Can Microvia Be Used in High-Frequency Applications?
Microvia Be Used in High-Frequency
If you’re designing high-frequency circuits, it’s important to use proper impedance control techniques. This ensures that the signals have the correct shape and size to minimize reflections and capacitive coupling between traces. The choice of substrate material is also crucial, as it can affect the dielectric constant of the material and impact signal quality. Another important issue is the size of the vias and stubs. Too large a stub can cause resonance, which can lead to high-frequency radiation and interference. As you can imagine, this is an undesirable outcome for high-speed signals. Microvias can prevent this by providing a low-resonance path between layers.
A microvia is a small hole that connects copper traces on a PCB and acts as a pathway for electrical current. Its function is especially useful in multilayer boards, where traditional vias would be too large. Typically, microvia are created by stacking multiple layers of metal on top of each other. A single hole is drilled in the upper layer and capped with copper to form an interconnect. The resulting structure is soldered or welded to the bottom layer, creating a solid connection between the two layers.
The Institute of Printed Circuit Boards (IPC) defines a microvia as a circular, shallow-depth via with a diameter smaller than 150um (0.006 inches). The IPC recommends that the depth of a microvia should be no more than 1mm. Microvias are used in the manufacturing process to provide a smooth, continuous connection between different layers on a printed circuit board. They also help to reduce weight, making them a popular option for high-density interconnection (HDI) designs.
Can Microvia Be Used in High-Frequency Applications?
Aside from reducing weight, microvias can improve the reliability of a circuit board. Unlike through-hole vias, which are often prone to corrosion and have inconsistent reliability, microvias are made layer by layer and are more resistant to thermal stress. Microvias can also help reduce the amount of copper needed on a circuit board, which saves both cost and space.
While the benefits of using microvias are clear, there are some issues to consider before you adopt this technology. One concern is that stacked microvias are prone to failure, particularly at the interface between the copper plating and inner copper layer. This can occur during the assembly process as the PCB is thermally cycled. The most common failure points are the plated interface between two stacked microvias, or the interface between a buried microvia and its capture pad.
To prevent these failures, it’s important to use a high-quality fabrication process and keep the aspect ratio of the microvias low. Also, be sure to use a non-conductive material when drilling the holes. This will prevent the formation of voids, which can affect the reliability of the PCB. Small, spherical voids may slightly increase the fatigue life of a microvia, but extreme voiding conditions can significantly decrease it. The voids can be caused by poor plating or by the presence of epoxy resin with copper in the microvia holes.