Dividing spaces into power, ground, and signals often leads to complications because such partitioning is neither necessary nor sufficient for a good result.
For complex boards—such as those with mixed analog/digital signals, high-speed signals, high currents, or SMPS—a full ground plane can be beneficial. However, it’s crucial to understand where the return currents are flowing, as even with a ground plane, it’s easy to make mistakes.
I suggest using the Manhattan layout with a gridded ground. The key advantage of the Manhattan layout is that it allows you to always find a route for your track. You don’t have to take a meandering route away from the return path or cut through a ground plane, which compromises its integrity.
Manhattan routing dedicates one layer for North-South connections and the other for East-West connections. This approach ensures you can always get from point A to point B with typically one via and avoids crossing tracks.
To start, create a gridded ground. On one layer, place a track every 20mm in columns. On the other layer, do the same in rows and connect them with vias at every intersection. This provides a ground almost as good as a plane while keeping both layers available for routing power and signals. Adjust the ground tracks to accommodate your ICs, but keep them close together.
Regarding the ground plane versus gridded ground, I’ve found that junior engineers often rely too heavily on the ground plane, thinking it will handle all isolation issues. This can lead to poor design decisions, such as running high currents past sensitive inputs.
To help them understand return currents better, I sometimes remove the ground plane and force them to consider return currents as discrete flows in separate tracks. Once the layout is fixed, the ground plane can be restored.
On a 4-layer board, dedicating one layer to a solid ground is feasible. On a 2-layer board, routing space is limited, making the Manhattan layout particularly useful. If you dedicate one layer to ground, even a simple layout can result in tracks cutting through the ground, compromising its integrity.
A gridded ground is a flexible alternative. You can increase the number of ground tracks where needed, and it works well with Manhattan routing. After completing the layout, you can flood it with ground copper, resulting in a better-routed board because you’ve considered all return currents.
Good PCB design is both an art and a science. Designing without a ground plane helps engineers develop an intuition for current flow, speeding up the learning process.