Microvias Impact Signal Propagation Delay
As electronic devices become more compact while offering increased functionality, the need to interconnect layers in multilayer printed circuit boards (PCBs) becomes increasingly critical. In response, PCB designers utilize microvias to facilitate the necessary connections. Compared to traditional through-hole vias, microvias provide a more efficient and compact way to connect layers in multilayer circuit boards. As a result, they are becoming the standard for high-end electronics and the key to the continued innovation of electronic devices across many industries.
Microvias are a vital component of high-performance circuit boards, as they reduce signal propagation delay, which is the time it takes for signals to travel from one layer of the PCB to another. They are also a valuable tool for increasing the density of the layers in a board, which allows manufacturers to fit more functionalities into a smaller space. Moreover, they can help reduce electromagnetic interference (EMI) issues that are often caused by signal reflection in the holes of traditional through-hole vias.
Nevertheless, it’s important to note that despite their benefits, the reliability of microvias is dependent on several factors, such as copper plating, fill material, and aspect ratio. Using the wrong copper foil for microvia fabrication can lead to gaps and flaws in the via body, which can compromise the quality of signal transmission and ultimately impact the performance of the final product.
How Do Microvias Impact Signal Propagation Delay?
The thickness of the copper foil used for microvia fabrication is crucial, as it impacts both its conductivity and heat dissipation capabilities. In order to achieve optimal results, it’s best to use a copper foil that is thin enough to enable good adhesion to the epoxy resin but thick enough to allow sufficient flexibility and conductivity. It’s also a good idea to choose a copper foil with low dielectric constants, as these can contribute to lower signal loss and reduced latency in signal paths.
Aspect ratio is a key factor in determining the quality of microvias, as it defines the relationship between the diameter of a via hole and its depth. Aspect ratio is particularly important in high-speed applications, where the smallest possible hole size is needed for maximum performance.
After drilling, PCB manufacturers need to fill and plate the microvias. Whether through a conformal or aggressive pulse plating process, it’s critical that manufacturers ensure a uniform deposit of copper across the via walls to prevent voids and contamination. Achieving this requires the right copper plating additives and a consistent and defect-free deposit of copper.
Whether they’re filled with epoxy and pure copper or pure copper, blind microvias can be plated from either the top or bottom. Staggered microvias are especially helpful for improving the performance of a board, as they can be deployed strategically to shift power and ground choke points away from overcrowded areas of the copper plane. This can improve performance, reliability and overall manufacturability in tight designs.
