Reliability is a term that's commonly used in our daily lives. Some cars are sought after for their high reliability; others avoided for the opposite reason. Reliability is a desired quality in a friend, a boss, a paycheck; yet its precise meaning can vary depending on the context.
When it comes to electrical connectors, though, reliability has a precise definition. In plain language: Reliability is “the probability that a connector will perform as required for a desired period of time during which it is subjected to a given set of environmental and/or mechanical stresses.”
This definition states that there is a defined set of performance levels that must be maintained for a defined time while the connector is operating under the defined set of conditions. Since any or all of these can change with the application, a connector reliability specification is a function of all three.
What is a Connector? Construction Basics
So what exactly is a connector, anyway? One general definition of a connector is that a connector “provides a separable connection between two elements of an electronic system without unacceptable signal distortion or power loss.”
The two key parts to this definition are “separable” and “unacceptable” performance loss, both of which depend on the connector application and its electrical and environmental requirements.
Below is a simplified drawing of a connector, showing the main components together with a close-up of the contact finish and interface.
Figure 1: Connector Electrical Components. (Source: TE Connectivity)
The electrical portion for each connection consists of a connector pin and a mating contact spring, which exerts a mechanical force on its associated pin to maintain electrical continuity. The pins and springs are each contained within a rigid shell; the two shells mate together, typically with a key mechanism to ensure correct orientation.
Electrical Connector Failure Modes and Mechanisms
If nothing ever failed, connector reliability would be a non-issue. When looking at what can go wrong in a connector, though, we can distinguish between failure modes and failure mechanisms. A failure mode is the particular way that the connector could fail functionally compared to the application requirements—for example, contact resistance that exceeds the specification or unacceptably high insertion force are both failure modes. A failure mechanism is a cause of a failure mode—for example, mechanical vibration and electrical overstress are both mechanisms that may lead to failure.
Here are some common failure mechanisms and their typical failure modes:
|
Failure Mechanism |
Typical Failure Mode |
|
Mechanical stress: vibration, shock, sustained bending stresses, repeated mating and un-mating |
Damage to connector shell and key; mis-mating and circuit damage; excessive wear leading to intermittent or open connections |
|
Excessive high temperatures |
Insulation breakdown; increased contact resistance |
|
Excessive low temperatures |
Damage to non-metallic components |
|
High humidity |
Increased contact resistance, corrosion |
Determining the Best Electrical Connectors: Measuring Connector Reliability
How do we develop reliability metrics for connectors? In most fields, reliability is determined using one of three available methods:
1) Actual use: monitors the performance of the product in service.
2) Predictive: predicts the reliability based on a model developed through empirical studies and/or testing.
3) Physics-of-failure: identifies potential failure mechanisms and develops an accelerated failure-testing program to induce failures and hence predict real-world performance.
For a number of reasons, though, these techniques are not suitable for connectors. Standard statistical metrics such as MTTF and MTBF (Mean Time To Failure and Mean Time Between Failures, respectively) are difficult to obtain. Instead, connector manufacturers give a set of guaranteed electrical and mechanical operating specifications and a set of qualification tests that sample products have passed.