IPC-D-620 Guide: Wire Harness Design Requirements for Cable Assemblies

If you’ve worked in wire harness manufacturing for any length of time, you’ve probably noticed something frustrating: everyone talks about IPC-A-620 for acceptance criteria, but when it comes to actually designing a harness that meets those criteria, the guidance has historically been scattered across dozens of documents. That’s exactly the gap IPC-D-620 was created to fill.

As someone who has spent years dealing with wire harness design for everything from consumer electronics to aerospace applications, I can tell you that having a unified design requirements document has been a game-changer. This guide breaks down everything you need to know about IPC-D-620, from its relationship with IPC-A-620 to the specific design requirements that will keep your harnesses reliable and manufacturable.

What is IPC-D-620?

IPC-D-620, officially titled “Design and Critical Process Requirements for Cable and Wiring Harnesses,” is the design requirements companion to IPC/WHMA-A-620. While IPC-A-620 tells you what an acceptable finished harness looks like, IPC-D-620 tells you how to design one that will meet those acceptance criteria in the first place.

The current revision, IPC-D-620A, was released in 2021 and supersedes the original 2015 version. This standard was developed jointly by IPC and the Wire Harness Manufacturers Association (WHMA) to provide design engineers, manufacturing engineers, and quality professionals with comprehensive guidance for cable and wire harness design.

Scope of IPC-D-620

The standard covers design requirements for:

• Cable assemblies and wire harnesses for all product classes
• Military and space applications (covered in Appendix A)
• Connector selection and termination requirements
• Wire and cable selection criteria
• Harness routing and protection
• Documentation and quality assurance requirements

IPC-D-620 is intended to work alongside other industry standards, not replace them. You’ll still need to reference applicable military specifications (MIL-SPEC), SAE standards, and customer-specific requirements where they apply.

IPC-D-620 vs IPC-A-620: Understanding the Difference

One of the most common points of confusion in the wire harness industry is the relationship between IPC-D-620 and IPC/WHMA-A-620. Let me clear this up once and for all.

Key Differences Explained

Aspect	IPC-D-620	IPC/WHMA-A-620
Primary Focus	Design requirements	Acceptance criteria
Target Audience	Design engineers	Inspectors, QA personnel
When Used	During design phase	During manufacturing/inspection
Content Type	“How to design” guidance	“What’s acceptable” criteria
Visual Content	Limited diagrams	700+ full-color images
Revisions	Currently at Rev A (2021)	Currently at Rev E (2022)

Think of it this way: IPC-D-620 is your design blueprint, while IPC-A-620 is your inspection checklist. A harness designed per IPC-D-620 requirements should naturally meet IPC-A-620 acceptance criteria when properly manufactured.

How They Work Together

The design-to-acceptance workflow looks like this:

1. Design Phase: Engineer uses IPC-D-620 to establish design requirements for wire sizing, connector selection, routing, and documentation
2. Manufacturing Phase: Production follows the design documentation and workmanship standards
3. Inspection Phase: Quality uses IPC-A-620 to verify the finished harness meets acceptance criteria

Both standards use the same three-class product classification system, ensuring consistency from design through final acceptance.

Product Class Classifications in IPC-D-620

Like its companion standard, IPC-D-620 organizes requirements around three product classes that reflect different reliability and performance requirements. Understanding these classes is fundamental to proper harness design.

Class 1: General Electronic Products

Class 1 applies to consumer products where basic functionality is the primary requirement. These products have the widest tolerances and most flexibility in design choices.

Typical Applications:

• Consumer electronics (toys, simple appliances)
• Non-critical industrial equipment
• Products with limited service life expectations

Design Considerations:

• Standard commercial-grade components acceptable
• Broader tolerances on crimp dimensions
• Less stringent environmental protection requirements

Class 2: Dedicated Service Electronic Products

Class 2 covers products that require extended life and consistent performance but aren’t life-critical. This is the most commonly specified class for commercial and industrial applications.

Typical Applications:

• Communications equipment
• Industrial control systems
• Commercial computers and servers
• Medical equipment (non-life-support)

Design Considerations:

• Higher quality components required
• Tighter tolerances than Class 1
• More robust environmental protection
• Documented process controls

Class 3: High-Performance/Harsh Environment Electronic Products

Class 3 represents the highest reliability level, where continued performance is critical and failure cannot be tolerated.

Typical Applications:

• Life support medical equipment
• Aerospace and defense systems
• Critical safety systems
• Applications with harsh environmental exposure

Design Considerations:

• Premium-grade components mandatory
• Strictest tolerances and workmanship requirements
• Full traceability required
• Extensive testing and documentation

Military/Space Applications

IPC-D-620 includes Appendix A specifically for military and space applications, which builds upon Class 3 requirements with additional considerations for:

• Extreme thermal cycling (-65°C to +125°C and beyond)
• Vibration and shock environments
• Radiation exposure
• Extended mission life requirements
• Derating requirements per MIL-HDBK-454

Wire and Cable Design Requirements

Proper wire and cable selection forms the foundation of any reliable harness design. IPC-D-620 provides comprehensive guidance on selecting the right conductors for your application.

Wire Sizing Criteria

Wire gauge selection must consider multiple factors beyond just current capacity:

Factor	Design Consideration
Current Carrying Capacity	Must account for bundling derating
Voltage Drop	Calculate for cable run length
Mechanical Strength	Consider flex cycles and routing
Environmental Exposure	Temperature, chemicals, UV
Weight Constraints	Critical for aerospace applications

Conductor Material Selection

Material	Advantages	Best Applications
Copper (Bare)	High conductivity, economical	General purpose, protected environments
Tin-Plated Copper	Corrosion resistant, solderable	Most commercial applications
Silver-Plated Copper	High-temp capability, low contact resistance	Aerospace, high-frequency
Nickel-Plated Copper	Extreme temperature range	Military, space applications

Insulation Requirements

IPC-D-620 requires designers to specify insulation materials appropriate for the operating environment:

Temperature Rating: Insulation must withstand maximum expected temperature plus appropriate margin. For Class 3 applications, this typically means selecting wire rated at least 25°C above maximum operating temperature.

Chemical Resistance: Consider exposure to fuels, hydraulic fluids, cleaning solvents, and other chemicals present in the operating environment.

Flexibility: For applications requiring repeated flexing, select stranded conductors with appropriate strand count and flexible insulation materials.

Cable and Harness Design Process

IPC-D-620 establishes a structured approach to harness design that ensures all requirements are captured and addressed.

Design Documentation Requirements

Every harness design should include:

Assembly Drawing: Shows complete harness configuration with all routing, breakouts, and terminations

Bill of Materials (BOM): Lists all components including:

• Wire types and gauges
• Connectors and terminals
• Protective sleeving and conduits
• Identification markers
• Hardware and mounting provisions

Wire List/Connection Diagram: Documents every wire’s:

• From/To connections
• Wire gauge and type
• Color code
• Length

Test Requirements: Specifies required electrical tests (continuity, hi-pot, insulation resistance)

Routing and Bend Radius Requirements

Proper routing prevents premature wire failure and ensures long-term reliability:

Wire Type	Minimum Bend Radius
Stranded wire (stationary)	3x outer diameter
Stranded wire (flexing)	10x outer diameter
Coaxial cable	Per manufacturer spec (typically 5-10x OD)
Shielded cable	6x outer diameter minimum
Ribbon/flat cable	10x thickness

Connector Selection Criteria

When selecting connectors per IPC-D-620, consider:

Electrical Requirements:

• Current rating per contact
• Voltage rating
• Contact resistance
• Insulation resistance

Mechanical Requirements:

• Mating cycles required
• Vibration and shock resistance
• Mounting method compatibility
• Keying and polarization needs

Environmental Requirements:

• Operating temperature range
• Sealing requirements (IP rating)
• Chemical exposure
• Altitude/pressure considerations

Read more IPC Standards:

Critical Process Requirements

IPC-D-620 addresses several critical manufacturing processes that must be properly specified in the design documentation.

Crimp Termination Requirements

Crimping is the most common termination method, and IPC-D-620 provides extensive guidance:

Wire Preparation:

• Strip length per terminal manufacturer specification
• No nicked or cut strands allowed for Class 2/3
• Strand separation limits defined by class

Crimp Tool Selection:

• Use manufacturer-specified tooling
• Tooling must be calibrated and maintained
• Document tool serial numbers for traceability (Class 3)

Crimp Inspection Criteria:

• Visual inspection per IPC-A-620
• Cross-section analysis for qualification (Class 3)
• Pull test requirements defined by wire gauge and terminal

Soldered Termination Requirements

When solder terminations are required, IPC-D-620 specifies:

Solder Selection:

• Lead-free solder for RoHS compliance
• Eutectic solder for military applications (unless specified otherwise)
• Flux compatibility with wire insulation

Termination Design:

• Cup terminals sized for wire gauge
• Turret and bifurcated terminals per J-STD-001 requirements
• Stress relief provisions for wire exit

Splicing Requirements

Splicing should be avoided where possible, but when necessary:

• Use approved splice methods (crimp, ultrasonic weld, solder)
• Document splice location on assembly drawing
• Environmental protection required (heat shrink, potting)
• No inline splices for Class 3 military/space unless specifically approved

Red Plague and White Plague Control

Two corrosion phenomena require special attention in harness design, and IPC-D-620 addresses both with dedicated white papers.

Red Plague (Cuprous Oxide Corrosion)

Red plague occurs when silver-plated copper conductors are exposed to moisture in the presence of oxygen, causing the formation of cuprous oxide at the silver-copper interface.

Prevention Requirements:

Control Measure	Implementation
Wire Selection	Use certified red plague-resistant wire
Storage Control	Humidity-controlled environment
Handling Procedures	Minimize exposure during processing
Sealing	Environmental sealing at terminations
Testing	Periodic inspection of inventory

IPC-D-620 references IPC-WP-113 (Guidance for the Development and Implementation of a Red Plague Control Plan) for detailed implementation guidance.

White Plague (Fluorine Attack)

White plague results from fluorine contamination attacking nickel plating on connectors and contacts, appearing as a white powdery residue.

Prevention Requirements:

• Avoid fluorine-containing materials in contact with nickel plating
• Control flux types used in soldering operations
• Proper cleaning and verification procedures
• Material compatibility verification during design phase

IPC-D-620 references IPC-WP-114 (Guidance for the Development and Implementation of a White Plague Control Plan) for detailed guidance.

Foreign Object Debris (FOD) Prevention

FOD control is critical for aerospace and defense applications and is addressed in IPC-D-620 with supporting guidance in IPC-WP-116.

Design Considerations for FOD Prevention

Connector Protection:

• Specify protective caps for open connectors
• Design for covered storage during manufacturing
• Include FOD inspection requirements in test procedures

Harness Construction:

• Avoid hollow cavities where debris can accumulate
• Specify cleaning and inspection hold points
• Design for accessibility during FOD inspection

Documentation:

• Include FOD control requirements in work instructions
• Specify acceptable cleanliness levels
• Document inspection criteria and methods

Quality Assurance Requirements

IPC-D-620 establishes quality requirements that must be incorporated into the design documentation.

Inspection Requirements by Class

Requirement	Class 1	Class 2	Class 3
Visual Inspection	Sample	100%	100%
Electrical Test	Sample	100%	100%
Documentation Review	Minimal	Full	Full + Verification
Traceability	Not required	Recommended	Required
First Article Inspection	Optional	Recommended	Required

Testing Requirements

Standard electrical tests for harness verification:

Continuity Testing: Verify all connections are made correctly with acceptable resistance

Dielectric Withstand (Hi-Pot): Verify insulation integrity between circuits and to chassis/shield

Insulation Resistance: Measure resistance between conductors and to ground

Additional Tests (as specified):

• Time Domain Reflectometry (TDR) for controlled impedance
• Shield effectiveness testing
• Environmental stress screening (ESS) for Class 3

Useful Resources for Wire Harness Engineers

For additional information on IPC-D-620 and wire harness design, these resources provide valuable reference material.

Official IPC Standards and Publications

• IPC-D-620A: Design and Critical Process Requirements for Cable and Wiring Harnesses – shop.ipc.org
• IPC/WHMA-A-620E: Requirements and Acceptance for Cable and Wire Harness Assemblies
• IPC-HDBK-620: Handbook and Guidelines for IPC/WHMA-A-620 (provides engineering rationale)
• IPC-WP-113: Red Plague Control Plan Guidance
• IPC-WP-114: White Plague Control Plan Guidance
• IPC-WP-116: FOD Control Plan Guidance

Related Military Standards

• MIL-HDBK-454: General Guidelines for Electronic Equipment
• MIL-STD-1553: Aircraft Internal Time Division Multiplex Data Bus
• NASA-STD-8739.4: Crimping, Interconnecting Cables, Harnesses, and Wiring

Industry Organizations

• IPC (Association Connecting Electronics Industries): www.ipc.org
• WHMA (Wire Harness Manufacturers Association): Industry consortium partnering with IPC
• SAE International: Aerospace wiring standards (AS50881, AS22759)

Training Resources

• IPC Certification Programs: CIS (Specialist), CSE (Expert), CIT (Trainer) levels available
• WHMA Training Programs: Wire harness manufacturing certification
• Electronics Group Training: IPC-620 certified training courses

Frequently Asked Questions About IPC-D-620

What is the difference between IPC-D-620 and IPC-A-620?

IPC-D-620 provides design requirements that engineers use when creating wire harness designs, while IPC-A-620 provides acceptance criteria that inspectors use to verify finished harnesses meet quality standards. Think of IPC-D-620 as “how to design it right” and IPC-A-620 as “how to verify it was built right.” Both standards use the same Class 1, 2, 3 classification system, so a harness designed per IPC-D-620 Class 2 requirements should pass IPC-A-620 Class 2 inspection criteria when properly manufactured.

Do I need both IPC-D-620 and IPC-A-620 for my facility?

It depends on your role in the supply chain. Design engineering groups primarily need IPC-D-620 for developing harness designs. Manufacturing and quality inspection teams primarily need IPC-A-620 for acceptance criteria and workmanship standards. However, most organizations involved in complete harness production benefit from having both standards, as understanding design intent (IPC-D-620) helps manufacturing build better harnesses, and understanding acceptance criteria (IPC-A-620) helps designers create more manufacturable designs.

Does IPC-D-620 replace MIL-SPEC requirements for military harnesses?

No, IPC-D-620 is intended to complement, not replace, applicable military specifications. Appendix A of IPC-D-620 provides additional requirements for military and space applications, but contract-specific military standards (MIL-DTL-specifications, NASA standards, etc.) still take precedence when specified in procurement documents. IPC-D-620 provides a consolidated design framework that works alongside these military requirements.

What training or certification is available for IPC-D-620?

Unlike IPC-A-620, which has an extensive certification program (CIS, CSE, CIT levels), IPC-D-620 does not currently have a dedicated certification track. However, understanding IPC-D-620 is valuable for anyone taking IPC-A-620 certification, as it provides the design rationale behind the acceptance criteria. Some training organizations offer combined design and acceptance training that covers both standards. Contact IPC or authorized training centers for current course offerings.

How often is IPC-D-620 updated, and how do I know which revision to use?

IPC-D-620 was first released in December 2015, with Revision A following in 2021. Updates typically occur every 5-7 years unless significant industry changes require faster revision. The revision in effect for your project should be specified by the customer or design authority in procurement documentation. If not specified, the latest revision is generally recommended for new designs. IPC maintains a document revision table at electronics.org showing current revision status for all standards.

Conclusion

IPC-D-620 fills a critical gap in the wire harness industry by providing consolidated design requirements that complement the well-established acceptance criteria in IPC-A-620. For design engineers, manufacturing engineers, and quality professionals, understanding both standards is essential for creating reliable, manufacturable cable and wire harness assemblies.

The standard’s three-class system ensures appropriate design rigor for applications ranging from consumer products to life-critical aerospace systems. By following IPC-D-620 design requirements, engineers can create harnesses that not only meet IPC-A-620 acceptance criteria but also perform reliably throughout their intended service life.

Key takeaways for implementing IPC-D-620 in your organization:

For Design Engineers: Use IPC-D-620 as your primary reference for wire sizing, connector selection, routing requirements, and design documentation. Supplement with customer-specific requirements and applicable military standards.

For Manufacturing Engineers: Understand the design intent behind IPC-D-620 requirements to optimize manufacturing processes and identify potential producibility issues early in the design phase.

For Quality Engineers: Use IPC-D-620 to verify design documentation is complete and requirements are properly flowed down, while using IPC-A-620 for finished product acceptance.

The combination of proper design (IPC-D-620) and rigorous acceptance criteria (IPC-A-620) provides a comprehensive framework for wire harness quality that has gained international acceptance across industries from consumer electronics to aerospace and defense.