Blind holes are from the outer layer to one or more inner layers. One side of the blind hole is on the outer layer, and the other side leads to the inside of the board, but it will not penetrate the entire board. Taking the 6-layer PCB as an example, the vias in L1-L2, L1-L3, L1-L4, L1-L5, L2-L6, L3-L6, L4-L6, and L5-L6 are all blind holes. That's why it's called a blind hole. A PCB with blind holes is called a blind hole PCB or blind hole PCB.
The use of buried holes and blind holes is an excellent method to increase the density of multi-layer PCB manufacturing, reduce the number of circuit board layers and circuit board size. In addition, blind hole and buried hole PCB suppliers have significantly reduced the number of plated through holes. In blind hole and buried hole PCB design, almost all BUM (Building Multi Layer PCB) boards use buried hole and blind hole structures.
Please note that most of the buried holes and blind holes used in blind buried hole plates have small diameters, such as 0.05-0.15 millimeters, so we also refer to this type of PCB with micropores as a microporous PCB. The buried hole is located in the inner layer. The production of buried hole PCBs is the same as that of double-sided PCBs. Blind holes are produced by CNC machines that control the depth of the z-axis and are used to drill small holes, but now with the continuous development of technology, laser drilling, plasma etching holes, and photo induced holes are commonly used.
Blind buried hole laser drilling usually uses three types of machines: carbon dioxide laser machine, excimer laser machine, and YAG ultraviolet laser machine. Here is a brief introduction to Hitachi's carbon dioxide laser machine. The laser wavelength of this machine is 9.4nm, and it can drill one blind hole in three times. It can drill 30000 blind holes on blind buried PCB per minute, with extremely high efficiency.
With the development of electronic products towards high density and precision, customized PCB manufacturers also need to develop corresponding printed circuit boards to match. The most effective way to increase PCB density is to reduce the number of through holes on the board, and accurately set up buried holes and blind holes in blind buried hole PCBs.
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