PCB HDI Technology
Stacked microvias are a key component of PCB HDI technology and provide high-density interconnections for improved signal integrity. They also offer a number of other benefits, including reduced thermal degradation and more space on the board for components. This allows designers to achieve the same level of functionality with a smaller footprint, making it an attractive solution for many electronics products.
Typically, a via is defined by an opening in the pcb hdi material that connects layers. The via is then plated with copper to create a conductive path. However, the size and placement of the via can affect signal integrity. For example, if the via is too close to other signals, it can increase crosstalk and noise coupling strength. Stacked microvias can reduce this effect by providing an alternative pathway for electrical signals.
The process of defining vias starts in the PCB stackup editor, where layer pairs are defined and materials selected. Once the stackup is complete, it can be sent to a PCB fabricator for review to determine if it is manufacturable. A good place to start is using Sierra Circuits’ stack-up tool, which will give you a great idea of how your proposed stackup will look and if it is suitable for HDI fabrication.
Applications of Stacked Microvias in PCB HDI Technology
There are several different types of HDI stackups, which have been developed for various applications. For instance, the 2+N+2 stackup is ideal for BGAs because it can support high I/O counts. This design utilizes staggered and stacked microvias in layers 1-3. In addition, it can be plated with copper, which is useful for signal transmission applications.
Another option for an HDI stackup is the type VI structure, which has been designed to allow the use of any-layer microvias. This is a more advanced structure that can be used for high-level interconnections, but it is not as scalable as the 2+N+2 approach.
When designing a PCB with stacked microvias, it is important to consider the layout and routing capabilities of the product. This will help ensure that the signals can be transmitted effectively through the stacked vias and the board’s layers. In addition, it is important to consider the size of the components and the overall size of the circuit board. This will help to determine the size of the stacked vias and the corresponding pads that need to be created for contacting them.
Once the microvias have been drilled, they must undergo a desmearing process to remove any residual material from the drilling process. This step is essential for ensuring a smooth, clean hole for the conductive signal to flow through. After the etching and desmearing processes are completed, the microvias can be metallized. This is usually accomplished by electroless copper plating, which helps to ensure a consistent microvia surface and improved signal flow. The next step is to fill the microvias with a conductive material, such as copper or silver epoxy. This is important for the signal transfer capability of the vias, as well as to reduce thermal degradation and improve the conductivity of the via walls.
