The way to distinguish between first-order, second-order and third-order is to look at the number of laser holes. How many times the PCB core board is pressed and how many times laser holes are drilled are the steps. This is the only difference.
1. After pressing once, drill holes==>Press the copper foil again on the outside==>Laser drilling, this is the first stage, as shown in the picture below
2. After pressing once, drill holes==> Press copper foil on the outside again==> Laser drilling, drilling==> Press copper foil on the outer layer again==> Laser drilling again. This is level two. The main thing is to see how many times you use laser, which is the level.
The second level is divided into two types: stacked holes and bifurcated holes.
As shown in the picture below, there are eight layers of two-stage stacked holes. The 3-6 layers are pressed together first, and the outer layers 2 and 7 are pressed on top and a laser hole is punched. Then laminate layers 1 and 8 and drill laser holes again. Just make two laser holes. Because these holes are stacked, the process will be more difficult and the cost will be higher.
The picture below shows an eight-layer second-order cross blind hole. This processing method is the same as the eight-layer second-order stacked hole above, and it also requires two laser holes. But the laser holes are not stacked together, so the processing difficulty is much less.
The third level, the fourth level, and so on.
HDI is the abbreviation of High Density Interconnector. It is a (technology) for producing printed boards. It is a circuit board with a relatively high line distribution density using micro-blind buried via technology. . HDI is a compact product designed for small capacity users.
It adopts a modular design that can be connected in parallel. One module has a capacity of 1000VA (height 1U) and is naturally cooled. It can be directly placed into a 19" rack and can connect up to 6 modules in parallel. This product uses a full digital signal process Control (DSP) technology and multiple patented technologies, with full-range load adaptability and strong short-term overload capability, regardless of load power factor and crest factor
Reference: Baidu Encyclopedia HDI board.