If you don't notice these things, it's better not to cover PCB with copper

If you don't notice these things, it's better not to cover PCB with copper

PCB manufacturers, PCB designers and PCBA manufacturers explain these things to you. If you can't notice them, it's better to cover PCB with copper instead of copper

Copper coating is an important part of PCB design. Whether it is domestic PCB design software or some foreign Protel, PowerPC B provides intelligence. So how to apply copper well? I will share some of my ideas with you, hoping to bring benefits to peers.

The so-called copper coating refers to taking the idle space on the PCB as the reference plane, and then filling it with solid copper. These copper areas are also called copper filling. The significance of copper coating is to reduce the ground wire impedance and improve the anti-interference capability; Reduce voltage drop and improve power efficiency; Connecting with the ground wire can also reduce the loop area.

In order to keep PCB from deformation as much as possible during welding, most PCB manufacturers also require PCB designers to fill the open area of PCB with copper sheet or grid shaped ground wire. If copper coating is handled improperly, it will not pay off. Is it "more beneficial than harmful" or "more harmful than beneficial"?

It is known that the distributed capacitance wired on the printed circuit board will play a role in high frequency. When the length is greater than 1/20 of the corresponding wavelength of the noise frequency, the antenna effect will be generated, and the noise will be transmitted outward through the wiring. If there is copper cladding with poor grounding in the PCB, copper cladding becomes a tool for spreading noise. Therefore, in a high-frequency circuit, do not think that a certain part of the ground wire is grounded. This is called "ground wire". It must be less than λ/ 20. Punch holes in the wiring and "ground well" it to the ground plane of the multilayer board. If the copper coating is properly treated, it can not only increase the current, but also shield the interference.

Generally, there are two basic methods of copper cladding, namely, large-area copper cladding and grid copper cladding. It is often asked whether large-area copper cladding or grid copper cladding is better. 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 board may be warped or even blistered. Therefore, for large area copper coating, several grooves are usually opened to relieve blistering of copper foil. The pure grid copper coating is mainly used for shielding. The effect of increasing 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. However, it should be pointed out that the grid is composed of lines in staggered directions. We know that for circuits, The width of the wiring 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 operating frequency, see the relevant books for details) When the working frequency is not very high, the side effects of the grid line may not be obvious. Once the electrical length matches the working frequency, it is very bad. You will find that the circuit can not work normally at all, and there are signals everywhere that interfere with the working of the system. Therefore, for colleagues who use grid, my suggestion is to choose according to the working conditions of the designed circuit board, instead of holding on to something. Therefore, high-frequency circuit requires high anti-interference multi-purpose grid, low-frequency circuit, high current circuit and other commonly used complete copper laying.

Having said that, we should pay attention to the following issues in order to achieve the desired effect of copper cladding:

1. If there are many PCBs with ground, such as SGND, AGND, GND, etc., the main "ground" shall be used as the reference for copper coating according to the different positions of the PCB. It is not necessary to separate copper coating digitally and analog. At the same time, before copper coating, the corresponding power lines should be thickened: 5.0V, 3.3V, etc. In this way, a number of polygon structures with different shapes are formed.

   
   

2. For the single point connection of different ground, the method is to connect through 0 ohm resistance, magnetic bead or inductance;

3. Copper clad near the crystal oscillator. The crystal oscillator in the circuit is a high-frequency emission source. The method is to surround the crystal oscillator with copper clad, and then ground the shell of the crystal oscillator separately.

4. If the problem of isolated islands (dead zones) is very big, it doesn't take much to define and add individual vias.

5. At the beginning of wiring, the ground wire should be treated equally. When wiring, the ground wire should be properly routed. You cannot add ground pins by adding vias. This is not good.

6. It is better not to have sharp angles on the board (<=180 degrees), because from the electromagnetic point of view, this constitutes a transmitting antenna! It will always affect other places, just big or small. I suggest using the edge line of the arc.

7. The open area of the wiring in the middle layer of the multilayer board shall not be covered with copper. Because it is difficult for you to make this copper clad "good grounding"

8. The metal inside the equipment, such as metal radiator and metal reinforcing strip, must be "well grounded".

9. The heat dissipation metal block of the three terminal voltage regulator must be well grounded. The grounding isolation belt near the crystal oscillator must be well grounded. In a word: if the grounding problem of copper coating on PCB is solved, it must be "more advantages than disadvantages". It can reduce the return area of the signal line and reduce the electromagnetic interference of the signal to the outside. PCB manufacturers, PCB designers, and PCBA manufacturers explain that you can't notice these things. It's better not to copper PCB