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4.1 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.

4.1.1 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. Minor cosmetic imperfections are generally permitted.

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). Uninterrupted service is desired but not critical to life support.

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. Downtime cannot be tolerated.

Process Note: The contract or assembly drawing must explicitly state the Class. If not specified, the manufacturer often defaults to Class 2, but this assumption carries risk.

4.1.2 Acceptance Criteria: The GO / NO-GO Principle

The IPC/WHMA-A-620 defines all acceptance criteria using three standard categories. Inspection personnel must understand that "Acceptable" is the minimum standard, while "Target" is the goal.

  • Target Condition: The ideal or "perfect" condition. This is the goal for process setup and tooling calibration.
  • Acceptable Condition: The condition is not perfect but maintains the integrity and reliability of the assembly. It meets the minimum requirement for the specified Class. The product is not defective.
  • Defect: The condition is unacceptable and violates the minimum performance or safety requirement. The assembly must be rejected or reworked.
  • Process Indicator: A condition that is technically acceptable (meets the minimum) but indicates the process is drifting or out of control. For Class 2/3, these often require documentation and process adjustment, even if the hardware is not scrapped.

Critical Distinction: A condition listed as "Acceptable" for Class 2 may be a "Defect" for Class 3. (e.g., exposed copper strands at the crimp brush).

4.1.3 Traceability Scope: Class 3 Mandates

For Class 3 high-reliability harnesses, the physical quality of the connection is insufficient; the history of the materials must also be proven.

Raw Material Genealogy

The MES (Manufacturing Execution System) must link the final harness Serial Number (SN) to the specific Lot/Batch Numbers of:

  • Wire/Cable Spools (traceable to the extrusion date/copper source).
  • Terminals and Connectors (traceable to plating batches).
  • Heat Shrink/Solder (traceable to chemical shelf life).

Tooling Traceability

The record must show which specific Crimp Applicator and Press produced the termination. This allows for rapid containment if a specific tool is later found to be out of calibration.

Test Data

Destructive test results (e.g., Pull Test values) must be linked to the production batch, proving that the setup was validated before the run began.

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.

Visual Standards

Inspection stations are equipped with IPC/WHMA-A-620 visual references for the specific Class.

Inspectors verify criteria (e.g., strand damage limits) based on the specific Class requirements, not generic judgment.

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.

Defect vs. Indicator

Process Indicators are tracked in the quality system to trigger Preventive Maintenance (e.g., crimp tool wear).

Prevents "Acceptable" but drifting processes from becoming "Defects."

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.


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