What is a buried via hole?

Mar. 28, 2018

Many people are not very clear about Blind vias.

Blind vias: Blind vias are types of vias that connect PCB inner traces to PCB traces, and do not penetrate the entire PCB board.

Buried vias: Buried vias are the type of vias that connect traces only between inner layers, so they are not visible from the PCB surface. This is also a blind buried hole.

The figure shows the structure of an 8 layer HDI PCB:

A: Plating Through Hole (L1-L8)

B: Buried Via Hole (L2-l7)

C: Blind Via Hole (L7-L8)

D: Blind Buried Hole (L1-L3)

Do you know several ways of hole?

In general, we often see three kinds of PCB vias, which are described as follows:

Through Hole: Plating Through Hole Short PTH

This is the most common kind of via hole. You just pick up the PCB and look at the light. The hole which can see the light shines is the “through hole”. This is also the simplest kind of hole, because when you are making it, you only need to use a drill bit or laser light to directly drill the circuit board completely, and the cost is relatively cheap. In contrast, some pcb circuit layers do not need to connect these through holes. For example, we have a six-story house. I bought it on the third floor and the fourth floor. I want to design a staircase inside to connect only the third floor. So it is ok for me the space on the fourth floor virtually invisible to the stairs on the first floor while connected to the sixth floor to use some space. So though the through hole is cheap, sometimes it will use more PCB space.

Blind hole: Blind Via Hole (BVH)

The outermost circuit of the PCB is connected to the adjacent inner layer with a plated hole. Since the opposite is not visible, it is called "blind pass." In order to increase the space utilization of the PCB circuit layer, a "blind-hole" process was born. This method requires special attention to the depth of the hole (Z-axis) should be just right. It can often cause the hole plating is difficult so almost no manufacturer. You can also connect the circuit layer in the individual circuit layer before you drill the holes first. Finally glued them together, but you need more precise positioning and alignment devices.

Buried Hole: Buried Via Hole (BVH)

The connection of any PCB circuit layer inside the PCB is not conducted to the outer layer. This process cannot be achieved by means of post-bonding drilling. It is necessary to drill holes in individual circuit layers. After the inner layers are partially bonded. they must first be electroplated before they can be completely bonded. Compared to the original “through holes” and "blind hole", buried via hole is more time-consuming, so the price is also the most expensive. This process is usually only used on HDI PCB board to increase the usable space of other circuit layers.