process of stacked vias
Stacked vias are a type of PCB interconnection in which the holes that make contact with component leads on a PCB’s top layer (also called the surface) are drilled directly into a layer underneath it. This creates a vertical path for signals to travel across the board, enabling higher speeds and better signal integrity than traditional single-layer connections. In addition, stacked vias can allow for a more flexible layout, giving designers more room for complex components and lower parasitic capacitance.
The most common use of stacked vias is in HDI designs, where they are used to connect different layers of the board. As the PCB industry moves toward more dense product form factors, there is a need for high-speed interconnects that can deliver reliable performance across the entire board. Standard vias, which are drilled into the surface of the board, often have a large diameter and take up valuable space that could be better served by using more narrowly-shaped stacked vias.
While there are many benefits to using stacked vias, the process can be difficult to implement and requires careful attention to detail. When creating a design with stacked vias, it is important to ensure that all the layers are properly connected and that the conductive hole is completely filled. Additionally, it is essential to plan for effective thermal management of the board, as excessive heat can lead to failure in the conductive holes.
Can you explain the process of stacked vias?
In addition to the challenges of implementing a proper design for stacked vias, there are also additional factors that must be taken into consideration during the manufacturing process. For example, the differential expansion between the different layers of a PCB can cause stress on the stacked vias. This can be mitigated by careful material selection, design optimization, and thorough testing.
There are two main types of stacked vias, blind and buried. A buried via is a solid copper pad that connects one layer of the PCB to another, while a blind via is a hole drilled through an IC die into the substrate. In order to manufacture a PCB with blind or buried vias, the designer must specify them in the design file by using the “Any Layer” drill option. This will create a via in every layer of the PCB, including the core layer.
The PCB manufacturer will then drill and plate the buried or blind vias in the core layer, followed by layers 2-3 and 5-6. These layers are then bonded together, which will create the final stacked via. The final step in the production process is to fill and plate the stacked vias with solder.
While stacked vias can be used in most circuit boards, they are not recommended for all applications. The challenging precision mandates associated with stacked vias can lead to a higher rejection rate in the fabrication process, which can drive up rework costs significantly. In addition, the tight tolerances required for fabricated stacked vias can lead to voiding in the copper wrap plating at the butt joints.
