What Is a Microvia?
Microvia
In the era of increasingly compact devices, PCB manufacturers rely on microvias to optimize space and provide high-density interconnections. While these tiny holes may seem like minor components, they play a major role in signal integrity and reliability, so it’s important to understand their impact on a circuit board’s overall design. Microvias are essential for the latest electronic innovations, from smartphones to advanced aerospace equipment, so it’s crucial to stay up-to-date on their trends and developments.
A microvia is a blind hole drilled in conductor-insulator-conductor multilayer to provide electrical interconnections in printed circuit boards. These small holes offer a density advantage over traditional through-hole connections and help manufacturers meet consumer demand for smaller, more portable electronics. To create these small, precise holes, laser drilling is used. The shortest pulses of short-pulse femtosecond excimer lasers can drill microvia holes with diameters of tens of micrometers and depths of a few millimeters. For larger, broader vias, longer-pulse Nd:YAG lasers are employed.
The size of a microvia can impact its physical properties, particularly in the way it handles heat. Larger vias can be prone to thermal cycling, which can cause the copper plating to expand and exert high stress on the thin via walls. As a result, the walls of a microvia can fracture under certain conditions. These failures can occur at the plated interface between two stacked vias or at the interface of a microvia with its capture pad.
What Is a Microvia?
While a microvia’s aspect ratio can affect its reliability, other factors such as the type of fill material and the copper plating process can also contribute to their longevity. Fill materials that do not have the right chemical and thermal properties can cause problems with signal transmission and can lead to premature fracturing. Copper plating with poor consistency and defect levels can also negatively impact a via’s performance, especially when it is exposed to high-temperature environments.
A microvia’s ability to accommodate different types of signals and circuits depends on its size, aspect ratio, and location within the layer stack-up. A blind microvia that connects one layer to another can be either unfilled or filled, while a buried microvia must be filled to ensure good electrical continuity. Blind and buried microvias can be stacked or staggered, and a layered stack-up is preferable because it will reduce the number of holes in a given area of the board. A layered stack-up will also be easier to route because it will allow the designer to place signal traces in a position where they will get the best possible signal quality and minimize signal loss.