PCB Tech - Places to pay attention to when PCB copper pours

There are certain processes and precautions for the design and production of circuit boards. The copper coating of circuit boards is a crucial step in PCB design and has a certain technical content. So how to do the design work of this link, there are senior engineers Summarized a few experiences:

In the case of high frequency, the distributed capacitance of the wiring on the printed circuit board will play a role. 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. In the presence of poorly grounded copper clad, the copper clad becomes a tool for noise transmission. Therefore, in a high-frequency circuit, do not think that if you connect a ground wire to the ground, this is the "ground wire". With a pitch less than λ/20, punch holes in the wiring 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.

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 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, digital ground and analog ground. It is not much to say that the copper pour is separated. 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 multi-deformation structures of 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 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 crystal oscillator separately.

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. 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 pin for the connection after the copper pour. This effect is very bad.

6. It is best not to have sharp corners on the 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 big or small That's it, I recommend using the edge of the arc.

7. Do not pour copper in the open area of the middle layer of the multi-layer PCB board. Because it is difficult for you to make this copper clad "good ground".

8. The metal inside the equipment, 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 on the PCB 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.