What is a blind via?

Blind via is the kind of via electronically connecting one outer layer with one or more inner layers in multilayer PCB boards. From its literal meaning, blind via is a kind of via that cannot be viewed or saw through from the surface of PCB boards. It starts from one outer layer, either top layer or bottom layer, and ends at inner layer. Via is similar to PTH hole, so blind via is also called blind hole. Blind 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 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. So there are part of the board space is wasted.

In order to avoid above problem and save board space, the blind via comes up on some PCB boards. Especially 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 blind via is one of the available options with the development of PCB manufacturing technology.

Blind via increases the manufacture difficulty and cost as well, because it has to end at a certain inner layer and usually of small size. Blind via is usually required to be very small 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 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 and smaller.

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