The way to distinguish first-order, second-order, and third-order is to look at the number of laser holes. The PCB core board is pressed several times, and the laser holes are drilled several times, which is the order. This is the only difference.

1. Drill holes after pressing once == "Press the copper foil again on the outside ==" and then laser drill holes, this is the first order, as shown in the figure below

2. Drill holes after pressing once ==》Press the copper foil again on the outside ==》Laser again==》Press the copper foil again on the outer layer==》Drill the laser again. This is the second order. It mainly depends on how many times your laser has been shot, that is, how many orders.

The second order has two types: stacked holes and bifurcated holes.

As shown in the figure below, there are eight layers of two-step stacked holes, 3-6 layers are laminated first, and the outer layer 2, 7 is laminated, and the laser hole is punched once. Then layer 1, 8 on it and make a laser hole again. It is to make two laser holes. Because such holes are superimposed, the process difficulty will be higher and the cost will be higher.

The following picture shows the eight-layer second-order cross blind hole. This processing method is the same as the eight-layer second-order stacked hole above. It also requires two laser holes. But the laser holes are not stacked together, so the processing difficulty is much less.

The third order, the fourth order and so on.
Expansion information

HDI is the abbreviation of High Density Interconnector. It is a kind of (technology) for the production of printed boards. It uses micro-blind and buried via technology for a circuit board with a relatively high line distribution density. HDI is a compact product designed for small-capacity users.