PCB wiring skills
1. The edges of the input and output terminals shall be parallel to each other to avoid reflection disturbance. If necessary, ground wire shall be added for isolation, and the wiring of two adjacent layers shall be perpendicular to each other, parallel and simple to produce parasitic coupling.
2. Add coupling capacitance between power supply and ground wire. The width of power supply and ground wire shall be widened as much as possible. It is better that the ground wire is wider than the power line width. Their relationship is: ground wire > power line > signal line. Generally, the signal line width is 0.2 ~ 0.3mm, the thinnest width can reach 0.05 ~ 0.07mm, and the power line is 1.2 ~ 2.5mm
3. For the common ground processing of digital circuit and analog circuit, the frequency of digital circuit is high and the sensitivity of analog circuit is strong. For the signal line, the high-frequency signal line may be far away from the sensitive analog circuit equipment as far as possible. For the ground wire, the whole PCB has only one node to the outside, so the problem of digital and analog common ground must be handled inside the PCB, Inside the board, digital and analog are actually separated. They are not connected to each other, but at the interface between PCB and the outside world (such as plug, etc.). There is a short circuit between digital ground and analog ground. Please note that there is only one connection point. There are also those that do not share land on the PCB, which is determined by the system design.
4. Try to shorten the connection between high-frequency element devices as much as possible, and try to reduce their dispersion parameters and electromagnetic interference with each other. The easily disturbed components shall not be too close to each other, and the input and output components shall be as far away as possible. There may be a high potential difference between some components or wires, and the interval between them should be increased to avoid accidental short circuit caused by discharge. The component equipment with high voltage shall be placed in a place not easy to touch during commissioning.
5. For the circuit operating at high frequency, the dispersion parameters between components shall be considered. General circuits shall be placed in parallel as far as possible. In this way, it is not only beautiful, but also simple assembly and welding. It is easy to produce in batch.
6. The conductors used at the input and output terminals shall avoid adjacent parallel as far as possible. It is better to add ground wire between lines to avoid feedback coupling.
7. The bend of printed wire is generally circular arc, and the right angle or included angle will affect the electrical function in high-frequency circuit. If it is necessary to take a right angle, two 135 degree angles are generally selected to replace the right angle.
8. Power cord design
According to the current of the printed circuit board, increase the width of the power line as much as possible and reduce the loop resistance. At the same time, make the direction of power line and ground wire and the direction of data transmission common, which helps to enhance the anti noise ability.
9. Ground wire design
The principles of ground wire design are:
(1) Numbers are separated from imitations. If there are both logic circuits and linear circuits on the circuit board, they shall be separated as far as possible. Single point parallel grounding shall be selected as far as possible for the grounding of low-frequency circuit. If it is difficult to connect the actual wiring, it can be connected in series and then connected to the ground. Multi point series grounding should be selected for high-frequency circuit, the ground wire should be short and rented, and grid like large-area ground foil should be used around high-frequency components as far as possible.
(2) The grounding wire shall be as thick as possible. If the grounding wire is made of sewn wire, the grounding potential changes with the change of current, so that the anti noise function is reduced. Therefore, the grounding wire should be thickened so that it can pass three times the allowable current on the printed board. If possible, the grounding wire shall be more than 2 ~ 3mm.
(3) The grounding wire forms a closed loop. For printed boards only composed of digital circuits, the grounding circuit is arranged in a cluster loop, which can improve the anti noise ability.
10. Decoupling capacitor configuration
One of the conventional methods of PCB design is to configure appropriate decoupling capacitors at each key part of the PCB.
The general configuration principle of decoupling capacitor is:
(1) The power input terminal is connected with 10 ~ 100uF electrolytic capacitors. If possible, it is better to connect more than 100uF.
(2) In principle, each integrated circuit chip shall be equipped with a 0.01pf ceramic chip capacitor. In case of insufficient gap in the printed board, a 1 ~ 10PF capacitor can be installed for every 4 ~ 8 chips.
(3) For equipment with weak anti noise ability and large power change during shutdown, such as RAM and ROM storage equipment, decoupling capacitor shall be directly connected between the power line and ground wire of the chip.
(4) The capacitor lead shall not be too long, especially the high-frequency bypass capacitor shall not have lead.
11. In addition, the following two points should be noted:
(1) When there are touch devices, relays, buttons and other components in the printed board, large spark discharge will be generated when operating them. The RC circuit shown in the attached figure must be selected to absorb the discharge current. Generally, R is 1 ~ 2k and C is 2.2 ~ 47uF.
(2) The input impedance of CMOS is very high and easy to be induced, so it is not necessary to connect the terminal to ground or positive power supply during application
Wiring, welding skills and precautions of circuit board, PCB wiring skills
PCB wiring skills