High-Density Interconnect Via Types and Structures

26 June 2023
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HDI (High-Density Interconnect) is an advanced technology that connects electronic components with extremely high density and speed. HDI provides superior electrical performance compared to traditional interconnects, making it ideal for applications requiring high data rates and low power consumption. HDI also offers a smaller footprint and lower profile than other interconnect technologies, making it suitable for space-constrained applications.

This blog post will look at HDIs, the type of vias used in HDIs, and their structure. Let's get started!

Applications and Advantages of HDIs

HDIs are typically made using microvia technology, allowing extremely small and closely spaced vias to be created in an HDI substrate. Microvias are typically less than 10 microns in diameter and can be spaced as close as 20 microns apart. This close spacing of vias results in a very HDI, which can support data rates over 10 Gbps.

Application

HDIs are used in a variety of applications, including:

High-speed digital logic circuits
Servers and storage systems
Networking and telecommunications equipment
High-end consumer electronics
Military and aerospace systems

Applications

HDIs offer some advantages over traditional interconnect technologies, including:

Higher Data Rates: HDIs can support data rates above 10 Gbps, making them ideal for high bandwidth applications

Lower Power Consumption: HDI interconnects have lower impedance and resistance, which results in lower power consumption.

Smaller Footprint: HDIs have a smaller footprint than other interconnect technologies, making them ideal for space-constrained applications.

Reduced Cost: HDI interconnects are typically less expensive than other high-density interconnect technologies.

HDIs are an essential part of the modern electronics landscape and are used in applications requiring high bandwidth and low power consumption.

HDI Via Types and Structures

There are several types of vias used in HDI designs. The most common are blind vias, buried vias, and through-hole vias. Each type has advantages and disadvantages, so choosing the right one for your particular application is essential.

Blind Vias

Blind vias are commonly used in HDI designs. They are created by drilling a hole through the outer layers of a PCB stackup and connecting it to an inner layer via a conductive pad. This type of via is "blind" because it does not extend through the board.

Blind vias are commonly used in HDI designs for several reasons:

They can be used to connect inner layers that are not adjacent to each other. This allows for more flexibility in routing and makes it easier to avoid crosstalk between signals.
Blind vias take up less space than through-hole vias, which is essential in high-density designs.
Blind vias can be used to connect multiple signals to the same inner layer, which helps create buses or other high-speed data paths.

Blind vias are typically created using a laser drilling process. A focused laser beam is used to drill a hole through the outer layers of the PCB. The hole is then filled with a conductive material, such as copper, and connected to an inner layer via a conductive pad.

Blind vias have many advantages over through-hole vias:

They are less expensive to create and take up less space
Blind vias can be used to connect multiple signals to the same inner layer, which helps develop buses or other high-speed data paths

Despite their advantages, blind vias have a few disadvantages:

They are more difficult to inspect than through-hole vias; this is because the conductive material that fills the via can obscure defects
Blind vias are more likely to fail than through-hole vias; this is because the conductive material that fills the via can act as a barrier, preventing repairs to the inner layers

Buried Vias

A buried via is a via that is not exposed on the surface of the PCB. Buried vias are typically used in HDI applications where space is limited. They are also used when routing signals between multiple layers are required.

There are several benefits to using buried vias:

They provide a more reliable connection than surface-mount vias.
They are less likely to be damaged during handling or assembly.
They can be used to route signals between multiple layers, which is often required in HDI applications.

Despite the benefits of buried vias, there are some challenges associated with their use:

They are more difficult to fabricate than surface-mount vias.
They are more challenging to inspect and repair.
They can be more expensive than surface-mount vias.

Despite the challenges, buried vias offer many benefits that make them well suited for HDI applications. With the ever-increasing demand for HDIs, the use of buried vias is likely to continue to grow.

Through-Hole Vias

Through-hole vias are an important part of HDI designs. They provide the means for electrical connection between layers of printed circuit boards (PCBs). HDI designs typically have multiple layers of circuitry, and through-hole vias allow signals to be routed from one layer to another.

Through-hole vias are typically made by drilling a hole through the PCB, then plating the inside of the hole with a conductive material such as copper. The via is then filled with an insulating material, and a conductive trace is run from one layer of the PCB to the other, passing through the via.

Through-hole vias have several advantages over other vias, such as blind vias and buried vias:

They are easier to manufacture and provide a more reliable electrical connection
Through-hole vias can be used to connect multiple layers of circuitry, which is often necessary for HDI designs

Despite their advantages, through-hole vias have some disadvantages:

They are not suitable for very high-density designs, as the holes can take up a lot of space on the PCB
They are more expensive to manufacture than other types of vias

Through-hole vias are a vital part of HDI design and can be used to connect multiple layers of circuitry. However, they have some disadvantages that should be considered before using them in a plan.

Final Thoughts

When choosing a via for your HDI PCB design, it is essential to consider the advantages and disadvantages of each type. Blind vias are the easiest to create but are not as reliable as buried or through-hole vias. Buried vias are more reliable than blind vias but are more challenging to develop. Through-hole vias are the most reliable via, but they are the most difficult to create.

The type of via you choose will depend on the requirements of your particular application. If reliability is more important than ease of creation, then a through-hole via may be the best choice. If ease of creation is more important than reliability, then a blind or buried via may be the better choice.