Printed Circuit Boards (PCBs) form the core skeleton of electronic products, not only carrying components but also determining device performance and reliability. This article delves into key elements such as PCB design principles, material selection, and quality control.
What is a PCB?
PCBs create electrical connections via copper foil traces on an insulating substrate, replacing complex wiring and enabling signal transmission and power distribution between components. Known as the “Mother of Electronic Products,” PCBs have evolved from early single-layer structures to complex forms like High-Density Interconnect (HDI) and Flexible Circuits, supporting demands from consumer electronics to aerospace.
Key Metric Evolution
| Era | Mainstream Layers | Line Width Precision | Material Development |
|---|
| 1950s | Single-Sided | >1mm | Paper-Based CCL |
| 1980s | 2-4 Layers | 0.2-0.5mm | FR-4 Standardization |
| 2000s | 6-8 Layers | 0.1mm | High-Frequency Materials |
| Present | 10-20+ Layers | <0.05mm | Rigid-Flex Combination |
Core Functions of PCB
- Electrical Interconnection – Enables complete signal transmission through precise routing; high-frequency circuits require controlled characteristic impedance.
- Mechanical Support – Provides a stable mounting surface for packages like BGA, QFN.
- Thermal Management – Dissipates heat through thermal vias, metal core substrates (e.g., LED lighting boards).
- Electromagnetic Compatibility – Reduces signal crosstalk through multilayer stackup planning of power/ground layers.
Real-world case: Smartphone motherboards use Any-layer HDI technology, achieving 0.3mm pitch BGA routing in a 10-layer stack while integrating antenna RF circuits.
Complete Overview of PCB Classification
Classification by Layer Count
- Single-Sided – Lowest cost, suitable for simple circuits (e.g., power modules)
- Double-Sided – Optimal cost-performance, interconnects via vias
- Multilayer – 4-30+ layers, supports complex IC interconnection (e.g., server motherboards)
Classification by Substrate
| Type | Characteristics | Application Scenarios |
|---|
| Rigid PCB | Dimensional stability, high strength | Computers, Industrial Controls |
| Flexible PCB | Bendable, fatigue-resistant | Wearable Devices, Camera Modules |
| Rigid-Flex | Balances stability & 3D routing | Medical Equipment, Aerospace |
PCB Material Selection Guide
Common Substrate Comparison
FR-4 Epoxy Glass Fabric
├── Advantages: Low cost(¥80-200/㎡), mature processing
├── Limitations: High high-frequency loss, moderate heat resistance
└── Applications: Consumer Electronics, Power Equipment
Rogers High-Frequency Series
├── Advantages: Stable dielectric constant, low loss tangent
├── Limitations: High cost (5-8x FR-4)
└── Applications: 5G Base Stations, Radar Systems
Metal Core PCB (MCPCB)
├── Advantages: Excellent thermal dissipation (1-3W/m·K)
├── Limitations: Difficult for multilayer fabrication
└── Applications: High-Power LEDs, Automotive Electronics
Polyimide Flexible Boards
├── Advantages: Withstands >100k bends
├── Limitations: High moisture absorption, requires pre-baking
└── Applications: Foldable Phones, Dynamic Equipment
Selection Decision Process
- Define Electrical Needs – For high frequency >1GHz, prefer low-loss materials
- Assess Environmental Conditions – For high-temp environments, choose high-Tg materials (>170℃)
- Mechanical Requirements – For vibrating environments, consider rigid-flex design
- Cost Optimization – Use FR-4 as the main material for consumer electronics, mixed materials locally
Layout Principles
- Block-based Layout – Partition by function (RF, Digital, Analog separation)
- Prioritize Thermal Management – Place high-power devices near the board edge or heat dissipation path
- Signal Flow Orientation – Minimize trace length for high-frequency signals
Routing Specifications
Trace Width vs. Current Capacity (1oz Copper)
┌────────────┬──────────────────┐
│ Current │ Recommended Width│
├────────────┼──────────────────┤
│ 1A │ 0.5mm │
│ 3A │ 1.5mm │
│ 5A │ 2.5mm │
└────────────┴──────────────────┘
- Strictly control length matching for high-speed differential pairs (±5mil)
- Avoid 90° angles, use 45° or arc traces
Quality Control: Full Process from Raw Material to Finished Product
Common Defects and Countermeasures
| Defect Type | Cause | Solution |
|---|
| Copper Foil Peeling | Insufficient material adhesion | Optimize lamination parameters |
| Signal Distortion | Impedance control deviation | Improve etch compensation |
| Poor Solderability | Incorrect pad design | Add solder mask dam |
| EMI | Unreasonable stackup structure | Adjust the grounding scheme |
Inspection Process
Raw Material Inspection → Inner Layer Imaging → AOI Inspection → Lamination
→ Drilling & Plating → Outer Layer Imaging → Solder Mask & Silkscreen → Electrical Test & Packaging
Modern PCB factories combine Automated Optical Inspection (AOI) with Flying Probe Test to ensure product yield >98%.
PCB Industry Chain Panorama
Upstream: Glass Fiber/Copper Foil/Resin → Midstream: CCL/Prepreg → PCB Manufacturing → Downstream: Electronic Assembly
China has become the world’s largest PCB production base, accounting for 56% of global output value, with the proportion of high-value-added products like HDI and flexible boards continuously increasing.