PCB hole is one of the most important parts of Multilayer PCB. The cost of drilling usually accounts for 30%-40% of the cost of PCB board making. In short, every hole in a PCB can be called a via.
Viewing the function, vias can be divided into two parts: one is used for electrical connection between layers; the other is for fixing or locating devices.
In term of process, these vias are generally divided into three categories, namely blind hole, buried hole and through hole.
The blind hole is located on the top and bottom surface of printed circuit board, and has a certain depth. It is used to connect the surface circuit and the inner circuit below. The depth of the hole usually does not exceed certain ratio (aperture).
The buried hole refers to the connecting hole inner layer of the printed circuit board, which does not extend to the surface of the printed circuit board. The above two types of holes are located in the inner layer of the printed circuit board. Before laminating, the through-hole molding process is used to complete the process, and several inner layers may be overlapped in the process of via forming.
This kind of hole passes through the whole circuit board and can be used to realize internal interconnection or as the installation locating hole of components. Because the through hole is easier to make and the cost is lower, most printed circuit boards use it instead of the other two.
From the design point of view, a PCB hole is mainly composed of two parts, one is the hole in the middle and the other is the area of bonding pad around the drill hole. The size determines size of the via hole. Obviously, in high-speed and high-density PCB hole plating design, Designers always hope the via is as small as possible, so that more wiring space can be left on the board. In addition, the smaller the via is, the smaller its parasitic capacitance is, which is more suitable for high-speed circuits.