Interlayer Connections in PCB: Vias Linking Different Layers of the Circuit Board
In the intricate world of electronics, a fundamental component that often goes unnoticed is the via - a miniature conductive pathway drilled into a Printed Circuit Board (PCB) to establish electrical connectivity between different PCB layers. This news article aims to shed light on the different types of vias and their significance in modern PCB designs.
## Types of Vias and Their Characteristics
1. **Through-Hole Vias**: These vias extend through all layers of the PCB, connecting the top to the bottom layer. They are mechanically drilled and copper plated, making them easy to manufacture. However, they can introduce signal delay and reflection in high-frequency designs. Suitable for simple designs where signal integrity is not a primary concern.
2. **Blind Vias**: Connect an outer layer to one or more inner layers without passing through the entire board. Reducing signal path length compared to through-hole vias, requiring precise drilling to avoid misalignment. Ideal for reducing signal delay and improving signal integrity in high-frequency designs.
3. **Buried Vias**: Connect only internal layers and are invisible from the surface. Suited for high-density designs but more challenging to drill accurately. Used in complex multilayer boards where space efficiency is crucial.
4. **Microvias**: Very small, laser-drilled vias (≤150 µm), used in High-Density Interconnect (HDI) boards. Minimize signal path length, reducing inductance and signal delay. Demand precise drilling techniques. Essential for high-frequency applications where signal integrity is paramount.
5. **Stacked Vias**: Multiple vias stacked vertically across layers. Used in high-density designs to increase routing efficiency. Beneficial for complex PCBs requiring numerous layer connections.
6. **Staggered Vias**: Vias offset from one another across layers. Not stacked directly, which can improve signal integrity by reducing coupling between layers. Useful in designs where minimizing electromagnetic interference (EMI) is important.
7. **Tented Vias**: Covered with a solder mask for protection or isolation. Protects the via from environmental factors and prevents solder from flowing into the via during assembly. Commonly used to prevent solder from entering vias during manufacturing.
8. **Via-in-Pad (VIP)**: A via placed directly beneath a component pad, often filled and capped. Improves thermal performance and reduces the risk of solder flow into the via. Suitable for applications requiring enhanced thermal management and protected via structures.
Each type of via is chosen based on factors such as board complexity, space constraints, signal integrity requirements, and budget.
## Enhancing Processing Power and Miniaturization
The implementation of microvias instead of through holes can increase the processing power of the PCB. They improve electrical characteristics and allow miniaturization for higher functionality in less space, making room for large pin-count chips in smartphones and other mobile devices. Moreover, microvias accommodate smaller component pitch sizes and shrink the PCB's overall size, making them ideal for BGA footprint components.
In high-speed designs, smaller vias are preferred since they reduce stray capacitance and inductance. This reduction is crucial for maintaining signal integrity and minimizing signal delay, particularly in applications such as high-frequency communication systems and advanced microprocessors.
When using filled vias, ensure the pad surface after filling is planar to avoid tombstoning defects. Always use conductive fill for thermal or high-power vias to ensure heat dissipation required for high-power components.
The aspect ratio of a via in a PCB is a significant factor in its reliability. It is the ratio of the PCB thickness to the diameter of the drilled hole or the drill depth to the diameter of the drilled hole for microvias. At Sierra Circuits, they offer an aspect ratio of 0.75:1 for microvias.
Lastly, microvias reduce the layer count in printed circuit board designs and enable higher routing density, eliminating the need for through-hole vias. This miniaturization and increased efficiency are key to advancing the capabilities of modern electronics.
[1] "Understanding Vias in Printed Circuit Boards." AllPCB, 2020, [2] "Types of Vias and Their Applications." Altium, 2021,
In the realm of high-frequency designs, careful selection of vias, such as microvias, becomes crucial due to their ability to reduce stray capacitance and inductance, ensuring signal integrity and minimizing signal delay. This is particularly valuable in applications like high-frequency communication systems and advanced microprocessors.
Moreover, the adaptation of data-and-cloud-computing technology can benefit from the implementation of controlled impedance via structures in PCB designs, as they help maintain electrical characteristics, facilitate miniaturization, and provide room for large pin-count chips in mobile devices.
