life is affected by cyclic wear-out failure mechanisms. As the connector contacts are repetitively
engaged and disengaged, plating surfaces are eroded and exposed to corrosive
elements of the surrounding atmosphere.
Repeated mating and un-mating also results in physical wear of the
contact material, affecting the integrity of the connecting interfaces, the
connector shell engagement interfaces, and the mounting/cable attachment
hardware. Surface contact points become
worn, making unsymmetrical contacts and corrosion results in non-conducting
films on the contact surface. The result can be a significantly increased
interface resistance, and in power connection applications, an increase in
temperature at the interface that can accelerate further contact interface
Relative failure modes of connectors are illustrated in Table 1. Most failures are open contact points or
intermittent connections. Heat may cause
these failures, but heat rise in a connector is normally very small, because the
conductor resistance is in the order of miliohms. Failures from overheating normally occur only
if excessive current is applied or if there is a defect in the contact, that
causes a localized hot spot.
Table 1. Normalized
Failure Mode Distributions
Relative Failure Mode
|Poor Contact or Intermittent
inadequate mounting can contribute to connector and system failures. Because
connectors do not contribute to, or enhance the circuit function, ideally it
should only minimally affect the circuit function. The following are examples
that can effect a circuit malfunction and may result in system failure as
a. Using a smaller connector with underrated
contacts to save on space in a power connection application can result in
reduced circuit efficiency and shortened connector life.
b. Using a connector with a standard insert,
instead of a moisture proof or hermetic seal design in a severe environmental
application can result in connector failure and possible damage to the
c. Choosing an inappropriate plating or
inadequate dielectric insert material can reduce the effectiveness of a
connection in high frequency applications by causing excessive insertion
d. Inadequate mounting in severe shock or
vibration applications can result in damage to the connector insert, contacts,
and shell, as well as potential cable damage. Inadequate keying can result in
miss-mating and subsequent circuit damage.
e. Threaded shells that are
subject to repeated mating and un-mating can wear and gall, resulting in loose
connections or jamming.
f. Inadequate floating can result in physical
damage to the contacts and insert when mating.
g. High sustained tensile,
torsion, and bending stresses placed on the connector by inadequate strain
relief, and poorly routed, bundled and dressed cable and wiring harnesses can
shorten connector life.
Excessive temperature causes
connectors to fail by breaking down the insulation or the conductivity of the
connector material. Failures usually
occur in an avalanche-type style, described as follows: as operating temperature
increases, insulation tends to become more conductive. Simultaneously, conductor resistance
increases, further increasing temperature.
This avalanching effect raises the temperature beyond the maximum
designed operating temperature, resulting in damage to the insert (insulation)
material and the conductor. The
resulting failure can be either partial or complete. Complete failures occur if the operating
temperature reaches the point where the conductor begins to melt, breaks down
electrical conductivity, or where the insulation fails. A graph of service life verses operating
temperature is shown in Figure 1. As shown, service life is
directly proportional to how close operating temperature is to the maximum rated
insert temperature of the device.
at elevated temperatures and humidity, within rated values, can result in
overall degradation of connector performance, e.g. increases in contact
resistance, corrosion of the shell, deterioration of the insert material,
lessening of locking spring effectiveness (resilience aging is accelerated),
jamming of corroded threaded coupling mechanisms, etc. Frequent inspections and preventative
maintenance may be in order.
temperatures can also cause
conductors to fail, but such failure mechanisms are relatively rare. Low temperatures actually tend to slow the
detrimental chemical effects, increase conductivity, and result in a longer
life. However, extremely low
temperatures can cause damage to the nonmetallic portions of the connector. The thermal coefficient of expansion of such
materials is lower than the metals and will contract
Figure 1. Service Life vs. Hot Spot