Blind Via

A via is an electrical connection between layers in a physical electronic circuit that goes through the plane of one or more adjacent layers. 

A via hole in a PCB consists of two pads in corresponding positions on different layers of the board, that are electrically connected by a hole through the board. The hole is made conductive by electroplating.

In terms of functions, vias can be divided into 2 kinds: one is used as electrical connections; the other is used to fix and align devices.

In terms of process technology, vias can be divided into 3 kinds: blind via, buried via and through via. Blind vias are exposed only on one side of the board, while buried vias connect internal layers without being exposed on either surface. Through vias pass through the entire circuit board, used to achieve internal interconnection or as a align hole. As the through-hole is much easier to achieve, with low cost, so the most printed circuit boards are with through-holes.

In terms of design, vias consist of two parts: drill hole and pad. The size of these two parts determines the size of vias. In high-speed and high-density PCB design, the smaller the via size is, the better, because there will be more space for traces. But smaller vias require more cost.

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