What is the function and principle of adding a Via near the Via hole of the trace as shown?
The vias of the PCB board are classified according to their functions and can be divided into the following types:
1. Signal via (via structure requires minimal signal impact)
2. Power supply, ground via (via structure requires the smallest distribution of vias)
3. Heat dissipation vias (via structure requires minimum thermal resistance of vias)
The via hole described above is a ground-type via.
Adding a ground via near the Via hole is the shortest return path for the signal.
Note: The signal is in the via hole of the layer, which is a discontinuity of impedance. The return path of the signal will be disconnected from this. In order to reduce the area enclosed by the return path of the signal, some ground must be placed around the signal via. Via holes provide the shortest signal return path and reduce the EMI emissions of the signal. This radiation increases significantly with the increase in the frequency of the signal.
The reflow diagram of the signal is as follows:
Under what situation should I use more holes?
Actually usually occurs in the following three situations:
1. The ground hole is used for heat dissipation;
2. The ground hole is used to connect the ground layer of the multi-layer board;
3. The position of the via hole used for the layering of the high-speed signal.
But all of these situations should be done with guaranteed power integrity.
In current electronic products, the general EMI test range is up to 1Ghz.,then the 1Ghz signal has a wavelength of 30cm, and the 1Ghz signal has a 1/4 wavelength of 7.5cm = 2952mil. That is to say, if the spacing of the vias can be less than 2952 mils, the connection of the formation can be well satisfied and a good shielding effect can be achieved. In general, we recommend that a hole per 1000 mil is sufficient.