Choosing the Best Layer for Groundplane in Multilayer PCB

Hello, are you struggling to decide which layer of your multilayer PCB is ideal for placing a groundplane? If so, you’re not alone. The placement of the groundplane is crucial for the performance of your PCB, especially when dealing with high-frequency signals.

Traditionally, many PCB designers opt to place the groundlayer on the top layer. However, recent insights from an EMC course suggest that placing the groundlayer on an inner layer might be more beneficial. The rationale behind this recommendation is that the groundplane needs to be “unbroken” for optimal performance.

According to the experts, it is advised not to use power planes but instead route each trace needed for a power pin individually. This approach ensures that the ground plane and power plane are separate entities, which is essential for high-frequency signal integrity.

Here are some advantages and disadvantages of placing the groundlayer on the top versus an inner layer:

• Groundlayer on Top:
  • Each SMD pin for ground directly connected (advantage)
  • Ground layer broken by placing parts (disadvantage)
  • Coupling of the return path in x-y direction uses less copper area (disadvantage)
• Groundlayer Inner:
  • Groundlayer more continuous (advantage)
  • Not broken by placing parts (ground layer runs under the parts) (advantage)
  • Every SMD pin that needs a ground level requires a via to connect to it (disadvantage)
  • Coupling of the return path in z direction uses the entire trace area (advantage)

Considering the arguments presented, what is your experience with choosing the best option for your PCB design? Keep in mind that you are working with SMD parts and a microcontroller operating at 72 MHz, which adds complexity to the decision-making process.