8.4 IPC-A-610 Classifications & Criteria

IPC-A-610 "Acceptability of Electronic Assemblies" serves as the primary visual acceptance standard for the electronics industry. It defines the "Target," "Acceptable," "Process Indicator," and "Defect" conditions for solder joints and mechanical assembly. Adherence to the correct Class is the primary determinant of manufacturing cost and reliability.

8.4.1 The Three Classes

• Class 1 (General Electronic Products): Function is the primary requirement. Cosmetic imperfections are acceptable. Example: Toys, disposable electronics.
• Class 2 (Dedicated Service): Continued performance and extended life are required. Uninterrupted service is desired but not critical. Example: Laptops, microwaves, general industrial.
• Class 3 (High Reliability): Downtime cannot be tolerated; end-use environment may be harsh; equipment must function on demand. Example: Life support, aerospace, automotive engine control.

8.4.2 Critical Differences: Class 2 vs. Class 3

• Through-Hole Vertical Fill:
  • Class 2: 50% vertical fill of the barrel is permitted (with exceptions for thermal mass).
  • Class 3: 75% vertical fill is mandatory. This requires precise wave solder profiling and often necessitates selective soldering for heavy copper boards.
• SMT Component Overhang (Lateral):
  • Class 2: Up to 50% of the component termination width may overhang the pad.
  • Class 3: Maximum 25% overhang allowed. This ensures maximum mechanical shear strength for vibration resistance.
• SMT Toe Overhang:
  • Class 2: Allowed if the joint length is sufficient.
  • Class 3: Strictly prohibited.

Final Checklist

Feature	Class 2 Requirement	Class 3 Requirement
Vertical Solder Fill	50% Minimum	75% Minimum
Side Overhang	Max 50% of Lead Width	Max 25% of Lead Width
End Joint Width	Min 50% of Lead Width	Min 75% of Lead Width
Cleanliness	Visually Clean	Ionic Contamination Test Required