The Application notice for PCB Copper clad
Copper clad can be treated as an important part of PCB design regardless of design software PCB made in China, but also some foreign Protel, Power PCB have provided intelligent copper clad, so how to apply copper well, I will share some ideas with everyone, hoping to bring benefits to peer.
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 known as copper pour. The significance of copper-coating is to reduce the grounding wire impedance and improve the anti-jamming ability; 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 copper sheet or grid-like ground wire in the PCB open area. If the copper plating is handled improperly, it will be instead of gaining any gains. What is the "benefit outweighs disadvantages" or "does more harm than profit"?
We all know that the distributed capacitance of PCB Layout will work in case of high frequency. When the length is larger than 1/20 of the corresponding wave length of the noise frequency, it will occur the effect on an antenna, and the noise will be emitted outward 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, we don't think that connect the ground line somewhere to the ground, this is the "ground line", it must be made with holes that are smaller 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 in shielding interference.
There are generally two basic methods for copper-clad, namely, large-area copper-clad and copper-mesh grids. It is also often asked whether large-area copper-clad or mesh-clad copper is good, and it is not easy to generalize. why? The large area of copper clad has the dual function of increasing the current and shielding, but it covers a large area of copper. If the wave is soldered, the board may be upturned 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 effect of increasing 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 staggered 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 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 who use the grid, my suggestion is to choose according to the design of the work of the circuit board, do not hold one thing and hold it. Therefore, the high-frequency circuit requires a high-frequency multi-use grid, and the low-frequency circuit has a large-current circuit and so on.
Having said so much, then in order to allow copper to achieve the desired effect, we need to pay attention to those issues in copper clad.
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, and so on. 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 isolated islands (dead zones), it would not be too much to define a single hole to add to it.
5. In the beginning of the wiring, the ground should be treated in the same way. When the cable is routed, the ground line should be taken well. It cannot rely on the addition of via holes after the copper plating to eliminate the connected ground pins. This effect is very bad.
6. It is best not to have sharp corners ("=180 degrees") on the board, because from the electromagnetic point of view, this constitutes a transmitting antenna! It's only a matter of whether it's big or small, but 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 "well grounded"
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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