Via is one of the important components of multi-layer PCB, and the cost of drilling usually accounts for 30% to 40% of the cost of PCB board. From the function of vias, it can be divided into two categories: electrical connection between layers and used for device fixation or positioning. Vias are generally divided into three categories from the perspective of the process, namely blind vias, buried vias and through vias. Blind holes are located on the top and bottom surfaces of the printed circuit board, with a certain depth, for the connection of the surface circuit and the underlying inner circuit, and the depth of the hole usually does not exceed a certain ratio (diameter). Buried vias refer to connection holes located in the inner layer of the printed circuit board, which do not extend to the surface of the circuit board. The above two types of holes are located in the inner layer of the circuit board, and are completed by the through hole forming process before lamination. During the formation of the via hole, several inner layers may be overlapped. The third type is called through-hole, which penetrates the entire circuit board and can be used for internal interconnection or as a mounting location hole for components. Because the through hole is easier to realize in the process and the cost is lower, most of the printed circuit boards use it instead of the other two kinds of through holes. From a design point of view, a via hole is mainly composed of a drill hole in the middle and a pad area around the drill hole. The size of these two parts determines the size of the via hole. The smaller the via, the smaller its own parasitic capacitance, which is suitable for high-speed circuits. However, the reduction in hole size also brings about an increase in cost, and is limited by process technologies such as drilling and plating.