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Package land in PCB
2021-10-13
View:14
Author:Kavie

        As the name implies, land is to wrap the entire signal line around the land.
    It is a problem that the ground on both sides of the signal line is not covered or not. I often see people struggling with the problem of land packaging when doing design. It may be limited by the size of the pcb board In PCB manufacturing, and I heard that wrapping the ground can better shield the signal, so try to draw two thin ground wires on both sides of the important clock line differential signal. In fact, this approach increases the interference to nearby signals.

PCB


     The main function of the land is to reduce crosstalk. So in addition to land coverage, what other methods can reduce crosstalk? Increasing the signal spacing also allows the signal to be tightly coupled to the reference plane. If it is a multi-layer board, reducing the distance between the reference plane and the signal layer can better control the impedance while allowing the signal to be tightly coupled with the reference plane, reducing the signal's interference to nearby signals. The crosstalk can be reduced by increasing the signal line spacing. At this time, the effect on the signal packet ground is not obvious. Especially when the space is relatively small, adding a thin ground wire is equivalent to adding another signal wire between the two signal wires, which acts as a bridge and conducts signal interference to the bottom. A signal. It should be better to remove this and ground wire to reduce crosstalk.
     Some people say that it is not only necessary to add ground wire to cover the ground, but also to drill more ground holes in the ground wire. Of course, this effect will be better. But since the ground hole can be drilled, it means that the minimum width of the ground line must be more than a dozen mils. In addition to the line spacing, the distance between the original two signal lines is enough to meet 4W, so the crosstalk itself is very small. Remove the ground line. The signal will not add much crosstalk.
     If it is a two-layer board and there is no reference plane, then the envelope of important signals is very important. The width of the ground wire should be as wide as possible, preferably at least twice the signal width. Punch more holes at the same time, and the spacing of the via holes is less than 1/5 of the signal wavelength on the signal line.
     In some non-high-frequency single-chip wiring, the crystal oscillator, serial port, important signal lines, interrupt signals, etc. are packaged and processed.
     The radio frequency analog signal includes the ground and common, which can effectively improve the signal quality, artificially provide the smallest loop, and increase the shielding.
     The ground hole like a differential package is definitely beneficial. It has been verified by simulation to increase the impedance drop at the layer change.