What are Blind and Buried Via

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It is easy to get caught up with all the exciting stuff going on in the PCB world. And it is no surprise, as an engineer, that you are confused about certain process elements. One such example is via.

The term "via" might sound familiar to you—if you are familiar with PCBs. The via is the part on a PCB that connects the signal layer to the ground layer. Via sizes are always defined relative to the signal and ground layers it connects. There are, in fact, many variations of vias that are needed for different kinds of connections and layer stack-up designs, such as blind and buried, and there is a significant difference between these vias types.

To learn more about these two types of via, keep reading for an insider look behind their function.

blind via

Blind Vias: Introduction

Blind vias connect the inner layer of a PCB to the outer layer. They are ideal for applications without access to the inner layers of the PCB. A blind via is a hole that has been drilled into an otherwise solid plane on one side of a board.

Blind vias can be used in any circuit or application, allowing higher-density boards to be created. They can be used in single- and double-sided PCBs, but they are more common on double-sided PCBs due to the increased complexity of drilling blind via holes through both sides of the board.

Blind vias are often used when a large pad or trace is placed over another, and the designer wants to utilize the area under the large pad or trace for some other purpose. For example, if you have a sizable through-hole component such as a capacitor, you may want to use the area around it for your design elements. In these cases, you can create blind vias by drilling holes in your board where you want them and then using an etch-resist pen to mark them out. You can then drill through those areas with an end mill or drill press and remove any remaining material with an abrasive wheel to expose the copper layer below.

Advantages of Using Blind Vias

  • Because they cannot be seen from the outside of the board, blind vias are often used in surface mount designs to provide an electrical connection between two layers that are not visible on the finished product.
  • The advantage of using Blind vias is that they can be easily installed on the PCB without having to go through multiple layers. This makes them much easier to install and use compared to through-hole components.
  • Blind via has a high impedance compared with other types of vias because there is no contact between the top and bottom layers. Therefore, it can be used for high-frequency applications such as RF circuits where impedance must be maintained or improved at frequencies above 1GHz
  • Blind vias can act as heat sinks for high-power components such as transistors or diodes. This can help dissipate heat from these components and prevent them from overheating and failing prematurely.

Buried Vias: Introduction

Buried vias are buried below the board's surface. They are used when the PCB designer needs to route signals from one side of the board to another. The via is placed in an unexposed area and then filled with solder or epoxy before being covered by a component lead so that it cannot be seen or felt.

Buried vias can be found in many places on your PCBs, but they are most commonly seen in areas with a lot of routing between layers or around sensitive components like microchips or capacitors.

The advantage of this method over traditional vias is that it allows you to make connections between layers without going through any traces on your top-level design. This can be beneficial when there are capacitive effects or other problems associated with routing traces in close proximity to each other.

Advantages of Using Buried Vias

  • The main reason buried via is used is because it eliminates the need for jumpers between boards. The problem with jumpers is that they can increase impedance, act as noise generators, and are bad for signal integrity. Buried vias solve this issue by ensuring that all signals go through a controlled impedance path from one layer to another.
  • Another advantage of using buried vias is that they reduce trace widths by eliminating the extra copper area needed for plating through holes (PTHs). This means you can have smaller traces and feature sizes on your PCBs without compromising performance or reliability.
  • They allow you to connect two different layers without having to make an electrical connection between them on the top side of the board. This can be useful if there's not enough room for a through-hole connection or if you are trying to avoid creating many holes in your board.
  • They are relatively easy to sell since they are very close to through-hole pads and therefore do not require special tools or techniques.
  • They do not take up much space on your board, which is crucial if you design something small that needs as much space as possible for components and connectors such as headers.

Final Thoughts

There are some other variations of vias that we would not go over here, but we think this covers the most important details you need to know. We hope you have better understood blind and buried vias and how they can help you with your PCB layout. The best way to get used to what they are and do is to use them on every board design you make. Check out Hemeixin to learn about microvias in HDI PCB.

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