Circuit board is made up of layers of copper foil circuits, and the connection between the different circuit layers is the via of the PCB prototyping. This is because the current manufacturing of the circuit board uses drilled holes to connect to different circuit layers. The purpose of connecting is to conduct electricity, so it is called the via hole of PCB prototyping. In order to conduct electricity, a layer of conductive material (usually copper) must be plated on the surface of the drilled hole. Electrons can move between different copper foil layers, because the surface of the original drilled hole is not conductive only with resin.
Generally, there are three kinds of vias for PCB protopying that we often see, which are described as follows:
Plating Through Hole, referred to as PTH
This is the most common type of through hole for PCB protopying. You only need to pick up the PCB and face the light, the hole that can see the bright light is the “through hole”. This is also the simplest hole, because when making it, you only need to use a drill or a laser to directly drill the circuit board, and the cost is relatively cheap. Although through holes are cheap, they sometimes use up more PCB space. For example, there is a six-floor house. I bought its third and fourth floors. I want to design a staircase inside and only connect between the third and fourth floors. For me, the space on the fourth floor is invisibly used by the original staircase connecting the first floor to the sixth floor used up some space.
Blind Via Hole (BVH)
Connect the outermost circuit of the PCB with the adjacent inner layer with electroplated holes. Because the opposite side cannot be seen, it is called the “blind hole”. In order to increase the space utilization of the PCB circuit layer, “blind via” process has emerged. The production method of PCB prototyping requires special attention to the depth of the drilling (Z axis) to be just right. You can drill holes in the circuit layers that need to be connected in the individual circuit layers in advance, and then glue them together, but it needs to be more precise positioning and alignment device. Take the above example of buying a house. A six-story house has only the stairs connecting the first floor and the second floor, or the stairs connecting the fifth floor to the sixth floor, which are called blind holes.
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 drilling after bonding. It must be drilled on the individual circuit layers. After the inner layer is partially bonded, it must be electroplated before it can be fully bonded. Compared with the original “through hole” and “Blind holes”, BVH takes more time, so the price is the most expensive. This process is usually only used for high-density (HDI) circuit boards to increase the usable space of other circuit layers. Take an example. A six-floor house has only the stairs connecting the third and fourth floors, which is called PCB prototyping buried via holes.
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