1.1 Quality baseline: IPC/WHMA-a-620 classes

The IPC/WHMA-A-620 standard is the central quality benchmark for the cable and wire harness manufacturing industry. It establishes clear, objective criteria for what constitutes an acceptable or rejectable condition in an electronic assembly. The standard defines acceptable tolerances, workmanship expectations, and the rigor of quality audits based on the Product Class specified by the customer.

The acceptance guideline: three product classes

The IPC/WHMA-A-620 standard defines three distinct product classes. These classes are based on the complexity, function, and consequence of failure for the end product. The chosen class directly dictates the acceptance criteria for common manufacturing challenges, such as damaged wire strands, insulation gaps, minor crimp deformation, and final routing geometry.

IPC Class	Application Risk	Reliability Expectation	Manufacturing Focus
Class 1	General Electronic Products (Consumer, Light Commercial)	Basic functionality is expected for a defined, typically short, service life.	The focus is on cost-effective production and basic interconnection reliability. Minor cosmetic imperfections are generally permitted.
Class 2	Dedicated Service (Industrial, Communications)	Extended service life where sustained, dependable performance is necessary, but a sudden failure isn’t critical to human life.	Considered the standard quality baseline, this class encourages documented, measurable process controls. Uninterrupted service is desired, but not strictly life-critical.
Class 3	High-Performance/Critical (Medical, Aerospace, Military)	Maximum Reliability; continuous, mission-critical performance where failure is unacceptable and potentially life-threatening.	Most Stringent: This class demands exceptional workmanship, maximum component traceability, and rigorous defect prevention. Unplanned equipment downtime cannot be tolerated.

Process Guideline: The required product class must be explicitly defined in the customer contract or on the master assembly drawing. When left unspecified, manufacturers often default to Class 2. However, making assumptions about the class carries significant financial and liability risks. Therefore, the product class should be formally defined and agreed upon before production begins.

Acceptance criteria: the GO / NO-GO principle

IPC/WHMA-A-620 categorizes all acceptance criteria into standardized conditions. The standard clarifies that “Acceptable” represents the minimum functional standard, while the “Target” condition is the ideal objective for engineering and process setup.

Target Condition: This is the optimal, ideal condition. It is the required goal for all process setups and tooling calibration before production begins.
Acceptable Condition: This condition may have minor visual imperfections but maintains the structural integrity and electrical reliability of the assembly. It meets the minimum physical requirements for the specified class. A product in this condition is functional and authorized for shipment.
Condition for Review (Defect): This condition is unacceptable and violates the minimum performance or safety requirements. The assembly must be rejected, quarantined, or reworked.
Process Indicator: This is a warning condition. It is technically “Acceptable” as it barely meets the minimum standard, but it signals that the manufacturing process is drifting out of its nominal control range. For Class 2 and Class 3 builds, process indicators should trigger an engineering review and process adjustment at the machine, even if the current unit is not scrapped.

Helpful Distinction: A specific condition correctly classified as “Acceptable” for a Class 2 assembly might be classified as a “Defect” for a more demanding Class 3 assembly. An example is the allowable limit for exposed copper strands at a crimp. Always inspect against the specific Target Class defined for the product.

The traceability scope: class 3 expectations

For Class 3 high-reliability harnesses, simply passing a visual inspection is not sufficient. Manufacturing operations are expected to forensically document the production history of the materials and processes for auditing purposes.

Raw material genealogy

The Manufacturing Execution System (MES) should link the final harness Serial Number (SN) directly to the specific Lot/Batch Numbers of all key materials:

Wire/Cable Spools (traceable back to the extrusion date and copper source).
Terminals and Connectors (traceable back to the supplier’s original plating batches).
Heat Shrink, Solder, and Potting Compounds (traceable to remaining shelf life limits and exact chemical batches).

Tooling traceability

The production record should ideally document which specific Crimp Applicator and which precise Press produced each termination. This enables rapid containment and investigation if a specific tool is later discovered to be drifting out of calibration.

Test data logs

Destructive test results, such as pull test values recorded during machine setup, should be electronically linked to the production batch record. This verifies that the machine setup was validated before the production run commenced.

Recap: IPC/WHMA-A-620 Class Requirements for Hardware Manufacturing

Class	Application Area	Reliability Expectation	Key Acceptance & Traceability Requirements
1	General Electronic Products (Consumer, Light Commercial)	Basic functionality for a defined, typically short service life.	Minor cosmetic imperfections generally permitted. Traceability not required.
2	Dedicated Service (Industrial, Communications)	Extended service life with dependable performance; failure not life-critical.	Default baseline. Requires documented, measurable process controls. Process indicators must trigger engineering review.
3	High-Performance/Critical (Medical, Aerospace, Military)	Maximum reliability; continuous, mission-critical performance; failure unacceptable.	Most stringent. Exceptional workmanship required. Full traceability of materials (Lot/Batch), tooling (applicator/press), and test data logs mandatory.