Due to the limitations of the process described above, this approach has become less popular.

2. Sequential lamination

Sequential lamination in the Altium blind hole
SMT chip factory can make blind holes and buried holes at the same time. First, make the circuit and PTH of the inner four layers (six layers + double layer, top layer double bottom layer, inner four layers). Then stack the four pieces into a four-layer board, and then punch holes. This method has a long technological process and high cost, and is not universal.

3. Forming process and non-mechanical drilling method
This method is the most popular in the industry, and many domestic manufacturers have similar manufacturing experience.

This method extends the concept of sequential lamination above, adding layer by layer on the outside of the board, and using non-machined blind holes as interlayer interconnections. Here are the three main methods:

Photoresist - Photoresist is formed using photoresist, which is also a permanent dielectric layer. Then develop the exposed film at a specific position to expose the copper pad at the bottom to form a bowl-shaped blind hole. After etching, smt manufacturers can get external circuits and blind holes. Instead of copper plating, copper paste or silver paste is filled to complete conduction. According to the same principle, it can be added layer by layer.
Laser Ablation - There are three types: CO2 laser, excimer laser, Nd:YAG laser.