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This article explores the role of stitching vias in maintaining signal integrity and electromagnetic compatibility (EMC) as signals transition between layers in a PCB stackup. We will examine how the number and placement of stitching vias can influence the behavior of electromagnetic fields, and how proper design can prevent unwanted signal degradation and interference. Through simulation and comparison of different configurations, we will demonstrate how stitching vias contribute to the overall efficiency and reliability of PCB designs, ensuring signals travel cleanly from one layer to the next while keeping fields under control.
In modern PCB design, managing signal integrity and minimizing electromagnetic interference (EMI) are essential for ensuring optimal performance and reliability, especially as circuit speeds continue to increase. One of the key components in achieving this is the use of stitching vias. These small yet crucial features connect different layers of a PCB to the return reference plane, helping to control the flow of return currents and stabilize electromagnetic fields during signal transitions.
They serve three essential purposes:
Providing a path for the return current to flow back to its source – This ensures a continuous and defined current loop, which is critical for maintaining the integrity of high-speed signals.
Serving as a stable reference for the electric field – By acting as a reliable reference point, stitching vias help stabilize field behavior and support proper signal propagation.
Maintaining equipotential across multiple metal structures – By connecting these structures with a low-impedance path, stitching vias help equalize potential differences, improving the overall electromagnetic performance of the PCB.
Together, these functions play a vital role in maintaining signal integrity and minimizing electromagnetic interference within the PCB. The significance of stitching vias becomes clear when analyzing their impact on electromagnetic field behavior during layer transitions.
With the help of Simbeor ® a simulation tool developed by simberian.com, it is possible to visualize how electromagnetic fields behave under different conditions, specifically, when two stitching vias are used compared to four. This analysis reveals how design choices affect the containment and propagation of electromagnetic fields.
In our scenario, a multilayer PCB stackup with several planes is examined. Here, electromagnetic fields spread in the cavity between the planes.
In the first, non-optimal scenario (left side of Figure 1), as signals transition between layers, the electromagnetic fields are confined by only two stitching vias. This limited number of vias allows the fields to propagate freely within the stackup, leading to uncontrolled energy dispersal.
By contrast, the second scenario (right side of Figure 1) involves the placement of four stitching vias around the signal path. These vias provide a 360-degree reference for the signal during its transition, containing the fields within a defined area, as seen in Figure 2.
