Buried Via Holes Used in High-Speed PCB Designs
Vias are barrel-shaped conductive holes on a printed circuit board (PCB). They connect the inner layers of the PCB and act as transmission lines for electrical signals. However, at high frequencies, vias can cause signal reflections and increase insertion loss, and can lead to impedance discontinuity if their size and shape are not carefully optimized. In addition, the unused portions of the via barrel can create parasitic effects such as capacitance and resonance that can degrade signal integrity.
To avoid these issues, designers use buried via hole, also known as blind vias, to connect the inner layers of a multilayer PCB without passing all the way through the outer surface of the PCB. They can be drilled mechanically or laser and are plated with copper before being soldered to the other layers of the PCB. Compared to standard through-hole vias, blind and buried vias have lower insertion loss and lower impedance discontinuity, making them ideal for high-speed designs.
There are two different types of buried vias: stacked and blind. Stacked vias are drilled on the inner layers to overlap with each other and have a flat hole wall, while blind vias don’t. Stacked vias are a more efficient alternative to traditional through-hole vias, as they can be fabricated with much smaller drill diameters. Moreover, they can be positioned close to each other, resulting in shorter distances for signal lines and reduced impedance discontinuity.
Are Buried Via Holes Used in High-Speed PCB Designs?
However, stacked vias require careful planning because they can add significant signal interference. To prevent this, a design engineer must ensure that the gap between the stacked vias is small enough to minimize signal interference. This requires careful analysis of the signal flow and signal transmission paths, as well as understanding the effects of the overlapping layers.
Aside from the benefits mentioned above, buried vias have several other advantages that make them an essential component in high-speed PCB design. They allow for a shorter signal path and more efficient routing, while providing improved electromagnetic compatibility (EMI). They can also reduce the overall cost of the PCB and enhance its performance by increasing the operating bandwidth.
As a result, more and more manufacturers are using buried vias in their products. The manufacturing process for a PCB with buried vias is more complex than regular through-hole boards, and it requires advanced manufacturing technology and attention to detail. Additionally, buried vias take longer to make than through-hole boards, which makes them more expensive. Despite these challenges, the increased performance offered by buried vias can outweigh the additional costs associated with their fabrication.
