The circuit board is composed of layers of copper foil circuits, and the connection between different circuit layers depends on the via. This is because nowadays, the circuit board is made by drilling holes to connect to different circuit layers. The purpose of the connection is to conduct electricity, so it is called the via. In order to conduct electricity, a layer of conductive material (usually copper) must be plated on the surface of the drilling holes, In this way, electrons can move between different copper foil layers, because only the resin on the surface of the original drill hole will not conduct electricity.
Generally, we often see three types of PCB guide holes (via), which are described as follows:
Through hole: plating through hole (PTH for short)
This is the most common type of through hole. As long as you hold the PCB up against the light, you can see that the bright hole is a “through hole”. This is also the simplest kind of hole, because when making, it is only necessary to use a drill or laser light to directly drill the whole circuit board, and the cost is relatively cheap. Though the through-hole is cheap, it sometimes uses up more PCB space.
Blind via hole (BVH)
The outermost circuit of the PCB is connected with the adjacent inner layer by electroplated holes, which are called “blind holes” because the opposite side cannot be seen. In order to increase the space utilization of PCB circuit layer, a “blind hole” process was developed. This manufacturing method needs to pay special attention to the proper depth of the drill hole (Z-axis). The circuit layers that need to be connected can be drilled in individual circuit layers in advance, and then bonded. However, a more precise positioning and alignment device is required.
Buried via hole (BVH)
Any circuit layer inside the PCB is connected but not connected to the outer layer. This process cannot be achieved by using the method of drilling after bonding. Drilling must be performed at the time of individual circuit layers. After local bonding of the inner layer, electroplating must be carried out before all bonding. It takes more time than the original “through holes” and “blind holes”, so the price is also the most expensive. This process is usually only used for high density (HDI) Printed Circuit Boards to increase the usable space of other circuit layers.