Micro Vias
Printed circuit boards (PCBs) provide the conductive pathways for electronic components to connect and function together. To establish these connections, holes must be drilled through the PCB’s layers and then filled with copper. These are referred to as plated through-holes, or vias, and can be of various sizes. If a hole’s diameter is smaller than a standard through-hole, it is considered a microvia.
Using microvias to create high-density interconnect (HDI) structures in a PCB reduces signal loss and increases reliability by minimizing the distance between components. However, implementing microvias is a complex process that requires precise manufacturing and adherence to strict design specifications. This article will examine how microvias are created in PCB manufacturing and offer tips for optimizing their use.
How are micro vias Created? The primary method for creating vias in a PCB is mechanical drilling, where a micro drill bit is used to create small holes through the layers of the board. This technique is commonly used for vias with a diameter of 0.1mm or more. However, for the very tiny holes required by microvias, a laser-drilling technology is necessary. This technology is capable of producing a much wider range of hole geometries, and can help to minimize the size of the holes that are created in the board’s materials.
How Are Micro Vias Created in PCB Manufacturing?
To ensure that the microvias in a PCB are able to handle the current loads they must carry, they must be constructed of materials with the appropriate electrical and thermal properties. Typically, copper is the material of choice for these vias, due to its excellent conductivity and ability to dissipate heat. The substrate material, which serves as the base for the metallization, must also be chosen carefully to ensure compatibility with the drilling and plating processes as well as to provide the desired strength and mechanical stability.
Aspect Ratio Management To be effective, microvias must be properly sized and spaced to ensure that they can accommodate the necessary electrical and thermal connections. This is essential for maintaining proper conductivity, managing electromagnetic interference (EMI), and ensuring that the PCB’s lamination processes are successful. In addition, the aspect ratio of a microvia should not exceed a recommended value to prevent plating issues and manufacturing defects.
Depending on the design of your circuit board, it may be possible to utilize both staggered and stacked microvias. However, data suggests that stacked microvias are more likely to experience failure than staggered ones. As such, it is generally advised to avoid stacked microvias that span more than two layers. Additionally, if a stacked microvia structure is incorporated into the design, it should be tracked away from any buried via holes. This will minimize the number of vias that are exposed to the environment, thereby reducing the likelihood of failure. In addition, a minimum annular ring width should be defined for the microvia, which is determined by adding two annular ring widths plus a fabrication allowance. This allows for the accurate placement of the via and ensures that it will be etched cleanly during the production process.
