The Importance of PCB Inspection
1. Ensuring Electronic Product Quality
Through inspection, issues in the Fabrication de circuits imprimés process can be promptly identified and corrected, preventing substandard products from entering the market. This safeguards the stability and safety of electronic products.
2. Enhancing Production Processes
Problems uncovered during inspection provide scientific grounds for product optimization and upgrades. Manufacturers can continuously refine production techniques based on inspection findings, thereby improving PCB quality and performance.
1. Basic Knowledge of PCB Inspection
1.1 Visual Inspection
Conduct a comprehensive visual inspection of the PCB to look for visible signs of damage, including:
- Component damage, missing or misaligned parts
- Solder joint cracking, cold solder, or virtual soldering
- Burned, broken, or corroded circuits
- Board contamination, scratches, or deformation
1.2 Electrical Safety Preparation
- Ensure test equipment (soldering iron, multimeter, etc.) has good insulation performance
- Avoid live operations to reduce circuit damage risks
- Confirm the working environment is dry and free from electrostatic interference before testing
1.3 Circuit Principle Understanding
- Be familiar with integrated circuit functions, electrical parameters, and pin roles
- Master the normal voltage range and waveform characteristics of key test points
1.4 Measurement Precautions
| Precaution | Specific Content |
|---|
| Short-circuit Prevention | Secure probes during testing to avoid short circuits between pins, especially for CMOS integrated circuits |
| Instrument Selection | Use high-impedance multimeters to measure DC voltage and reduce measurement errors |
| Gestion thermique | Ensure power integrated circuits have good heat dissipation to avoid overheating damage |
| Solder Quality | Ensure solder joints are firm, without cold solder or solder adhesion, and check for short circuits after soldering |
1.5 Fault Judgment Principles
Do not easily conclude that an integrated circuit is damaged. Confirm through multiple measurements and exclude external factors.
2. PCB Debugging Methods
2.1 Preliminary Inspection
- Visual inspection: Confirm no mechanical damage or obvious short circuits
- Power test: Measure the resistance between the power and ground lines to ensure a sufficient resistance value
2.2 Step-by-Step Installation and Testing
- Power Module Installation: First, install the power section and test the output using an adjustable regulated power supply
- Modular Installation: Install components module by module, performing functional tests after each module installation
- Overall Test: Conduct system-level functional tests after all modules are installed
3. PCB Fault Diagnosis Methods
3.1 Voltage Measurement Method
- Check whether the voltage of each chip’s power pins is normal
- Identify power issues: abnormal voltage, excessive ripple, or instability
3.2 Signal Injection Method
- Inject signals from the input end and sequentially detect waveforms at each point
- Locate signal abnormalities: attenuation, distortion, or interruption
3.3 Sensory Inspection Method
Use multiple sensory means to identify problems:
- Vision: Physical damage to components, burn marks
- Hearing: Abnormal sounds (discharge sounds, oscillation sounds)
- Smell: Burnt odor, chemical smell
- Touch: Overheated components, loose connections
4. PCB Failure Analysis
4.1 Failure Cause Classification
| Failure Category | Specific Causes |
|---|
| Material Issues | Substrate defects, unqualified solder materials, and material aging |
| Design Defects | Overly dense wiring, insufficient current load, inadequate heat dissipation |
| Processing Techniques | Printing deviations, incomplete etching, and inaccurate drilling |
| Environmental Factors | High temperature, high humidity, vibration, corrosive gases |
| Improper Use | Overload, short circuit, incorrect operation |
4.2 Failure Analysis Methods
- Inspection visuelle: Observe physical damage under a microscope
- Essais électriques: Use multimeters and oscilloscopes to test conductivity and insulation
- Thermal Analysis: Use thermal imagers to identify overheating areas
- Chemical Analysis: Material composition analysis to determine contamination or corrosion
- FMEA Analysis: Systematically identify potential failure modes
5. PCB Quality Acceptance Guide
5.1 Visual Inspection Standards
- Qualité de surface: No scratches, dents, oil stains, or fingerprints
- Circuits and Pads: Complete circuits, flat pads without oxidation
- Silk Screen Markings: Clear and accurate, including component symbols, numbers, and polarity
5.2 Electrical Performance Testing
| Type de test | Test Method | Qualification Standard |
|---|
| Conductivity Test | Multimeter/Conductivity Tester | No short circuits/open circuits |
| Insulation Resistance Test | Insulation Resistance Tester | Resistance value meets design standards |
| Withstanding Voltage Test | Withstanding Voltage Tester | No breakdown/flashover |
5.3 Dimension and Tolerance Inspection
- Outline Dimensions: Length, width, and thickness meet design requirements
- Hole Position and Aperture: Accurate positioning of mounting holes and positioning holes
- Line Spacing: Line width and spacing comply with design specifications
5.4 Manufacturability and Assemblability Evaluation
- Process Feasibility: Design complies with manufacturing process capabilities
- Sélection des matériaux: Material performance meets standard requirements
- Component Installation: Pad design facilitates installation and soldering
- Maintenance Convenience: Reasonable setting of test points, easy component replacement
5.5 Document Review
- Design Documents: Complete and accurate circuit diagrams, layout diagrams, Gerber files
- Production Process Records: Raw material inspection reports, process parameter records
- Test Reports: Complete electrical performance and dimensional inspection reports
6. Common PCB Inspection Issues and Solutions
6.1 Common Inspection Issues
- Cold Solder/Virtual Solder: Solder joints appear good, but the electrical connection is unreliable
- Solder Balls/Dross: Small solder balls generated during soldering may cause short circuits
- Copper Foil Peeling: Insufficient adhesion between substrate and copper foil
- Poor Solder Mask: Incomplete coverage or uneven thickness
6.2 Solutions and Preventive Measures
- Optimize soldering process parameters (temperature, time, flux usage)
- Strengthen incoming material inspection to ensure board and solder quality
- Improve design to avoid sharp-angle routing and copper foil imbalance
- Regularly maintain inspection equipment to ensure measurement accuracy
Through systematic testing methods and rigorous quality acceptance procedures, the reliability and service life of PCB boards can be significantly enhanced, providing a solid foundation for the overall quality of electronic products.