PCB Over-hole

When walking multilayer board, often need to hit the hole, then how to classify the hole? and look down.

(1) Through-hole: this hole through the entire circuit board, can be used for internal interconnection or as a component of the installation of the locating hole (for connecting layer; Creating a drilling file, punching on the PCB and electroplating in the hole, usually much larger than the signal line);

(2) Buried hole: refers to the printed circuit board in the inner layer of the connection hole, it will not extend to the surface of the circuit board;

(3) Blind hole: The connecting hole in the inner layer and the surface of the printed circuit board, with a certain depth, for the surface line and the following inner line connection, hole depth and aperture usually does not exceed a certain proportion.

< usually we say 8-layer 1-step or 10-Layer 2-step plates, where the order refers to the number of layers that the blind hole passes through (related to the number of times the inner plate is pressed) >

Blind or buried holes can provide greater wiring density, but also increase PCB manufacturing costs, usually only used in high-capacity circuits, buried holes difficult to debug .

This is the classification of the Vias in the PCB:

So what is the structure of the vias themselves?

For the structure of the hole, there are three main parts: one is hole, the other is the pad area around the hole, and the third is the power layer quarantine.

Through the hole of the process is on the hole wall cylindrical surface by the chemical deposition of a layer of metal, used to connect the middle layers need to be connected to the copper foil, and the upper and lower sides of the hole into a common pad shape, can be directly connected to both sides of the line, also can not connect.

So what are the main effects of vias on our signals?

Obviously the parasitic effect:

(1) parasitic capacitance (parasitic capacitance will affect the signal rise time, reduce the speed of the circuit, the smaller the capacitance value, the smaller the impact);

(2) Parasitic inductance (the maximum impact on the parasitic inductance value is the length of the Vias).

In the high-speed digital circuit, the parasitic inductance has a greater impact than the parasitic capacitance, and the parasitic series inductance of the vias weakens the bypass capacitor and weakens the filtering effect of the whole power system.

The size of the vias is generally determined by the process limitations that can be made by the plate mill, the aperture of the mechanical bore and the laser bore and the different product requirements to design the vias at different aperture ratios.

PCB Over-hole