Classification of the through hole
From the point of view of function, the through hole can be divided into two categories: one is used as an electrical connection between the layers; The second is used for the fixing or positioning of components. In terms of process, via hole can be divided into three categories: blind hole, buried hole and through hole.
The blind hole is located on the top and bottom surfaces of the PCB and has a certain depth for the connection of the surface and inner circuits. The depth of the hole usually does not exceed a certain ratio (aperture).
A through hole is a hole through the entire circuit board that can be used for internal interconnection or as a component for installation. Because the through hole is easier to realize in the process and the cost is lower, it is used in most PCB proofing.
The composition of the Via
From a design point of view, the via hole is mainly composed of two parts, one is the middle of the hole, the other is the hole around the pad area. The size of these two parts determines the size of the through hole. In high-speed, high-density PCB design, designers always want as small as possible through the hole, so that the board can leave more routing space. But the decrease of hole size brings the increase of cost, and the size of hole is limited by drilling and electroplating technology. The smaller the hole, the longer it takes to drill, and the more likely it is to be off-center; and when the hole is more than six times the diameter of the hole, there is no guarantee that the copper plating will be uniform.
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