PCB Technical - What problems should be paid attention to when PCB board copper pours

What problems should be paid attention to when PCB board copper pours

The so-called copper pour is to use the unused space on the PCB as a reference surface and then fill it with solid copper. These copper areas are also called copper filling. 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. Everyone knows that at high frequencies, 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 clad in the PCB of the circuit board factory, the copper clad becomes a tool for noise transmission. Therefore, in a high-frequency circuit, do not think that the ground wire is connected to the ground. This is the "ground wire", which must be less than λ/20 to punch holes in the wiring to "good ground" with the ground plane of the multilayer circuit 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.

In copper coating, in order to achieve the desired effect of copper coating, those issues need to be paid attention to in copper coating:

1. If the PCB board has more grounds, such as SGND, AGND, GND, etc., according to the position of the PCB board, the most important "ground" is used as a reference to independently pour copper, digital ground and analog It is not too much to separate the ground and the copper pour. At the same time, before the copper pour, first thicken the corresponding power connection: 5.0V, 3.3V, etc., in this way, a plurality of different shapes of multi-deformation structures 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. The metal inside the device, such as metal radiators, metal reinforcement strips, etc., must be "good grounding".

4. The island (dead zone) problem, if you think it is too big, it won't cost much to define a ground via and add it in.

5. Do not pour copper in the open area of the middle layer of the multilayer circuit board. Because it is difficult for you to make this PCB board copper "good grounding".

6. The 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.

7. 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 adding via holes to eliminate the ground pins for the connection after the copper pour. This effect is very bad.

8. It is best not to have sharp corners on the PCB board (<=180 degrees), because from the perspective of electromagnetics, this constitutes a transmitting antenna! There will always be an impact on others, but it is large or It's only small, I recommend using the edge of the arc.

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 board is dealt with properly, it is definitely "pros outweigh the disadvantages". It can reduce the return area of the signal line and reduce the signal pair.
External electromagnetic interference.

In short: if the grounding problem of the copper on the PCB board is dealt with, it is definitely "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.