Blind & Buried Vias

There are several kinds of holes in printed circuit boards' fabrication, among them, Vias are the copper-plated holes that connect the layers of the board. The standard via is named as a through-hole via. But blind via and buried via is often used as an instead when through-hole via is not suitable. Blind vias and buried vias are used to make connections between PCB layers where space is limited.

What are the blind vias and buried vias?

Blind vias connect the outer layer to one or more inner layers but never pass through the entire circuit board. The vias for each connection-level need define in a separate drill file in PCB design.

Buried vias only connect two or more inner layers without going through to the outer layers. The vias are "buried" on the board and not visible from the outside. Buried vias also require a separate drill file. As usual, the larger you choose the annular rings on the inner layers, the more stable the connections.

Advantages and disadvantages of blind vias and buried vias

1. Reduce PCB volume

The application of blind vias and buried vias can meet the density constraints of lines and pads on a typical PCB design without increasing the number of layers in the boards and size of printed circuit boards.

2. Save surface space

As the shortening vias only pass through necessary layers, more surface area is available for electronic components. The buried vias will not affect any trace or surface mount component on the top or the bottom layers of PCBs. And it will add space on outer layers through place trace or an SMD pad on the outer layer directly over the buried vias is possible.

3. Many possibilities for PCB design

Blind vias can widen the BGA breakout channel and reduce layer count for density PCB design.

4. More expensive

The technology of Blind vias and buried vias require additional operation during the PCB fabrication. The cost of the board using this technology is usually higher than a regular standard multilayer board with the same count of layers and processes. Engineers always use blind vias or buried vias when necessary due to the higher cost in PCB mass production or PCB assembly prototype.

Some tips in the manufacturing of blind vias and buried vias

1. A via must go through an even number of copper layers

2. A via cannot end at the top side of a core in the board

3. A via cannot start from the bottom side of the board core

4. A via cannot begin or end at the inside or the end of another blind/buried via

With years of experience in PCB manufacturing, engineers and production facility in NextPCB are equipped to handle the complexity required in blind vias and buried vias technology. The benefit in NextPCB is that whether the vias are laser or mechanically drilled, the best or the cheapest technology is applied to suitable for customers' requirements. Please contact the online service if you have any questions about blind vias or buried vias in the project of PCB assembly prototype or PCB mass production.