Microvias Can Be Used in High-Power Applications
As technology tends towards miniaturization, printed circuit boards have shrunk in size, allowing powerful electronics to fit into our devices. One of the most important developments has been the use of microvias, which reduce PCB thickness, provide conductive pathways across multiple layers and enable higher-speed signal transmission. However, microvias also present challenges and must be carefully designed to ensure high reliability. This is why understanding their many different types, benefits and design considerations is critical for PCB designers.
Microvias are small holes drilled in the surface of the PCB that can be filled with copper or left empty for non-conductive purposes (blind). They are often used to connect between different layers in the same board, providing a more flexible connection path than conventional through-hole (TH) connections. Traditionally, these holes have been plated through using conformal plating and pulsed plating to eliminate voids in the via body. However, these processes require precise control to avoid over-filling, which can lead to metallurgical defects that impact performance and reliability.
To reduce the risk of defects, laser drilling is used to drill holes in the PCB layer that will receive a microvias. This process delivers precise energy pulses and accurate positioning to ensure a quality drilled hole that is free of voids, which can compromise the conductive integrity of the via. To further minimize the chance of issues, the thickness of the copper foil used to fill a microvia is tightly controlled. Thicker copper foils improve conductivity, but they can be more difficult to work with in the fabrication process.
How Microvias Can Be Used in High-Power Applications
The most common microvia defect is debris-based interconnect defects (ICDs). These types of defects occur when the copper plating in a via has an insufficient bond to the metal substrate underneath it. They can result in a weak copper band that is more susceptible to stress during assembly and usage, which may cause it to break off.
Another type of ICD affecting microvias is copper fatigue, which results from repeated thermal cycling. This stress can cause the copper plating to fracture near the via’s neck region, where it curves inward and concentrates stress. This problem is most prevalent in high-aspect ratio through-hole vias, where the neck region is especially vulnerable.
A third type of ICD that affects microvias is copper oxidation, which is caused by oxygen diffusion through the copper. This can happen during assembly, storage or usage, and causes the conductive path to degrade and short out. In addition, oxidation can cause the copper to lose conductivity and become brittle, which could lead to failure of the microvia.
Stacked microvia structures are those that have microvias stacked in the same plane. This allows PCB designers to take advantage of the flexibility offered by microvias by creating layers that transition in different areas of the board. Alternatively, they can use staggered microvias to increase space available for other components, traces or other features that cannot be moved away from overcrowded areas. However, data compiled in recent years indicates that stacked microvia structures are more likely to experience manufacturing failures than staggered structures.
