PCB News - PCB processing copper clad processing experience​

Copper plating is to use the unused space on the PCB as a reference surface and then fill it with solid copper. These copper areas are also called copper filling. The significance of copper coating is to reduce the impedance of the ground wire and improve the anti-interference ability; reduce the voltage drop and improve the efficiency of the power supply; in addition, it is connected to the ground wire to reduce the loop area. If the PCB has many grounds, such as SGND, AGND, GND, etc., how to pour copper? My approach is to use the most important "ground" as a reference to independently pour copper according to the position of the PCB processing board., Digital ground and analog ground are separated to coat copper without much to say. At the same time, before pour copper, first thicken the corresponding power connection: V5.0V, V3.6V, V3.3V (SD card power supply), and so on. In this way, multiple deformable structures with different shapes are formed.

There are several problems to be dealt with in copper coating: one is the single-point connection to different grounds, and the other is the copper coating near the crystal oscillator. The crystal oscillator in the circuit is a high-frequency emission source. The method is to coat copper around the crystal oscillator, and then separate the crystal oscillator shell Grounded. The third is the problem of isolated islands (dead zone). If you think it is too big, it will not cost much to define a ground via and add it.

In addition, whether large-area copper pour is better or grid copper pour is better, it is not good to generalize. Why? Large-area copper-clad, if wave soldering, the board may be up and even blistering. From this point of view, the heat dissipation of the grid is better. Usually it is a multi-purpose grid with high anti-interference requirements for high-frequency circuits, and circuits with large currents in low-frequency circuits are commonly used with complete copper.

In digital circuits, especially circuits with MCUs, circuits with working frequencies above the mega-level, the role of copper coating is to reduce the impedance of the entire ground plane. A more specific processing method I generally operate in this way: each core module (also all digital circuits) will be copper-clad in different areas when allowed, and then use wires to connect the copper-clad copper. The purpose of this is also In order to reduce the influence between various levels of circuits.

I won’t say much about the mixed circuit of digital circuit and analog circuit, the independent routing of the ground wire, and the final summary to the power supply filter capacitor. Everyone knows it. However, there is one point: the distribution of ground wires in analog circuits cannot be simply laid as a piece of copper. Because analog circuits pay much attention to the interaction between the front and rear stages, and the analog ground also requires single-point grounding, can it be Simulated copper coating has to be dealt with according to the actual situation.