Micro Vias in PCBs
As electronic devices continue to shrink, designers must find ways to route signals and power across the multilayered PCBs that they use in their designs. One way to do this is by using micro vias. These tiny copper-plated holes are drilled through PCB layers, and they provide a pathway for electrical currents to travel between adjacent layers. They are an essential part of the modern electronics industry due to their ability to enhance circuit density and maximize functionality in small spaces.
Vias are a critical component of printed circuit boards (PCBs), which are used in all kinds of electronic products and devices. They are conductive pathways that connect different PCB layers to each other, allowing for the transmission of electrical and thermal signals between components and the board. There are several types of vias, with the most common ones being through-hole and blind microvias. These are cylindrical holes that extend completely through the PCB’s layers and are plated with a thin layer of conductive metal, typically copper. They are a key technology in the modern electronics industry because of their ability to increase the efficiency of circuit densities while also improving performance.
There are a few different types of micro vias that manufacturers can use in their production process. The most common type of these are through-hole and blind microvias, which are drilled completely through the PCB’s layers and then plated with copper to establish an electrical connection between the layers. The other type of microvia is called a buried microvia, which are holes that extend completely through an inner layer but do not reach any external surface of the PCB.
The Purpose of Micro Vias in PCBs
Another type of microvia is a stacked microvia, which is a stack of blind and buried microvias that are deposited on top of each other to allow the inner layers of the PCB to be connected. Stacked microvias can be arranged in various patterns to improve performance and reliability, such as staggered or offset microvias.
While a through-hole or buried microvia can be placed in the center of a pad on a PCB, a stacked microvia must be offset from the center of the pad to avoid excessive stress on the pad material. This can lead to microvia failures such as interfacial separation, barrel cracks, and corner/knee cracks, which are all associated with thermomechanical stresses caused by a mismatch in the coefficient of thermal expansion between the copper metallization in the stacked microvia structure and the pad material.
In order to ensure that these microvia structures are made correctly, manufacturers must perform rigorous inspection and test on their products. AOI (automated optical inspection) systems can be used to inspect for via alignment and copper coverage, as well as voids or delaminations. This allows for 100% inspection of vias in high-speed manufacturing environments, and the integration of these systems with SPC (statistical process control) systems makes it possible to monitor trends over time.
In addition to inspection and test equipment, it is also important for PCB fabricators to have good quality controls in place for the production of microvias. This includes a desmearing process that removes any contaminants from the drilling of the holes, and a plating step that uses electroless copper to ensure uniform copper coverage on the via walls. This helps to prevent problems such as incomplete copper fill and void formation, which can cause poor conductivity and other defects in the finished product.
