Typical Connector Failure Modes and Mechanisms
The “Connector Basics” series from APEX Electrical Interconnection Consultants continues with an introductory look at typical connector failure modes and mechanisms.
When we discuss connector failure, we need to refine the concept into two distinct components – failure modes and failure mechanisms. How do we define “failure”? Webster’s New World Dictionary lists a variety of terms, but for our purposes the following would seem to most appropriate: “To be lacking or insufficient, to stop operating or working.”
Failure Mode Versus Failure Mechanism
The term “failure” is directly associated with failure mode. However, the reason for the failure is of primary importance so that countermeasures to fix the problem may be recommended. We use the term “failure mechanism” to describe the reason for failure.
- Failure mode is the particular way in which a component would fail functionally or with respect to defined acceptance criteria. For example, contact resistance in excess of a defined maximum value would be a failure mode, as would a higher-than-allowed insertion force or the failure of a relay to open (in this case a loss of function). Generally, the most common failure mode for an electric contact would be high contact resistance.
- Failure mechanism is the reason electrical, physical, chemical, or mechanical stresses may induce failure. These mechanisms may act individually or in combination.
As previously mentioned, the most common failure mode for electric contacts would be high contact resistance. Clearly, a condition of “zero” or low normal force would lead to failure. That particular failure could be caused by parts outside the specification, contact damage as a result of stubbing/overstressed contact members, and stress relaxation/creep-related effects.
In addition, the inclusion of high-resistance material at the contact interface could lead to the excess contact resistance failure mode. The formation and ingression of oxides and various corrosion products associated with the environment could be at play. Fretting corrosion, an organic film, and particulates such as plastic housing material, dirt, or dust should also be considered as potential failure mechanisms.
A General Failure Discussion
Typically, there are two types of failure – failure by function or failure by definition.
A failure by function may occur during product specification/verification testing programs or as a failure to perform during operation in the field. Failure by function means that the device/component fails to perform a required operation; it doesn’t work.
A failure by definition would mean that an acceptance standard (such as contact resistance) falls outside of acceptable limits.
A component/device that suffers a failure by definition might still perform its intended operation; the failure may be more related to reliability and the ability to function throughout its intended life. For example, both contact resistance and an increase in contact resistance have a defined upper limit. Values outside these limits are felt to be precursors to either a complete open or intermittent operation. It can be shown that a 10X increase in contact resistance is equivalent to a 99% loss in available contact area – clearly a precarious situation.
The failed device should be subjected to a thorough investigation to determine the failure mechanism and identify the individual component. The failure modes will generally be identified as either electrical or mechanical in nature. It is only through this process that effective countermeasures may be recommended.
Ed Bock is a senior consultant at APEX Electrical Interconnection Consultants. For more than 44 years, he has worked in the connector industry (33 with AMP) in the areas of contact physics, electrical contact phenomenon, fretting corrosion, contact lubrication, and wear studies (tribology). He is recognized as a prime researcher in the area of fretting corrosion, the principal failure mechanism for non-noble contact finishes (tin and tin-lead).