What Are Buried Vias?

09 June 2023
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You have probably come across buried vias while learning how to design PCBs. Buried vias are those ubiquitous ones buried underneath the top layer of a printed circuit board. They do not get any attention except for maybe the odd design engineer who circles this and makes a note to remove them during fab. However, buried vias have their purpose, so you should not just chuck them out of your designs. To guide you through this topic, I have prepared this simple guide that should help you to understand what they are and how they can help you to design a better PCB.

Buried Vias: Introduction

Buried vias in PCB is an essential conductive connection between inner layers within the circuit board or a conductive pad from one level to another. Referring to a buried via as a hole or aperture through the circuit board material is technically correct, but it provides a confusing image. As the name implies, a buried via is usually placed where it will not be noticed or is intended to be hidden from view. The term “buried” means that the actual visa has been put behind or below the surface layer of the printed circuit board.

Buried vias can be used for numerous reasons. Some include providing pathways for heat dissipation, increasing thermal efficiency in the manufacturing process, adding paths for electrical current, and many more.

Buried Vias Advantages over Other Vias

Buried vias are an excellent option if you need to route power or ground signals on the top and bottom layers of your PCB and the inner layers. They are also ideal for connecting dissimilar materials such as copper traces to FR4 boards. The main advantages of using buried vias in PCB design are:
You can use larger diameter vias without worrying about increased thermal resistance or high-frequency performance issues; for example, you can use 2mm dia vias instead of 0.5mm dia vias on FR4 boards (0402).
It is easier to avoid shorting problems when using buried vias in PCB design because they are buried under components and solder masks/silkscreen.
Buried vias can be used to route signals between different layers, such as power planes and ground planes, which makes them a helpful tool when designing complex circuits with multiple layers; they allow you to route signals between different layers without having to use large through-holes that may cause signal integrity problems or affect mechanical integrity of your circuit board assembly.
Buried vias are more difficult to accidentally drill through when soldering since copper covers them on both sides. This makes them much more reliable than other types of vias.
Using buried vias in your design allows for better layout efficiency and cost savings than other types of vias because there are no extra traces required around each via pin or pad location.
They are hidden from view inside the board, which means they do not affect the aesthetics of your design. This makes them ideal for applications where aesthetics play an essential role in determining if a product is suitable for marketing or not, such as consumer electronics.
Another advantage of buried vias is that they allow for more routing options. For example, when you want to route from one side of a board to the other, you might have to go through several layers to avoid placing your traces on top of each other. This can create a lot of congestion in a design and make it harder for your board manufacturer to manufacture your design successfully. With buried vias, however, you can route around this congestion by using these vias as jumpers between layers.

Using Buried Vias in a PCB

Buried vias connect a layer to the substrate or another layer. They are placed in the same plane as the pads of the component they are connecting. Buried vias can also be combined with standard surface mount vias to connect two layers that are not in the same plane. A buried via is created by drilling through one layer and into the substrate, then filling it with solder before plating it. This method is commonly used in high-speed designs where thermal conductivity is critical. The solder joint creates a thermal path between the top and bottom layers, which increases heat dissipation from components on one side of a board to other components on the other side of the board.

Buried vias are often used when there is no room left for a through-hole connection between two parts because they allow more flexibility in routing signals and traces across multiple layers without adding extra holes or using jumpers. For example, if you have two layers stacked on top of each other, you could use buried vias to connect them instead of having to drill through both layers at once or having a jumper wire between them.

Tips to Use Buried Vias in PCB Effectively

Because the buried via is not visible, it can be challenging to design around them. Here are some tips to help you use them effectively:
Make sure your design has enough space between components. The minimum spacing between components should be greater than the minimum spacing between buried vias to prevent damage to components during drilling or etching.
Before you start designing your PCB layout, think about where you might want to use buried vias and where they might be helpful in your design. Also, consider how these features will affect other aspects of your board design, such as trace widths, clearance spacing, and routing complexity.
Make sure your drill size matches your substrate thickness. A drill too small for the substrate thickness may cause damage to surrounding parts when drilling holes in them. If possible, use drills slightly larger than necessary so they do not overdrill any holes.
Ensure that there is no chance of solder bridging between traces on different layers because of the small separation caused by the plated-through hole.

Final Word

The importance of buried vias cannot be overstated. Even if you have never considered the importance of this component, now is the time to consider it. There are plenty of reasons why these components are helpful, but if you want to know some of their ins and outs, you should immediately incorporate them into your next project. For more details, visit Hemeixin PCB.