PCB circuit board design principles and anti - jamming measures

PCB circuit board design principles and anti - jamming measures

Printed circuit board (PCB board) is the electronic components of the circuit components and devices. It also provides an electrical connection between the circuit element and the device. With the rapid development of electricity in the technology, PCB board density is getting higher and higher. PCB circuit board design has a great impact on the ability to interfere with interference. Therefore, in the PCB circuit board design. Must comply with the general principles of PCB design and should meet the requirements of anti-jamming design.

PCB board design of the general principles

The To make the best performance of electronic circuits, components and cloth layout and wiring is very important in order to design good quality, low cost PCB board should follow the following general principles:

1. layout

First, to consider the size of the PCB board size. PCB size is too large, the printed line length, impedance increases, anti-noise capacity decreased, the cost increases; too small, the heat is not good, and adjacent lines vulnerable to interference in determining the PCB size And then determine the location of special components. Finally, according to the functional unit of the circuit, all the components of the circuit layout.

The following principles apply when determining the location of special components:

(1) to minimize the connection between high-frequency components, try to reduce their distribution parameters and the mutual electromagnetic interference. The components that are susceptible to interference can not be too close to each other, and the input and output components should be kept as far away as possible.

(2) some components or wires may have a higher potential difference between, should increase the distance between them, so as not to lead to accidental short circuit discharge. Components with high voltage should be arranged as far as possible in the debugging hand difficult to reach the place.

(3) weighs more than 15 grams of components, should be fixed with a bracket, and then welding. Those large and heavy, more heat and more components, should not be installed on the printed circuit board, but should be installed in the machine chassis chassis, and should consider the cooling problem. The thermal element should be away from the heating element.

(4) For the potentiometer, adjustable inductance coil, variable capacitor, micro switch and other adjustable components of the layout should consider the structural requirements of the machine. If the machine is adjusted, it should be placed on the printed circuit board to facilitate the adjustment of the place; if the machine outside the adjustment, its position and adjust the knob on the chassis panel to adapt to the location.

(5) should be left out of the printing plate positioning holes and fixed stent occupied by the location.

The When the layout of all the components of the circuit is based on the functional unit of the circuit, the following principles apply:

(1) according to the circuit of the process of arranging the location of the various functional circuit unit, so that the layout of the signal flow, and the signal as much as possible to maintain a consistent direction.

(2) to each function circuit of the core components as the center, around it to the layout. Components should be even, neat and compactly arranged on the PCB. Minimize and shorten the lead and connection between the components.

(3) in the high frequency of the circuit, to consider the distribution of components between the parameters. The general circuit should arrange the components as parallel as possible. This is not only beautiful. And easy to install welding. Easy to mass production.

(4) at the edge of the circuit board components, from the edge of the circuit board is generally not less than 2 mm The best shape of the circuit board for the rectangular aspect ratio of 3: 2 into 4: 3 circuit board size greater than 200x150mm should consider the circuit board The mechanical strength of the machine.

2. Wiring

The principle of wiring is as follows:

(1) input and output conductors should be used to avoid adjacent parallel. The best line between the line, in order to avoid feedback coupling.

(2) The minimum width of the printed wire is mainly determined by the adhesion strength between the conductor and the insulating substrate and the current value flowing through them. When the thickness of the copper foil is 0.05 mm and the width is 1 to 15 mm. Through the current of 2A, the temperature will not be higher than 3 ℃, therefore. Wire width of 1.5 mm to meet the requirements. For integrated circuits, especially digital circuits, usually choose 0.02 ~ 0.3 mm wire width. Of course, as long as allowed, or as far as possible with wide lines. Especially the power cord and ground. The minimum spacing of the wires is mainly determined by the worst case insulation resistance and breakdown voltage. For integrated circuits, especially digital circuits, as long as the process allows, can make the pitch as small as 5 ~ 8 mm.

(3) printed wire bend generally take a circular arc, and the right angle or angle in the high-frequency circuit will affect the electrical performance. In addition, try to avoid using a large area of copper foil, otherwise. Long time heat, easy to occur copper foil expansion and shedding phenomenon. Must use a large area of copper foil, it is best to use grid-like. This will help to eliminate the copper foil and the substrate between the adhesive heat generated by the volatile gas.

Pad

The pad center hole is slightly larger than the device lead diameter. The pad is too easy to form a weld. The pad diameter D is generally not less than (D + 1.2) mm, where d is the lead aperture. For high-density digital circuits, the minimum diameter of the pad is desirable (D + 1.0) mm.

PCB and circuit anti - jamming measures

Printed circuit board anti-jamming design and specific circuit has a close relationship, here only on the PCB anti-jamming design of several commonly used measures to do some instructions.

1. Power cord design

According to the size of the printed circuit board current, as far as possible to add the power line width, reduce loop resistance. At the same time, the power line, ground direction and data transmission direction, which will help enhance the anti-noise ability.

2. Ground design

The principle of ground design is:

(1) numerically and analogously. If the circuit board has both logic and linear circuits, make them as close as possible. Low-frequency circuit to the ground should be used as a single point of parallel grounding, the actual wiring can be part of the difficulties in parallel and then grounded. High-frequency circuit should be used in multi-point series ground, the ground should be short and rent, high-frequency components around the grid as large as possible to foil a large area.

(2) grounding wire should be as thick as possible. If the ground wire with a very sewing line, the ground potential changes with the current changes, so that anti-noise performance. So the ground wire should be bolded so that it can pass three times the allowable current on the printed circuit board. If possible, the ground wire should be above 2 ~ 3mm.

(3) The ground wire forms a closed loop. Only by the digital circuit composed of printed circuit board, the grounding circuit cloth loop can improve the anti-noise ability.

3. Decoupling capacitor configuration

One of the conventional practices of PCB design is to configure the appropriate decoupling capacitors at each critical part of the PCB.

The general configuration principle of the decoupling capacitor is:

(1) The power input terminal is connected with 10 ~ 100uF electrolytic capacitor. If possible, then more than 100uF better.

(2) in principle, each integrated circuit chip should be arranged a 0.01pF ceramic capacitors, in case of PCB gap is not enough, can be arranged every 4 ~ 8 chip 1 ~ 10pF but the capacitor.

(3) for anti-noise ability is weak, turn off the power changes in the device, such as RAM, ROM memory devices, the chip should be directly connected between the power cord and ground decoupling capacitor.

(4) Capacitive lead can not be too long, especially high frequency bypass capacitor can not have lead.

In summary, want to make high-quality printed circuit board products, pre-PCB design wiring is very critical, know the PCB board some of the principles of the characteristics, to comply with the relevant PCB design specifications, will be able to create excellent high-grade PCB board.