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PCB board when the precautions

Copper coating is an important part of PCB circuit board design. Whether it is the domestic QingYueFeng PCB design software, or some foreign Protel or PowerPCB, which provide intelligent copper-clad function, how can we apply good copper? I will have some ideas for myself. Share with everyone and hope to bring benefits to your peers.

The so-called copper clad is to use the unused space on the PCB as a reference plane, and then fill it with solid copper. These copper regions are also called copper clad. The significance of copper-coating is to reduce the impedance of the ground wire and improve the anti-jamming capability; reduce the voltage drop and increase the efficiency of the power supply; connecting with the ground wire can also reduce the loop area. Also for the purpose of not deforming the PCB as much as possible during welding, most PCB manufacturers also require the PCB designer to fill the open area of the PCB with copper skin or grid-like ground wire. If the copper plating is handled improperly, it will It is not to be rewarded. What is the "benefit outweighs disadvantages" or "does more harm than good"?

Everyone knows that at high frequencies, the distributed capacitance of the wiring on the printed circuit board will work. When the length is larger 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 shield in the PCB, copper coating becomes a tool to spread noise. Therefore, in a high-frequency circuit, don't think that if you place a ground wire somewhere, this is "Lines" must be made with holes less than λ/20, with holes in the wiring, and "good grounding" with the ground plane of the multilayer board. If the copper-coating process is appropriate, copper-clad copper not only has an increased current, but also plays a dual role of shielding interference.

There are generally two basic methods for copper-clad copper plating, namely, large-area copper-clad and copper-mesh grids. It is also often said that large-area copper-clad or mesh-clad copper is good, and it is not easy to generalize. Why? A large area of copper, with the dual role of increasing the current and shielding, but a large area of copper, if the wave soldering, the board may be up, or even blistering. Therefore, a large area of copper, will generally open a few slots to ease the copper foil blistering, a simple grid of copper is mainly shielding effect, the role of increasing the current is reduced, from the perspective of heat dissipation, the grid is good (It reduces the heating surface of copper) It also plays a role in electromagnetic shielding. However, it should be pointed out that the grid is composed of the traces in the interleaving direction. We know that for the circuit, the trace width 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 working frequency is available, and the relevant books can be found. When the operating frequency is not very high, the grid line may not be very effective. Once the electrical length and the operating frequency match, it is very bad. You You will find that the circuit is not working at all, and everywhere it is emitting signals that interfere with the operation of the system. So for the colleagues using the grid, my suggestion is to choose according to the design of the circuit board work situation, do not hold on to hold a thing. Therefore, the high-frequency circuit requires a high-use multigrid mesh, and the low-frequency circuit has a large-current circuit and so on.

Having said so much, we need to pay attention to what issues need to be paid attention to in copper coverage in order to allow copper to achieve the desired effect:

1. If the PCB has many grounds, SGND, AGND, GND, etc., it is necessary to independently cover the copper, digital ground, and analog ground with the most important “ground” as the reference, depending on the position of the PCB board. It is not much to say that the copper is covered separately, and before the copper is coated, the corresponding power connection is first bolded: 5.0V, 3.3V, etc. In this way, multiple deformed structures with different shapes are formed.

2. For different single point connections, the approach is to connect through 0 ohm resistors or beads or inductors;

3. The copper near the crystal oscillator, the crystal oscillator in the circuit is a high-frequency emission source, the approach is to surround the crystal oscillator copper, and then the crystal shell is grounded separately.

4. If you think of the problem of islands (dead zones), it would not be too much to define a single hole to add.

5. In the beginning of the wiring, deal with the ground line www.pcblover.com and treat it the same way. When you route the cable, you should take the ground line well. You can't rely on adding vias to remove the ground pins for the connection. The effect is very bad.

6. It is better not to have sharp corners ("=180 degrees") on the board, because from the electromagnetic point of view, this constitutes a transmitting antenna! For other things there will always be an impact is only big or small However, I suggest using the edge of the arc.

7. The empty area of the middle layer of the multilayer board is not covered with copper. Because you can hardly make this copper "good grounding"

8. Metals inside the equipment, such as metal radiators, metal reinforcement strips, etc., must be “well grounded”.

9. The thermal block of the three-terminal regulator must be well grounded. The grounding strip near the crystal must be well grounded. In short: Copper on the PCB, if the grounding problem is handled properly, it must be "benefit outweighs the disadvantages", it can reduce the return area of the signal line and reduce the external electromagnetic interference signal.


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