Analysis of copper placement in PCB

- Aug 18, 2018-

Analysis of copper placement in PCB

If there are many PCB sites, such as SGND, AGND, GND, etc., the main "ground" shall be used as the reference for independent copper covering according to different PCB board locations, that is, the ground shall be connected together.

There are several reasons for laying copper in general.1. EMC. For large areas of ground or power supply copper, it will play a shielding role, and some special ones, such as PGND, will play a protective role.

2. PCB process requirements.Generally, for the purpose of ensuring the effect of electroplating, or the lamination is not deformed, the PCB board with less wiring is covered with copper.

3. Signal integrity requirement, give high frequency digital signal a complete backflow path, and reduce the wiring of dc network.Of course, there are also heat dissipation, special device installation requirements for copper, and so on.There are several reasons for laying copper in general.

1. EMC. It can shield large area of ground or power supply copper, and some special cases, such as PGND, can protect it.

2. PCB process requirements.Generally, for the purpose of ensuring the effect of electroplating, or the lamination is not deformed, the PCB board with less wiring is covered with copper. 

3. Signal integrity requirements: give high frequency digital signals a complete backflow path and reduce the wiring of dc network.Of course, there are also heat dissipation, special device installation requirements for copper, and so on.

A shop, a major advantage of copper is to reduce ground impedance (there was a large part of the so-called anti-jamming is to reduce ground impedance) of the digital circuit exists in a large number of peak pulse current, thereby reducing ground impedance is more necessary to some, is generally believed that for the whole circuit composed of digital devices should be large floor, for the analog circuit, formed by laying copper ground wire loop will cause electromagnetic coupling interference hampered (high frequency circuit.So, it's not like a circuit is all about copper.

Circuit laying copper significance lies in: 1, laying copper and ground wire is linked together, so that we can reduce the circuit area 2, spread a large area of copper equivalent to reduce the ground resistance, reduced the pressure drop in both, whether it is digital, or simulation should be laying copper in order to increase the ability of anti-interference, and at the time of high frequency should also spread their digital and analog ground to separate copper, then they are connected by a single point, the single point of wires can be used on a magnetic ring around a few laps, and then linked together.But if the frequency is not too high, or if the working conditions of the instrument are not too bad, it can be relatively relaxed.Crystal oscillator in the circuit can be calculated as a high frequency source, you can lay copper around, and then the shell of crystal oscillator grounded, which will be better.

3. What is the difference between the copper-covered whole and the grid?To reduce the high frequency interference (the reason on the circuit version) according to the routing criterion: the power source and the stratum should be as wide as possible.If from the point of view of high frequency, it is even more wrong. The most taboo in high frequency wiring is sharp routing.In fact, why do that is entirely a technical requirement: look at the manual welding of that painting, almost no;You see this picture must have above table 1 of the chip that is because when the patch there is a process called wave soldering to the board he local heating if carpet copper on the surface of the 2 specific heat coefficient is not the same as the board is stuck up and board a stuck up the question becomes, in Shanghai to cover (also is the need of technology) pin of the chip is very easy to get wrong rejection rate will line up this approach is flawed: under our current corrosion process:Film is very easy to adhere to the above so that, in the strong acid project behind, that point may not corrode, waste is also quite a lot, but only if the board is broken and the top is the chip and die together with the board!From that point of view, do you understand why you drew it that way?Of course, there are some tables without grid. From the perspective of product consistency, there may be 2 situations: 1.2. Instead of wave soldering, he adopted more advanced backward welding, but in this case, the investment of the whole assembly line is 3-5 times higher