PCB Working Principle

Working Principle of Circuit Boards

The core function of a circuit board is to facilitate the transmission and distribution of electrical signals, delivering power and control signals to various electronic components. Its working principle can be summarized as follows: Conductive copper traces and different circuit paths interconnect electronic components, enabling current flow and signal transmission.

For example, in a computer motherboard, the circuit board not only connects key components such as the CPU, memory, and graphics card but also supplies power through power circuits and coordinates their operation via control signals. The circuit board’s stability and reliability directly impact the electronic device’s overall performance.

1. Physical Structure Fundamentals

• Substrate Material: Typically made of insulating materials like fiberglass (FR4) or flexible substrates (e.g., polyimide), providing mechanical support and electrical isolation.
• Conductive Layer: Etched copper traces form precise wiring to establish electrical connections between components.
• Multilayer Design: Complex circuits use stacked layers (e.g., 4/6/8-layer boards) with vias for interlayer connections, optimizing signal integrity and space efficiency.

2. Signal and Current Transmission Mechanisms

• Signal Transmission: High-frequency signals are routed using microstrip or stripline designs to control impedance and minimize reflections and crosstalk (e.g., USB 3.0 differential pairs require 90Ω impedance matching).
• Power Distribution: Power planes reduce impedance, while decoupling capacitors suppress high-frequency noise to ensure stable voltage.
• Grounding System: Dedicated ground planes in multilayer boards provide low-impedance return paths, preventing ground bounce issues.

3. Typical Functional Modules

• Digital Circuits: CPU-memory bus routing requires length matching to meet timing constraints.
• Analog Circuits: Audio signal paths must be isolated from switching power supplies to avoid EMI.
• Mixed-Signal Systems: ADCs/DACs often use star grounding to separate analog and digital grounds.

4. Collaborative Workflow (e.g., Computer Motherboard)

1. Power Phase: The 24-pin ATX power connector converts voltages via DC-DC regulators (e.g., 12V→1.2V for CPU core).
2. Signal Processing: The Northbridge (or modern SoC) communicates with GPUs via PCIe lanes at 8 GT/s.
3. Clock Synchronization: Crystal oscillators generate reference clocks, multiplied by PLLs for subsystem distribution.

5. Key Performance Factors

• Material Properties: High-frequency circuits use low-loss dielectrics (e.g., Rogers RO4003C).
• Layout Rules: Sensitive signals follow the 3W rule (spacing ≥3× trace width) to reduce crosstalk.
• Thermal Management: High-current traces adhere to IPC-2152 ampacity standards, with thermal vias for heat dissipation.

6. Failure Modes & Reliability

• Open/Short Circuits: Caused by electromigration or mechanical stress.
• Signal Integrity Issues: Impedance mismatches lead to ringing or eye diagram collapse.
• Environmental Durability: Validated via HALT (Highly Accelerated Life Testing) for thermal/humidity resistance.

Modern PCB design relies on EDA tools (e.g., Cadence Allegro) for signal integrity (SI), power integrity (PI), and EMC simulations, ensuring accurate translation from schematics to physical boards. Advancements like HDI (High-Density Interconnect) and embedded passives continue to drive electronics toward higher performance and miniaturization.