As PCB factory china knows that，the stack-up of the layers is clear, but the question that comes to mind is about the connection of these layers. These layers can be interconnected with all layers or a few selected ones. As the layers are stacked up one over the other, having insulation between them, the only way to connect them is vias.

  Via can connect the layers of the PCB. It is actually a hole created to make a connection between the layers. The hole can be for the connection of two layers, three layers, or as many as you need. A hole is created in the PCB, and its walls are plated so that it can create a connection.

Primarily, there are three types of vias used in PCB.

1. Plated Through Hole (PTH)
2. Blind Via
3. Buried Via

  PTH is the simple type of via that joins all layers together. It is just like drilling the PCB until the drill bit comes out from the other side. After drilling, the hole is plated so that connections can be made.

  Blind via can be seen from one side because it creates the connection of the surface layer with any layer present under it. It can be used to create a connection with internal layers, and there can be one or more internal layers.

  Buried vias are buried under the PCB. They are not visible from either side. These vias create a connection between the inner layers only. Thus, these are the most complicated vias.

  According to the connections, the PCB layers are arranged. The vias are created as per the requirement. For the plating of via, the board is drilled and then cleaned to remove the dust and debris. A thin layer of copper is applied first. Then, the board is passed through an electroplating process. There are a series of chemical and electroplating baths. After this process, the vias create a connection between the layers.