Blind Via Hole: The outermost circuit of the PCB is connected to the adjacent inner layer with a plated hole. Because you can’t see the opposite side, it is called “blind via”. In order to increase the space utilization of the PCB circuit layer, the “blind hole” process came into being. This production method requires special attention to the depth of the drilling (Z2 axis) to be just right. This method often makes it difficult to electroplate in the hole, so almost no manufacturer adopts it; you can also drill holes in the circuit layers that need to be connected in advance when they are in individual circuit layers, and then glue them together, but it requires more precise positioning and alignment devices.

Buried hole: Buried hole, the connection of any circuit layer inside the PCB but not connected to the outer layer. This process cannot be achieved by drilling after bonding. It must be drilled in individual circuit layers. After partially bonding the inner layer, it must be electroplated first, and finally all can be bonded. It takes more time than the original “through hole” and “straight hole”, so the price is also the most expensive. This process is usually only used in high-density (HDD circuit boards to increase the available space of other circuit layers.