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.

1.4.1.1 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)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.

1.1.2

Process MandatesNote: forThe Criticalcontract Applicationsor (Classassembly 3)

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Manufacturingmust aexplicitly Classstate 3the harnessClass. isIf significantlynot morespecified, demandingthe thanmanufacturer often defaults to Class 2, requiringbut tighterthis controlsassumption acrosscarries every stage of the assembly process.risk.

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

  4.1.2 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 categoriescategories. forInspection anypersonnel specificmust attributeunderstand (e.g.,that conductor"Acceptable" deformationis orthe strandminimum damage):standard, while "Target" is the goal.

1. Acceptable:Target Condition: The ideal or "perfect" condition. This is the goal for process setup and tooling calibration.
2. Acceptable Condition: The condition is preferrednot perfect but maintains the integrity and reliability of the assembly. It meets allthe designminimum and performance requirements.
2. Acceptable, Targetrequirement for Processthe Indicator:specified Class. The condition is acceptable but is considered a signal that the process may be drifting. Requires monitoring butproduct is not yet a defect.defective.
3. Defect: The condition is unacceptable and violates the minimum performance or safety requirement. The assembly must be rejected or reworked.
4. 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.

TheCritical difference between Class 2 and Class 3 often determines whether a Target for Process IndicatorDistinction: A condition listed as "Acceptable" for Class 2 becomesmay anbe outrighta Defect"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.
ToolDefect Calibrationvs. Indicator	AllProcess criticalIndicators terminationare toolingtracked isin underthe aquality strictsystem to trigger Preventive Maintenance (PM) schedule.(e.g., crimp tool wear).	CalibrationPrevents logs"Acceptable" provebut thatdrifting crimpprocesses applicatorsfrom andbecoming pull-test machines are operating within spec."Defects."
Process Metrics	CpkCpk 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.