J.W. McBride

The degradation of road tested automotive connectors

The increasing amount of telematic and other electronic systems in the modern motor vehicle demands high performance and reliability in ever decreasing space. The automotive connector is well known to be the weak link in electronic systems due to the multi-environmental conditions seen in the motor vehicle. These conditions of large temperature changes, high humidity, and corrosive atmospheres have significant and varied affect upon the connector. Sample signal and power automotive connectors which are currently undergoing road testing, are being monitored to evaluate stress levels during real operation. Environmental conditions such as, temperature, humidity and vibration levels of these connectors are being monitored in situ. Connector temperature data from vehicles operated in the United Kingdom is presented in this paper. An empirical model is also presented demonstrating some of the general features of connector temperature behaviour. Scanning electron micrographs, elemental analysis and contact resistance measurements are also taken to determine the level of degradation of these connectors. Evidence of fretting corrosion was found at the contact interface on tin plated terminals from sealed and unsealed connectors; however gold terminals exhibited minimal wear.

A review of micro-contact physics for microelectromechanical systems (MEMS) metal contact switches

Innovations in relevant micro-contact areas are highlighted, these include, design, contact resistance modeling, contact materials, performance and reliability. For each area the basic theory and relevant innovations are explored. A brief comparison of actuation methods is provided to show why electrostatic actuation is most commonly used by radio frequency microelectromechanical systems designers. An examination of the important characteristics of the contact interface such as modeling and material choice is discussed. Micro-contact resistance models based on plastic, elastic-plastic and elastic deformations are reviewed. Much of the modeling for metal contact micro-switches centers around contact area and surface roughness. Surface roughness and its effect on contact area is stressed when considering micro-contact resistance modeling. Finite element models and various approaches for describing surface roughness are compared. Different contact materials to include gold, gold alloys, carbon nanotubes, composite gold-carbon nanotubes, ruthenium, ruthenium oxide, as well as tungsten have been shown to enhance contact performance and reliability with distinct trade offs for each. Finally, a review of physical and electrical failure modes witnessed by researchers are detailed and examined.

Intermittency phenomena in electrical connectors

Fretting is known to be a major cause of contact deterioration and failure, particularly in tin-plated contacts. During fretting the contact resistance generally increases slowly with time. Superimposed on this slow increase in contact resistance are rapid changes in contact resistance within fractions of a second, called intermittences or short duration discontinuities. Although intermittences have been reported by several authors, they are frequently overlooked in traditional fretting experiments and not much is known about their origin. The present study aims at filling this gap. A test apparatus has been built to measure the contact voltage-drop profile during an intermittence and fretting experiments on tin-plated copper contacts have been carried out. The results lead to a set of requirements for a model to explain intermittency phenomena.

Arc motion and gas flow in current limiting circuit breakers operating with a low contact switching velocity

Arc motion in low voltage (240 VAC) high current (10/sup 3/-10/sup 4/A.) current limiting-circuit breakers is dominated by arc root mobility. The mobility is influenced by the gas flow and gas composition in the contact region, but there is little experimental data on these effects. New pressure and spectral data measurement during arc movement are presented using a flexible test apparatus and an arc imaging system. These measurements are used to investigate gas flow characteristics in the arc chamber. The chemical and physical phenomena occurring during the arc motion are discussed. The combination of optical and spectral data provides new insight into the arc motion. The influences of arc chamber material, contact material, and contact opening speed, are investigated to improve arc control for a low contact opening velocity.

Electrical contact bounce in medium duty contacts

The basic phenomena of electrical contact bounce with the passage of current, in the medium duty range (1 to 30 A AC and DC), are investigated. Experimental results presented show that by considering individual impacts, an understanding of how current affects contact bounce is achieved. An automated test system is used to evaluate contact bounce. The surface degradation is evaluated by endurance testing, allowing the development of empirical relations between mechanical and electrical bounce. With this understanding it is shown how arc energy dissipation can be reduced by the designed reduction of impact kinetic energy, leading to prolonged contact life.<<ETX>>

The Relationship Between Contact Resistance and Contact Force on Au-Coated Carbon Nanotube Surfaces Under Low Force Conditions

Carbon nanotube (CNT)-coated surfaces are investigated to determine the electrical contact performance under low force conditions. The surfaces under investigation are vertically aligned multiwalled CNTs formed on a silicon substrate and coated with an Au film. These planar surfaces are mated with a hemispherical Au plated probe mounted in a nanoindentation apparatus. The maximum contact force used is 1 mN. The contact resistance of these surfaces is investigated as a function of the applied force and is also studied under repeated loading cycles. The surfaces are compared with a reference Au-Au contact under the same experimental conditions and the results compared to established contact theory. The results show that the vertically aligned multiwalled CNT surface provides a stable contact resistance. This paper shows the potential for the application of CNT surfaces as an interface in low force electrical contact applications.

Electrical contact phenomena during impact

The authors outline the theory of impact as it applies to electrical contacts. The concept of the coefficient of restitution is evaluated as a means of modeling the events at impact. The events occurring during the impact of electrical contacts are vital to the long-term reliability of the contacts; so design parameters are considered in terms of their influence upon the dynamics of impact and bounce. Experimental studies are presented which include the measurement of impact forces, impact time, and both current and voltage characteristics. The influence of preimpact arcing is evaluated in the medium current range, and is shown to have an effect on the events occurring during the first impact. A mathematical model is proposed for electrical contact bounce, but it is shown that reducing the arcing may not always reduce contact wear.<<ETX>>

Fretting corrosion and the reliability of multicontact connector terminals

The harsh operating environment of the automotive application makes the semi-permanent connector susceptible to intermittent high contact resistance which eventually leads to failure. Fretting corrosion is often the cause of these failures. However, laboratory testing of sample contact materials produces results that do not correlate with commercially tested connectors. A multicontact (M-C) reliability model is developed to bring together the fundamental studies and studies conducted on commercially available connector terminals. It is based on fundamental studies of the single contact interfaces and applied to commercial multicontact terminals. The model takes into consideration firstly, that a single contact interface may recover to low contact resistance after attaining a high value and secondly, that a terminal consists of more than one contact interface. For the connector to fail, all contact interfaces have to be in the failed state at the same time.

The erosion and arc characteristics of Ag/CdO and Ag/SnO/sub 2/ contact materials under DC break conditions

Break operation studies have been conducted upon Ag/CdO and Ag/SnO/sub 2/ contact materials under dc conditions between 1-16 A. The apparatus used allows contact materials to be continually tested with a controlled break velocity. Results are presented on erosion data in terms of mass transfer. Surface analysis methods are used, scanning electron micrographs reveal distinct structures and areas on the contact surface, and elemental analysis (EDS) shows migration of metal species with current. The metal-oxide used in the contact is shown to influence the arc and erosion characteristics of break only operations. The Ag/CdO contacts exhibit lower erosion than Ag/SnO/sub 2/ contacts under these controlled conditions.

Arc root mobility during contact opening at high current

This paper presents a test system, designed for the investigation of short circuit arcs related to miniature circuit breakers operating in a 240 Volt, ac supply. An optical fibre imaging system presented previously is used to identify arc root motion, with short circuit current up to 6kA. Two methods arc used to measure contact motion, a non-contact linear position sensor, and the optical fibre array. The optical fibre array uses software image processing to identify the position of the arc roots in the arc chamber. The identification of the arc roots allows for a study of the arc immobility at the initial stages of the event. Initial results are presented on the effect of supply polarity on arc root motion.