Given the vital rule of data center availability and since the inlet temperature of the IT equipment increase rapidly until reaching a certain threshold value after which IT starts throttling or shut down because of overheat during cooling system failure. Hence, it is especially important to understand failures and their effects. This study presented experimental investigation and analysis of a facility-level cooling system failure scenario in which chilled water interruption introduced to the data center. Quantitative instrumentation tools including wireless technology such as wireless temperature and pressure sensors were used to measure the discrete air inlet temperature and pressure differential though cold aisle enclosure, respectively. In addition, Intelligent Platform Management Interface (IPMI) and cooling system data during failure/recovery were reported. Furthermore, the IT equipment performance and response for opened and contained environments were simulated and compared. Finally, an experiment based analysis of the Ride Through Time (RTT) of servers during chilled water interruption of the cooling infrastructure presented as well. The results showed that for all three classes of servers tested during the cooling failure, CAC helped keep the server’s cooler for longer. The containment provided a barrier between the hot and cold air streams and caused slight negative pressure to build up, which allowed the servers to pull cold air from the underfloor plenum. In addition, the results show that the effect of CAC in containment solutions on the IT equipment performance and response could vary and depend on the server’s airflow, generation and hence types of servers deployed in cold aisle enclosure. Moreover, it was shown that when compared to the discrete sensors, the IPMI inlet temperature sensors underestimate the Ride Through Time (RTT) by 42% and 12% for the CAC and opened cases, respectively.

Stress sensors have shown potential to provide “health monitoring” of a wide range of issues related to packaging of integrated circuits, and silicon carbide offers the advantage of much higher temperature sensor operation with application in packaged high-voltage, high-power SiC devices as well as both automotive and aerospace systems, geothermal plants, and deep well drilling, to name a few. This paper discusses the theory and uniaxial calibration of resistive stress sensors on 4H silicon carbide (4H-SiC) and provides new theoretical descriptions for four-element resistor rosettes and van der Pauw (VDP) stress sensors. The results delineate the similarities and differences relative to those on (100) silicon: resistors on the silicon face of 4H-SiC respond to only four of the six components of the stress state; a four-element rosette design exists for measuring the in-plane stress components; two stress quantities can be measured in a temperature compensated manner. In contrast to silicon, only one combined coefficient is required for temperature compensated stress measurements. Calibration results from a single VDP device can be used to calculate the basic lateral and transverse piezoresistance coefficients for 4H-SiC material. Experimental results are presented for lateral and transverse piezoresistive coefficients for van der Pauw structures and p- and n-type resistors. The VDP devices exhibit the expected 3.16 times higher stress sensitivity than standard resistor rosettes.

Electronics in automotive underhood environments is used for a number of safety critical functions. Reliable continued operation of electronic safety systems without catastrophic failure is important for safe operation of the vehicle. There is need for prognostication methods, which can be integrated, with on-board sensors for assessment of accrued damage and impending failure. In this paper, leadfree electronic assemblies consisting of daisy-chained parts have been subjected to high temperature vibration at 5g and 155°C. Spectrogram has been used to identify the emergence of new low frequency components with damage progression in electronic assemblies. Principal component analysis has been used to reduce the dimensionality of large data-sets and identify patterns without the loss of features that signify damage progression and impending failure. Variance of the principal components of the instantaneous frequency has been shown to exhibit an increasing trend during the initial damage progression, attaining a maximum value and decreasing prior to failure. The unique behavior of the instantaneous frequency over the period of vibration can be used as a health-monitoring feature for identifying the impending failures in automotive electronics. Further, damage progression has been studied using Empirical Mode Decomposition (EMD) technique in order to decompose the signals into Independent Mode Functions (IMF). The IMF’s were investigated based on their kurtosis values and a reconstructed strain signal was formulated with all IMF’s greater than a kurtosis value of three. PCA analysis on the reconstructed strain signal gave better patterns that can be used for prognostication of the life of the components.

There are various designs for segregating hot and cold air in data centers such as cold aisle containment (CAC), hot aisle containment (HAC), and chimney exhaust rack. These containment systems have different characteristics and impose various conditions on the information technology equipment (ITE). One common issue in HAC systems is the pressure buildup inside the HAC (known as backpressure). Backpressure also can be present in CAC systems in case of airflow imbalances. Hot air recirculation, limited cooling airflow rate in servers, and reversed flow through ITE with weaker fan systems (e.g. network switches) are some known consequences of backpressure. Currently there is a lack of experimental data on the interdependency between overall performance of ITE and its internal design when a backpressure is imposed on ITE. In this paper, three commercial 2-rack unit (RU) servers with different internal designs from various generations and performance levels are tested and analyzed under various environmental conditions. Smoke tests and thermal imaging are implemented to study the airflow patterns inside the tested equipment. In addition, the impact leak of hot air into ITE on the fan speed and the power consumption of ITE is studied. Furthermore, the cause of the discrepancy between measured inlet temperatures by internal intelligent platform management interface (IPMI) and external sensors is investigated. It is found that arrangement of fans, segregation of space upstream and downstream of fans, leakage paths, location of sensors of baseboard management controller (BMC) and presence of backpressure can have a significant impact on ITE power and cooling efficiency.

The increasing complexity of electronics in systems used in safety critical applications, such as for example self-driving vehicles requires new methods to assure the hardware reliability of the electronic assemblies. Prognostics and Health Management (PHM) that uses a combination of data-driven and Physics-of-Failure models is a promising approach to avoid unexpected failures in the field. However, to enable PHM based partly on Physics-of-Failure models, sensor data that measures the relevant environment loads to which the electronics is subjected during its mission life are required. In this work, the feasibility to manufacture and use integrated sensors in the inner layers of a printed circuit board (PCB) as mission load indicators measuring impacts and vibrations has been investigated. A four-layered PCB was designed in which piezoelectric sensors based on polyvinylidenefluoride-co-trifluoroethylene (PVDF-TrFE) were printed on one of the laminate layers before the lamination process. Manufacturing of the PCB was followed by the assembly of components consisting of BGAs and QFN packages in a standard production reflow soldering process. Tests to ensure that the functionality of the sensor material was unaffected by the soldering process were performed. Results showed a yield of approximately 30% of the sensors after the reflow soldering process. The yield was also dependent on sensor placement and possibly shape. Optimization of the sensor design and placement is expected to bring the yield to 50 % or better. The sensors responded as expected to impact tests. Delamination areas were present in the test PCBs, which requires further investigation. The delamination does not seem to be due to the presence of embedded sensors alone but rather the result of a combination of several factors. The conclusion of this work is that it is feasible to embed piezoelectric sensors in the layers of a PCB.

This paper presents a failure mode detection methodology using a piezoresistive silicon based stress sensor. Data from experiment is used to validate algorithms developed for detection. Dedicated test vehicles are designed and fabricated, where the process parameters and materials are carefully selected to produce delamination between molding compound and PCB after fabrication. The test vehicles are then subjected to thermal cycling of −40°C to 125°C to grow the delamination area. After every 150 cycles, the samples are examined using Scanning Acoustic Microscopy (SAM), and the results are correlated with stress sensor signal. It is demonstrated that the propagation of the delamination area can be detected using the stress sensor. Collected data is also used to examine the applicability of statistical pattern recognition algorithms for detecting the failure. The algorithms considered in the study include Mahalanobis Distance (MD) and Singular Value Decomposition (SVD), which do not require a prior knowledge about failures and are just searching for deviation from norm in the data. The results from the analysis indicate that both techniques are suitable to stress sensor measurements, and thus are capable of detecting failure during reliability testing.

PARC, a Xerox Company, is developing a low-cost system of peel-and-stick wireless sensors that will enable widespread building environment sensor deployment with the potential to deliver up to 30% energy savings. The system is embodied by a set of RF hubs that provide power to automatically located sensor nodes, and relay data wirelessly to the building management system (BMS). The sensor nodes are flexible electronic labels powered by rectified RF energy transmitted by an RF hub and can contain multiple printed and conventional sensors. The system design overcomes limitations in wireless sensors related to power delivery, lifetime, and cost by eliminating batteries and photovoltaic devices. Sensor localization is performed automatically by the inclusion of a programmable multidirectional antenna array in the RF hub. Comparison of signal strengths while the RF beam is swept allows for sensor localization, reducing installation effort and enabling automatic recommissioning of sensors that have been relocated, overcoming a significant challenge in building operations. PARC has already demonstrated wireless power and temperature data transmission up to a distance of 20m with less than one minute between measurements, using power levels well within the FCC regulation limits in the 902–928 MHz ISM band. The sensor’s RF energy harvesting antenna achieves high performance with dimensions below 5cm × 9cm.

Identifying fugitive methane leaks can improve predictive maintenance of the extraction process, can extend gas extraction equipment lifetime, and eliminate hazardous work conditions. We demonstrate a wireless sensor network based on cost effective and robust chemi-resistive methane sensors combined with real time analytics to identify leaks from 2 scfh to 1000 scfh. The chemi-resistive sensors were validated to have a sensitivity better than 1 ppm in methane plume detection. The real time chemical sensor and wind data is integrated into an inversion models to identify the location and the magnitude of the methane leak. This integrated sensing and analytics solution can be deployed in outdoor environment for long term monitoring of accidental methane plume emissions, generate recommendations about fixing them, and ensure compliance with local government regulations.

Significant thermal gradients and hotspots is a major safety and operational issue in microprocessors, hence accurate real-time monitoring hot spots is a critical need. This thermal monitoring is typically performed using temperature sensors embedded in the chip or processor board. The location of the temperature sensors is primarily determined by the sensor space claim rather than the ideal location for thermal management. This manuscript presents an optimization methodology to determine the most beneficial locations for the temperature sensors inside of the microprocessors, based input from high resolution surface infrared thermography combined with inverse heat transfer solvers to predict hot spot locations. Specifically, the infrared image is used to obtain the temperature map over the processor surface, and subsequently delivers the input to a 3D inverse heat conduction methodology, used to determine the temperature field within the processor. In this paper, simulated thermal maps are utilized to assess the accuracy of the method. The inverse methodology is based in a function specification method combined with a sequential regularization in order to increase accuracy in the results. Together with a number of sensors, the temperature field within the processor is then used to determine the optimal location of the temperature sensors using a genetic algorithm optimization combined with a Kriging interpolation. This combination of methodologies was validated against the Finite Element Analysis of a chip incorporating heaters and temperature sensors. An uncertainty analysis of the inverse methodology and the Kriging interpolation was performed separately to assess the reliability of the procedure.

Flexible electronics have a myriad of potential applications in fields such as healthcare, soldier situational awareness, soldier rehabilitation, sports performance, and textile manufacturing among other areas. The primary benefits that flexible electronics provide to both the producers and consumers are their light weight, low power consumption, efficiency, low cost of production, flexibility, and scalability. In comparison to rigid electronics, these systems would be subjected to a greater amount of mechanical and thermal stress in real-time due to their ability to be flexed, rolled, folded, and stretched. Environmental conditions such as bending, mechanical shock, water immersion, sweat, UV radiation, and temperature exposure could degrade the performance of these embedded electronic systems. At this time, there is a lack of suitable test standards and reliability data about flexible electronics manufacturing, assembly, and real-time use. In this paper, a fully flexible medical electronics system was built in full dimension to study the assembly and operation-related failure mechanisms of flexible and wearable electronics. The fabricated flexible electronics system measures pulse and muscle activity, and then transmits this data to a paired mobile device. The pulse rate was measured using an LED and a photo diode, while an electromyography (EMG) sensor was used to measure muscle activity. After collecting the data, the microcontroller sends it to a Bluetooth module, which can in turn transmit this information to a paired mobile device. Through experimentation with the fabricated flexible electronics device, unexpected degradation and quality issues were observed. In flexible PCBs, the space between the IC lead could not be isolated by the solder mask because of its large feature size and as a result, increases the risk of shortage between IC leads when subjected to mechanical stress. In addition, during the assembly process, high reflow temperature was found to subject a huge thermal stress on the connections between the solder pad and copper trace. Proper support of the solder pad should be designed to compensate the thermal stress during the reflow process, and prevent the copper joint on top of the board from being damaged. A set of guidelines for flexible medical electronics and an implementable reliability test standard can, therefore, be established for medical device manufacturers based on these reliability assessments.

Interpreting sensor data requires knowledge of sensor placement and the contextual environment surrounding the sensor. For a single sensor measurement, it is easy to document the context usually by visual observation. However, for millions of sensors reporting data back to a server, the contextual information needs to be automatically extracted from either data analysis or leveraging complimentary data sources. Data layers that overlap spatially or temporally with sensor locations, can be used to extract the context and validate the measurement. The second challenge is to minimize the amount of sensor data transmitted through the internet while preserving signal information content. Here we demonstrate two methods for communication bandwidth reduction: computation at the edge and compressed sensing. We validate the above methods on wind and chemical sensor data to: (1) eliminate redundant measurement from wind sensors and (2) extract peak value of a chemical sensor measuring a methane plume. We present a general cloud based framework to validate sensor data based on statistical and physical modeling and contextual data extracted from geospatial data.

The operation of today’s data centers increasingly relies on environmental data collection and analysis to operate the cooling infrastructure as efficiently as possible and to maintain the reliability of IT equipment. This in turn emphasizes the importance of the quality of the data collected and their relevance to the overall operation of the data center. This study presents an experimentally based analysis and comparison between two different approaches for environmental data collection; one using a discrete sensor network, and another using available data from installed IT equipment through their Intelligent Platform Management Interface (IPMI). The comparison considers the quality and relevance of the data collected and investigates their effect on key performance and operational metrics. The results have shown the large variation of server inlet temperatures provided by the IPMI interface. On the other hand, the discrete sensor measurements showed much more reliable results where the server inlet temperatures had minimal variation inside the cold aisle. These results highlight the potential difficulty in using IPMI inlet temperature data to evaluate the thermal environment inside the contained cold aisle. The study also focuses on how industry common methods for cooling efficiency management and control can be affected by the data collection approach. Results have shown that using preheated IPMI inlet temperature data can lead to unnecessarily lower cooling set points, which in turn minimizes the potential cooling energy savings. It was shown in one case that using discrete sensor data for control provides 20% more energy savings than using IPMI inlet temperature data.

Flexible electronics provide new design options not afforded by rigid electronics in a variety of applications including wearable electronics, robotics and automotive systems. However, the processes for the manufacturing of complex electronic assemblies using fine-pitch components are not as well developed as those for rigid electronics. The lack of structural rigidity of flexible printed circuit cards requires attention to assembly configuration for double-sided flexible assemblies. In addition, mechanisms are needed to compensate for the deformation and warpage of the flexible substrate and components during assembly. In this paper, the stresses in solder joints of double-sided flexible assemblies have been measured during thermal excursions using x-ray micro-computed tomography in conjunction with digital volume correlation. The method allows for non-invasive measurement and does not require cross-sectioning of the part for the purpose of deformation and strain measurement. In addition, the measurements are not limited to the joints in the line of sight. The three-dimensional measurements of deformation and strain have been visualized on the geometry of the solder joints in the package. Digital volume correlation (DVC) method has been used to find the displacements and strains in interconnects of operational electronics. The x-ray microscopic computed tomography (μCT) system has been used to generate the 16 bit digital volume data. The x-ray detector has ability to image the x-ray attenuation of x-rays through the object. Reliability testing of SAC 305 solder interconnects has been performed on double-sided flexible circuit board using x-ray μCT by heating the package to 100°C. The flexible circuit board used in this experiment is of BGA 256-144 combination, two packages, A-PBGA256-1.0mm-17mm and A-CABGA144-1.0mm-13mm. A 3D printed fixture has also been used to support the flexible board and keep it flat while in the CT scan machine. The reference and deformed scans are then re-constructed 3D using Volume Graphics, and Digital Volume Correlation performed using MATLAB modules. Reliability of double-sided flexible printed circuit boards will be discussed and any crack, defects, or deformation in the solder interconnectivity which might occur while heating the package on flexible board is presented. The solder joint strains during thermal excursions are also compared between the flexible and rigid printed circuit assemblies.

The revolutionary changes in automotive industry towards fully connected automated electrical vehicles necessitates developments in automotive electronics at unprecedented speed. Signal, control, and power electronics will heterogeneously be integrated at minimum space with sensors and actuators to form highly compact and ultra-smart systems for functions like traction, lighting, energy management, computation, and communication. Most of these systems will be highly safety relevant with the requirements in system availability exceeding today’s already high automotive standards. Other than the human drivers of today, passengers in the automated car do not pay constant attention to the driving actions of the vehicle. Hence, reliability research is massively challenged by the new automotive applications. Guaranteeing the specified lifetime at statistical average is no longer sufficient. Assuring that no failure of an individual safety relevant part occurs unexpectedly, becomes most important. The paper surveys the priority actions underway to cope with the tremendous challenges. It highlights practical examples in all three directions of reliability research. i) Experimental reliability tests and physical analyses: New and highly efficient accelerated stress tests are able to cover the complex and multi-fold loading situation in the field. New analytics techniques can identify the typical failure modes and their physical root causes. ii) Virtual techniques: Schemes of validated simulations allow capturing the physics of failure proactively in the design for reliability process. iii) Prognostics health management (PHM): A new concept is introduced for adding a minimum of PHM features at the various levels of automotive electronics to provide functional safety as required for autonomous vehicles. This way, the new generation of reliability methods will continuously provide estimates of the remaining useful life (RUL) for each relevant part under the actual use conditions to allow triggering maintenance in time.

Efficient and compact cooling technologies play a pivotal role in determining the performance of high performance computing devices when used with highly parallel workloads in supercomputers. The present work deals with evaluation of different cooling technologies and elucidating their impact on the power, performance, and thermal management of Intel ® Xeon Phi™ coprocessors. The scope of the study is to demonstrate enhanced cooling capabilities beyond today’s fan-driven air-cooling for use in high performance computing (HPC) technology, thereby improving the overall Performance per Watt in datacenters. The various cooling technologies evaluated for the present study include air-cooling, liquid-cooling and two-phase immersion-cooling. Air-cooling is evaluated by providing controlled airflow to a cluster of eight 300 W Xeon Phi coprocessors (7120P). For liquid-cooling, two different cold plate technologies are evaluated, viz, Formed tube cold pates and Microchannel based cold plates. Liquidcooling with water as working fluid, is evaluated on single Xeon Phi coprocessors, using inlet conditions in accordance with ASHRAE W2 and W3 class liquid cooled datacenter baselines. For immersion-cooling, a cluster of multiple Xeon Phi coprocessors is evaluated, with three different types of Integrated Heat Spreaders (IHS), viz., bare IHS, IHS with a Boiling Enhancement Coating (BEC) and IHS with BEC coated pin-fins. The entire cluster is immersed in a pool of Novec 649 (3M fluid, boiling point 49 °C at 1 atm), with polycarbonate spacers used to reduce the volume of fluid required, to achieve target fluid/power density of ∼ 3 L/kW. Flow visualization is performed to provide further insight into the boiling behavior during the immersion-cooling process. Performance per Watt of the Xeon Phi coprocessors is characterized as a function of the cooling technologies using several HPC workloads benchmark run at constant frequency, such as the Intel proprietary Power Thermal Utility (PTU), and industry standard HPC benchmarks LINPACK, DGEMM, SGEMM and STREAM. The major parameters measured by sensors on the coprocessor include total power to the coprocessor, CPU temperature, and memory temperature, while the calculated outputs of interest also include the performance per watt and equivalent thermal resistance. As expected, it is observed that both liquid and immersion cooling show improved performance per Watt and lower CPU temperature compared to air-cooling. In addition to elucidating the performance/watt improvement, this work reports on the relationship of cooling technologies on total power consumed by the Xeon-Phi card as a function of coolant inlet temperatures. Further, the paper discusses form-factor advantages to liquid and immersion cooling and compares technologies on a common platform. Finally, the paper concludes by discussing datacenter optimization for cooling in the context of leakage power control for Xeon-Phi coprocessors.

Continued CMOS scaling accompanied with a stall in the voltage scaling has led to high on-chip power densities. High on-chip power densities elevate the temperatures, substantially limiting the performance and reliability of computing systems. The use of Phase Change Materials (PCMs) 1 has been explored as a passive cooling method to manage excessive chip temperatures. The thermal properties of PCMs allow a large amount of heat to be stored at near-constant temperature during the phase transition. This heat storage capability of PCM can be leveraged during periods of intense computation. For systems with PCM, development of new management strategies is essential to maximize the benefits of PCM. In order to design and evaluate these management strategies, it is necessary to have an accurate PCM thermal model. In our recent work, we proposed a detailed phase change thermal model, which we integrated into a compact thermal simulation tool, HotSpot. In this paper, we build a hardware testbed incorporating a PCM unit on top of the chip package. We then validate the accuracy of our previously proposed thermal model by comparing the HotSpot simulation results against the measurements on the testbed. We observe that the error between the measured and simulated temperatures is less than 4°C with 0.65 probability. Finally, we implement a soft PCM capacity sensor that monitors the remaining PCM latent heat capacity to be used for development of thermal management policies. We evaluate a set of thermal management policies on the testbed. We compare policies that adjust the sprinting frequency based on current temperature against the policies that take action based on the remaining PCM capacity.

It has been reported that tablet computer surface temperatures can rise from room temperature up to 47°C. Holding a warm or hot computer surface might cause user’s thermal discomfort and possibly skin burns. The use of a tablet often requires holding the device for prolonged time with multiple fingers and palm areas in contact with the tablet lower surface. Previous research has not tested whole finger/palm thermal sensation at a specific surface temperature in a moderate environmental heat range. The current research investigates user’s thermal sensations on the palm and fingers, in response to warm/heat stimuli in a tablet size device with a longer contact duration than used in previous studies, to provide ergonomic design guidelines for electronic device designers and manufacturers. A tablet-size heating surface was developed comprising of nine rectangular aluminum heating pads connected with computer-controlled heaters and thermal sensors. Participants were asked to report their finger/palm thermal sensation and comfort every 45 seconds when they held the prototype for 90 seconds. Results showed a positive linear relationship between surface temperature and user’s thermal sensation and thermal discomfort. Duration of holding the prototype had no significant effect on user’s thermal comfort, but it did significantly affect thermal sensation ratings.

This paper reports on a proof-of-concept study of applying a two-dimensional (2D) microfluidic-based tactile sensor for tissue palpation under the influence of misalignment. Two unavoidable misalignment issues, uncertainty in contact point and non-ideal normal contact, severely distort the genuine elasticity distribution of a tissue region, yielding false identification of abnormality. The core of the 2D tactile sensor is one whole microstructure embedded with an electrolyte-enabled 2D resistive transducer array underneath. This unique configuration allows the tactile sensor to interact with a tissue region in a continuous manner that mimics manual palpation: the whole microstructure (fingertip) presses a tissue region and the corresponding deflection distribution is captured concurrently by the embedded transducer array (distributed sensors under the skin). This continuous manner tackles the misalignment issues encountered by an individual sensor or a sensor array, in that any misalignment encountered by the 2D sensor is manifested as an increasing trend of the distributed deflection-depth relations along the tilt direction. Tissue phantoms with embedded nodules and extrusions are prepared and are measured using the 2D tactile sensor, validating the capability of the tactile sensor to identify abnormalities in soft tissue under the influence of misalignment.

The local surface temperature, heat flux, heat transfer coefficient, and Nusselt number were measured for an inline array of circular, normal jets of single-phase, liquid water impinging on a copper block with a common outlet for spent flow, and an experimental 2-D surface map was obtained by translating the jet array relative to the sensors. The effects of variation in jet height, jet pitch, confining wall angle, and average jet Reynolds number were investigated. A strong interaction between the effects of the geometric parameters was observed, and a 5° confining wall was seen to be an effective method of managing the spent flow for jet impingement cooling of power electronics. The maximum average heat transfer coefficient of 13,100W=m 2 K and average Nusselt number of 67.7 were measured at an average jet Reynolds number of 14,000.

This paper reports on a microfluidic-based tactile sensor capable of detecting forces along two directions and torque about one direction. The 3-Degree-Of-Freedom (3-DOF) force/torque sensor encompasses a symmetric three-dimensional (3D) microstructure embedded with two sets of electrolyte-enabled distributed resistive transducers underneath. The 3D microstructure is built into a rectangular block with a loading-bump on its top and two microchannels at its bottom. Together with electrode pairs distributed along the microchannel length, electrolyte in each microchannel functions as a set of three resistive transducers. While a normal force results in a resistance increase in the two sets of transducers, a shear force causes opposite resistance changes in the two sets of transducers. Conversely, a torque leads to the opposite resistance changes in the two side transducers in each set. Soft lithography and CNC molding are combined to fabricate a prototype tactile sensor. The experimental results validate the feasibility of using this microfluidic-based tactile sensor for 3-DOF force/torque detection.