'Terminal Pull-Out Force: Testing and Design Targets'
Short answer: terminal pull-out force is the axial load a terminated joint withstands before the wire, pin or terminal separates, and it is one of the few electrical-connection properties you can verify with a simple tensile test. Typical targets run from about 10 N for a small signal terminal to over 200 N for a heavy power crimp, set mainly by wire gauge, crimp geometry and retention features. Test it by pulling the wire away from the terminal at a controlled rate, usually around 25 mm per minute, and recording the peak force.
Pull-out force sits at the intersection of mechanical design and electrical reliability. A joint that passes continuity on the bench can still fail in the field if vibration, thermal cycling or a poor crimp lets it loosen and arc. This guide explains what pull-out force measures, how it is tested, realistic design targets by terminal type, and the design and plating levers that move the number.
What Pull-Out Force Means for a Terminal
Pull-out force — often called retention or pull-off force — is the axial force required to separate a terminal from its mating wire, pin or housing. It is distinct from insertion and withdrawal force, which describe the effort to mate and unmate a connector, though the two are related through the contact spring design.
The number matters because it is a proxy for reliability. A high pull-out force generally means the crimp or press-fit is mechanically sound, which correlates with low, stable electrical resistance. Standards bodies specify minimum values because a loose joint is a safety and fire risk: an under-crimped terminal can heat, oxidize and eventually arc. For a signal terminal it is uncommon to see values under about 10 N accepted; for power circuits the requirement climbs with wire size.
How Pull-Out Force Is Tested
The test is a destructive tensile pull. The terminal is held in a fixture or its mating half, the wire or pin is gripped, and a tensile tester pulls them apart at a controlled rate — commonly around 25 mm per minute, which is close to one inch per minute used in many legacy standards. The peak force before separation or before the wire slips from the crimp is recorded.
Test setup details matter. Gripping too close to the crimp can mask a weak joint; gripping with jaws that crush the wire changes the failure mode. Sample size should be large enough to expose variation from crimp tooling and material, typically at least five to ten samples per lot for qualification. Results are reported as the minimum and the mean, because the minimum governs whether the design passes.
For press-fit pins, the related test is insertion and retention force in the plated through-hole, where a minimum retention force keeps the pin seated through assembly, vibration and reflow. For connector contacts, the same equipment measures insertion and withdrawal force, which sets the user's plug-in feel and the contact's wear behavior. The broader stamped terminal design guide covers how these forces are shaped by geometry, and the terminal materials article explains the alloy and temper choices behind them.
Design Targets by Terminal Type
Targets vary widely with wire size and application. The values below are indicative industry ranges, not limits, and should always be confirmed against the applicable standard for your product.
| Terminal type | Typical wire / pin size | Indicative pull-out target | Notes |
|---|---|---|---|
| Small signal crimp | 28-22 AWG | 10-30 N | Retention features and crimp quality dominate |
| Power crimp terminal | 18-12 AWG | 50-150 N | Scales strongly with conductor area |
| Heavy power lug | 8-2 AWG | 150-400 N+ | Governed by crimp compression and barrel design |
| Press-fit pin (PCB) | 0.5-1.0 mm pin | 10-40 N retention | Set by hole size and compliant feature |
| Quick-disconnect tab | 0.110-0.250 in | 20-80 N | Insertion and withdrawal force both matter |
| Solder tab | Wire or pad | Not pull-tested the same way | Joint strength depends on solder process |
The trend is simple: pull-out force scales with conductor cross-section and with the amount of metal-to-metal engagement. Thin signal terminals rely on formed retention lances and barbs, while heavy lugs rely on deep crimp compression that cold-welds the strands.
What Sets Pull-Out Force
Five factors dominate. Crimp geometry — barrel length, compression ratio and whether the crimp is a closed or open barrel — sets how much metal grips the conductor. Material temper sets how much the terminal springs back and how much force the contact features can sustain. Plating changes friction: a low-friction coating such as gold produces a softer insertion feel and a lower withdrawal force than matte tin, which grips harder. Retention features such as lances, barbs and wings add mechanical lock, especially for press-fit and housing retention. Finally, housing interference and the condition of tooling set the repeatability of all of it.
| Design lever | Effect on pull-out force | Notes |
|---|---|---|
| Larger conductor area | Increases | Strongest single driver |
| Deeper crimp compression | Increases | Over-crimp can crack strands |
| Retention lances / barbs | Increases | Adds mechanical lock |
| Harder temper | Increases | Risks cracking if too hard |
| Matte tin plating | Higher friction, higher force | Common and cost-effective |
| Gold plating | Lower friction, lower force | Chosen for signal stability |
| Tighter hole interference | Increases (press-fit) | Balance against board damage |
Design and Plating Levers in Practice
When a pull-out test fails, the fix is rarely "use thicker metal." It is usually geometry: lengthen the barrel, add a retention lance, or correct the crimp tooling so compression is even. Material comes second, and plating last. Plating matters most for the electrical side — a nickel underplate with a gold flash keeps resistance stable — while matte tin gives a firmer mechanical grip at lower cost. The crimp and solder tab guide covers how the joint type changes which lever is available.
At BQUQ we stamp terminals to ±0.05 mm on critical features, which keeps crimp compression and retention geometry consistent batch to batch — the main source of pull-out variation in production.
Frequently Asked Questions
Q: What is a normal pull-out force for a crimp terminal?
A: It scales with wire size. Small signal crimps typically target 10-30 N, general power crimps 50-150 N, and heavy power lugs 150-400 N or more. Always confirm against the standard that applies to your product and wire gauge rather than using a single number.
Q: At what speed should a pull-out test run?
A: A controlled rate around 25 mm per minute is common, reflecting legacy one-inch-per-minute practice. The exact rate should come from the applicable standard, because pull rate affects the measured peak on ductile joints. Keep rate, grip position and fixture identical across samples for valid comparison.
Q: Why did my terminal pass continuity but fail pull-out?
A: Continuity only proves contact, not mechanical integrity. A joint can conduct while a poor crimp or weak retention feature lets it loosen under vibration, after which resistance rises and the joint heats. Pull-out force tests the mechanical soundness that keeps the electrical connection stable over life.
Q: Does plating affect pull-out force?
A: Yes. Plating friction changes how hard the joint grips. Matte tin grips harder and generally raises pull-out and withdrawal force, while gold lowers friction and gives a smoother, more stable signal contact. Choose plating by the electrical requirement, then verify the mechanical force separately.
Q: Can you hold tolerances tight enough to keep pull-out consistent?
A: Yes. We hold ±0.05 mm on critical stamped terminal features, which controls crimp compression and retention geometry — the main drivers of variation. Send the drawing with wire size and the applicable standard to sc@bquq.com, and BQUQ returns an indicative quote within 12 working hours.
Related Resources
- Stamped Terminal Design Guide: geometry that controls insertion, retention and crimp performance.
- Terminals and Contacts: stamped terminals, pins and contacts on progressive dies.
- About BQUQ: an ISO9001-certified source factory in Dongguan running stamping, CNC, springs, collets and heat sinks under one roof.
- Contact us: send your drawing to sc@bquq.com for a quote within 12 working hours.
Authored by the BQUQ Engineering Team. BQUQ is an ISO9001-certified source factory in Dongguan, China, running CNC machining, metal stamping, custom springs, heat sink and collet lines under one roof. Send drawings to sc@bquq.com or WhatsApp +86 13713157787 for a quote within 12 working hours. www.bquq.com
