I’m designing a 4-layer PCB where the two inner layers are solid ground planes, and the outer layers carry signals. Since I’ve always added ground pours on 2-layer designs, I’m wondering should I still add ground pours with stitching vias on the outer layers when internal ground planes are already present?
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Your 4-layer stackup (signal–ground–ground–signal) is excellent, each signal layer references a solid adjacent ground plane, giving you a low-impedance return path for current.
Keep in mind that for digital designs, signal integrity depends more on edge rates than on clock frequency. Modern ICs with fast rise and fall times can generate high-frequency components, even at relatively low clock speeds, so maintaining continuous return paths remains important.
You generally don’t need ground pours on the outer layers in this configuration. However, adding them can still offer some benefits. They reduce copper etching during fabrication and can slightly improve thermal performance. As long as your ground vias already connect efficiently to the internal planes and your design isn’t pushing into high-speed territory, extra stitching vias aren’t required. That said, a modest number won’t hurt, provided it doesn’t inflate fabrication costs.
One additional point worth mentioning is to place ground return vias close to any signal or power vias when signals transition between layers. This helps maintain a consistent return path in the vertical direction, ensuring the signal always has a nearby reference plane and minimizing loop inductance.
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