How Do Microvias on PCBs Affect Signal Integrity?

Microvias on PCBs Affect Signal Integrity

A microvia is a specialized hole that’s used in PCBs to improve signal integrity and reduce electromagnetic interference (EMI). Microvias come with specific advantages for use in high-speed digital and RF applications. They’re also useful in reducing the risk of debris-based interconnect defects (ICDs), which can cause reliability issues during assembly and usage.

The Institute of Printed Circuits (IPC) defines a microvia as a hole with a 1:1 aspect ratio and a depth no deeper than 0.010 inches. This size was originally chosen because it was difficult to drill smaller holes, but the technology for lasers has improved and now this size is routinely achieved. Microvias are used in high-density interconnect (HDI) circuit boards, which connect very fine-pitch surface-mount components such as ball grid array (BGA) and chip-scale package (CSP).

Because of their small size, microvias are more sensitive to the environment around them than regular vias. This means they must be designed and fabricated with special care to ensure they’re properly connected to the copper on the PCB. This can be done by leaving a recess on top of the hole or using a filler material that’s more resistant to contamination.

It’s also important to choose a material for the filler material of a microvia that’s conducive to conductive path performance. Copper is ideal, as it’s a good conductor and can be plated with a high degree of accuracy. Other metals, such as gold or silver, are less suitable for conductive path use, as they’re softer and not as durable as copper.

How Do Microvias on PCBs Affect Signal Integrity?

Drilling and plating microvias pcb requires a lot of precision, and the process can be prone to errors. This can lead to voids in the copper or other contaminants that interfere with circuit performance. To avoid this, it’s a good idea to use a low DK/low DF plating material. These types of materials are more chemically resistant to contamination and able to stand up better to high temperatures.

Aside from abrasion and corrosion, voids in a microvia can affect its fatigue life and reliability. They can also lead to the formation of a weak copper connection, which will break under stress and make it harder for signals to travel between layers on the PCB. The impact a void has on a microvia’s lifetime depends on several factors, including the size and shape of the void, its location and its severity. Small, spherical voids can increase the fatigue life of a microvia, while extreme voiding conditions can significantly reduce it.

Besides their ability to provide superior signal integrity, microvias can be stacked to improve PCB density and allow for more connections between layers. However, this requires that designers use specialized software that can handle the complexities of working with them. This can include reworking their design tools to account for the new via shapes, as well as adjusting their routing algorithms to accommodate the stacking. In the end, the benefits of using microvias more than offset these challenges.

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