Key Points of PCB Design
PCB design is the foundation of electronic products. The quality of the PCB directly affects how well the device works, how reliable it is, and how much it costs to produce. There are several important parts of designing printed circuit boards (PCBs). This includes planning the layout, deciding the routing strategies, and making sure the power and signal are good. The manufacturing process requirements are also important.
1. PCB Layout Planning
PCB layout is the primary phase of design, where proper component placement optimizes signal flow, reduces interference, and improves thermal efficiency.
1.1 Functional Partitioning and Isolation Design
- Analog/Digital/RF Zone Isolation: Achieved through physical spacing (≥5mm) and ground plane separation
- High-Voltage and Low-Voltage Area Division: Power conversion modules should maintain 10-15mm spacing from sensitive signals
- Thermal-Sensitive Component Placement: BGA packages require a 5mm keep-out zone; heat-generating components (e.g., power MOSFETs) should be near board edges
1.2 Mechanical and Thermal Design Standards
- Coordinate System Setup: Origin at the center of the corner mounting holes (±0.05mm accuracy)
- Thermal Management Planning:
- Natural convection layout: High-heat components on the PCB top
- Forced air cooling: Components aligned with the airflow direction
- Structural Compatibility: Connectors must align with enclosure openings (±0.2mm tolerance)
2.1 Fundamental Routing Principles
- 3W Rule: Trace spacing ≥3× trace width (e.g., 15mil spacing for 5mil width)
- Orthogonal Layer Routing: Adjacent signal layers use perpendicular routing (0°/90° crossing)
- Via Optimization: High-speed signals changing layers require adjacent ground return vias (spacing ≤λ/10)
2.2 Special Signal Handling
| Signal Type | Routing Requirements | Typical Parameters |
|---|
| Differential Pairs | Length matching (±5mil) | 100Ω±10% impedance |
| Clock Signals | Guard traces | 6mil width |
| RF Signals | Curved corners | 50Ω impedance |
3. Power Integrity Design
3.1 Multilayer Board Power Architecture
- Plane Segmentation:
- Digital (1.2V/1.8V) and analog power isolation
- 20H Rule: Power plane recessed 20× dielectric thickness from ground
- Decoupling Capacitor Placement:
- Bulk capacitors (10μF) at power inputs
- Small capacitors (0.1μF) near IC pins (≤3mm)
3.2 Voltage Conversion Design
- DC-DC Layout Essentials:
- Inductor-to-switch distance ≤5mm
- Feedback traces routed away from noise sources
- Ripple Control:
- Load transient response ΔV<2%
- ≥40dB noise attenuation @100MHz
4. Advanced Signal Integrity Optimization
4.1 Transmission Line Control
- Impedance Matching Calculation:
Microstrip impedance formula:
Z0 = [87/sqrt(εr+1.41)] * ln[5.98h/(0.8w+t)]
- Termination Strategies:
- Source-series termination (22-33Ω)
- End-parallel termination (50Ω to ground)
4.2 Crosstalk Mitigation Techniques
- 3D Spacing Rules:
- Same-layer spacing ≥3H (H = height to reference plane)
- Adjacent-layer staggered routing
- Shielding Methods:
- 1 ground trace per 5 high-speed signals
- Critical signals in stripline configuration
5. DFM (Design for Manufacturing) Standards
5.1 Process Capability Parameters
| Parameter | Standard Process | High-Precision Process |
|---|
| Min Trace Width | 0.1mm | 0.05mm |
| Min Drill Size | 0.2mm | 0.1mm |
| Pad Spacing | 0.15mm | 0.08mm |
5.2 Special Structure Design
- Thermal Via Arrays: 0.3mm diameter, 0.6mm pitch
- Copper Balancing: <30% copper area difference per side
- Panelization Design: V-cut lines avoiding high-density routing areas
6. Design Verification Process
6.1 Pre-Production Checklist
- Electrical Rule Check (ERC): Open/short verification
- Design Rule Check (DRC): 300+ process rules
- Signal Integrity Simulation: Setup/hold margin >15%
- Thermal Analysis: Junction temperature <80% rating