this paper introduces the problems to be considered in the layout of components.
Normally, all components should be arranged on one side of the printed circuit board, with each component pin list A solder pad for the sole use, and should "
When printing a limited number without a device
Work, install and maintain.
The tree on the surface of the specification, nameplate, for easy inspection of the
No device on the surface of the board.
Line length and assembly of components
Even density. In
The state circuit schematic diagram is sequentially arranged in a straight line, compacted to make up the printed guide
Arrangement, parallel or heavy to the edge of the printed board, with water
Self-lifting to meet electrical requirements. Elements should be parallel to each other
To overlap, structural parts should be used to fix.
The ruler is neat and beautiful,
Shall not superimpose components, if required
Neat and beautiful.
This will not only facilitate processing, installation and maintenance, but also maintain the appearance of
3) if due to the south limit of the plate, it is not possible to
Installation of all electronic components on a printed board, or out of screen
The whole machine must be divided into several printed marks
Function to adjust maintenance and repair separately.
The board shall be installed so that each printed circuit assembled shall form an independent one.
When the components are arranged on the printed circuit board,
Be careful not to have components all over the board. Leave one around the edge of the board
Fixed space. Big empty
Small according to printed electricity
The area of the road plate and the way it is fixed are located on the edge of the printed circuit board
At least 2m electricity shall be greater than the edge of the received edge of the printed circuit at least 2 m from the printed circuit within the printed circuit,
Each side has 5 ~ 10mm space.
5) the position of the device-free placement should avoid the mutual influence, do not cross up and down and recuperate the arrangement. The adjacent components should be protected from each other
Hold the distance. The distance should not be too small to avoid the element for mutual contact. If the potential difference between adjacent components is high, the
At least leave the 200V/mm safe voltage gap.
The mounting height of components is as low as possible, and the opening surface of components and lead wires should not exceed Smms, so as to improve
Stability and preventing adjacent components from colliding. The span of the pad at both ends of the component should be slightly larger than the axial size of the component, with curved feet
A distance should be set aside to prevent zigan bending from damaging components.
The layout of adjustable elements such as potentiometer, adjustable inductance coil variable capacitor, fretting switch and so on should be considered.
Machine structure requirements. For heavy and large components, such as transformers, choke coils, large capacitors, relays, etc., as far as possible
To place on a printed board near the fixed end and lower the center of gravity.
