Dicas para PCB Copper-cladPostado em 17/07/2020
PCB revestido de cobre precisa prestar atenção às dicas
O que é PCB revestido de cobre
O chamado PCB revestido de cobre é usar o espaço ocioso no PCB as a reference plane, and then fill it with solid copper. These copper areas are also called copper filling. The significance of copper cladding is to reduce the impedance of the ground wire, improve the anti-interference ability, reduce the voltage drop, and improve the efficiency of the power supply. Connecting to the ground wire can also reduce the loop area. It is also for the purpose of making the PCB not deformed as much as possible. Most PCB manufacturers will also require the PCB designer to fill the copper area or the grid-like ground wire in the open area of the PCB. If the copper is not handled properly, it will Gain or loss. Is copper-clad “benefits outweigh the disadvantages” or “wrongs outweigh the benefits”?
Analysis of the advantages and disadvantages of copper-clad
Everyone knows that at high frequencies, 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. Noise will be emitted through the wiring. If there is poorly grounded Copper Clad in the PCB, the Copper Clad becomes a tool for transmitting noise. Therefore, in high-frequency circuits, don’t think that if you connect the ground wire somewhere, this is the “ground wire”. Be sure to make via holes in the wiring at a distance of less than λ/20 to “good ground” the ground plane of the multilayer board. If the copper clad treatment is proper, the copper clad not only increases the current, but also plays a dual role of shielding interference.
There are two basic methods of copper clad, namely large-area copper clad and grid copper. It is often asked whether large-area copper-cladding is good or grid copper-cladding, which is not easy to generalize. why?
Large-area copper cladding has the dual function of increasing current and shielding. But for large-area copper cladding, if over-wave soldering, the board may warp, or even blisters. Therefore, a large-area copper cladding usually has several grooves to ease the blistering of copper foil. The simple grid copper-cladding is mainly shielding, and the effect of increasing the current is reduced. From the perspective of heat dissipation, the grid is beneficial (it reduces the heating surface of copper) and plays a role in electromagnetic shielding. But it should be pointed out that the grid is made up of traces in alternating directions.
PCB copper-clad tips
So in PCB copper-cladding, what issues need to be paid attention to in order to make copper-clad achieve our expected effect?
Here are some tips:
- If the PCB has more grounds, such as SGND, AGND, GND, etc., it depends on the position of the PCB board. Separate copper-cladding with the main “ground” as a reference. It is self-explanatory to separate copper from digital ground and analog ground. At the same time, before copper-cladding, first thicken the corresponding power connections: 5.0V, 3.3V, etc., so that a number of different shapes of multi-deformation structures are formed.
- For the single point connection of different grounds, the method is to connect through 0 ohm resistance or magnetic beads or inductance.
- The copper-clad near the crystal oscillator, the crystal oscillator in the circuit is a high-frequency emission source. The method is to wrap copper around the crystal, and then ground the crystal’s case separately.
- The problem of isolated island (dead zone), if it feels big, then add a ground via.
- When starting wiring, treat the ground wire equally. When routing, you should run the ground wire well. You cannot rely on adding vias to eliminate the ground pin connected by copper-cladding. This effect is very bad.
- It is best not to have sharp corners on the board (<=180 degrees). Because from the perspective of electromagnetics. This constitutes a transmitting antenna. For others, there will always be an impact, It’s just that the impact is big or small. I recommend using the edge of the arc.
- Do not Copper-clad in the open area of the middle layer of the multilayer board. Because it is difficult for you to make this copper “good ground”.
- The metal inside the device. For example, metal radiators, metal reinforcement bars, etc., must be “good grounded”.
- The heat dissipation metal block of the three-terminal regulator must be well-grounded. The grounding isolation zone near the crystal must be well-grounded.
In short: PCB copper-clad, if the grounding problem is solved, it must be “benefits outweigh disadvantages.” It can reduce the return area of the signal line and reduce the electromagnetic interference of the signal to the outside.
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