What is a Buried Via?

Buried Vias are an essential component of modern printed circuit board (PCB) design, specifically multi-layered PCBs. They are small holes that are drilled into the board to connect the different layers of a PCB. Buried vias differ from blind and through-hole vias because they are located between two inner layers of the PCB and do not penetrate through the surface of the board. This allows for the creation of more complex and compact board layouts, making them ideal for modern electronics with smaller form factors. Buried vias are used to route signals and power between layers while minimizing the number of layers needed, reducing the overall cost and size of the board.

Cross-sectional view of buried vias

In this article, we will dive deeper into the technical aspects of buried vias, how they work, and the different types of buried vias commonly used in PCB design.

What are the benefits of using Buried Vias in PCBs?

Buried vias are an important element of modern PCB design and offer several benefits that can improve the performance, reliability, and cost-effectiveness of electronic devices. Here are some specific benefits of using buried vias in PCB design:

• Reduced Layer Count: Buried vias allow designers to reduce the number of layers in a PCB design, which in turn reduces the cost and size of the board. With buried vias, it is possible to create a high-density interconnect (HDI) structure that combines multiple layers of circuitry into a single layer, which can save space and reduce costs.
• Increased Routing Density: Buried vias enable designers to increase the routing density of a PCB, which allows more components to be placed on the board without increasing the size. This can be particularly important in high-performance applications where space is limited, and signal paths need to be kept short.
• Improved Signal Integrity: Buried vias can help improve signal integrity by reducing the length of the signal path between components. This can reduce the risk of signal degradation and improve the overall performance of the device.
• Decreased Production Time and Costs: Buried vias can also help reduce production time and costs by simplifying the manufacturing process. Since buried vias do not penetrate through the surface of the board, they require less drilling and plating than through-hole vias, which can save time and money.
• Design Flexibility: Buried vias offer designers greater flexibility in terms of where they can place components on the board. By reducing the number of layers, designers can free up more space for components and create more complex routing patterns.
• Compatibility with Advanced Technologies: Buried vias are compatible with advanced technologies such as HDI and micro via technology, which can help increase the functionality and reliability of electronic devices.

These advantages make buried vias an essential element of modern PCB design and a valuable tool for electronics engineers and designers.

Different Types of Buried Vias

Several different types of buried vias are commonly used in PCB design. Each type has its advantages and disadvantages, which make them suitable for different applications. Here are some of the most common types of buried vias, along with their advantages and disadvantages:

Stacked Vias

Stacked vias are a type of buried via that connects two or more inner layers in a PCB. They are typically used when multiple layers need to be connected, but only a few of them require the connection. In other words, stacked vias are used when there is a need to connect specific layers in a PCB without having to create a through-hole that passes through the entire board.

• Advantages: Their ability to reduce the number of layers required for the PCB, which can lead to cost savings.
• Disadvantages: Stacked vias can be more challenging to manufacture, and they may require more space than other types of vias.

Sequential Lamination Vias

Sequential lamination vias are a type of buried via that is created by laminating two or more PCBs together. The via is drilled through each layer of the PCB stack and then plated. This allows the different layers to be connected without having to create a through-hole that passes through the entire board.

Sequential Lamination in PCB Manufacturing

• Advantages: Sequential lamination vias offer excellent signal integrity and are suitable for high-frequency applications. They can also reduce the number of layers needed, which can lead to cost savings.
• Disadvantages: This type of vias can be challenging to manufacture and may require additional processing steps.

Conclusion

Buried vias are a vital component of modern PCB design, enabling the creation of complex and compact board layouts. They offer several benefits, including reducing layer count, increasing routing density, improving signal integrity, decreasing production time and costs, and offering design flexibility. Different types of buried vias can be used, each with its advantages and disadvantages, making them suitable for various applications. Understanding the different types of buried vias and how they work can help electronics engineers and designers create better-performing and more cost-effective electronic devices.

A Buried Via hole connects layers inside a multi-layer PCB. These vias cannot be seen on the surface of a Printed Circuit Board. Buried vias are difficult to construct, as they need to be created in layers within the PCB. Designers like to use these vias, as they do not take up board space on every layer, thereby enabling smaller PCBs.

High-density PCBs usually use buried vias.