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In this November issue of Design007 Magazine, we’re focusing on power and ground planes, the ones that help your signals get to their final destination in today’s PCBs.
Planes aren’t magic, but they are big time-savers. Without planes, designers would have to create thousands of traces to accomplish the same objectives. While designers might be tempted just to use a sheet of copper, planes are more than simple copper pours. They provide a decisive advantage in that they have extremely low impedance: Since it’s a sheet of copper, the impedance is almost non-existent.
As a result, power planes provide low impedance and stable power to every component on the board, much like a large power bus. Next to a signal layer, a power plane can shield signals and stop crosstalk and noise. They make great heat sinks too.
Ground planes stabilize reference voltage, improve thermal performance, and help preclude EMI issues. They offer a low-impedance return path, which helps eliminate jitter and reflections.
Power and ground plane design is often a battle of tradeoffs. Selecting the correct copper thickness of power planes is a good example: Thin copper with high currents can cause IR drop, which can lead to timing errors. This can be mitigated by using thicker copper, but this also affects your signal integrity planning, not to mention your fabricator’s workload.
