bluuebunny/crossref_metadata_2025 huggingface dataset:
Reliability Study of High-Temperature-Resistant Mounting Structure Considering Shear Behavior of Joint Layer
Authors: Yamagiwa Masanori , Fujita Masato , Yu Qiang , Sugihara Hiromi
Published: January 2011

Wide band gap semiconductor devices such as Silicon Carbide (SiC) or Gallium Nitride (GaN) capable of operation at high temperature over 300 degrees offer the potential of higher performance with reduced size, weight and eventually cost in power electronics equipment. For these high-temperature-resistant devices, the authors have proposed a new chip mounting structure that the stress relaxation function rests with the circuit metal on the substrate rather than the joint layer. In this study, to evaluate thermal fatigue of the new structure precisely, material properties of the high-temperature-resistant joint layer were measured by a new method and this method enabled analysis using measured properties. The joint layer which became very thin was formed by a low temperature sinter technology using silver (Ag) nano particles. The shear test to obtain the nonlinear properties of the joint layer was carried out by a proposed new method using bimetal fixtures which are composed of two materials whose Coefficient of Thermal Expansion (CTE) is different. Displacement of shear direction on the joint layer formed between the fixtures can be generated by heating the fixtures. Micro displacement was measured by Digital Image Correlation Method (DICM) using optical microscope and minute load on the joint layer was detected by strain gauge attached at fixture. Using the properties of the joint layer obtained as the test results, shear behavior on the chip joint was evaluated by Finite Element Analysis (FEA). Furthermore, harsh Thermal Cycle Test between −50 and 300 degree Celsius was carried out in the samples as the same structure as FEA model. From these results, the fatigue mechanism became clear and an improvement of the thermal cycle life was discussed.
Design of a Passive Cooling System for a Solid-State 15kV / 100kVA Intelligent Universal Transformer
Authors: Warzoha Ronald , Fleischer Amy , Bird Simon D. , Gandhi Mahesh , Sundaram Ashok
Published: January 2011

As the use of alternative energy sources increases globally, there exists a need for a smart grid system to handle the increased power capacity. As part of this new power grid, a new type of intelligent universal transformer (IUT) has been developed to enhance power quality, throughput and efficiency to tackle green initiatives and enable distribution automation based on a control system. Using solid-State technology, specifically the SGTO module developed by the Electronic Power Research Institute (EPRI) and Silicon Power Corporation (SPCO), the IUT has the capacity to better optimize the existing transmission system while simultaneously delivering reliable diverse power, such as 400Hz service, DC service for hybrid-electric (plug-in) vehicles and three-phase power from a single phase line. This paper explores the thermal challenges associated with the design of the intelligent universal transformer, specifically designing for a high system heat load of 6 kW in an ambient temperature of 50°C. The system must use natural convection to prevent the use of mineral oils in a forced convection case such that there is no ecological concern. The system must also meet weight constraints, sufficiently handle a common household current draw of 110A and uphold its structural integrity. The high system heat load is applied using IcePak and a sufficient design is solved for numerically using FLUENT.
Characterizing and Minimizing Voids in Quad Flat No-Lead Pack (QFN) Device Assembly Using Pb-Free Solder Alloys
Authors: Dhanasekaran Rangaraj , Gadepalli Harish , Ramkumar S. Manian , Jensen Tim , Briggs Ed
Published: January 2011

Quad Flatpack No lead (QFN) packages have become a popular choice in electronics packaging due to its small form factor. They are also gaining rapid industry acceptance because of its excellent thermal and electrical performance. The bottom side of the QFN package has a large thermal pad. This exposed die attach pad effectively conducts heat to the PCB and also provides a stable ground connection. Effective soldering of this surface to the pad on the PCB is required for good thermal dissipation and component functionality. The exposed thermal pad presents various challenges during the surface mount assembly process. One major challenge is solder void formation. Voids are primarily formed due to the entrapment of volatiles in flux outgassing during the reflow process. The primary objective of this study is to determine optimal parameters to minimize void formation in QFN packages (QFN16, QFN20, QFN28 and QFN32), specifically the reflow profile, lead-free solder paste and stencil aperture opening for the thermal pad. A systematic DOE based approach was used to arrive at conclusions, using the ratio of void volume on the thermal pad to the actual volume of solder paste printed as the response variable. Various graphs are presented to understand the impact of different parameters. Interaction graphs are used to determine optimal settings for each parameter.
Comparison of Numerical Modeling to Experimental Data in a Small Data Center Test Cell
Authors: Cruz Ethan , Joshi Yogendra , Iyengar Madhusudan , Schmidt Roger
Published: January 2011

Information Technology (IT) equipment compaction has become a significant air cooling challenge at the data center level. Computational Fluid Dynamics and Heat Transfer (CFD/HT) models have been employed as the dominant technique for the design and optimization of both new and existing data centers. Understanding the limitations of a CFD/HT models’ ability to predict the actual data center temperature field and flow characteristics becomes a critical component in optimizing the actual data center rather than optimizing the model of the data center. This is most important near the IT equipment where temperature and flow specifications from the IT equipment manufacturers must be maintained for reliable operation. This study is a continuation of earlier comparisons of CFD/HT models to experimentally measured temperature and flow fields in a small data center test cell. This study compares the experimentally collected data for three different layouts of perforated tiles to a CFD/HT model with seven turbulence models not previously evaluated. Insight into the location of the deviation between the different turbulence models and experimental data are discussed, along with the computational effort involved in running the CFD/HT models. It was found that the zero equation (or mixing length model) and the Spalart-Allamaras turbulence models produced the smallest deviations from experimental data, but the former required only a fifth of the computational effort of the latter. The laminar flow model required the least computational effort, running more than twice as fast as the zero equation turbulence model, and produced deviations similar to those of the six different k-ε turbulence models.
Damage Accumulation and Life-Prediction Models for SnAgCu Leadfree Electronics Under Shock-Impact
Authors: Lall Pradeep , Shantaram Sandeep , Angral Arjun , Kulkarni Mandar , Suhling Jeff
Published: January 2011

Relative damage-index based on the leadfree interconnect transient strain history from digital image correlation, explicit finite-elements, cohesive-zone elements, and component’s survivability envelope has been developed for life-prediction of two-leadfree electronic alloy systems. Life prediction of pristine and thermally-aged assemblies, have been investigated. Solder alloy system studied include Sn1Ag0.5Cu, and 96.5Sn3.5Ag. Transient strains during the shock-impact have been measured using digital image correlation in conjunction with high-speed cameras operating at 50,000 fps. Both the board strains and the package strains have been measured in a variety of drop orientations including JEDEC horizontal drop orientation, vertical drop orientation and intermediate drop orientations. In addition the effect of sequential stresses of thermal aging and shock-impact on the failure mechanisms has also been studied. The thermal aging condition used for the study includes 125°C for 100 hrs. The presented methodology addresses the need for life prediction of new lead-free alloy-systems under shock and vibration, which is largely beyond the state of art. Three failure modes have been predicted including interfacial failure at the copper-solder interface, solder-PCB interface, and the solder joint failure. Explicit non-linear finite element models with cohesive-zone elements have been developed and correlated with experimental results. Velocity data from digital image correlation has been used to drive the attachment degrees of freedom of the submodel and extract transient interconnect strain histories. Explicit finite-element sub-modeling has been correlated with the full-field strain in various locations, orientations, on both the package and the board-side. The survivability of the leadfree interconnections under sequential loading (thermal aging and shock-impact) from simulation has been compared with pristine circuit assemblies subjected to shock-impact. Sequential loading changes the failure modes and decreases the drop reliability as compared to the room temperature experimental results. Damage index based survivability envelope is intended for component integration to ensure reliability in harsh environments.
Analysis for Single Board Computer Module Cooling Under Natural Air Convection Condition
Authors: Zhang Jiahui , Weber Dave , Waggel Jason , Pollice Tony , Matuonto Marco
Published: January 2011

As the state-of-the-art technology for energy saving, variable-frequency drives (VFDs) can be applied in nuclear power plant to drive recirculation pumps for coolant flow control. Due to requirement of high reliability, such as in nuclear industry, air natural convection cooling plays an important role in and while brings out a great challenge to thermal management for electronic unit. With an application of single board computer module in control system, another cooling challenge comes from heat flux increase caused from smaller footprint, since all of components, such as processor, chipset, memory and power supply etc., are built into one board. In the paper, cooling technologies for the single board computer module are investigated and developed, focusing on natural air heat convection from heat sink to ambient and heat conduction from board to heat sink. Based on thermal analysis associated with mechanical consideration, one heat sink is used to cool multiple components on the board. Two TIMs (thermal interface materials) and one heat spreader are employed for heat conduction from CPU and chipset to heat sink, respectively. Extrusion heat sink is selected with a comprehensive consideration of cost and thermal performance. A numerical simulation model is developed and validated against testing results. With the verified model, effects of fin arrangement on heat sink performance are analyzed. A study is conducted for optimization of base plate and fin thickness, and accordingly a heat sink is developed for the present application. Environmental conditions, such as temperature, altitude, and humidity etc., are analyzed to investigate their influence on cooling performance of natural air convection.
Thermal Characteristics of a Synthetic Jet Integrated Heat Sink Design for Air-Cooled Electronics
Authors: Utturkar Yogen , Arik Mehmet , Icoz Tunc
Published: January 2011

Thermal management is currently one of the key limitations in the design of electronic systems. Parallel to the advancements in the electronics industry and increase in power dissipation the development of effective, low-cost, compact heat removal solutions become extremely critical to ensure a failsafe and reliable operation. While liquid cooling is poised to provide the cooling capability for next generation electronics, its use in present-day products is less prevalent due to risks associated with condensation, leakage, and pumping power. Consequently, air-cooling strategies still continue to vie for near-term cooling needs in the electronic industry. In cohort with these trends, an advanced air-cooling solution in form of a synthetic jet assisted heat sink has been investigated in the present study. The study focuses on key design aspect of the heat sink fin design, synthetic jet design and characterization, and the interaction of unsteady air jets with the heat sink fins. Numerical simulations are employed to investigate 3D unsteady flow dynamics and experimental setup is designed and built for validation. The paper systematically presents the design trade-offs associated with the number of jets in the thermal solution and the jet driving conditions (voltage and frequency), in terms of the thermal performance and the cost. Overall, the synthetic jet integrated heat sink has demonstrably been shown to dissipate up to 4.7 times better than conventional natural convection heat sink with a COP value of greater than 40 within a volume of 25 in3.
Effects of Transient Heating on Two-Phase Flow Response in Microchannel Heat Exchangers
Authors: Miler Josef L. , Flynn Roger , Refai-Ahmed Gamal , Touzelbaev Maxat , David Milnes , Steinbrenner Julie , Goodson Kenneth E.
Published: January 2011

Two-phase microfluidic heat sinks promise high heat flux cooling at reduced pumping power compared to pumped liquid microchannel heat sinks. However, flow instabilities caused by bubble nucleation and expansion severely reduce heat transfer performance of two-phase microfluidic heat sinks. This study probes the governing physics of bubble nucleation and expansion by comparing the effects of pulsed heating to steady-state heating in a single microchannel. Pulsed heating at 8 Hz causes an increase in the average hotspot temperature of as much as 8°C compared to steady-state heating. Upstream and downstream temperature response does not vary significantly between heating conditions. The results correspond well with thin-film evaporation models for bubble growth. This study provides insight for designing two-phase microfluidic cooling system subjected to transient hotspots.
PCR for Derivation of Parameter Dependencies, Thermo-Mechanical Norris-Landzberg Acceleration Factors, Goldmann Fatigue Constants for Leadfree Electronics
Authors: Lall Pradeep , Shirgaokar Aniket , Arunachalam Dineshkumar , Suhling Jeff , Strickland Mark , Blanche Jim
Published: January 2011

Goldmann Constants and Norris-Landzberg acceleration factors for lead-free solders have been developed based on principal component regression models (PCR) for reliability prediction and part selection of area-array packaging architectures under thermo-mechanical loads. Models have been developed in conjunction with Stepwise Regression Methods for identification of the main effects. Package architectures studied include, BGA packages mounted on copper-core and no-core printed circuit assemblies in harsh environments. The models have been developed based on thermo-mechanical reliability data acquired on copper-core and no-core assemblies in four different thermal cycling conditions. Packages with Sn3Ag0.5Cu solder alloy interconnects have been examined. The models have been developed based on perturbation of accelerated test thermo-mechanical failure data. Data has been gathered on nine different thermal cycle conditions with SAC305 alloys. The thermal cycle conditions differ in temperature range, dwell times, maximum temperature and minimum temperature to enable development of constants needed for the life prediction and assessment of acceleration factors. Goldmann Constants and the Norris-Landzberg acceleration factors have been benchmarked against previously published values. In addition, model predictions have been validated against validation data-sets which have not been used for model development. Convergence of statistical models with experimental data has been demonstrated using a single factor design of experiment study for individual factors including temperature cycle magnitude, relative coefficient of thermal expansion, and diagonal length of the chip. The predicted and measured acceleration factors have also been computed and correlated. Good correlations have been achieved for parameters examined. Previously, the feasibility of using multiple linear regression models for reliability prediction has been demonstrated for flex-substrate BGA packages [Lall 2004, 2005], flip-chip packages [Lall 2005] and ceramic BGA packages [Lall 2007]. The presented methodology is valuable in the development of fatigue damage constants for the application specific accelerated test data-sets and provides a method to develop institutional learning based on prior accelerated test data.
Package Designs and Associated Challenges for Environment Sensitive MEMS Sensors
Authors: Sarihan Vijay , Wen Jian , Li Gary
Published: January 2011

Effective packaging of MEMS devices has lagged the development of unique sensors suitable for a variety of applications. Packaging challenges are often what prevent wider application and extensive commercialization of MEMS Sensors. MEMS devices are designed for sensing the environment. Their detection capability should not be adversely impacted by the package and the package reliability should not be compromised by the environment. Two different Sensor applications are used to highlight the packaging challenges. In one case the Sensor electrical output response was becoming nonlinear in the range of valid operating temperatures after packaging. The ASIC controller was not able to compensate for this nonlinearity. In the second application package design caused electrical response resonance within the operating environment range. Advanced package design methodology was developed to couple simulations for package reliability prediction for different failure modes with Sensor performance predictions to deliver cost effective and reliable packages. The predictive design methodology was extensively validated with experimental results at every stage.
Thermal Reliability of Low-Cost High-Power LED Package Module Under WHTOL Test
Authors: Chen C. H. , Tsai W. L. , Tang C. Y. , Tsai M. Y.
Published: January 2011

The LED issues, associated with high cost, high junction temperature, low luminous efficiency, and low reliability, have to be solved before gaining more market penetration. With special features of low-junction-temperature and low-cost design, COP (Chip-on-Plate) LED package modules with and without phosphors are evaluated in terms of their thermal resistance and reliability under wet high temperature operation life (WHTOL) test. The WHTOL test is with the condition of 85°C/85% RH and 350mA of forward current for 1008 hrs, specified in JESD22 Method A101-B. First of all, the thermal behaviors of the COP package module are investigated by experimental measurement, and a computational fluid dynamics approach. The reliability under WHTOL test is then carried out. The results show that all COP package modules with phosphors in the silicone encapsulant failed after 309 hrs at WHTOL test, but all those without phosphors passed for 1008 hrs. The failure sites are located at aluminum wire debonding to the chip and copper pads of the substrate. However, the aluminum wire bonding of the COP package modules are replaced to gold wire bonding, then all COP package modules with and without phosphors pass for 1008 hrs. For the passing package modules, their thermal resistances are found to increase more than two fold after 1008 hrs of the WHTOL test from 41°C/W to 87.1°C/W. This is due to the thermal conductivity decreasing in the die attach and thermal grease and the contact resistance increasing after the moisture absorption. Moreover, for the thermal behavior of the COP package modules under the natural and forced convections in the WHTOL test, the results show that there exists the difference of 17°C/W in the junction-to-air thermal resistances, which might result in different reliability data. In addition, it is also indicated that the junction-to-air thermal resistances are very sensitive to the flow conditions of the chamber, but not for junction-to-aluminum substrate and junction-to-heat sink thermal resistances. Therefore, the standard test of the WHTOL should specify flow conditions in the test chamber.
Drop Test for Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG) Surface Treatment Application That is Suitable to a Low-Cost, Fine Pitch and Easy Fabrication
Authors: Ahn Junehyeon , Kim Hongkwon , Byun Kangho , Lee Youngmin , Jang Donghoon , Kim Byungsung
Published: January 2011

For an application of fine pitch Ball Grid Array (BGA) or Land Grid Array (LGA) packages, ENEPIG is a promising surface finish technology of low cost, fine pitch and easy fabrication. In this paper, we study the drop test, one of the most important items of hand held device reliability test, of ENEPIG surface finished packages. This paper focuses on the drop test performance of a bond between the main board and three kinds of packages. Those packages are designed with a daisy chain for a detection of open/short during the drop test. The main board has a bar type outline and is suitable for an In-Situ data acquisition. Drop tester is composed of a drop test unit, a high speed resistance meter and a data acquisition system (PC). JEDEC Condition B (1,500G and 0.5milliseconds duration time and half-sine pulse) in JESD22-B111 Table 1 or in JESD22-B104-C Table 1 is applied as a test condition. After the drop test, the joint geometry and the intermetallic compound (IMC) of failure samples are analyzed through the cross section method. The result shows no breaks at the solder joint of package side. All breaks, however, are originated from the solder joints of main board side. It is a significant outcome of this work to show no performance difference between ENEPIG and Electrolytic Ni/Au.
Impact of Double Walled Telecommunication Cabinet on Solar Load: Natural and Forced Convection
Authors: Muralidharan Bharathkrishnan , Iqbal Mariam Feroz Ahamed , Mulay Veerendra , Agonafer Dereje , Hendrix Mark
Published: January 2011

Access networks provide the last mile of connectivity to telecommunications customers throughout the world. Voice, data, and video services through fiber, copper, and wireless media are all delivered to the end user by the access portion of the network. In an access network, thermal management of active electronics and optical devices is critical to network reliability and performance. In these networks, outside plant telecom enclosures provide environmental protection for both active electronics and optical devices. These enclosures must incorporate cooling systems that support thermal requirements of the electronic and optical components. And, with ever-increasing sensitivity to environmental impacts, the enclosures and cooling systems must have minimal aesthetic and acoustic impact to their surroundings. Additionally, the enclosures must be developed with high sensitivity to cost as they are typically deployed in large number throughout a telecom service area. A number of thermal technologies are employed for thermal control of these enclosures. These includes air conditioning, heat exchangers, thermoelectric coolers, direct air filtering, and double-walled construction. In this paper, the double-walled construction technique and its impact on thermal performance will be discussed in detail.
Thermal Fatigue Reliability of High-Temperature-Resistant Joint for Power Devices
Authors: Sugihara Hiromi , Yamagiwa Masanori , Fujita Masato , Oshidari Toshikazu , Yu Qiang
Published: January 2011

The power electronics equipments for Electric vehicles such as the inverter are strongly demanded on downsizing and weight reduction. For these requirements, Silicon Carbide (SiC) devices are receiving particular attention. SiC devices are characterized by lower-loss and higher temperature operation compared with Si devices. Using the devices under high temperature, the cooling equipments can be miniaturized. However, a function of stress relaxation that the existing solder has is difficult to be expected in a high-temperature-resistant joint layer for SiC devices, because the joint layer is generally hard. So, the authors have proposed a new mounting structure that a metal circuit on a substrate has the function instead of the joint layer. In this study, high-temperature-resistant mounting structures that the chip was bonded by low temperature sintering method using Ag nano-particles to substrate with Ag/Ni plating are prepared. Thermal Cycle Test (TCT) using these samples of harsh temperature range was conducted. As a result a new critical issue on the chip joint was identified. To clarify the thermal fatigue mechanism, the Finite-Element-Analysis (FEA) was carried out. The analysis model simulated a thin layer of Ag/Ni plating and the high-temperature-resistant joint layer. By the FEM results, the thermal fatigue, particularly occurring crack, was affected by the micro structures.
The Characterization of Damage Propagation of BGA Flip-Chip Electronic Packages Under Mechanical Shock Loading
Authors: Helms Kayleen L. E. , Shah Ketan R. , Gerbus Dan , Vasudevan Vasu S. , Radhakrishnan Jagadeesh , Berry Will
Published: January 2011

Increasing power and I/O demands in HDI (high density interconnect) components coupled with the industry-wide conversion to lead-free products has introduced additional risk for solder joint reliability (SJR) of BGA (ball grid array) Flip-Chip electronic packages. One particular concern is SJR under mechanical shock (dynamic bend) loading. While leaded alloys provided good performance in shock for many years due to the unparalleled ability of lead’s slip systems to absorb the energy in shock events, lead-free alloys cannot provide the same benefit. To mitigate this risk, better approaches for understanding damage propagation are needed to enable better design to limit and reduce the SJR risk during shipping and end-user handling. To this end, a characterization study is undertaken to monitor damage progression at the second-level interconnect in BGA’s on flip-chip electronic packages during mechanical shock loading. The study uses a board-level, strain-monitoring approach plus the dye and peel failure analysis technique to track the initiation and propagation of solder joint cracks under loading. The approach being used differs from conventional reliability testing in that both design and load variables are used to quantify damage growth and strain response to bridge the understanding of design feature impact to traditional reliability testing. The scope of the study includes investigating the impact of such factors as package placement, board layout, and enabling load on the monitored board strain and the damage propagation observed. From this study, directions and design guidelines for improving solder joint reliability of future BGA’s on flip-chip electronic packages under mechanical shock loading conditions are proposed.
Palladium Thiolate Bonding of Carbon Nanotube Thermal Interfaces for High-Temperature Electronics
Authors: Hodson Stephen L. , Bhuvana Thiruvelu , Cola Baratunde A. , Xu Xianfan , Kulkarni G. U. , Fisher Timothy S.
Published: January 2011

Carbon nanotube (CNT) arrays are attractive thermal interface materials with high compliance and conductance that can remain effective over a wide temperature range. Here we study CNT interface structures in which free CNT ends are bonded using palladium hexadecanethiolate Pd(SC16H35)2 to an opposing substrate (one-sided interface) or opposing CNT array (two-sided interface) to enhance contact conductance while maintaining a compliant joint. The palladium weld is particularly attractive for its mechanical stability at high temperatures. A transient photoacoustic (PA) method is used to measure the thermal resistance of the palladium bonded CNT interfaces. The interfaces were bonded at moderate pressures and then tested at 34 kPa using the PA technique. At an interface temperature of approximately 250°C, one-sided and two-sided palladium bonded interfaces achieved thermal resistances near 10 mm2K/W and 5 mm2K/W, respectively.
Deformation of Resin Material Due to Curing in the Thermal Process
Authors: Sone Ryusuke , Yu Qiang , Shibutani Tadahiro
Published: January 2011

Electronic devices have been developed with the transition of structures and materials. However, in the development, the miniaturization and the high integration of electronic device parts have been accorded priority over mechanical strength reliability. As a result, a lot of reliability issues have been exposed. Connective reliability issue which arises from warpage is one of the most important of them all in high integration electronic devices. To evaluate this warpage accurately, this paper focused on curing of resin materials which used in electronic devices during the thermal process. The deformation and the warpage behavior which arises from curing of resin materials were clarified by examinations. And the mechanism of the warpage of resin materials receiving the thermal loads was examined.
Cooling of Data Centers Using Airside Economizers
Authors: Karajgikar Saket , Mulay Veerendra , Agonafer Dereje , Schmidt Roger
Published: January 2011

The power trend for Server systems continues to grow thereby making thermal management of Data centers a very challenging task. Although various configurations exist, the raised floor plenum with Computer Room Air Conditioners (CRACs) providing cold air is a popular operating strategy. These rising heat load trends in data center facilities have raised concerns over energy usage. The environmental protection agency has reported that the energy used in 2006 by data center industry was 1.5% of the total energy usage by entire nation. The experts agree that by year 2010, this usage will approach 2% of the annual energy use nationwide. This has been the driving force behind the new solutions or technologies such as free cooling. Recent studies show that the outside air can be drawn in to cool the IT equipment without any undue electronic component failure due to contaminant. In this paper, different cases employing air side economizer are discussed. Numerical models are created to study the qualitative impact of the solution under various operating conditions.
Evaluation of Air-Side Economizer Use in a Compute-Intensive Data Center
Authors: Patterson Michael K. , Atwood Don , Miner John G.
Published: January 2011

Moore’s Law continues to drive increased compute capability and greater performance per watt in today’s and future server platforms. However the increased demand for compute services has outstripped these gains and the energy consumption in the data center continues to rise. The challenge for the data center operator is to limit the operational costs and reduce the energy required to run the Information and Communications Technology (ICT) equipment and the supporting infrastructure. The cooling systems can represent a large portion of the energy use in the support infrastructure. There is significant focus in industry today on applying advanced cooling technologies to reduce this energy. One potential solution is the use of air-side economizers in the cooling system. This technology can provide a reduction in cooling energy by being able to maintain the required temperatures in the data center with the mechanical refrigeration turned off, significantly reducing the PUE for the data center. This paper reviews recent industry activities around the recommended environmental conditions in the data center, the impact to the ICT equipment of air-side economizers, where they can best be applied, and provides data from a case study recently concluded at Intel’s site in New Mexico. In that case study servers from an engineering compute data center were split into a standard configuration (closed system, tight temperature control) and a very aggressive air-side economization section (open system, significant out-door air quantities, moderate temperature control). Both sections performed equally well over a year long on-line test, with significant energy savings potential demonstrated by economizer side. The American Society of Air-conditioning Heating and Refrigerating Engineers (ASHRAE) has recently published new ICT-vendor consensus-based recommendations for the environmental conditions in data centers. These new limits are discussed in light of the successful experiment run in New Mexico as the revised operational envelop allows a far greater number of hours per year when a data center can be run in “free-cooling” mode to obtain the energy savings. Server design features as well as lessons learned from the experiment and their applicability to the potential use of air-side economizers is also discussed.
Large-Scale Stress Analyses for Fatigue Reliability at Die-Mount Solder of Plastic IC Packages
Authors: Kugimiya Tetsuya , Hirohata Kenji , Mukai Minoru , Miyake Eitaro , Akiba Hiroshi , Ohno Nobutada , Kawakami Takashi
Published: January 2011

In this paper, the influence of the interface debonding area between the molding material and the metal frame on the fatigue reliability at die-mount solder joints in plastic IC packages was studied by means of large-scale finite element analyses. There are several factors causing the interface debonding between the molding material and the metal frame, such as manufacturing process, moisture absorption and deformation under field conditions. The debonding will change the structural stiffness of the packages and deformation shape during a thermal or mechanical load. Therefore, it is a critical issue for fatigue reliability. In this paper, three-dimensional large-scale finite element analysis is used for evaluating the influence of the debonding area on fatigue reliability under thermal cycling. The die-mount solder considered is the high-temperature solder 5Sn/95Pb. which is described by the nonlinear kinematic hardening model of Armstrong and Frederick in the finite element constitutive model. From the result of stress analyses, the debonding area has a large influence on inelastic strain, which is related to fatigue reliability. Large-scale finite element analysis is capable of providing useful guidance for structural design and material selection of plastic IC packages.
An Experimental Study of Onset Condition for Electrohydrodynamic Jetting
Authors: Kim Hyojun , Song Junyoung , Jeong Jaeik , Chung Jaewon
Published: January 2011

Electrohydrodynamic (EHD) printing has recently received considerable attention for its potential of high resolution printing. In typical EHD printing, at the constant flow rate condition, the electric field applied between the nozzle and the electrically conductive substrate induces cone jet, so that a droplet smaller than nozzle diameter can be ejected. However, for real application, fluid should be supplied to the nozzle by the constant pressure for multi-nozzle EHD. In this work, at the constant back pressure condition in the reservoir, EHD jetting phenomena were observed changing bias voltage. In addition, the onset voltage for EHD jetting was measured changing glass capillary nozzle diameter (outer diameter: 23, 42μm), hydrostatic back pressure head on the reservoir and the distance between the nozzle and the bottom electrode.
A Multiscale Damage Accumulation Theory for Solder Joint Failure
Authors: Bhate Dhruv , Mysore Kaushik , Subbarayan Ganesh
Published: January 2011

In heterogeneous micro structures that include several grains, secondary phases and interfaces, cracks are known to initiate and grow through different mechanisms. The failure processes however are not well understood. Solder alloys in general, and Pb-free alloys in particular possess complex, heterogeneous microstructures that evolve in fracture in ways that are challenging to model. Often, underlying a fracture observed under a microscope is a hierarchy of fracture-related phenomenon from atomic to macro length-scales. In this paper we develop a failure model inspired by information theory and continuum thermodynamics to capture the multiscale fracture processes in solder joints. We systematically develop measures of dissipation from continuum thermodynamics for materials described by J2 plasticity theory. Crack growth is known to be dissipative and such measures are natural candidates for predicting failure within a mechanics framework. The dissipation estimates, multiple fracture mechanisms and the notions of continuity, monotonicity and composition borrowed from information theory suggest a single model as being capable of predicting both ductile and brittle types of failures.
High Strain Rate Behavior of Sn3.8Ag0.7Cu Solder Alloys and Its Influence on the Fracture Location Within Solder Joints
Authors: Chan Dennis , Nie Xu , Bhate Dhruv , Subbarayan Ganesh , Dutta Indranath
Published: January 2011

Significant work has been done on the characterization of SnAgCu solder alloys at low strain rates (10−6 to 10−2s−1), and as a result, the behavior of solder over these strain rate regimes is well understood. On the other hand, there is a lack of accurate and consistent data for solder at high strain rates. In this paper, we will present data obtained using a servo-hydraulic mechanical tester and split-Hopkinson bar for the Sn3.8wt%Ag0.7wt% Cu solder alloy over strain rates spanning 0.001 to 500s−1. It is shown that the saturation stress correlates well with strain rate over nine decades on a log-log plot. It is also shown that a fit using Anand model based on low strain rate regime (4×10−6 to 2×10−4s−1) data captures the high strain rate results to a reasonable accuracy. It is commonly observed that in low strain rate failure, as in thermo-mechanical fatigue, failure tends to occur through the bulk of the solder. However in high strain rate failures, as those seen in drop tests, fractures occur through the intermetallic layer. We present finite element simulations of ball shear and ball pull tests using the above high strain rate data. It is demonstrated how the shift in failure mode from the bulk solder to intermetallic compound may be explained based on the high strain rate behavior of the SnAgCu solder alloy.
Assembly and Reliability Studies on Reworked and Non-Reworked QFN Packages
Authors: Pradhan Salil , Billaut Francois , Gopakumar Sunil
Published: January 2011

Quad Flat No lead (QFN) packages are being used as alternative components to some of the large form-factor packages due to their smaller footprint, improved thermal and electrical performance. During the past few years, there has been a surge of published papers by end users and component manufacturers on the topic of assembly and reliability of the QFN packages. Both empirical and simulation data has been published, which has helped several manufacturers to develop design guidelines and assembly processes for these packages. There exists a gap in the current published work on the assembly and reliability of high I/O count QFNs on thick boards. In addition, reliability of the rework process on QFNs is not well documented. Therefore, objectives of this research were the following: • Evaluate the second level reliability in thermal cycling for reworked and non-reworked QFNs; • Evaluate the reliability of different sized QFNs on 125 mil thick boards and compare with existing literature; • Failure analysis and recommendations for reliability improvement; • Land pattern comparison; and • Rework process improvement. Studies have been conducted on different QFN packages between 32 pins and 164 pins on 125 mil thick boards with Organic Solder Preservative (OSP) surface finish. Experimental design includes the use of different package sizes, alternate thermal pad patterns, and use of tin-lead versus lead free processes. A subset of some of the package types has also been reworked using variations of the standard BGA rework processes to evaluate its reliability. All packages were daisy chained. Boards were subjected to thermal cycling test between 0 to 100 deg C for 6000 hours. Data is analyzed using Weibull distribution. Failure mechanisms have been analyzed using dye penetration tests and cross sections. The reliability results are discussed in terms of package construction, type of land patterns and rework. Recommendations for process improvement are delineated.
Modelling Reliability of Power Electronics Packaging
Authors: Bailey Chris , Lu Hua , Yin Chunyan
Published: January 2011

Power Electronics uses semiconductor technology to convert and control electrical power. Demands for efficient energy management, conversion and conservation, and the increasing take up of electronics in transport systems (i.e. all electric car) there has been tremendous growth in the use of power electronics semiconductor devices such as Insulated Gate Bipolar Transistors (IGBT’s). The packaging of the power electronics devices involves a number of challenges for design engineers in terms of reliability and thermal management. For example IGBT modules will contain a number of semiconductor dies within a small footprint bonded to substrates with aluminium wires and wide area solder joints. The reliability of the package will depend on thermo-mechanical behavior of these materials. This paper details the results from a major UK project involving academics and industrial partners to investigate the reliability of IGBT modules. The focus of the presentation will be on the modelling tools developed to predict reliability and also the development of prognostics techniques to predict the remaining life of the package.
Hydrodynamically-Confined Microflows for Cell Adhesion Strength Measurement
Authors: Christ Kevin V. , Turner Kevin T.
Published: January 2011

Cell adhesion plays a fundamental role in numerous physiological and pathological processes, and measurements of the adhesion strength are important in fields ranging from basic cell biology research to the development of implantable biomaterials. Our group and others have recently demonstrated that microfluidic devices offer advantages for characterizing the adhesion of cells to protein-coated surfaces [1,2]. Microfluidic devices offer many advantages over conventional assays, including the ability to apply high shear stresses in the laminar regime and the opportunity to directly observe cell behavior during testing. However, a key disadvantage is that such assays require cells to be cultured inside closed microchannels. Assays based on closed channels restrict the types of surfaces that can be examined and are not compatible with many standard techniques in cell biology research. Furthermore, while techniques for cell culture in microchannels have become common, maintaining the viability of certain types of cells in channels remains a challenge.
E-cadherin N-glycosylation Modulates the Strength of Adherens Junctions
Authors: Shareef Sarah J. , Nita-Lazar Mihai , Kukuruzinska Maria A.
Published: January 2011

Metastasis, the spread of cancer cells throughout the body, claims 90% of solid tumor deaths. During metastasis, cancer cells undergo discohesion. An understanding of how to control and strengthen cell adhesion through junction formation could lead to methods for decreasing metastatic tendencies.
Nanotechnology Based Point-of-Care Diagnostics and Therapeutics for Neurological Disorders
Authors: Varadan Vijay K.
Published: January 2011

This talk is aimed at presenting novel solutions developed recently by the author’s group for many neurological disorders including Parkinson’s disease, Alzheimer’s disease, depression, anxiety, sleep apnea and sleep disorders using the fundamental research and developments in nanotechnologies and wireless sensor network. Point-of-care (POC) diagnostics promises to bring diagnostic testing out of the laboratory directly to patients and the general public wherever they may be. The key to POC diagnostics is capable of bringing immediate answers so that health care professionals can make rapid and accurate diagnosis of disease so as to ensure the effectiveness of therapy and early detection for preventive therapy. Selected movies illustrating the applications of both invasive and non-invasive wireless nanosensor systems to patients and surgical procedures will be shown at the talk.
Cellulose Electro-Active Paper for Biomedical Applications
Authors: Kim Jaehwan , Chen Yi
Published: January 2011

In our early work, cellulose has been discovered as a smart material. This newly discovered material is termed as electro-active paper (EAPap) that has merits in terms of lightweight, flexible, dryness, biodegradable, biocompatible, easy to chemically modify and cheap [1]. The actuation principle of cellulose EAPap actuator is known to be a combination of piezoelectric effect and ion migration effect. Since this new material is biodegradable and biocompatible, there are a lot of possible biomedical applications. This paper presents bacterial cellulose composites made by blending chitosan, poly(ethylene glycol) and gelatin for potential biomedical application of tissue engineering scaffold and would dressing material. The bacterial cellulose composites were successfully prepared by immersing wet bacterial cellulose pellicle in to chitosan, PEG or gelatin solutions followed by freeze-drying. The products look like a foam structure. Cell adhesion studies for these composites were carried out using 3T3 fibroblast cells. They showed much better biocompatibility than pure bacterial cellulose. Also, the concept of smart bandage is explained, which can come up with medical treatment layer of cellulose, sensing layer, antenna layer and integration of these layers. Issues in developing smart bandage are addressed in this paper.
Magnetic Targeting of Therapeutics
Authors: Dormer Kenneth , Po Sunny , Chen Kejian , Scherlag Benjamin , Rutel Isaac , Nguyen Kytai , Kyriyavar Satish , Grady Brian , Shapiro Benjamin , Gao Xinsheng , Du Xiaoping , Bourne David , Fung Kar-Ming , Kopke Richard
Published: January 2011

Multiple formulations of nano-sized particles, capsules, dendrimers, lipids, ceramics and genetic materials are being investigated in multiple labs for delivery of therapeutic moieties to targeted tissues. Interest is driven by reducing health care costs while increasing therapeutic efficacy and cost of treatment. One technology, magnetic targeting, incorporates iron oxide nanoparticles, to target nanomedicine payloads, down the gradients of external magnetic fields. When iron oxide crystal domains are less than ∼20–40 nm, particles become superparamagnetic (SPION), that is exhibit no remanent induction but very high magnetic susceptibility in the presence of an external magnetic field. Thus, targeting can be vectored by magnetic lines of flux. Particles can be pulled out of the microcirculation and across membranes into tissues. Two target organs that can employ magnetic targeting are the heart (epicardium) and inner ear (cochlea).
Characterization of a Magnetic Microactuator for Manipulating Nanoparticles in Gene Delivery Applications
Authors: Flick Eva , Li Wenzhong , Norpoth Jonas , Jooss Christian , Steinhoff Gustav , Gatzen Hans H.
Published: January 2011

Magnetically driven gene delivery provides a valuable approach for a single cell transfection. Therapeutic genes can be manipulated by conjugating them to magnetic nanoparticles. The magnetic force required for the manipulation of such complexes can be provided by an electromagnetic micro-actuator designed as micro pole row. The analytical calculations, simulations, and the thin-film fabrication of this micro pole row were carried out previously [1]. This paper presents characterization results of the first microactuator fabrication batch.