PCB Tech - Introduction to some advantages and disadvantages of PCB circuit board copper

Introduction to some advantages and disadvantages of PCB circuit board copper

The so-called copper pour is to use the unused space on the PCB circuit board as the 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.

Copper-clad is an important part of PCB circuit board design. Whether it is the domestic Qingyuefeng PCB design software, some foreign Protel, PowerPCB provide intelligent copper-clad function, then how to apply copper, I will have some ideas on my own Share with everyone, hoping to bring benefits to colleagues.

The so-called copper pour is to use the unused space on the PCB circuit board as the 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. Also for the purpose of making the PCB circuit board as non-deformed as possible when soldering, most PCB manufacturers will also require PCB circuit board designers to fill the open area of the PCB circuit board with copper or grid-like ground wires. Inappropriate handling, there will be no reward or loss. Is the copper coating "more advantages than disadvantages" or "disadvantages than advantages"?

Everyone knows that under high frequency conditions, 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 circuit board, the copper pour becomes a tool for spreading noise. Therefore, in a high-frequency circuit, do not think that the ground wire is connected to the ground. This is "Ground wire", must be less than λ/20, punch holes in the wiring, and "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 for copper coating, namely large-area copper coating and grid copper. It is often asked whether large-area copper coating is better than grid copper coating. It is not good to generalize. why? 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 circuit board may be uplifted or even blistered. Therefore, for large-area copper coating, several grooves are generally used to alleviate the blistering of the copper foil. The pure mesh copper coating is mainly used for shielding, and the effect of increasing the current is reduced. From the perspective of heat dissipation, the mesh is beneficial (It lowers the heating surface of the copper) and plays a role of electromagnetic shielding to a certain extent. But it should be pointed out that the grid is made up of traces in staggered directions. We know that for the circuit, the width of the trace has a corresponding "electrical length" for the operating frequency of the circuit board (the actual size is divided by the actual size). The digital frequency corresponding to the working frequency is available, see related books for details). When the working frequency is not very high, perhaps the role of the grid line is not very obvious. Once the electrical length matches the working frequency, it will be very bad. You will find that the circuit does not work properly at all, and signals that interfere with the operation of the system are being emitted everywhere. So for colleagues who use grids, my suggestion is to choose according to the working conditions of the designed circuit board, and don't cling to one thing. Therefore, high-frequency circuits have high requirements for multi-purpose grids for anti-interference, and low-frequency circuits have circuits with large currents, such as commonly used complete copper.

Having said so much, then we are in the copper pour, in order to make the copper pour achieve our expected effect, then the copper pour needs to pay attention to those issues:

1. If the PCB circuit board has more grounds, such as SGND, AGND, GND, etc., according to the position of the PCB circuit board, the most important "ground" is used as a reference to independently pour copper. The ground and the analog ground are separated to pour copper, and at the same time, before the copper pour, first thicken the corresponding power connection: 5.0V, 3.3V, etc., in this way, multiple deformations of different shapes are formed structure.

2. For single-point connection to different grounds, the method is to connect through 0 ohm resistors or magnetic beads or inductance;

3. 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.

4. 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.

5. At the beginning of the wiring, the ground wire should be treated the same. When wiring, the ground wire should be routed well. You can't rely on adding via holes to eliminate the ground pin for connection after copper pour. This effect is very bad.

6. It is best not to have sharp corners (<=180 degrees) on the circuit board, because from the perspective of electromagnetics, this constitutes a transmitting antenna! For other things, it is only big or small. I recommend using the edge of the arc.

7. 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 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 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.