PCB News - Significance and design difficulties of circuit board copper

Significance and design difficulties of circuit board copper

The so-called copper pour is to use the unused space on the circuit board as a reference surface and then fill it with solid copper. These copper areas are also called copper filling.
The meaning of the circuit board copper coating is to reduce the ground wire impedance and improve the anti-interference ability; reduce the voltage drop and increase the power supply; connecting to the ground wire can also reduce the loop area. Also out of the intention of making the PCB as undistorted as possible during soldering, most PCB manufacturers will also require PCB designers to fill the open areas of the PCB with copper or grid-like ground wires. If the circuit board copper coating is not handled properly, the gain will not be worth the loss. Is the copper coating "more advantages than disadvantages" or "harms more than advantages"?
Everyone knows that under high frequency conditions, the distributed capacitance of the wiring on the printed circuit board will have an effect. When the length is greater than 1/20 of the corresponding wavelength of the noise frequency, the antenna effect will occur, and the noise will be emitted through the wiring. If there is a poorly grounded copper pour on the PCB, the copper pour becomes a noise-transmitting thing. Therefore, in a high-frequency circuit, do not think that a certain part of the ground wire is connected to the ground. "Line", must be less than λ/20, punch holes in the wiring, and "outstanding grounding" with the ground plane of the multilayer circuit board. If the copper coating is handled properly, the copper coating not only increases the current, but also has the dual effect of shielding interference.
There are generally two basic methods for copper coating on circuit boards, namely large-area copper coating and grid copper. It is often asked whether large-area copper coating is good or grid copper coating is good, and the poor are confused.
Why? Large-area copper coating has the dual effect of increasing current and shielding. However, if large-area copper coating is used for wave soldering, the circuit board may be uplifted or even blistered. Therefore, for large-area copper coating, several grooves are generally used to relieve the blistering of copper foil. The pure mesh copper coating is still the shielding effect, and the effect of increasing the current is reduced. From the perspective of heat dissipation, the mesh has The advantage (it reduces the heating surface of the copper) has a certain electromagnetic shielding effect.
However, what needs to be pointed out is that the grid is made up of traces in staggered directions. We know that for circuits, the width of traces has a corresponding "electrical length" (the actual size is divided by the operating frequency of the circuit board). The digital frequency corresponding to the operating frequency is available. For details, see related books). When the operating frequency is not very high, perhaps the effect of the grid lines is not very obvious. Once the electrical length matches the operating frequency, it will be very bad. It will be found that the circuit cannot operate normally at all, and signals that disturb the operation of the system are emitted everywhere. Therefore, for colleagues who use grids, it is recommended that they can choose according to the design of the circuit board and do not cling to one thing. Therefore, the high-frequency circuit has a multi-purpose grid with high requirements for anti-interference, and the low-frequency circuit has a circuit with a large current, such as commonly used intact copper.

Having said that, in the copper pour, in order to make the circuit board copper to achieve the desired effect, what issues need to be paid attention to in the circuit board copper pour:
1. The heat-dissipating metal block of the three-terminal regulator must be well grounded. The ground isolation belt adjacent to the crystal oscillator must be well grounded.
2. For single-point connection of different grounds, the method is to connect through 0 ohm resistance, magnetic beads or inductance.
3. The metal inside the device, such as metal radiators, metal reinforcement strips, etc., must be "outstanding grounding".
4. The island (dead zone) problem, if you think it is too big, it won't cost much to define a ground hole and add it.
5. Do not pour copper in the open area of the middle layer of the multilayer circuit board. Because it is difficult for you to make this copper clad "outstanding grounding".
6. Pour copper adjacent to the crystal oscillator, and the crystal oscillator in the circuit is a high-frequency emission source. The method is to pour copper around the crystal oscillator, and then ground the shell of the crystal oscillator separately.
7. At the beginning of the wiring, the ground wire should be treated the same. When routing the ground wire, the ground wire should be routed well. It cannot rely on the copper pour to eliminate the ground pin for the connection by adding vias. This effect is not good.
8. It is best not to have sharp corners (<=180 degrees) on the circuit board. From the point of view of electromagnetics, this constitutes a transmitting antenna! Regarding other things, there will always be a big or a small impact. Shenzhen Zhongke Circuit recommends using the edge of the arc.
9. If the PCB has many grounds, such as SGND, AGND, GND, etc., it is necessary to use the most important "ground" as a reference to independently pour copper, digital ground and analog ground according to the different PCB board surface orientation. It is not necessary to separate the copper pour. At the same time, before the copper pour, first thicken the corresponding power connection: 5.0V, 3.3V, etc., in this way, multiple deformed structures with different shapes are formed.
In short: if the grounding problem is dealt with, the copper pour on the circuit board 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.