Quality and Reliability of Elastomer Sockets

Integrated Circuit (IC) sockets provide hundreds to thousands of electrical interconnects in enterprise servers, where quality and reliability are critical for customer applications. The evaluation of IC sockets, according to current industry practices, relies on the execution of stress loads and stress levels that are defined by standards, having no consideration to the physics of failure (PoF), target operating environment, or contact resistance behavior over time. In a similar manner, monitoring of contact resistance during system operation has no considerations to the PoF or environmental conditions. In this dissertation a physics of failure approach was developed to model the reliability of elastomer sockets that are used in an enterprise server application. The temperature and relative humidity environment, at the IC socket contact interface, were characterized as a function of external environmental conditions and microprocessor activity. The study applied state-of-the-art health monitoring techniques to assess thermal gradients on the IC socket assembly and to establish an operating profile that could be used for the development of a PoF model. A methodology was developed for modeling and monitoring contact resistance of electrical interconnects. The technique combined a PoF model with the Sequential Probability Ratio Test (SPRT). In the methodology the resistance behavior is characterized as a function of temperature. The effective a-spot radius was extracted from the characterization data and modeled with a power-law. A PoF model was developed to estimate the resistance of an elastomer contact, based on the effective a-spot radius and the ambient temperature. The methodology was experimentally demonstrated with a temperature cycle test of the elastomer socket. During the evaluation the difference between estimated and observed resistance values were tested with the SPRT. The technique was shown to be very accurate for modeling contact resistance and to be highly sensitive for the detection of resistance degradation. A qualitative reliability model was developed for the mean contact resistance of an elastomer socket, using fundamental material properties and user defined failure criteria. To derive the model, the resistance behavior of contacts under nominal mechanical load was studied as a function of time and temperature. The elastomer contact was shown to have a very complex resistance behavior, which was modeled by multiple statistical distributions. It was shown that elastomer sockets, in spite of experiencing stress relaxation at the macroscale (elastomer), can exhibit decreases in contact resistance, a result of stress redistribution at the microscale (Ag particles), which increases Ag-Ag particle stress and the effective contact area

Effect of Joule Heating on the Reliability of Stamped Metal Land Grid Array Sockets

Performance requirements in high end microprocessors have increased tremendously in the last several years, leading to higher I/O counts and interconnect densities. As greater currents pass through the microprocessor interconnect, higher temperatures driven by Joule heating are expected to pose reliability risks to high pin count microprocessor sockets. In this study Joule heating and its effect on the reliability of stamped metal land grid array (LGA) sockets was investigated using a combination of experimental and numerical methods. A methodology to determine socket temperature environments under electrical loading was developed. Knowledge of socket operating temperatures can allow original equipment manufacturers (OEMs) and socket manufacturers to test for and mitigate failure mechanisms under thermal aging. The factors that influence Joule heating and contribute to premature socket failure were examined. Processor temperature, contact alloy and contact pitch were all found to significantly influence socket temperatures driven by Joule heating, with the contact alloy and processor temperature having the most significant effects. The resulting temperatures at higher currents were found to significantly influence the mechanical properties of the polymer housing and adversely affect socket stress relaxation behavior. The properties of the polymer housing were found to be sensitive to temperature owing to its visco-elastic nature. Polymer housing relaxation was therefore identified as a principle contributor to failure in stamped metal sockets under high temperature environments. In the latter part of the study, numerical modeling was used to develop a methodology for assessing socket life expectancy under temperature and deformation loads. A full visco-elastic characterization of the polymer housing was conducted and the measured properties were subsequently used to model socket stress relaxation time to failure. The results of this study indicate that socket temperatures under electrical loading can be significantly higher than those called for by EIA test specifications for LGA sockets. Passing tests that are not stringent enough to account for worst case scenarios can pave the way for field failures. The methodology outlined in this dissertation may be used to determine socket temperature environments and their effect on socket life expectancy

Intermittent fault diagnosis and health monitoring for electronic interconnects

Literature survey and correspondence with industrial sector shows that No-Fault-Found (NFF) is a major concern in through life engineering services, especially for defence, aerospace, and other transport industry. There are various occurrences and root causes that result in NFF events but intermittent interconnections are the most frustrating. This is because it disappears while testing, and missed out by diagnostic equipment. This thesis describes the challenging and most important area of intermittent fault detection and health monitoring that focuses towards NFF situation in electronics interconnections. After introduction, this thesis starts with literature survey and describes financial impact on aerospace and other transport industry. It highlights NFF technologies and discuss different facts and their impact on NFF. Then It goes into experimental study that how repeatedly intermittent fault could be replicated. It describes a novel fault replicator that can generate repeatedly IFs for further experimental study on diagnosis techniques/algorithms. The novel IF replicator provide for single and multipoint intermittent connection. The experimental work focuses on mechanically induced intermittent conditions in connectors. This work illustrates a test regime that can be used to repeatedly reproduce intermittency in electronic connectors whilst subjected to vibration ... [cont.]

Smart Devices and Systems for Wearable Applications

Wearable technologies need a smooth and unobtrusive integration of electronics and smart materials into textiles. The integration of sensors, actuators and computing technologies able to sense, react and adapt to external stimuli, is the expression of a new generation of wearable devices. The vision of wearable computing describes a system made by embedded, low power and wireless electronics coupled with smart and reliable sensors - as an integrated part of textile structure or directly in contact with the human body. Therefore, such system must maintain its sensing capabilities under the demand of normal clothing or textile substrate, which can impose severe mechanical deformation to the underlying garment/substrate. The objective of this thesis is to introduce a novel technological contribution for the next generation of wearable devices adopting a multidisciplinary approach in which knowledge of circuit design with Ultra-Wide Band and Bluetooth Low Energy technology, realization of smart piezoresistive / piezocapacitive and electro-active material, electro-mechanical characterization, design of read-out circuits and system integration find a fundamental and necessary synergy. The context and the results presented in this thesis follow an “applications driven” method in terms of wearable technology. A proof of concept has been designed and developed for each addressed issue. The solutions proposed are aimed to demonstrate the integration of a touch/pressure sensor into a fabric for space debris detection (CApture DEorbiting Target project), the effectiveness of the Ultra-Wide Band technology as an ultra-low power data transmission option compared with well known Bluetooth (IR-UWB data transmission project) and to solve issues concerning human proximity estimation (IR-UWB Face-to-Face Interaction and Proximity Sensor), wearable actuator for medical applications (EAPtics project) and aerospace physiology countermeasure (Gravity Loading Countermeasure Skinsuit project)

Commercially available pressure sensors for sport and health applications: A comparative review

Pressure measurement systems have numerous applications in healthcare and sport. The purpose of this review is to: (a) describe the brief history of the development of pressure sensors for clinical and sport applications, (b) discuss the design requirements for pressure measurement systems for different applications, (c) critique the suitability, reliability, and validity of commercial pressure measurement systems, and (d) suggest future directions for the development of pressure measurements systems in this area. Commercial pressure measurement systems generally use capacitive or resistive sensors, and typically capacitive sensors have been reported to be more valid and reliable than resistive sensors for prolonged use. It is important to acknowledge, however, that the selection of sensors is contingent upon the specific application requirements. Recent improvements in sensor and wireless technology and computational power have resulted in systems that have higher sensor density and sampling frequency with improved usability – thinner, lighter platforms, some of which are wireless, and reduced the obtrusiveness of in-shoe systems due to wireless data transmission and smaller data-logger and control units. Future developments of pressure sensors should focus on the design of systems that can measure or accurately predict shear stresses in conjunction with pressure, as it is thought the combination of both contributes to the development of pressure ulcers and diabetic plantar ulcers. The focus for the development of in-shoe pressure measurement systems is to minimise any potential interference to the patient or athlete, and to reduce power consumption of the wireless systems to improve the battery life, so these systems can be used to monitor daily activity. A potential solution to reduce the obtrusiveness of in-shoe systems include thin flexible pressure sensors which can be incorporated into socks. Although some experimental systems are available further work is needed to improve their validity and reliability

Fatigue Risks in the Connections of Sign Support Structures

This research effort develops a reliability-based approach for prescribing inspection intervals for mast-arm sign support structures corresponding to user-specified levels of fatigue-induced fracture risk. The resulting level of risk for a particular structure is dependent upon its geographical location, the type of connection it contains, the orientation of its mast-arm relative to north and the number of years it has been in service. The results of this research effort indicate that implementation of state-of-the-art reliability-based assessment procedures can contribute very valuable procedures for assigning inspection protocols (i.e. inspection intervals) that are based upon probabilities of finding fatigue-induced cracking in these structures. The engineering community can use the results of this research effort to design inspection intervals based upon risk and thereby better align inspection needs with limited fiscal and human resources

Space benefits: The secondary application of aerospace technology in other sectors of the economy

Benefit cases of aerospace technology utilization are presented for manufacturing, transportation, utilities, and health. General, organization, geographic, and field center indexes are included

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

Integrated sensors for process monitoring and health monitoring in microsystems

This thesis presents the development of integrated sensors for health monitoring in Microsystems, which is an emerging method for early diagnostics of status or “health” of electronic systems and devices under operation based on embedded tests. Thin film meander temperature sensors have been designed with a minimum footprint of 240 m × 250 m. A microsensor array has been used successfully for accurate temperature monitoring of laser assisted polymer bonding for MEMS packaging. Using a frame-shaped beam, the temperature at centre of bottom substrate was obtained to be ~50 ºC lower than that obtained using a top-hat beam. This is highly beneficial for packaging of temperature sensitive MEMS devices. Polymer based surface acoustic wave humidity sensors were designed and successfully fabricated on 128° cut lithium niobate substrates. Based on reflection signals, a sensitivity of 0.26 dB/RH% was achieved between 8.6 %RH and 90.6 %RH. Fabricated piezoresistive pressure sensors have also been hybrid integrated and electrically contacted using a wire bonding method. Integrated sensors based on both LiNbO3 and ZnO/Si substrates are proposed. Integrated sensors were successfully fabricated on a LiNbO3 substrate with a footprint of 13 mm × 12 mm, having multi monitoring functions for simultaneous temperature, measurement of humidity and pressure in the health monitoring applications

Biomedical Engineering

Biomedical engineering is currently relatively wide scientific area which has been constantly bringing innovations with an objective to support and improve all areas of medicine such as therapy, diagnostics and rehabilitation. It holds a strong position also in natural and biological sciences. In the terms of application, biomedical engineering is present at almost all technical universities where some of them are targeted for the research and development in this area. The presented book brings chosen outputs and results of research and development tasks, often supported by important world or European framework programs or grant agencies. The knowledge and findings from the area of biomaterials, bioelectronics, bioinformatics, biomedical devices and tools or computer support in the processes of diagnostics and therapy are defined in a way that they bring both basic information to a reader and also specific outputs with a possible further use in research and development