![]() It also nicely scales to higher layer counts if needed. This type of design, with ground on the outer layers and low impedance connections to GND directly with traces, is definitely the safest design from an EMI and ESD standpoint. ![]() It can also provide a nice easy path for ESD back to GND and eventually to the device chassis or earth without needing to follow a path through a via to an internal layer. This stackup uses ground on the outer layers to provide high shielding against external EMI. Instead, you should use one of these alternative 4-layer stackups to create your PCB stackup and layout. The typical routing mistake that results in the basic 4-layer stackup involves routing high-speed signals between the surface layers without providing a clear return path, resulting in lots of radiated EMI from the board. If you need to do something more advanced, like placement and routing of high speed components on both sides of the board, you’ll need to use an alternative stackup. For many types of designs, this is just fine as long as you don’t make some simple layout and routing mistakes. The basic stackup you’ll often see recommended is a SIG/GND/PWR/SIG type stackup, where the internal layers are planes or large polygons. New designers who graduate from a 2-layer board into a 4-layer board are probably ready to start working with power and ground planes, and there is a standard stackup most fabricators will give you to help build out your design.
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