Grounding Method for Multi-Layer PCB Boards (I)

Four-layer PCBs are typically used for high-density, high-frequency applications and offer more than 20 dB better electromagnetic compatibility (EMC) compared to two-layer boards. In a four-layer board setup, a complete ground plane and a full power plane can be used. This allows the various circuit ground wires to be connected to the ground plane effectively, with working noise managed separately.

There are several methods to connect each circuit’s ground wires to the ground plane:

1. Single-Point Grounding: All circuit grounds connect to a single point on the ground plane, either in a series or parallel configuration.
2. Multi-Point Grounding: Each circuit is grounded close by with short ground wires, ideal for high-frequency grounding.
3. Mixed Grounding: Combines single-point and multi-point grounding.

Single-point grounding is ideal for low-frequency, low-power applications with a single power layer and is commonly used in analog circuits. High-frequency digital circuits benefit from parallel grounding, often achieved using ground vias. Most modules use a mix of these methods to connect the circuit ground to the ground plane efficiently.

Grounding Method for Multi-Layer PCB Boards (II)

If the entire plane is not used as a common ground, as in modules with multiple ground lines, the ground plane may need to be divided, often in conjunction with the power plane.

Key principles for grounding include:

1. Plane Alignment: Ensure alignment to prevent overlap between unrelated power and ground planes, which could cause interference.
2. Layer Coupling: At high frequencies, layers can couple through the PCB’s parasitic capacitance.
3. Signal Bridges: For signal lines between ground planes (e.g., digital and analog grounds), use ground bridges and nearby vias to provide the shortest return path.
4. High-Frequency Lines: Avoid running high-frequency lines (e.g., clock lines) close to isolated ground planes to reduce unwanted radiation.
5. Minimum Loop Rule: Keep the loop area formed by signal lines and their return paths as small as possible to reduce external radiation and interference. When dividing the ground plane and routing signals, consider ground plane distribution and key signal routing to avoid issues from plane segmentation.

This overview of grounding methods and considerations provides PCB designers with key guidelines for optimal grounding and minimized interference in multi-layer boards.

KKPCB conducts research on special processing technologies such as ordinary double-sided boards, thick copper circuit boards, high-frequency circuit boards, HDI circuit boards, rigid-flexible circuit boards, FPC flexible boards, buried blind hole circuit boards, and IC carrier boards. Provides PCB design, PCB layout, PCB prototyping and PCB assembly services.