IPC/WHMA-A-620 (the governing standard for wire harness manufacturing) accepts both wire crimp and solder terminations, but under different acceptance criteria and for different applications. In high-vibration environments, a soldered joint can develop fatigue cracks at the wicking boundary in service.
Conversely, many PCB connections and solder-cup terminals don’t call for crimping at all, as the connector geometry requires soldered terminations. Ultimately, the method that fails your program isn’t the technically inferior one; it’s the one specified without accounting for vibration load, production volume, and connector geometry. Mismatched termination choices surface late in the production cycle, when rework and qualification problems are most expensive to fix.
How a Wire Crimp Works
A wire crimp is a mechanical cold-weld formed by controlled deformation of a terminal barrel around a conductor. A calibrated wire crimp tool compresses the terminal and wire strands into a single solid mass at the wire end. The resulting gas-tight connection blocks oxygen from reaching the copper, preventing corrosion and maintaining stable resistance over the harness’s service life.
Conductor size, terminal geometry, and tooling must all match for the joint to meet specifications. IPC/WHMA-A-620 Table 19-8 defines minimum pull-force requirements by wire gauge. A crimped termination that doesn’t meet those values fails acceptance regardless of visual appearance.
Crimping wire in a validated production process delivers repeatable results across thousands of terminations, greatly reducing operator-to-operator variation. In a properly executed crimp, the conductor strands typically break before the crimp separates under pull-test conditions.
How Soldering Works
Soldering creates a metallurgical bond by melting a solder alloy onto the conductor and terminal. The molten alloy wets the base metals and forms a continuous joint when it cools. A well-executed solder joint can create a very low-resistance connection, though the advantage over a quality crimp is negligible in most harness applications.
The trade-offs matter in wire harness assembly. Solder wicking draws the molten alloy up through wire strands by capillary action, turning flexible stranded wire into a rigid section beyond the visible joint. When that wire vibrates, stress concentrates at the point where the solder stops.
Over time, this stress concentration can lead to fatigue cracks and potential conductor failure. A cold solder joint, caused by insufficient heat or poor technique, produces high resistance and an unreliable connection.
Solder work also introduces a risk of wire insulation failure. Heat from a soldering iron can soften or damage insulation near the joint, leaving the bare conductor exposed. In production environments, operator skill determines how consistently that risk stays under control. Soldering is harder to validate at volume than a tooling-controlled crimp process.
Crimp vs. Solder: Comparison Table
The crimp vs. solder decision comes down to application environment and production requirements. Both methods meet IPC/WHMA-A-620 when properly executed, but their performance profiles are not interchangeable.
| Attribute | Crimp | Solder |
|---|---|---|
| Connection method | Mechanical cold weld | Metallurgical bond |
| Vibration resistance | Generally excellent | Generally lower in continuous vibration |
| Repeatability | High, tool-controlled | Operator-dependent |
| Production speed | Fast | Slower |
| Operator skill required | Moderate | High |
| IPC/WHMA-A-620 acceptance | Pull-force requirements | Visual workmanship requirements |
| Best environment | Production harnesses, high vibration | PCB and specified solder applications |
What IPC/WHMA-A-620 Says About Crimp and Solder
IPC/WHMA-A-620 sets different acceptance criteria for crimped and soldered terminations across three application classes.
The standard defines three application classes:
- Class 1: General electronics where the basic function is the primary requirement
- Class 2: Dedicated service products, including industrial equipment, where extended performance is expected
- Class 3: High-performance applications where connection failure isn’t acceptable
Acceptance criteria for crimped terminations
The standard requires pull-force verification by wire gauge. Manufacturers document parameters such as crimp height, and out-of-spec measurements can lead to rejection in higher-reliability programs.
Acceptance criteria for soldered terminations
The standard sets visual workmanship requirements covering wetting, fillet shape, and wire insulation clearance. A bad solder joint that passes visual inspection may still fail electrically. The standard’s criteria are minimum thresholds, not quality guarantees.
What the standard doesn’t say
IPC/WHMA-A-620 doesn’t declare one method superior. Both methods can satisfy Class 2 and Class 3 requirements when the termination type matches the application. Selecting crimping or soldering based on tooling availability rather than specification is a common source of qualification failures.
When to Use Crimp Terminations
Crimped terminations are the standard for high-vibration and harsh-environment harnesses. Production programs specify crimping because solder joints can crack under continuous movement.
Use crimped terminations when your program includes:
- High-vibration environments: Automotive circuits, industrial equipment, and harsh-environment assemblies where solder fatigue is a known risk
- Insulated crimp connectors: Terminal selection and wire crimp tool must match the connector manufacturer’s crimp force specification
- Pull-force acceptance requirements: Any program requiring documented mechanical verification at the termination level
- Repair work: Always follow the original engineering specification rather than substituting based on available tooling
In most cases, crimp bare copper conductors rather than pre-tinned wire. Solder under the crimp can creep and loosen the joint over time, raising resistance. A wire crimp tool that isn’t calibrated to the terminal manufacturer’s specification produces joints that may pass visual inspection but fail pull-force testing.
When to Use Solder Terminations
Solder remains correct for PCB-mounted connectors, solder-cup terminals, and connector pins where impedance matching requires a direct metallurgical bond. Low-vibration assemblies in controlled environments can use solder when the engineering specification calls for it. Approved repair work and prototype builds are also accepted solder applications under IPC/WHMA-A-620.
Use solder terminations when your program includes:
- PCB connections: Component leads and board-mounted connectors where soldering is the specified method
- Solder-cup terminals: Connector styles where the manufacturer doesn’t specify crimping
- Low-vibration assemblies: Controlled environments where the engineering specification permits solder
- Prototype builds: Connections that may need modification before you lock the final specification
Crimping requires matched production tooling and calibration, while soldering relies more on operator skill and heat control. Solder wicks up inside the wire insulation when heat reaches stranded wire, so even low-vibration solder applications require a controlled technique.
Crimp Quality and Common Failure Modes
A good crimp and a bad crimp can look identical under visual inspection. Pull-force testing is the most reliable method for confirming mechanical performance. Cross-section analysis confirms whether the wire and the terminal have cold-welded into a gas-tight mass. A high-quality crimp shows no air gaps between wire strands under magnification.
Common failure modes include:
- Wrong die selection: A die that doesn’t match the terminal type produces inconsistent compression and an unreliable joint
- Conductor damage: Nicking copper strands during stripping creates a weak point before the crimp begins
- Insulation intrusion: Wire insulation left inside the crimp barrel prevents full conductor contact
- Incorrect crimp force: Too low and the joint is mechanically weak; too high, and the compression damages the strands
Calibrated tooling and trained operators significantly reduce these failure modes. Use heat shrink over unsealed crimp connections in moisture-prone environments to complete protection of the gas-tight joint. Before production begins, manufacturing teams review drawings to verify that terminal selection, wire gauge, and tooling are compatible.
Manufacturers call this review Design for Manufacturability (DFM). DFM is a manufacturability check of your existing drawings, not a product development service. It catches termination specification mismatches before they become production failures.
Work With IPC/WHMA-A-620-Trained Operators
Cloom Tech manufactures custom wire harnesses to your exact drawings and specifications, with crimped or soldered terminations as your program requires. We use IPC/WHMA-A-620-trained operators for all crimp terminations.
All assemblies meet ISO 9001, IATF 16949, and IPC/WHMA-A-620 standards, with pull-force testing and full inspection before shipment. If you need a custom wire harness built to your specification, get a free quote and DFM review here.
FAQs on Crimp vs. Solder for Wire Harnesses
Is crimping better than soldering for wire harnesses?
Neither method is universally better. Wire crimping vs. soldering is an application question, not a quality ranking. Crimping suits high-vibration environments and programs with pull-force acceptance requirements. Solder suits PCB connections and low-vibration assemblies when the specification permits.
What pull force should a crimped connection have?
Pull-force requirements vary by wire gauge. IPC/WHMA-A-620 Table 19-8 lists the minimum acceptable value for each gauge. A crimped termination that doesn’t reach that threshold fails mechanical acceptance regardless of appearance.
Can you use solder on automotive wire harnesses?
Solder is acceptable when the engineering specification calls for it. High-vibration circuits in harsh environments ‌use crimped terminations because solder joints are rigid and prone to fatigue cracking. Lower-vibration circuits may permit solder where the engineering specification allows it.
What tools are used for crimping wire harnesses?
Professional wire harness assembly uses ratcheting hand tools, production presses, and applicators matched to specific terminal types and wire crimp connectors. Pull-force testers verify mechanical performance after each termination. Calibrated tooling, matched to the terminal manufacturer’s specifications, ensures consistent, high-quality crimp output throughout a production run.
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