How Micro Vias Can Be Used in Distributed Sensor Networks

How Micro Vias Can Be Used

The size of microvias on a circuit board can make or break a device’s functionality. As microvia technology advances, designers can pack more components onto a smaller board, increasing the device’s input/output density while improving the reliability of the PCB. However, leveraging microvias requires careful PCB design and fabrication. Incorrectly placed or inadequately plated microvias can cause poor circuit performance and even premature failure. Incorrectly designed boards can lead to rework, production delays, and potentially lost sales for the manufacturer. To ensure the best possible results, it’s important to work with a PCB manufacturer that can provide proper design support and specialized microvia drilling processes.

In the context of printed circuit boards, microvias refer to small holes that connect layers of a board’s copper planes. They are often used to route power and ground to and from electrical components in a high-density package (HCP) or multi-chip module (MCM). These holes, also called buried vias, are filled with conductive epoxy or pure copper before being plated with gold for soldering.

Unlike through-hole vias, micro vias have a low aspect ratio and are typically no larger than 0.060 in diameter. IPC standards define a microvia as a hole with an aspect ratio of 0.75:1 or less, though a smaller aspect ratio is common. Stacked and staggered microvias are two ways to form connections across multiple layers in a circuit board. Both types are capable of connecting a circuit board’s traces, but each has its own unique advantages and benefits.

How Micro Vias Can Be Used in Distributed Sensor Networks

The most important factor to consider when designing a PCB with microvias is the aspect ratio of the holes. Having a low aspect ratio ensures that the microvia is small enough to be effectively platenable while allowing for a strong connection with other copper layers in the PCB.

A high aspect ratio can result in thermal cycling stress that could lead to the failure of a microvia, particularly at its plated interfaces. These include the interface between stacked microvias and at the interface of a via with its capture pad. Other failure modes may also occur at the knee of a microvia, where copper slopes into the top of the via.

In addition to the aspect ratio, another factor that influences microvia reliability is its internal fill and copper wrap plating. Plating a microvia with pure copper or epoxy + copper resin is essential to ensure its long-term reliability. Adding additives to the plating process can help prevent copper from concentrating along the walls and top of the via body, leading to voids.

In general, laser-drilled microvias have a lower tendency to develop manufacturing defects than mechanically drilled holes. This is because mechanical drilling can produce vibration that causes the drill bit to wear out more quickly and create defects in the holes. This is not an issue with laser-drilled microvias, which can be drilled precisely and with minimal vibration.