Improved micro-contact resistance model that considers material deformation, electron transport and thin film characteristics

This paper reports on an improved analytic model forpredicting micro-contact resistance needed for designing microelectro-mechanical systems (MEMS) switches. The originalmodel had two primary considerations: 1) contact materialdeformation (i.e. elastic, plastic, or elastic-plastic) and 2) effectivecontact area radius. The model also assumed that individual aspotswere close together and that their interactions weredependent on each other which led to using the single effective aspotcontact area model. This single effective area model wasused to determine specific electron transport regions (i.e. ballistic,quasi-ballistic, or diffusive) by comparing the effective radius andthe mean free path of an electron. Using this model required thatmicro-switch contact materials be deposited, during devicefabrication, with processes ensuring low surface roughness values(i.e. sputtered films). Sputtered thin film electric contacts,however, do not behave like bulk materials and the effects of thinfilm contacts and spreading resistance must be considered. Theimproved micro-contact resistance model accounts for the twoprimary considerations above, as well as, using thin film,sputtered, electric contact

Arcing Failure of ROHS Compliant Electromagnetic Relays

Electronic relay contacts have traditionally been made of materials, primarily Ag/CdO, which are resistant to welding under short, high power pulses. However, since 2006, RoHS prohibits the use of cadmium in electronics, driving the elimination of Ag/CdO and its replacement with Ag/SnO2. The reliability of relays made with Ag/SnO2 contacts has been shown to be vendor specific. This thesis focuses on developing an understanding of the metallurgical and design factors that vary by manufacturer and their effect on welding susceptibility of Ag/SnO2 electromagnetic relay contacts and other related relay failure mechanisms. In addition, it aims to predict a safe operating area of power and energy over which specific relay contacts will not weld under high power DC conditions. Relays from various manufacturers were subjected to capacitor discharge pulses of 250 V at 10-80 uF to characterize relay reliability. Failure analysis was then conducted on the welded contacts using scanning electron microscopy (SEM) and wavelength-dispersive spectroscopy (WDS) in order to address material properties and design variations that affect the welding susceptibility of relays. The incidence and extent of degradation is correlated to material characteristics including contact composition, oxide content, hardness, contact geometry, and surface roughness using a physics of failure approach. The relays with a higher percent content of indium oxide exhibited a greater reliability than those without. Both power and energy were then varied to further investigate the one cycle to failure boundary region and a failure map is presented

Preliminary Study on Making Arc Characteristics of AgSnO2 Contact

In order to analyze the making arc characteristics of AgSnO2 contact, experiments were carried out with a self-developed experimental equipment. It was found that contact resistance had no obvious change with the increase of the number of experiments.In the later stage of the experiment, the contact bounces occurred during the contact closing process, which not only prolonged the making arc duration, but also increased making arc energy. When the contact was eroded to a certain extent by arc, making welding occurs

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

ELECTRICAL CONTACT BOUNCE AND THE CONTROL DYNAMICS OF SNAP-ACTION SWITCHES

Experimental and theoretical studies are made of a typical snap-action rocker switch, to establish the wear mechanisms in the pivoting contact. The rocker switch, used extensively in consumer goods, operates in the medium duty current range, (1 - 30 Amps). Highspeed photographic studies have shown that the main cause of wear is arcing, occurring during separation and bounce at the pivot contacts. To reduce the bounce a computer-based mathematical model of the system dynamics is developed and optimised; this results in recommended design changes. These changes are tested under full current endurance conditions, and show significant improvements in wear. The model of the switch dynamics relates the mathematics of motion to the bounce occuring at the pivot contact, without the influence of current. To show the effect of current and arcing, an automatic test system is developed for the controlled testing of electrical contacts. The system has the ability to evaluate arc energy, bounce times, and contact resistance. The results presented detail the influence of d.c current on contact bounce time, and identify the importance of the subsequent bounce time; which is defined for a single make operation, as the total duration of the bounces occurring after the first bounce. To compare the erosion profiles of the switch and test system, the system is operated under full load current endurance conditions, to evaluate wear. This comparison shows that the wear in the real switch contacts is greater, as result of the additional contact movement of slip and rolling.Arrow-Hart (Europe) Ltd, Plymouth, Devo

Failure analysis informing intelligent asset management

With increasing demands on the UK’s power grid it has become increasingly important to reform the methods of asset management used to maintain it. The science of Prognostics and Health Management (PHM) presents interesting possibilities by allowing the online diagnosis of faults in a component and the dynamic trending of its remaining useful life (RUL). Before a PHM system can be developed an extensive failure analysis must be conducted on the asset in question to determine the mechanisms of failure and their associated data precursors that precede them. In order to gain experience in the development of prognostic systems we have conducted a study of commercial power relays, using a data capture regime that revealed precursors to relay failure. We were able to determine important failure precursors for both stuck open failures caused by contact erosion and stuck closed failures caused by material transfer and are in a position to develop a more detailed prognostic system from this base. This research when expanded and applied to a system such as the power grid, presents an opportunity for more efficient asset management when compared to maintenance based upon time to replacement or purely on condition

Data-driven prognostics for critical electronic assemblies and electromechanical components

The industrial digitalisation enables the adoption of robust, data-driven maintenance strategies that increase safety and reliability of critical assets such as electronics. And yet, an implementation of data-driven methods which primarily address the industrialisation of diagnostic and prognostic strategies is opposed by various, application specific challenges. This thesis collates such restricting factors encountered within the oil and gas industry, in particular for the critical electrical systems and components in upstream deep drilling tools. A fleet-level, tuned machine learning approach is presented that classifies the operational state (no-failure/ failure) of downhole tool printed circuit board assemblies. It supports maintenance decision making under varying levels of failure costs and fleet reliability scenarios. Applied within a maintenance scheme it has the potential to minimise non-productive time while increasing operational reliability. Likewise, a tailored and efficient deep learning data pipeline is proposed for a component-level forecast of the end of life of electromagnetic relays. It is evaluated using high resolution life-cycle data which has been collected as a part of this thesis. In combination with a failure analysis, the proposed method improves the prognostics capabilities compared to traditional methods which have been proposed so far in order to assess the operational health of electromagnetic relays. Two case studies underpin the need for tailored prognostic methods in order to provide viable solutions that can de-risk deep drilling operations. In consequence, the proposed approaches alleviate the pressure on current maintenance strategies which can no longer meet the stringent reliability requirements of upstream assets

Analysis of the control system of a high tension test laboratory on composite materials for aeronautic applications

As everybody know energy delivered by a lightning is much higher than energy managed daily by humans and so two requirements a lightning lab should satisfy: first and most important safety for people for buildings and for electrical circuitS. From the first requirements follows the second: as much as simplicity in the design of the circuit