Table of Contents
Purpose and Importance of Inspection
Printed Circuit Boards (PCBs) are the core components of electronic products, and their quality directly determines the performance and reliability of the final product. Incoming Quality Control (IQC) aims to efficiently identify and screen out non-conforming boards through standardized processes, preventing problematic boards from entering production and reducing post-sales failures and hidden costs. According to data from IPC International, strict incoming inspection can reduce post-sales failure rates by over 30% (Source: IPC 2023 Annual Report).
Inspection Environment and Basic Conditions
| Inspection Condition | Standard Requirement |
|---|---|
| Illumination Intensity | 500 Lux or above (natural light or fluorescent lamp) |
| Inspection Distance | 30–45 cm |
| Light Angle | 30°–60° between the object and the light source |
| Viewing Angle | 30°–60° to the inspected surface, nearly perpendicular to the light source |
| Inspector Vision | 0.8 or above, no color blindness |
| Auxiliary Tools | Drawings, samples, and inspection specification documents |
Detailed Inspection Items and Methods
1. Packaging and Labeling Inspection
- Content: Whether the outer packaging is moisture-proof and undamaged; whether the product name, model, quantity, and other identifications are clear.
- Method: Visual full inspection.
- Standard: Intact packaging, correct labeling, and desiccant placement meet requirements.
2. Visual Inspection
- Items:
- Board surface clean, free from stains, oxidation, scratches, and burrs;
- Character printing clear, content correct, no blurring or broken printing;
- Solder mask (green oil) even, no blistering, wrinkles, or copper exposure;
- The solder pad is intact, free from oxidation, detachment, or coverage.
- Board edges and V-CUT smooth, no cracking or burrs.
- Method: Visual + magnifying glass assistance, sampling, or full inspection.
- Standard: According to IPC-A-600G Class 2 (industrial grade).
3. Dimensional and Structural Verification
- Tools: Calipers, optical measuring instruments, and sectioning equipment (for multilayer boards).
- Items:
- Length, width, thickness, hole diameter, line width/line spacing, etc..
- Layer-to-layer registration for multilayer boards (offset ≤50μm);
- Warpage: Generally required to be ≤0.75% of board length (varies depending on board thickness).
- Standard: IPC-6012B, GB/T 4677.
4. Electrical Performance Testing
- Continuity Test: Use a multimeter or flying probe tester, impedance deviation <5%;
- Insulation Resistance: Test at 500VDC, resistance value should be ≥100MΩ (IPC-TM-650 2.6.3);
- Withstanding Voltage Test: Apply high voltage according to product specifications to verify safety.
5. Solderability and Soldering Heat Resistance Test
- Solderability: Immersion in solder at 235±5℃ for 2–3 seconds, the solder wetting rate should be ≥95%;
- Soldering Heat Resistance: Immerse in tin at 260±5°C for 10 seconds without bubbling, delamination, or green solder mask peeling.
6. Environmental Reliability Testing (Sampling)
- Temperature Resistance: Simulate reflow soldering (peak 260℃±5℃, 10 seconds);
- Damp Heat Test: Place in 85℃/85% RH environment for 96 hours, no performance degradation after testing.
Common Problems and Countermeasures
| Problem | Root Cause Analysis | Solution and Acceptance Standard |
|---|---|---|
| Batch Warpage | Storage or material issues | Supplier pre-baking (125℃/2 hours), warpage ≤0.75% |
| Poor Pad Solderability | Oxidation or contamination | Wetting balance test, solder spread area ≥95% (J-STD-003B) |
| Leaf green peeling off or blistering. Green coating peeling or bubbling | Process or insufficient curing | Adhesion Test (3M Adhesive Method), No Peeling |
| Blurred/Missing Characters | Printing process issues | Compared with samples, critical identifications must be clear |
| Hole Deviation or Insufficient Annular Ring | Drilling accuracy deviation | Use hole gauge inspection, annular ring ≥0.1mm |
Recommended Inspection Equipment List
- Basic Tools: Magnifying glass, calipers, multimeter;
- Professional Equipment: AOI optical inspector, impedance tester, constant temperature solder pot, constant temperature and humidity chamber, and sectioning equipment.
Standard References
- IPC-A-600: Acceptability of Printed Boards;
- IPC-6012: Qualification and Performance Specification for Rigid Printed Boards;
- J-STD-003: Solderability Tests;
- GB/T 4677: Chinese National Standard (equivalent to IPC methods).
Summary and Recommendations
Enterprises should customize inspection specifications based on their own product requirements and IPC standards, regularly collect incoming quality data, and promote supplier process improvement to achieve an effective balance between quality and cost.
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