HDI: High density interconnect, high density interconnect, non-mechanical drilling, microblind hole ring up to 600mil, inner and outer layers of wiring width/cable gap up to 4mil are called HDI.

Blind hole: By abbreviation blind, realize the connection as well as the inner and outer layers

Burn hole: Through the abbreviation burials, realize the connection between the inner layer and the inner layer

Under normal conditions, 8-bit single-chip microcomputer products use two layers of holes. 32-bit single-chip intelligent hardware, using 4-6 layers of holes; Linux and Android class intelligent hardware, using 6-layer hole to 8-layer one, one step HDI wire board;

Compact products (such as smartphones) typically use 8 to 10 and 2 layer circuit boards.

Other pcb holes are introduced

From the first layer to the last layer, there is only one kind of hole. Both outside and inside, the holes are penetrated. It's called the orifice plate.

It doesn't matter if you use layers or not. The two layers you typically use are all orificesand many switches and military circuit boards are used to perform 20 layers.

A drill is used to drill holes and copper is plated into the holes to form paths.

It should be noted here that the inner diameter of the hole is usually 0.2mm, 0.25mm and 0.3mm, but usually 0.2mm is more expensive than 0.3mm. The bit is slow because it is too thin and prone to fracture.