The significance of pouring copper is to reduce the impedance of the ground wire, improve the anti-interference ability; reduce the voltage drop, improve the power supply efficiency; connect with the ground wire, and reduce the loop area. Also for the purpose of keeping the PCB from deforming as much as possible during soldering, most PCB manufacturers will also require PCB circuit board designers to fill copper or grid-like ground wires in the open area of the PCB circuit board.
We all know that in the case of high frequency, the distributed capacitance of the wiring on the printed circuit board will work. When the length is greater than 1/20 of the corresponding wavelength of the noise frequency, an antenna effect will occur, and the noise will be emitted through the wiring. . If there is a poorly grounded copper pour in the PCB, the copper pour becomes a vehicle for noise transmission.
Therefore, in high-frequency circuits, don't think that connecting a certain part of the ground wire to the ground is the "ground wire". Be sure to punch holes in the wiring with a spacing of less than N/20, and "good ground" with the ground plane of the multilayer board. If the copper cladding is handled properly, the copper cladding can not only increase the current, but also play a dual role of shielding interference.
There are generally two basic methods for pouring copper, that is, large-area copper pouring and grid copper. People often ask whether it is better to pour copper on a large area or to pour copper on a grid. It's not good to generalize!
A large area of copper clad has the dual functions of increasing current and shielding, but if a large area of copper clad is subjected to wave soldering, the board may warp or even bubble. Therefore, for large-area copper cladding, several slots are generally opened to alleviate copper foil blistering.
The pure grid copper is mainly shielding, and the effect of increasing the current is reduced. From the perspective of heat dissipation, the grid is beneficial (it reduces the heating surface of copper) and plays a certain role in electromagnetic shielding.
But it should be pointed out that the grid is composed of traces in staggered directions. We know that for a circuit, the width of the trace has its corresponding "electrical length" for the operating frequency of the circuit board (the actual size is divided by The digital frequency corresponding to the working frequency can be obtained, see related books for details), when the working frequency is not very high, perhaps the effect of the grid line is not very obvious, once the electrical length matches the working frequency, it is very bad, you will It was found that the circuit was not working properly at all, and signals were being emitted everywhere that interfered with the system's operation. So for colleagues who use grid copper pouring, my suggestion is to choose according to the working conditions of the designed circuit board.
Therefore, high-frequency circuits with high anti-interference requirements use grid copper, and low-frequency circuits with large currents often use complete copper.
Then in the copper pouring, in order to make the copper pouring achieve our expected effect, what issues need to be paid attention to in the copper pouring:
1. If there are many grounds on the PCB circuit board, such as SGND, AGND, GND, etc., according to the position of the PCB board, the main "ground" should be used as the reference for independent copper pouring, and the digital ground and ground should be separated. To pour copper. At the same time, before pouring copper, first thicken the corresponding power connection: 5.0V, 3.3V, etc. In this way, multiple deformable structures of different shapes are formed.
2. For the single-point connection of different grounds, the method is to connect through a 0 ohm resistor or a magnetic bead or an inductance.
3. Do not cover the open area of the wiring in the middle layer of the PCB multilayer circuit board with copper. Because it is more difficult for you to make this copper pour "good ground".
4. The island (dead zone) problem, if you think it is too big, it will not take much to define a ground via and add it.
5. The metal inside the equipment, such as metal radiators, metal reinforcement strips, etc., must be "good grounded".
6. The heat dissipation metal block of the three-terminal regulator must be well grounded. The ground isolation zone near the crystal oscillator must be well grounded.
7. Copper pour near the crystal oscillator. The crystal oscillator in the circuit is a high-frequency emission source. The method is to pour copper around the crystal oscillator, and then ground the shell of the crystal oscillator separately.
8. Try not to have sharp corners on the circuit board, because from an electromagnetic point of view, this constitutes a transmitting antenna, and it is recommended to use arc edge lines.
9. At the beginning of wiring, the ground wires should be treated equally, and the ground wires should be routed well when wiring. You cannot rely on adding vias after pouring copper to eliminate the connected ground pins. This effect is not good.
In short: if the grounding problem of the copper clad on the PCB circuit board is handled well, it must be "better than harm". It can reduce the return area of the signal line and reduce the electromagnetic interference of the signal to the outside.
