What is a buried via?
Buried via is the kind of PTH via electronically connecting two or more inner layers for multilayer PCB boards. From its literal meaning, buried via is a kind of via buried inside the PCB board that cannot be viewed or saw from the surface. It starts from one inner layer and ends at another inner layer. Via is similar to PTH hole, so buried via is also called buried hole. Buried via is used only for multilayer PCB boards, as there is only through via for single sided and double sided boards.
It is common to have holes or vias in all PCB boards, either used for mechanical fixing, soldering DIP components, or electrical connection between different layers. The most common one is through holes, or through vias. Through vias start from top layer and end at bottom layers, which are made through the boards. If there are certain one or more layers not necessary to have connection with this through via, then the traces have to avoid those places with through vias at those certain layers. Moreover, it is not able to place pads or SMD components at the places with through vias. So there are part of the board space is wasted due to through vias.
In order to avoid above problem and save board space, there are options of blind vias and buried vias. Nowadays the electronic products are getting smaller and smaller, thinner and thinner, more and more complicated, so the PCB boards have to be smaller and smaller. In this case, it requires all possibilities to maximize the usage board space, and buried via is one of the available options with the development of PCB manufacturing technology. Kindly please refer to article “What is a blind via” for more details about blind vias or through vias.
The vias are buried inside the board, so there is no interference to the outer layers and surface pads. It provides more free space to layout pads for SMD components.
Buried via increases the manufacture difficulty and cost as well, because it has to be buried inside boards and usually has very small size, like 4mils, in order to save space. Such small vias have to be made by laser drilling, which is not able to be made by CNC mechanical drilling machine. With the development of laser technology and the application of laser technology in PCB industry, the laser drilling cost of such small vias would be smaller in the future.
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