1.1 Quality Baseline: IPC/WHMA-A-620 Classes

The IPC/WHMA-A-620 standard is the mandatory quality benchmark for the cable and wire harness industry. It establishes the criteria for acceptance and rejection of all assemblies, ensuring consistency and reliability regardless of the manufacturer. Understanding this standard is essential because the required workmanship and audit rigor depend entirely on the Product Class designated by the customer.

1.1.1 The Acceptance Mandate: Three Product Classes

The IPC/WHMA-A-620 defines three classes based on the complexity, function, and consequence of failure. These classes dictate the acceptance criteria for defects such as stripped wire strands, insulation gaps, crimp deformation, and final routing.

IPC Class	Application Risk	Reliability Mandate	Manufacturing Mandate
Class 1	General Electronic Products (Consumer, Disposable)	Functionality required for a short, specified life.	Focus on maximum economy and basic reliability.
Class 2	Dedicated Service (Industrial, Communications)	Extended service life where sustained performance is necessary, but failure is non-critical.	Standard Quality Baseline; requires measurable process controls (Cpk).
Class 3	High-Performance/Critical (Medical, Aerospace, Military)	Maximum Reliability; continuous, mission-critical performance where failure is unacceptable.	Most Stringent: Requires superior workmanship, maximum traceability, and near-zero defects.

1.1.2 Mandates for Critical Applications (Class 3)

Manufacturing a Class 3 harness is significantly more demanding than Class 2, requiring tighter controls across every stage of the assembly process.

A) Workmanship and Inspection

• Zero-Defect Philosophy: For critical attributes like crimp deformation, wire strand damage, and insulation gap, the acceptable tolerance window is minimized or eliminated. Any condition deemed "Acceptable" for Class 2 may be a Reject for Class 3.
• Visual Inspection: Requires higher magnification inspection and detailed logging of acceptance attributes.
• Destructive Testing: The frequency of mandatory destructive tests, such as the Terminal Pull Test and Micro-Section Analysis, is often increased.

B) Process and Material Control

• Traceability: Class 3 demands complete lot traceability for every component in the harness (wire, terminals, connectors, heat shrink). The MES system must be able to link the final harness serial number back to the raw material lot number.
• Tool Calibration: All crimp tools, wire strippers, and pull-test equipment must be under a strict calibration and maintenance schedule. The Crimp Height Measurement (CHM) must be logged and audited more frequently.
• Cleanliness: Requirements for cleanliness (e.g., flux residue limits, use of gloves) are highly controlled, particularly for harnesses used in vacuum or harsh chemical environments.

1.1.3 Acceptance Criteria: The GO / NO-GO Principle

The IPC/WHMA-A-620 defines all acceptance criteria using three standard categories for any specific attribute (e.g., conductor deformation or strand damage):

1. Acceptable: The condition is preferred and meets all design and performance requirements.
2. Acceptable, Target for Process Indicator: The condition is acceptable but is considered a signal that the process may be drifting. Requires monitoring but is not yet a defect.
3. Defect: The condition is unacceptable and violates the minimum performance requirement. The assembly must be rejected or reworked.

The difference between Class 2 and Class 3 often determines whether a Target for Process Indicator for Class 2 becomes an outright Defect for Class 3.

Final Checklist: IPC Class Implementation

Mandate	Criteria	Verification Action
Product Class Definition	The required IPC Class (1, 2, or 3) is defined by the customer contract and documented on the assembly drawing.	Ensures all manufacturing procedures, tooling, and inspection efforts are aligned to the correct risk level.
Traceability Mandate	Full lot genealogy is maintained for Class 3 projects.	MES system audit verifies that wire lot and terminal lot can be traced back to the supplier.
Tool Calibration	All critical termination tooling is under a strict Preventive Maintenance (PM) schedule.	Calibration logs prove that crimp applicators and pull-test machines are operating within spec.
Process Metrics	Cpk monitoring is implemented for critical processes (e.g., strip length and crimp height).	Ensures the production process maintains the necessary statistical margin (≥1.33) required for Class 3 reliability.