PCB Technical - Do you know that copper is paved in the PCB design?

1. Reasons for copper paving:

1. EMC, for large-area ground or power supply copper, will play a shielding role, some special grounds, such as PGND play a protective role.

2. PCB process requirements, generally in order to ensure the effect of electroplating, or lamination is not deformed, copper is laid on the PCB board layer with less wiring.

3. The signal integrity is required to provide a complete return path for high-frequency digital signals and reduce the wiring of the DC network. Of course, there are also reasons such as heat dissipation, special device installation requires copper and so on.

2. The benefits of copper paving:

The biggest advantage of copper paving is to reduce the impedance of the ground wire (a large part of the so-called anti-interference is also brought about by the reduction of the ground wire impedance). There are a large number of spike currents in the digital circuit. Therefore, it is more necessary to reduce the ground wire impedance. Circuits composed entirely of digital devices should be grounded in a large area, while for analog circuits, the ground loop formed by laying copper will cause electromagnetic coupling interference to outweigh the gains (except for high-frequency circuits). Therefore, it is not that all circuits require ordinary copper (BTW: the performance of mesh copper paving is better than that of a whole block)

3. The significance of copper paving lies in:

1. Pave the copper and connect with the ground wire, so as to reduce the loop area

2. A large area of copper is equivalent to reducing the resistance of the ground wire and reducing the voltage drop. The digital ground and the analog ground should also be separated to lay the copper when the frequency is high, and then connected with a single point. The single point can be connected with a wire around a magnetic ring several times. However, if the frequency is not too high, or the working conditions of the instrument are not bad, it can be relatively relaxed. The crystal oscillator can be regarded as a high-frequency emission source in the circuit. You can spread copper around and ground the shell of the crystal oscillator, which will be better.

Fourth, the difference between the whole piece of copper and the grid:

To analyze specifically, there are about 3 functions:

1. Beautiful;

2. Suppress noise;

3. In order to reduce high-frequency PCB interference (the reason on the circuit board: ww.pcblx.com), according to the routing criterion: the power supply and the ground layer should be as wide as possible, why do we need to add a grid? Isn't it inconsistent with the principle? If you look at it from a high-frequency point of view, it is even more wrong. In high-frequency wiring, the most taboo is sharp traces. If there are more than 90 degrees in the power layer, there are many problems. In fact, why do it like that is entirely a process requirement: see if the hand-soldered type is painted like that, almost none; if you see such a painting, there must be a chip on it, because there is a kind of craftsmanship when mounting. Called wave soldering, he needs to heat the board locally. If the specific heat coefficients of the two sides are not the same if all copper is spread, the board will lift up, and the problem will come when the board is up. The pin of the chip is in the upper steel cover (which is also required by the process). It's easy to make mistakes and the scrap rate goes straight up. In fact, this approach has its shortcomings: under our current corrosion process: the film is easy to stick to it. In the later strong acid project, that point may not be corroded, and there are a lot of waste products., But only if the board is broken and the chip on it is finished with the board! From this perspective, do you know why you have to paint like that? Of course, some surface mounts are not gridded. From the point of view of product consistency, there may be 2 situations: a. His corrosion process is very good; b. Instead of wave soldering, it uses more Advanced reflow welding, but in this case, the investment of the entire assembly line will be 3-5 times higher.