Real Project Snapshot — Ipc 620 Wire Harness Inspection Guide
Anonymized example from our case bank, shared so buyers can see how this scope is actually executed in production.
Industry: earthmoving-equipment | Region: Australia | Year: 2023 → 2024
Scenario: An Australian heavy machinery manufacturer requested quotes for multiple custom wire harness models but provided incomplete technical drawings at the initial inquiry stage.
Challenge: Missing critical specifications, including relay models, Deutsch connector models, and Hammond enclosure details, prevented accurate quoting and risked production errors for the 200-piece batch.
Solution: We implemented an engineering-to-engineering clarification process, compiling a detailed technical checklist to guide the client's internal engineering team to provide the missing specs, ensuring all requirements were locked down before sampling.
Result: Achieved full specification lock-down, enabling accurate quoting for 3 sample units and the 200-piece production run, preventing costly rework and material delays.
Concrete numbers: 3 sample units, 200-piece batch size, Deutsch connectors specified, Hammond enclosures specified
You received a batch of wire harnesses from your supplier. They look fine to the naked eye. But do they actually meet workmanship standards? Without a systematic inspection framework, “looks fine” is not a quality strategy—it’s a liability.
IPC/WHMA-A-620 is the only industry-consensus standard that defines acceptance criteria specifically for cable and wire harness assemblies. Currently on Revision E (released October 2022), this 338-page document contains over 700 full-color photographs showing exactly what “acceptable” and “defect” look like for every critical process. This guide distills the most important inspection criteria into a practical resource you can use on the production floor.
What Is IPC/WHMA-A-620?
IPC/WHMA-A-620 (commonly called “IPC-620”) is the requirements and acceptance standard for cable and wire harness assemblies. Developed jointly by IPC (Association Connecting Electronics Industries) and WHMA (Wiring Harness Manufacturer’s Association), it covers materials, methods, tests, and acceptance criteria for crimped, mechanically secured, and soldered interconnections.
Unlike general quality management standards like ISO 9001 or IATF 16949, IPC-620 is a workmanship standard. It does not tell you how to organize your quality system. It tells you exactly what a properly crimped terminal, a correctly routed harness, and a compliant solder joint should look like—with photographic evidence for every criterion.
What IPC-620 Covers
The 3-Class System Explained
IPC-620 uses a three-class system to define the level of workmanship required. The class determines which criteria are “acceptable,” which are “process indicators,” and which are outright “defects.” Your customer’s contract or purchase order should specify the required class. If no class is specified, Class 2 is the default.
| Criteria | Class 1 — General | Class 2 — Dedicated Service | Class 3 — High Reliability |
|---|
Hommer’s Take
“The most common mistake I see is buyers who don’t specify a class on their purchase order. The manufacturer assumes Class 1 to keep costs low, the customer expects Class 3 because it’s medical equipment, and the dispute starts at incoming inspection. Always specify the class in writing—before production begins, not after.”
Hommer Zhao — Engineering Director, WellPCB
Key Distinction: Process Indicator vs. Defect
IPC-620 uses three verdict levels: Acceptable (meets criteria), Process Indicator (not ideal but not a reject—fix the process), and Defect (reject required). A condition that is a process indicator in Class 1 may be a defect in Class 3. Understanding this distinction prevents unnecessary rework.
Crimp Inspection Criteria
Crimping is the most critical process in wire harness manufacturing, and IPC-620 devotes more pages to crimp acceptance than any other topic. A good crimp creates a gas-tight connection between conductor and terminal. A bad crimp creates an intermittent failure waiting to happen.
Open Barrel Crimp — Visual Criteria
Acceptable (All Classes)
- Wire strands visible at inspection window
- Bellmouth present on wire entry side
- Crimp impression centered on barrel
- No insulation trapped in conductor crimp area
- Insulation crimp securely grips insulation
-
Crimp applied to insulation instead of conductor -
No conductor strands visible at inspection window -
Cut or nicked strands exceeding class limit -
Crimp not fully compressed (loose barrel) -
Wire extends beyond crimp barrel into contact area
Crimp Height & Pull Force Testing
Visual inspection alone is not sufficient. IPC-620 requires mechanical verification through crimp height measurement and pull force testing. Crimp height must be measured with a micrometer (not calipers) and compared to the terminal manufacturer’s specification. Pull force minimums are defined in UL 486A-B and reference tables within IPC-620 itself.
| Wire Gauge (AWG) | Minimum Pull Force (N) | Typical Crimp Height Tolerance |
|---|
For production runs, IPC-620 requires first-piece and last-piece pull testing at a minimum. High-reliability applications (Class 3) often require crimp force monitoring (CFM) on every crimp. Learn more about testing methods in our wire harness quality testing guide.
Solder Termination Inspection
IPC-620 aligns its soldering requirements with IPC J-STD-001 (Requirements for Soldered Electrical and Electronic Assemblies). When a wire harness includes soldered terminations—cup terminals, turret terminals, or PCB connections—the solder joint quality criteria apply.
Solder Cup Terminal Criteria
Acceptable
- Solder ≥75% (Class 1/2) or 100% (Class 3)
- Smooth, shiny or satin solder fillet
- Wire visible at top of cup
- No cold solder joints (grainy, dull surface)
- Solder below 75%
- Solder bridges between adjacent cups
- Fractured or disturbed solder joint
- Insulation melted or charred from heat
Wire preparation is where many defects originate. Automated stripping machines can nick conductors. Manual stripping can cut too deep. IPC-620 defines strict limits on how much damage is permissible—and those limits get tighter with each class.
| Condition | Class 1 | Class 2 | Class 3 |
|---|
For a deeper dive into conductor and insulation materials and how they affect strippability, see our wire harness materials guide.
Hommer’s Take
“I tell our quality team: if you have to squint at a nick and debate whether it’s 9% or 11% of strands, it’s time to recalibrate the stripping blade. The goal isn’t to push borderline parts through inspection—it’s to eliminate the conditions that create borderline parts in the first place.”
Hommer Zhao — Engineering Director, WellPCB
Harness Assembly & Protection
Once wires are terminated, they must be routed, bundled, and protected according to the assembly drawing. IPC-620 covers lacing, cable ties (tie wraps), taping, braided sleeving, conduit, heat shrink tubing, and strain relief.
Cable Tie (Tie Wrap) Inspection
Acceptable
- Tie is snug but does not deform insulation
- Tail trimmed flush (no sharp edge)
- Positioned per drawing within ±12 mm
- Lock mechanism fully engaged
- Tie over-tightened causing insulation damage
- Tail extends more than specified, creating snag hazard
- Tie placed over splice or branch point incorrectly
- Lock not fully engaged (tie can rotate freely)
Heat Shrink Tubing
Heat shrink must fully recover (shrink) to conform tightly to the underlying surface. IPC-620 acceptance criteria include: no splits, cracks, or charring; uniform shrinkage with no bridging over air gaps; and adequate overlap (minimum 2x the wire outside diameter for splices). For Class 3, adhesive-lined heat shrink is required for all environmental seals.
Wire routing must follow the assembly drawing. Minimum bend radius for standard wire is 3x the cable outside diameter (10x for coaxial cable). Sharp bends, kinks, or wires crossing over sharp edges without protection are defects in all classes. Learn more about proper harness design in our wire harness design guide.
Labeling & Marking Requirements
Labels are not an afterthought—they are a quality requirement. IPC-620 specifies that labels must be legible, durable, and properly positioned. For regulated industries like medical devices and automotive, label traceability is a compliance requirement.
Practical IPC-620 Inspection Checklist
Use this checklist as a starting point for incoming inspection or in-process quality audits. Customize it based on your specific product class and customer requirements.
Wire Harness IPC-620 Inspection Checklist
Hommer’s Take
“A checklist is only as good as the person using it. We invest in IPC-620 CIS certification for every inspector on our floor—not just because customers ask for it, but because certified inspectors catch 47% more defects than untrained operators in our internal studies.”
Hommer Zhao — Engineering Director, WellPCB
IPC-620 Certification Levels
IPC offers a tiered certification program for IPC-620. Requiring certification from your supplier is the most reliable way to ensure their team can actually interpret and apply the standard correctly.
When evaluating suppliers, ask not just “Are you IPC-620 certified?” but “How many CIS-certified operators and CIT trainers do you have on staff?” A single CIT who certified 50 operators five years ago is very different from a team with current certifications. For more supplier evaluation criteria, see our guide to choosing a wire harness manufacturer .
Precision wire cutting equipment calibrated to IPC-620 strip length tolerances
References
Frequently Asked Questions
What is the difference between Class 1, 2, and 3 in IPC/WHMA-A-620?
Class 1 is general electronic products where the main requirement is function. Class 2 is dedicated service products needing extended life and reliable performance, such as industrial equipment. Class 3 is high-reliability hardware — aerospace, medical life-support, military — where downtime cannot be tolerated and acceptance criteria are tightest.
Is IPC/WHMA-A-620 certification mandatory?
It is not a legal requirement, but it is frequently mandated by contract. Many OEMs require their supplier to employ IPC/WHMA-A-620 Certified IPC Trainers (CIT) and Certified IPC Specialists (CIS), and to build and inspect to a specified class. Check your purchase order — the required class is usually called out there.
Which revision of IPC/WHMA-A-620 is current?
The current revision is IPC/WHMA-A-620E, released in October 2022. It runs roughly 338 pages and contains over 700 color photographs defining acceptable, defect, and process-indicator conditions for crimped, soldered, and mechanically secured connections.
What are the most common crimp defects found during inspection?
The recurring ones are insufficient conductor crimp (loose wire brush), insulation trapped inside the conductor crimp, missing or excessive bell-mouth, and wire strands cut or nicked during stripping. Crimp height and pull-force testing catch most of these before they reach final inspection.
Can I inspect to IPC/WHMA-A-620 without owning the standard?
Not reliably. The standard's value is its photographic acceptance criteria, so inspectors need access to the controlled document to make defensible accept/reject calls. Most manufacturers maintain a current copy on the floor and train inspectors against it rather than relying on memory.
What is the difference between IPC/WHMA-A-620 and IPC-A-610?
IPC/WHMA-A-620 covers cable and wire harness assemblies — crimps, splices, connectors, lacing, and overall harness workmanship. IPC-A-610 covers printed circuit board assemblies — solder joints, component placement, and PCB-level criteria. They are complementary standards for two different assembly domains.