The circuit layout of HDI high-frequency boards is extremely dense, and the production price is slightly higher than that of conventional circuit boards. Only some high-end electronic products will use HDI high-frequency circuit boards, and HDI high-frequency boards include all "blind hole boards" and "buried hole boards". So, what are the differences between identifying blind hole boards and buried hole boards!

① Blind hole: refers to a through hole that connects the inner layer of the PCB to the surface layer of the PCB, but this type of hole does not penetrate the entire board. Buried hole: a through-hole that only connects the wiring between the inner layers, which cannot be seen from the surface of the PCB alone. In this regard, PCB boards with buried blind holes may not necessarily be HDI circuit boards, but HDI high-frequency boards must have blind holes.

② Taking a six layer circuit board as an example: the first/second order refers to PCB boards that require laser drilling, known as "HDI high-frequency boards". The first order HDI board refers to blind holes: 1-2, 2-5, 5-6, that is, 1-2, 5-6 require laser drilling; Second order HDI board finger blind holes: 1-2, 2-3, 3-4, 4-5, 5-6. Two laser punches are required.

③ As for drilling, it is necessary to first drill 3-4 buried holes, press 2-5, then drill 2-3, 4-5 laser holes, perform 2 press 1-6, then drill 1-2, 5-6 laser holes again, and finally drill through the hole.

④ The second order HDI high-frequency board can be divided into two types: staggered second-order HDI high-frequency board and stacked second-order HDI high-frequency board. The staggered second-order HDI high-frequency board refers to blind holes 1-2 and 2-3 that are staggered, while the stacked second-order HDI high-frequency board refers to blind holes 1-2 and 2-3 stacked together.