Designing a PCB of multiple layers often comes with the requirement of connecting different layers of the PCB. Thus, the circuits of different PCB vias connect the circuits of other layers. Vias are barrel-shaped conductive holes. While designing a PCB, various kinds of vias can be employed according to the circuit requirements. According to IPC, there are eight different types of vias. As it is clear from the heading, we are going to discuss everything about buried vias.
What are Buried Vias?
A buried via connects the internal layers of the PCB as the name suggests buried vias are buried under the outer layers of the PCB which in turn helps the designers maximize the surface of the PCB allowing more space for component placement. While designing a PCB with complex circuitry, buried via holes are very helpful as they provide more space for components, improved signal integrity, simplified routing, and a clean design.
High-Density Interconnect (HDI) PCBs are the backbone of the devices that we use in our day-to-day lives like smartphones, tablets, etc. HDI PCBs have a large number of components in a compact space creating minimal room for routing. Buried Vias help in maximizing the use of valuable surface space and managing complex interconnections.
The Differences among Buried Vias, PTH Vias and Blind Vias
Buried vias are excellent for utilization of space on PCB as well as preserving signal integrity and simplifying routing but its manufacturing is much more complex which also affects its cost. Apart from buried vias, the two most commonly used vias are blind vias and through-hole vias. Let’s see how they differ from buried via holes in many features. The following table describes the difference between these vias.
| Feature | Buried Vias | Through-Hole Vias | Blind Vias |
| Space utilization | Maximizes surface area for components and traces by hiding vias within the layers | Occupies surface space on both sides, reducing the available area for components and traces | Partially occupies surface space on one side, allowing more room than through-hole vias. |
| Signal integrity | Improved signal integrity by reducing surface traces and enabling shorter signal paths | Potential for signal degradation due to longer signal paths and more surface traces | Better signal integrity than through-hole vias but not as good as buried via holes |
| Manufacturing complexity | More complex | Simplest to manufacture | Less complex than buried vias |
| Routing complexity | Simplifies routing by allowing more flexible internal layer connections | Increases routing complexity due to the need to avoid surface components and traces | It Simplifies routing on the side of the blind but still requires careful planning |
| Cost | Higher cost due to manufacturing complexity | Cost is lower due to simplicity | intermediate cost, higher than through-hole but lower than buried via holes |
| Applications | Used in high-density, high-performance PCBs such as HDI boards | Common in simpler, less dense PCBs | Used in moderately complex PCBs where some surface area needs to be conserved |
Applications of Buried Via PCBs
Modern electronic devices carry a large number of components within a limited space; buried via holes are very desirable for the efficient use of this space. The sectors where the employment of buried via holes in PCB enhances the overall performance of the device are-
Communication devices: Devices using 5G infrastructure perform high-speed signal transmission and complex signal processing with the use of buried via holes. The length of signal paths is shorter which reduces the risk of external interference.
Automotive Electronics: In the automotive sector, the performance and efficiency of vehicles, especially electric and hybrid cars, heavily rely on the power electronics used in them. Buried via PCB reduces the risk of parasitic capacitance and inductance due to which power conversion and distribution become more efficient.
Aerospace and Defence: Whether in aerospace facilities or military facilities, the circuit board is required to have an extremely compact design to achieve more sophisticated functions. Therefore, their demand for buried via PCBs is very high, mainly reflected in HDI PCBs.
Medical Devices: The medical field requires the use of many small but highly sophisticated equipment, such as hearing AIDS, pacemakers and so on. For this purpose, there needs to be enough space on the board surface to install more electronic components and distribute more electrical routes, and this is where the buried via PCBs comes into play.
Consumer Electronics: Usually, we use mobile phones, game consoles, tablets and other consumer electronics, although the size is small, but has a surprising variety of powerful functions. This all relies on complex high-density PCBs within the device, which tend to be in the form of buried via PCBs.
Advantages of Buried Vias in PCBs
Buried vias are very advantageous in enhancing the performance of the PCB. The major advantages of Buried Vias are discussed below.
Efficient Use of Space: By using buried vias lots of surface area is saved which can be used for placing more components and traces which in the end increases the density of the PCB. This is especially important in modern electronic devices where space is a major concern. Apart from saving space on the surface it also helps in reducing the number of layers of the PCB by using buried via holes internal layers can directly be connected without disturbing the external layers.
Improving Signal Integrity: The risk of signal degradation is minimized by the use of buried via holes because of these vias the signal path is short and more direct thus it is handy in improving the performance of the PCB at higher frequencies.
Thermal Management: Since more surface area is free due to buried vias, free space can be used to add thermal vias and heat sinks, thus overall thermal management of the PCB is improved. Along with that, buried vias can also be used to create heat paths that dissipate heat from the components that are sensitive to higher temperatures.
Reduced Electromagnetic Interference: Unlike through holes, buried via holes are not exposed to the environment, rather they are shielded inside the PCB layers this shielding protects it from electromagnetic interference and reduces the potential risk of cross-talk.
Key Considerations for Buried Vias in PCB Design
If you want to employ buried via holes in your PCB design, some considerations need to be addressed to achieve an effective design. These major considerations may include cost implications and compatibility with the fabrication process. Let’s take a look at how these are the major considerations in the manufacturing process.
Compatibility with Fabrication Process: The PCB design using buried via hole is not compatible with every PCB material thus the designers must ensure that the PCB materials such as dielectric materials and copper layers are compatible with the buried vias. Apart from that it is also necessary for the designers to ensure the manufacturer can produce PCBs with buried via holes.
Cost Implications: Manufacturing buried via PCBs is a complex process and this complexity also affects its price, which is higher than through hole, and blind vias. But it also offers many advantages like efficient utilization of PCB surface area, enhanced signal integrity, and thermal management. All of these advantages can justify the higher cost and if the PCB is to be produced in large volumes then the price will be lower.
