The second order HDI PCB is troublesome. One is alignment, the other is punching and copper plating. There are many kinds of second order designs. One is stagger position of each order. When it is necessary to connect the next adjacent layer, it is connected in the middle layer through wires, which is equivalent to two first order HDIs. The second is that two first order holes overlap, and the second order is realized by overlapping. The processing is similar to the two first order holes, but there are many process points to be specially controlled, that is, the above mentioned. The third method is to directly drill from the outer layer to the third layer (or N-2 layer). The process is different from the previous one, and the drilling is more difficult.

For the third order, the second order analogy is.

Examples are as follows:

The first and second order of 6-layer PCB refer to PCB boards that need laser drilling, namely HDI boards

First order HDI board of 6-layer circuit board refers to blind holes: 1-2,2-5,5-6. That is, 1-2,5-6 needs laser drilling

Second order HDI board of 6-layer circuit board refers to blind holes: 1-2,2-3, 3-4, 4-5, 5-6. That is, two laser drilling is required First drill 3-4 buried holes, then press 2-5, then drill 2-3, 4-5 laser holes for the first time, then press 1-6 for the second time, then drill 1-2, 5-6 laser holes for the second time, and finally drill through the hole. It can be seen that the second order HDI plate has been pressed twice and laser drilled twice

In addition, the second order HDI board is also divided into staggered hole second order HDI board and stacked hole second order HDI board. The staggered hole second order HDI board means that the blind holes 1-2 and 2-3 are staggered, while the stacked hole second order HDI board means that the blind holes 1-2 and 2-3 are stacked together, for example: blind: 1-3, 3-4, 4-6