When it comes to blind and buried vias, we can start with the traditional multilayer board. The structure of standard multi-layer board is composed of inner circuit and outer circuit, and then the process of drilling and metallization in the hole is used to achieve the function of internal connection between each layer of circuit. However, due to the increase of circuit density, the packaging method of parts is constantly updated.
Through holes are generally divided into three types: blind and buried vias and through-holes.
Blind via, with a certain depth, is located on the top and bottom surface of printed circuit board . It is used to connect the surface circuit and the inner circuit below. The depth and aperture of the hole usually do not exceed a certain ratio.
Buried via refers to the connecting hole in the inner layer of printed circuit board, which does not extend to the surface of the circuit board.
Blind and buried vias are located in the inner layer of PCB. Before lamination, through-hole is used to complete the molding process, and several inner layers may be overlapped in the process of via forming.
Through-holes, which pass through the entire circuit board, can be used for internal interconnection or as installation positioning holes for components. It is easier to realize through-hole in process and the cost is lower, so it is used in general printed circuit board.
In the traditional manufacturing process of multi-layer plate, drilling machine is used to set the depth of z-axis after pressing, but there are several problems in this method:
a. Only one piece can be drilled at a time, and the output is very low.
b. The requirements for the levelness of drilling machine table are strict, and the setting of each drilling depth should be consistent, otherwise it is difficult to control the depth of each hole.
c. It is difficult to electroplate in the hole. Especially if the depth is larger than the aperture, it will be almost impossible to deal well with the hole electroplating.
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