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Copper pour is an important part of PCB design. The so-called copper pour is to use the unused space on the PCB as a reference surface and fill it with solid copper. These copper areas are also called copper pour.
The significance of copper coating is to reduce the impedance of the ground wire and improve the anti-interference ability; reduce the voltage drop and improve the efficiency of the power supply; connecting with the ground wire can also reduce the loop area. Also for the purpose of making the PCB as undistorted as possible during soldering, most PCB manufacturers also require PCB designers to fill the open areas of the PCB with copper or grid-like ground wires.
Everyone knows that in high frequency situations, 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 noise propagation tool.
Therefore, in the high-frequency circuit board circuit, do not think that the ground wire is connected to the ground. This is the "ground wire". Be sure to punch holes in the wiring with a spacing of less than λ/20 to "good ground" with the ground plane of the multilayer board. If the copper coating is handled properly, the copper coating not only increases the current, but also plays a dual role of shielding interference.
There are generally two basic methods of copper pour, which are large-area copper pour and grid copper. It is often asked whether large-area copper pour is better or grid copper pour is better. It's not easy to generalize!
Large-area copper coating has the dual functions of increasing current and shielding. However, if large-area copper coating is used for wave soldering, the board may lift up and even blisters. Therefore, for large-area copper coating, several grooves are usually opened to relieve the blistering of the copper foil.
The pure copper-clad grid is mainly used for shielding, and the effect of increasing the current is reduced. From the perspective of heat dissipation, the grid is good (it reduces the heating surface of the copper) and plays a role of electromagnetic shielding to a certain extent.
Therefore, high-frequency circuits have high requirements for anti-interference and multi-purpose grid copper, and low-frequency circuits with large currents usually use complete copper.
In copper coating, in order to achieve the desired effect of copper coating, what issues need to be paid attention to in copper coating:
1. If the PCB has many grounds, such as SGND, AGND, GND, etc., according to the position of the PCB board, the main "ground" is used as a reference to independently pour copper, and the digital ground and analog ground are covered separately. copper. At the same time, before pour copper, thicken the corresponding power connection: 5.0V, 3.3V, etc. In this way, multiple deformable structures with different shapes are formed.
2. For single-point connections to different grounds, the method is to connect through 0 ohm resistors or magnetic beads or inductance
3. Copper coating 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.
4. The island (dead zone) problem, if you think it's big, it won't cost much to define a ground via and add it in.
5. At the beginning of the wiring, the ground wire should be treated the same. When routing the ground wire, the ground wire should be routed well. You cannot rely on the copper pour to eliminate the ground pin for the connection by adding vias. This effect is not good.
6. Try not to have sharp corners on the board, because from the perspective of electromagnetics, this constitutes a transmitting antenna, and it is recommended to use the arc edge line.
7. Do not pour copper in the open area of the middle layer of the multilayer board. Because it is more difficult for you to make this copper clad "good ground".
8. The metal inside the device, such as metal radiators, metal reinforcement strips, etc., must be "good grounding".
9. The heat dissipation metal block of the three-terminal regulator must be well grounded. The ground isolation strip near the crystal oscillator must be well grounded.
In short: if the grounding problem of the copper pour on the PCB is dealt with, it must be "pros outweigh the disadvantages". It can reduce the return area of the signal line and reduce the electromagnetic interference of the signal to the outside.
