Buried, blind, through – hole technology buried, blind, through – hole combination technology is also an important way to improve the printed circuit density. In general, buried and blind holes are tiny holes. In addition to increasing the number of wiring on the board, buried and blind holes are interlayer interconnection with “nearest”, which greatly reduces the number of through holes and isolation panel setting, thus increasing the number of effective wiring and interlayer interconnection in the board and improving the interconnection density. Therefore, compared with the conventional all-hole structure, the interconnect density of the buried, blind, through-hole multilayer board increases at least 3 times with the same size and number of layers. If the printed board with the buried, blind, through-hole combination has the same technical index, its size will be greatly reduced or the number of layers will be significantly reduced. So on the surface of high density PCB installation, buried, blind hole technology have been applied more and more, not only in the large computers, communications equipment and other surface mount PCB using, but also in the field of civil and industrial has been widely used, and even in some thin plate has been applied, such as various PCMCIA, Smard, thin plate above six layers of IC card, such as blind hole multilayer PCB line treatment.

They are generally divided into three classes, which are buried via, blind via and through Via. Blind holes are located on the top and bottom surface of the PRINTED circuit board and have a certain depth for connection between the surface circuit and the inner circuit below. The depth of the hole usually does not exceed a certain ratio (aperture). A burrow is a connection hole in the inner layer of the printed circuit board that does 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. Before laminating, the through-hole forming process is used to complete. Several inner layers may be overlapped during the formation of the through-hole. The third type, known as through-holes, runs through the entire circuit board and can be used for internal interconnection or as mounting positioning holes for components. Half hole multilayer PCB line processing

Pass Hole: It is one of the most common ones, and simply shows it to the light when you hold your PCB up to the light. Through hole multilayer PCB line processing

Blind Hole :Blind Via Hole connects the outermost circuit of PCB to the adjacent inner layer by electroplating Hole. Since the opposite side cannot be seen, it is called “Blind through Hole”.

Buried hole :Buried hole, PCB inner any circuit layer connection but not conduction to the outer layer. This process cannot be achieved by means of drilling holes after bonding, which must be carried out in individual circuit layers. After partial bonding of the inner layer, it must be electroplated before all bonding can be completed. It is more time-consuming than the original “through hole” and “blind hole”, so the price is also the most expensive. This process is usually only used on high density (HDI) circuit boards to increase the available space for other circuit layers.