Power Plane and Ground Plane in PCB Design: Best Practices

Best Practice

Description

Layer Stack-Up

• Use a balanced layer stack-up to ensure mechanical stability and minimize warpage. 

• Power and ground planes should be adjacent to each other to reduce EMI.

• For boards with four or more layers, use power planes because even layer stackups are best practice.

Ground Planes for Two-Layer Boards

• For two-layer boards, use a ground plane instead of a power plane, relying on tracks to deliver power from a power source.

Power Plane Size

• Extend power planes to cover the entire PCB to provide a low impedance path and reduce voltage drops.

Via Placement and Stitching

• Use multiple vias to connect power planes to pads and traces. This reduces the inductance and ensures a robust connection.

• Implement via stitching along the edges of power planes to improve shielding and reduce EMI.

Decoupling Capacitors

• Place decoupling capacitors close to power pins of ICs. 

• Use a mix of capacitor values to filter different frequencies effectively.

Noise Isolation

• Separate analog and digital power planes to minimize noise coupling.

• Use ferrite beads or inductors where necessary.

Star Point Grounding

• Use a star point for grounding to avoid ground loops and ensure a single point of reference for ground potential.

Domain Splitting

• Split power planes into multiple domains to accommodate components with different voltage requirements. 

• Follow EMI/EMC best practices to mitigate noise and crosstalk.

• Consider using separate power rails for each circuit instead of a common power plane for high efficiency and minimal EMI/EMC issues.

Optimal Layout Tools

• Use layout tools like OrCAD X to support cross-team collaboration, analysis, and simulation of designs to ensure proper power plane management. 

Best Practice

OrCAD X Feature

Layer Stack-Up

Cross Section Editor: Manage and visualize layer stack-ups to ensure even layers and stability. Allows designers to create and manage different stack-ups within a design, ensuring layers are correctly aligned and balanced. Useful for defining dielectric and conductive layers for mechanical and electrical performance.

Ground and Power Shapes

Shape Creation Tools: Create and manage ground planes easily using various shape tools in OrCAD X. Simplifies the creation of power and ground planes using tools like rectangular and polygonal shape creators. Enables precise placement and adjustment of these planes.

Shape Management: Automatically adjust and manage shapes as needed. Dynamically adjusts shapes as components and traces are added or modified, maintaining design integrity without the need for manual repouring. Useful for creating larger power planes and ensuring proper connectivity and thermal management.

Via Placement and Stitching

Via Arrays: Create and place via arrays in various patterns to enhance connectivity and reduce EMI. Facilitates the creation of via arrays in different configurations, such as staggered or centered, to improve electrical performance and EMI shielding. Provides robust connections between layers and components.

Component Placement

Constraint-Driven Placement: Uses constraint management to define rules for components such as decoupling capacitors, ensuring they are positioned close to power pins to filter noise effectively. 

Collaboration and Teamwork

OrCAD X supports real-time collaboration, allowing multiple team members to work on the same project simultaneously. 

Features like version control, shared workspaces, and centralized libraries ensure all team members are on the same page, reducing errors and improving project management. It also includes tools for commenting and reviewing.