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What do Through Holes, Blind Holes and Buried Holes in PCB Printed Circuit Bboard Mean Respectively?

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A. Through Holes in PCB Printed Circuit Boards:

Through Hole: Plating Through Hole (PTH) in integrated circuit design, a through hole is a small opening in the insulating oxide layer that allows a conductive connection between different layers, the combined pack and unpack (pack and unpack, PAU) process is used to prepare through hole arrays.

Circuit boards in different layers of conductive graphics between the copper foil line is used to conductive or connected to such holes, but can not be inserted into the component legs or other reinforcing materials of the copper-plated holes. Printed circuit board (PCB) is formed by the accumulation of many layers of copper foil stacked. The layers of copper foil are not interoperable with each other because each layer is covered with an insulating layer, so they need to rely on through-holes (via) for signal linking, hence the Chinese term through-hole.

Through-holes are also the simplest type of holes, as they can be made by drilling the entire board directly with a drill or laser, which is relatively inexpensive. But relatively, some circuit layers do not need to connect these through-holes, but the through-hole is the whole board through, which will form a waste, especially for the design of high-density HDI boards, circuit boards inch by inch. So although the through-hole is cheap, but sometimes use up more space on the PCB.

B. Blind Holes in PCB Printed Circuit Boards:

Blind Via Hole: Blind Via Hole (BVH) is a through hole that connects the surface layer and the inner layer without penetrating the whole board. Blind vias are located on the top and bottom surfaces of the printed circuit board, with a certain depth, for the connection of the surface layer circuits and the inner layer circuits underneath, and the depth of the hole usually does not exceed a certain ratio (aperture diameter).

The outermost circuit layer of a PCB is connected to the neighboring inner layer by plated holes, which are called "blind holes" because the opposite side cannot be seen. In order to increase the space utilization of PCB circuit layers, the "Blind Hole" process was created.

Blind vias are located on the top and bottom surfaces of a circuit board and have a certain depth, and are used to connect the surface layer circuits to the inner layer circuits below, and the depth of the vias generally has a specified ratio (aperture diameter). This type of production requires special attention, the depth of the drilled holes must be just right, if you do not pay attention to the hole will cause plating difficulties. Therefore, few factories use this method of production. In fact, let the prior need to connect the circuit layer in the individual circuit layer when the first drilled holes, and then finally glued together is also possible, but requires a more precise positioning and alignment devices.


C. PCB Printed Circuit Board in The Buried Hole:

Buried hole: Buried Via Hole (BVH) buried holes are made in the inner layer of the hole, the table bottom layer is not visible, for the inner layer of signal interconnection. That is, the printed circuit board (PCB) internal connection between any circuit layer, but not with the outer layer of conduction, that is, not extended to the surface of the circuit board means that the conduction holes.

This production process can not be reached through the circuit board bonding and then drilling, it is necessary to individual circuit layer when the drilling operation, the first partial bonding of the inner layer after the plating process, and finally all bonded. Since the process is more laborious than the original through-hole and blind-hole, it is also the most expensive. This process is usually used only for high-density circuit boards to increase the space utilization of other circuit layers.

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