Precautions when PCB copper
There are certain processes and precautions in the design and production of circuit boards. Copper plating on circuit boards is a crucial step in PCB design and has a certain technical content. So how to do the design work in this link well, there are senior engineers. Summarized several experiences:
Everyone knows that under high frequency, the distributed capacitance of the wiring on the printed circuit board will work. When the length is longer 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 poorly grounded copper in the PCB, copper becomes a tool for transmitting noise. Therefore, in high-frequency circuits, do not think that the ground wire is connected to the ground somewhere. This is the "ground wire." "Be sure to punch holes in the wiring at a pitch smaller than λ / 20, and" good ground "with the ground plane of the multilayer board. If the copper-clad is handled properly, copper-clad will not only increase the current, but also play a dual role of shielding interference.
In copper cladding, in order for copper cladding to achieve our expected results, copper cladding needs to pay attention to those issues:
1. If the PCB has a lot of ground, including SGND, AGND, GND, etc., it is necessary to independently cover the copper, digital ground and analog ground according to the different positions of the PCB board surface, using the main "ground" as the reference reference. It is not too much to separate the copper clad. At the same time, before the copper clad, the corresponding power supply wiring is thickened: 5.0V, 3.3V, etc. In this way, a plurality of multi-deformed structures with different shapes are formed.
2. For single-point connection to different grounds, the method is to connect through 0 ohm resistors or magnetic beads or inductors.
3. Copper clad near the crystal. The crystal in the circuit is a high-frequency emission source. The method is to clad the copper around the crystal and then ground the shell of the crystal separately.
4. If the problem of isolated island (dead zone) is too large, it will not take much to define a ground via.
5. When starting the wiring, the ground wire should be treated equally. When the wire is routed, the ground wire should be routed well. You cannot rely on copper through copper holes to eliminate the ground pins for connection. This effect is very bad.
6. It is best not to have sharp corners appear on the board (<= 180 degrees), because from the perspective of electromagnetics, this constitutes a transmitting antenna! It will only have a large or small impact on other people. That's it, I recommend using arc edges.
7. Do not cover copper in the open area of the middle layer of the multilayer board. Because it is difficult for you to make this copper “good ground”.
8. Metals inside the equipment, such as metal radiators, metal reinforcement bars, etc., must be “good grounded”.
9. The heat-dissipating metal block of the three-terminal regulator must be well grounded. The ground isolation band near the crystal must be well grounded. In short: if the copper on the PCB is properly grounded, it must be "prossing more than disadvantages". It can reduce the reflow area of the signal line and reduce the external electromagnetic interference of the signal.