Micro Vias Can Be Used in 3D Packaging
As electronic devices become smaller, it becomes increasingly difficult to route conductive pathways across the multiple layers of the printed circuit board (PCB). Traditional through-holes — also called plated through-holes or through-board vias — are too large for this task. To meet this need, designers use microvias to provide a conductive pathway for components and traces between layers of the PCB.
Microvias are smaller than regular through-holes and can be used in a variety of ways to support the latest trends in HDI (high density interconnect) technology. These small holes offer several advantages over traditional through-holes, including less space for parasitic capacitance and increased speed of routing. However, they can present challenges in the manufacturing process due to their tiny size and high tolerance requirements.
For example, the diameter of a micro vias must be precise enough to allow the proper flow of copper through the hole and the surrounding layers of the PCB. Additionally, the plating process must be able to fill these tiny structures with copper without forming voids or causing other reliability issues.
How Micro Vias Can Be Used in 3D Packaging
In order to address these challenges, engineers employ a combination of design techniques and fabrication process enhancements. These include a wide range of material technologies that improve conductivity, adhesion and thermal expansion properties. Additionally, innovations in PCB substrate materials have helped to improve the physical strength and mechanical stability of boards with high densities of microvias.
The metallization of microvias is typically done with pure copper, since this is the most effective material for conductive plating. To help with the metallization process, manufacturers often employ additives to ensure that the copper is evenly spread throughout the body of the via structure. This helps to prevent voids from forming, which can impact the electrical performance of the microvia.
As for the layout of the microvias, there are two common options: stacked and staggered. Stacked microvias resemble the layout of a through-hole via, with a single layer transition spanning both the x and y coordinates. Staggered microvias are similar, but they separate the layer transitions in the x and y coordinate planes, allowing for components or traces to be placed closer together.
Regardless of the type of microvia used, thorough inspection and quality control are essential to ensuring that these vital features are manufactured according to the desired specifications. To accomplish this, engineers must carefully examine the raw materials and laminates to ensure that they are compatible with the drilling and metallization processes as well as the required tolerances. In addition, advanced imaging and microscopy tools are used to inspect the dimensions and integrity of the microvias after drilling and metallization.
To make sure that a design will work with microvias, it is best to consult with a PCB fabricator prior to building the proposed stackup. This way, the engineer can ask questions and get feedback about the manufacturability of the stackup with the chosen materials. This can save time and money in the long run.
