Function and principle of Via hole

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Function and principle of Via hole [Copy link]

What is the function and principle of adding a grounding via hole near the via hole for routing as shown in the figure? The vias on PCB boards can be divided into the following categories according to their functions: 1. Signal vias (the via structure requires minimal impact on signals) 2. Power and ground vias (the via structure requires the via's distributed inductance to be minimal) 3. Heat dissipation vias (the via structure requires the via's thermal resistance to be minimal) The vias mentioned above are grounding type vias. Add grounding near the routing via holes. The function of the via is to provide the shortest return path for the signal. Note: The via at the layer change is a discontinuous point of impedance, and the return path of the signal will be disconnected from here. In order to reduce the area surrounded by the return path of the signal, some ground vias must be drilled around the signal via to provide the shortest signal return path and reduce the signal's Radiation. This radiation increases significantly with the increase of signal frequency.

Below are two signal return diagrams:

Figure 1:

Figure 2:

The question raised above is the situation shown in Figure 2.

In what cases should more ground holes be drilled?

There is a saying: drilling too many vias will destroy the continuity and integrity of the ground layer. The effect is counterproductive.

First of all, if too many vias are drilled, it will cause the continuity and integrity of the power layer and the ground layer. This situation should be avoided resolutely. These vias will affect the integrity of the power supply, thereby causing signal integrity problems, which is very harmful.

Drilling ground vias usually occurs in the following three situations:

1. Drilling ground vias is used for heat dissipation;

2. Drilling ground vias is used to connect the ground layers of multilayer boards;

3. Drilling ground vias is used to position vias for high-speed signal layer change.

But all of these situations should be carried out under the condition of ensuring power integrity.

That is to say, as long as the interval of ground vias is controlled well, is it allowed to drill more ground vias? Is it okay to drill ground vias at intervals of one-fifth of the wavelength? If I make more ground vias to ensure the connection of the multilayer board, even if there is no partition, will it affect the integrity of the ground layer and the power layer?

Answer: If the copper foil of the power layer and the ground layer is not separated, the impact is not great.

In current electronic products, the maximum EMI test range is generally 1Ghz. Then the wavelength of the 1Ghz signal is 30cm, and the 1/4 wavelength of the 1Ghz signal is 7.5cm＝2952mil. That is, if the interval of the vias can be less than 2952mil, it can well meet the connection of the ground layer and play a good shielding role. Generally, we recommend that it is sufficient to make ground vias every 1000mil.