Guide to Micro Via
A microvia is a small hole on a PCB that allows electrical signals to pass through from one layer of the board to another. These are essential for high-density interconnection (HDI) boards and other applications where traditional through-hole vias can be too large.
Microvias allow the designer to create complex, dense PCB designs without sacrificing performance or reliability. Choosing the right type and placement of these vias is crucial, and understanding their functions and benefits can help you to make informed design decisions that will optimize your circuit’s performance. The IPC defines a microvia as a blind structure with a 1:1 aspect ratio between the via diameter and depth. This means that a microvia’s depth should not exceed the thickness of its annular ring.
These small structures are often used in high-speed PCBs to reduce signal attenuation, as they can be more effective at eliciting signals than larger micro via, which can suffer from increased signal loss and parasitic effects such as electromagnetic interference (EMI). In addition, the smaller size of a microvia means that it can be implemented in thinner dielectric layers, further reducing EMI and improving signal integrity.
A Beginner’s Guide to Micro Via
To manufacture a microvia, the holes are first pre-drilled. Then, a laser is used to drill into the copper surface of the PCB, creating the necessary connections between layers. The resulting holes are then plated with copper, connecting the adjacent layers and providing a conductive path for electrical signals. The metallization process can be achieved using electroless copper plating, which ensures uniform micro coverage of the via walls.
Another important consideration when designing a microvia is the choice of substrate material. The right laminate will contribute to the reliability of the structure, as it will impact the dielectric constants that are needed to minimize signal attenuation and phase delays. This is particularly critical in high-frequency designs that use microwave or millimeter-wave strip line conductors, which are suspended within the dielectric of the PCB.
Lastly, it’s important to consider the effect of voiding on the reliability of a microvia. This can be a significant cause of failure, as it can lead to stress concentrations that increase the chance of cracking. To avoid this, it’s best to stagger the placement of multiple microvias on a PCB and avoid stacking them directly on top of each other.
In addition to these considerations, it’s important to discuss the selection of a microvia material set with your PCB fabricator, as they may have certain fabrication limitations that can affect their manufacturability and effectiveness. Epec engineers have extensive experience helping our customers to select the appropriate materials for microvias, ensuring that the resulting product will meet their quality, performance and cost requirements. To get started, contact a representative today.
