Key Takeaways (Executive Summary)
- The Verdict: For wire harnesses subjected to vibration (vehicles, machinery), crimping is superior to soldering because it avoids "wicking," which makes wires brittle.
- The Mechanism: A proper crimp is not just "squished" metal; it is a gas-tight cold weld that prevents oxidation and allows the wire strands to move naturally.
- The Standard: Most industrial and automotive standards (like IPC/WHMA-A-620) prohibit soldering crimp terminals because it masks bad connections and creates stress points.
- The Exception: Soldering is still used for specific applications like coaxial connectors or lap-splicing in repair scenarios where crimping tools won't fit.
- The Debate: "Solid" vs. "Flexible"
If you ask a hobbyist or an old-school mechanic, they might tell you that soldering is the gold standard. "It makes the wire into a solid block of metal," they say. "It can't come loose."
While true for circuit boards (PCBs), this logic is dangerous when applied to wire harnesses.
In the professional manufacturing world—whether aerospace, automotive, or medical—crimping is the king of reliability. Why? Because wire harnesses move. They vibrate. They flex. Soldering fights against that movement; crimping works with it.
The Science: Why Soldering Fails in Harnesses
The biggest enemy of a soldered wire harness is a phenomenon called wicking.
When you apply solder to a stranded wire, the molten tin/lead is drawn up under the insulation by capillary action. This turns a flexible stranded wire into a solid, rigid rod.
When that wire vibrates (like in a car engine), the stress concentrates exactly at the point where the solder stops and the flexible wire begins. Eventually, fatigue cracks form, and the wire snaps right behind the connector.
Comparison Table: Crimping vs. Soldering
Compare these methods based on industrial reliability standards.
|
Feature |
Crimping (Cold Weld) |
Soldering (Thermal Bond) |
|---|---|---|
|
Vibration Resistance |
High: Strands remain flexible, absorbing shock. |
Low: Wicking creates brittle stress points. |
|
Consistency |
High: Automated tools apply identical pressure every time. |
Low: Dependent on operator skill (heat, flux, timing). |
|
Process Speed |
Fast: A machine can crimp 3,000+ terminals per hour. |
Slow: Requires heating, cooling, and cleaning. |
|
Electrical Resistance |
Low (Gas-tight connection). |
Low (If joint is perfect), High (If "cold solder"). |
|
Heat Damage |
None. |
High risk of melting wire insulation. |
The Physics of a Good Crimp: It's "Gas-Tight"
A high-quality crimp doesn't just fold metal wings over the wire. It applies so much force that the wire strands and the connector terminal deform into a single, solid mass.
If you cut a proper crimp in half and look at it under a microscope (a cross-section analysis), you shouldn't see any air gaps between the strands. The hexagon or honeycomb pattern formed is "gas-tight." This means oxygen cannot get in to corrode the copper, ensuring the electrical connection lasts for decades.
What Do The Standards Say? (IPC/WHMA-A-620)
The industry bible for wire harness quality is IPC/WHMA-A-620.
- IPC Class 2 & 3 usually require crimping for all terminal connections.
- Soldering Crimped Terminals: It is largely discouraged to solder a terminal after crimping it. If the crimp is good, the solder adds no value. If the crimp is bad, the solder is just hiding a defect.
- Tinning Before Crimping: NEVER DO THIS. If you tin (solder) a wire before crimping it, the solder will eventually "creep" or flow under the pressure of the crimp, causing the connection to loosen over time.
When Is Soldering Actually Used?
We aren't saying soldering is useless. It has its place:
- PCBs: Soldering components to a rigid board is standard.
- Coaxial Cables: Many RF connectors (like SMA or BNC) require the center pin to be soldered for impedance matching.
- Splices: In repair situations where you can't access the wire end, a lap solder splice (covered by adhesive heat shrink) is an acceptable fix.
Frequently Asked Questions (FAQ)
Q: Can I dip my wire in solder before crimping to make it stronger? A: No. This is a major failure point. Solder is a soft metal. Under the pressure of the crimp, the solder will deform and "creep" over time, leading to a loose connection and high resistance (heat). Always crimp raw copper strands.
Q: How do you test if a crimp is good? A: We use a Pull Tester. We clamp the wire and the terminal and pull until it breaks. Standards like UL 486A dictate exactly how many pounds of force a crimp must withstand based on the wire gauge (e.g., an 18 AWG wire must hold at least 20 lbs).
Q: Isn't soldering better for corrosion resistance? A: Not necessarily. A "gas-tight" crimp prevents oxidation just as well as solder. For extreme environments, we use adhesive-lined heat shrink over the crimp to seal it completely.
About the Author
Michael Wang
Senior Technical Engineer
As the technical lead at TeleWire, Michael bridges the critical gap between complex engineering requirements and precision manufacturing. With deep expertise in Design for Manufacturing (DFM) and signal integrity, he oversees the technical validation of custom interconnect solutions for mission-critical automotive, industrial, and medical applications.
