1. Overview of Circuit Boards
A circuit board (Printed Circuit Board, PCB), also known as a printed wiring board, is a critical component of electronic devices, playing a vital role in supporting and interconnecting electronic components. It uses copper traces to achieve precise electrical connections, ensuring that electronic components function stably according to the intended design.
Main Classifications of Circuit Boards:
By Layer Count: Single-sided board, double-sided board, multilayer board
By Material: Rigid PCB, Flexible PCB (FPC), Rigid-Flex PCB (FPCB)
By Application: High-frequency board, aluminum substrate (for heat dissipation), high-density interconnect board (HDI)
2. PCB Structure and Key Components
| Component | Function |
| Pads | Metal areas for soldering component leads |
| Vias | Metal holes connecting different circuit layers (through-hole, blind via, buried via) |
| Traces (Conductors) | Copper foil lines for electrical connections |
| Mounting Holes | Mechanical holes for securing the PCB |
| Connectors | Board-to-board or external connections (e.g., USB ports) |
| Copper Pour (Fill) | Reduces impedance and improves noise immunity |
| Solder Mask (Green Oil) | Insulation protection to prevent short circuits |
| Silkscreen Layer | Marks component positions, part numbers, etc. |
3. PCB Manufacturing Process
Core Processes:
①Design:
Use EDA software (e.g., Altium Designer, Cadence) to create schematics and generate PCB layouts.
②Fabrication:
Traditional Etching Method:
Copper-clad laminate → Photoresist coating → Exposure → Development → Etching → Drilling → Copper plating → Solder mask → Silkscreen
Modern Techniques:
Laser Direct Imaging (LDI), Plated through-hole filling, HDI microvia technology
③Assembly:
SMT (Surface Mount Technology, automated) or manual soldering (DIP through-hole components).
Comparison of Common PCB Fabrication Methods:
| Method | Characteristics | Application Scenarios |
| Chemical Etching | High precision, but high pollution | Small batch lab production |
| Thermal Transfer | Low cost, suitable for simple circuits | Hobbyist DIY projects |
| Laser Engraving | No chemical pollution, fast processing | Rapid prototyping |
| Mass Production | High-precision multilayer, automated | Large-scale manufacturing |
4. PCB Testing Methods
| Method | Principle | Pros & Cons |
| Bed-of-Nails Test | Probe contacts test points, automated detection | High efficiency, but high fixture cost |
| Flying Probe Test | Mobile probes test points sequentially | Flexible, suitable for small batches |
| AOI Inspection | Optical scanning to compare defects | Fast, but may miss cold solder joints |
| X-ray Inspection | Inspects hidden solder joints (e.g., BGA) | High cost, used for high-precision boards |
5. PCB Repair Techniques
Repair Steps:
①.Visual Inspection:
Check for burnt marks, broken traces, bulging capacitors, etc.
②Static Testing:
Use a multimeter to measure power-to-ground resistance (to rule out shorts).
Check key components (diodes, capacitors, resistors, etc.).
③Dynamic Testing:
Power on and measure voltages/signal waveforms (e.g., with an oscilloscope).
Compare with data from a known-good board (e.g., IC pin voltages).
④Replacement Method:
Swap suspected faulty components for verification.
Common Failures:
Short Circuits: Often caused by solder debris or damaged components.
Open Circuits: Due to trace corrosion or via fractures.
Cold Solder Joints: Weak or oxidized SMT solder connections.
6. Development Trends
High-Density Integration: Smaller trace width/spacing (e.g., below 3mil).
High-Frequency & High-Speed: 5G/6G driving demand for advanced materials (e.g., PTFE).
Eco-Friendly Processes: Lead-free soldering, green etching technologies.
Smart Inspection: AI-enhanced AOI for improved defect detection.
Conclusion
PCBs serve as the “skeleton” of electronic products, requiring balanced consideration of electrical performance, mechanical strength, and cost. Mastering fundamental principles, manufacturing processes, and repair techniques enables efficient troubleshooting and design optimization.