bluuebunny/crossref_metadata_2025 huggingface dataset:
A theory‐based intervention to reduce alcohol drinking in excess of guideline limits among undergraduate students
Authors: Hagger Martin S. , Lonsdale Adam , Chatzisarantis Nikos L. D.
Published: January 2011

Objectives. Undergraduate students frequently exceed guideline limits for alcohol intake in a single session and are highly susceptible to associated health, social, and economic problems. Psychological theory suggests that interventions aimed at reducing alcohol consumption should target both motivational and volitional phases of action to be effective. This study reports an integrated theory‐based intervention aimed at reducing undergraduates’ alcohol consumption in excess of guideline limits.

Design. The study adopted a 2 (motivation: mental simulation vs. no mental simulation) × 2 (volitional: implementation intention vs. no implementation intention) randomized controlled design presented in an online format.

Methods. Undergraduate students (N= 238; females, n= 133, M age = 20.11, SD= 2.09; males, n= 105, M age = 20.38, SD= 1.35) completed baseline psychological measures and self‐reported alcohol consumption as units consumed and heavy episodic drinking occasions followed by the intervention manipulation (if any). One month later participants completed follow‐up measures of the psychological variables and alcohol consumption.

Results. Significant reductions in alcohol consumption were observed at follow‐up. Participants receiving a mental simulation intervention reported significantly fewer units of alcohol consumed and heavy episodic drinking occasions. Among participants with high baseline alcohol consumption, participants in the combined mental simulation and implementation intention intervention group consumed significantly fewer units than other groups.

Conclusion. Results support the use of these theory‐based strategies to reduce alcohol drinking in excess of guideline limits among undergraduates. There was preliminary support for the interaction between the two strategies among heavier drinkers. Targeting both motivational and implemental phases of action poses a high probability for success in changing alcohol‐related behaviour in this population.
Material Behavior of Mixed Formulation Solder Joints
Authors: Zhang Yifei , Kurumaddali Kanth , Suhling Jeffrey C. , Lall Pradeep , Bozack Michael J.
Published: January 2011

The transition from tin-lead to lead free soldering in the electronics manufacturing industry has been in progress for the past 10 years. In the interim period before lead free assemblies are uniformly accepted, mixed formulation solder joints are becoming commonplace in electronic assemblies. For example, area array components (BGA/CSP) are frequently available only with lead free Sn-Ag-Cu (SAC) solder balls. Such parts are often assembled to printed circuit boards using traditional 63Sn-37Pb solder paste. The resulting solder joints contain unusual quaternary alloys of Sn, Ag, Cu, and Pb. In addition, the alloy composition can vary across the solder joint based on the paste to ball solder volumes and the reflow profile utilized. The mechanical and physical properties of such Sn-Ag-Cu-Pb alloys have not been explored extensively in the literature. In addition, the reliability of mixed formulation solder joints is poorly understood. In this work, we have explored the physical properties and mechanical behavior of mixed formulation solder materials. Seven different mixture ratios of 63Sn-37Pb and SAC305 solder materials have been formed, which include five carefully controlled mixtures of the two solder alloys (by weight percentage) and the two extreme cases (pure Sn-Pb and pure SAC). For the various percentage mixtures, the melting point, pasty range, stress-strain curves, mechanical properties (modulus, strength), and creep curves have been characterized. The variations of the mechanical properties and creep rates with aging at room temperature (25 °C) and elevated temperature (100 °C) have also been measured. Finally, the microstructures realized with the various mixtures have been found and correlated to the mechanical measurements and microstructures found in actual mixed formulation BGA solder joints. The results for the mechanical and physical properties show a very complicated dependence on the mixture ratio.
Damage Mechanics of Carbon Nano Tubes Under Uniaxial Tension
Authors: Basaran Cemal , Ragab Tarek
Published: January 2011

A procedure is proposed for computing the stresses in an armchair Single-Walled Carbon NanoTube (SWCNT) under uniaxial tension. Computation is based on molecular dynamics simulations and the virial stress theorem. The proposed approach is compared with other methods used in the literature for calculating the stresses in CNTs. The loading is applied under two different boundary conditions and different strain rates and the results are compared. It is shown that the method commonly used in the literature for calculating the stresses in CNTs under estimates the ultimate strength by around 35%. It is shown that the value of the displacement increment used to apply the tensile strain is crucial.
Advanced Integrated Cooling Systems for Thermal Management in Data Centers
Authors: Abe Yoshiyuki , Fukagaya Masato , Kitagawa Takashi , Ohta Haruhiko , Shinmoto Yasuhisa , Sato Masahide , Iimura Ken-ichi
Published: January 2011

For a drastic energy conservation in data centers (more than 30%), a new advanced concept of thermal management systems of integrated cooling network in server racks is proposed, and a series of developmental studies toward the realization of the concept have been conducted. The concept consists of the following technological items: - Plug-in thermal network cables, - Narrow channel heat exchangers (single-phase and two-phase), - Thin flat-type heat pipes, - Development of nano-fluids for heat transfer enhancement. In this concept, CPUs in server racks are directly cooled with the aid of advanced 1.5 mm thick flat-type heat pipes or 3 mm thick narrow channel heat exchangers, though CPUs in server racks, at present, are cooled down with massive heat sinks by forced air flow in the racks. In the case of heat pipes, condensation regions are cooled by either single-phase or two-phase narrow channel heat sink instead of air-cooled finned heat sink. These cooling units are accommodated in server racks. In addition, plug-in thermal network cables, in which a working fluid for narrow channel heat exchangers is running, are integrated among server racks, and thermal energy dissipated in server racks are inclusively merged and managed by the thermal network cables. The working fluid heated up by the dissipated heat is recuperated in an outdoor cooling system. An attempt at the applications of silver nano-fluids as a working fluid in heat pipes and thermal network is also conducted in the present study. Silver nano-fluids are thermochemically synthesized by a microwave heating technique, which allows for superior stable suspension characteristics.
Integrated Design and Management of a Sustainable Data Center
Authors: Watson Brian J. , Shah Amip J. , Marwah Manish , Bash Cullen E. , Sharma Ratnesh K. , Hoover Christopher E. , Christian Tom W. , Patel Chandrakant D.
Published: January 2011

The environmental impact of data centers is significant and is growing rapidly. However, there are many opportunities for greater efficiency through integrated design and management of data center components. To that end, we propose a sustainable data center that replaces conventional services in the physical infrastructures with more environmentally friendly IT services. We have identified five principles for achieving this vision: data center scale lifecycle design, flexible and configurable building blocks, pervasive sensing, knowledge discovery and visualization, and autonomous control. We describe these principles and present specific use cases for their application. Successful implementation of the sustainable data center vision will require multi-disciplinary collaboration across various research and industry communities.
The Environmental Footprint of Data Centers
Authors: Shah Amip , Bash Cullen , Sharma Ratnesh , Christian Tom , Watson Brian J. , Patel Chandrakant
Published: January 2011

Numerous evaluation metrics and standards are being proposed across industry and government to measure and monitor the energy efficiency of data centers. However, the energy use of data centers is just one aspect of the environmental impact. In this paper, we explore the overall environmental footprint of data centers beyond just energy efficiency. Building upon established procedures from the environmental sciences, we create an end-to-end life-cycle model of the environmental footprint of data centers across a diverse range of impacts. We test this model in the case study of a hypothetical 2.2-MW data center. Our analysis suggests the need for evaluation metrics that go beyond just operational energy use in order to achieve sustainable data centers.
Characterization of Cure-Dependent Viscoelastic Behavior for Molding Compound and Application to Package Warpage Simulation
Authors: Chiu Tz-Cheng , Kung Je-Li , Lai Yi-Shao
Published: January 2011

In this study a process-dependent viscoelastic model is developed for considering the constitutive relationship of an epoxy molding compound. The process dependence is realized by incorporating the phenomenological models for the cure kinetics, the cure-dependent volume shrinkage, and the cure-dependent viscoelastic stress relaxation modulus into the constitutive model for the molding compound. The cure-dependent viscoelastic model is incorporated into numerical finite element analysis to simulate warpage of an overmolded chip scale ball grid array (BGA) package under uniform cooling from reflow to room temperature. The simulation results are compared to Shadow Moire´ experimental data for validating the modeling methodology. Additional finite element analyses are performed to investigate the influence of molding compound constitutive behavior (temperature-dependent elastic or viscoelastic) on the package warpage prediction, and to consider the package warpage evolution during the post-mold curing (PMC) process.
Heat Transfer Enhancement Using Laminar Gas-Liquid Segmented Fluid Streams
Authors: Muzychka Y. S. , Walsh E. J. , Walsh P.
Published: January 2011

Heat transfer enhancement using segmented non-boiling gas-liquid streams is examined. Segmentation results in a two phase flow of liquid/gas having a constant liquid fraction, i.e. no phase change occurs. In this flow configuration, enhanced heat transfer occurs as a result of a shorter effective thermal length and internal fluid circulation in the liquid plugs. A simple theory for laminar segmented flows is developed based on Graetz theory and comparisons made with existing data from the literature and new data obtained in a companion study.
Unified Thermal and Power Management in Server Enclosures
Authors: Tolia Niraj , Wang Zhikui , Ranganathan Parthasarathy , Bash Cullen , Marwah Manish , Zhu Xiaoyun
Published: January 2011

Improving the cooling efficiency of servers has become an essential requirement in data centers today as the power used to cool the servers has become an increasingly large component of the total power usage. Unfortunately, most previous approaches have individually focused on reducing either the server power or the power used by the fans to cool the servers. This paper presents Zephyr, a systems approach to managing fan power that combines conventional server power optimizations with fan power management to optimize overall energy efficiency. By combining distributed system design with concepts from heat transfer theory, Zephyr can reduce cooling power by up to 21% when compared to a feedback-based controller and up to 30% when combined with cooling-aware workload migration policies. Overall, the combined Zephyr system can reduce total system power by up to 29% without impacting application performance.
Cooling Effect of Several Rods on a Heated Flat Surface by Impinging Jet
Authors: Ichimiya Koichi , Fujimori Yosuke
Published: January 2011

This paper describes the heat transfer and flow characteristics on / around several rods set on a flat heated surface by a single circular impinging jet. A nozzle is located (1) above the space between rods or (2) above a center rod. This system corresponds to the cooling of electric device. Three dimensional unsteady governing equations were solved numerically by using a finite difference method. The SIMPLE algorithm was employed to solve the coupling between the continuity and momentum equations through the pressure term. The QUICK scheme was implemented to calculate the convection flux through the cell faces of control volumes. Numerical conditions are Reynolds number Re = 1500, the dimensional space H/D = 0.67, a side of a rod = 10mm and a pitch of two rods in lattice arrangement Pi = 20mm. The velocity vector and temperature distribution were obtained and this temperature distribution was visualized using thermosensitive liquid crystal. The local Nusselt numbers on impingement surface and several rods were evaluated. The second nozzle position was effective for heat removal.
Evaluation of the Bonding Strength at the Three-Dimensional Vertex in Silicon-Resin Joints
Authors: Koguchi Hideo , Nakajima Masato
Published: January 2011

Portable electric devices such as mobile phone and portable music player become compact and also their performance improves. High density packaging technology such as CSP (Chip Size Package) and Stacked-CSP is needed to realize advanced functions. CSP is a bonded structure composed of materials with different properties. A mismatch of material properties may cause stress singularity at the edge of interface, which lead to the failure of bonding part in structures. Singular stress field in residual thermal stresses occurs in a cooling process after bonding the joints at a high temperature. In the present paper, the strength of interface in CSP consisted of silicon and resin is investigated. Boundary element method and an eigen value analysis based on finite element method are used for evaluating the intensity of singularity of residual thermal stresses at a vertex in a three-dimensional joint. Three-dimensional boundary element program based on the fundamental solution for two-phase isotropic body is used for calculating the stress distribution in the three-dimensional joint. Angular function in the singular stress field at the vertex in the three-dimensional joint is calculated using eigen vector determined from eigen analysis. The strength of bonding at the interface in several silicon-resin specimens with different thickness of resin is investigated analytically and experimentally. Stress singular analysis applying an external force for the joints is firstly carried out. After that, singular stress field for the residual thermal stresses varying material property of resin with temperature is calculated. Combining singular stress fields for the external force and the residual thermal stress yields a final stress distribution for evaluating the strength of interface. A relationship between the external force for delamination in joints and the thickness of resin is derived. Finally, a critical intensity of singularity for delamination between silicon and resin is determined.
Development of Boundary Condition Independent Compact Thermal Models for Opto-Electronic Packages
Authors: Raghupathy Arun Prakash , Aranyosi Attila , Ghia Urmila , Ghia Karman , Maltz William
Published: January 2011

In the current study, a network-based resistor model has been developed for thermal analysis of a complex optoelectronic package called SFP (Small Form-factor Pluggable Device). This is done using the DELPHI (DEvelopment of Libraries of PHysical models for an Integrated design) Methodology. The SFP is an optical transceiver widely used in telecommunication equipments such as switches and routers. The package has a detailed construction, and typically has four heat generating sources. The detailed model for the SFP is constructed and validated using a natural convection experiment. The validated detailed model is used for generating the Boundary-Condition-Independent (BCI) Compact Thermal Model (CTM). Codes for solving the network topology and interfacing with the optimization subroutine were written using Matlab 7. The resulting CTM is extensively validated with multiple boundary condition sets. The CTM for the SFP shows maximum relative of errors less than 10% for the junction temperature on all of its active components and less than 20% for the heat flows through its sides for extreme set of boundary conditions.
Minimum Energy Design for Manufacturability of Air Cooled Heat Sinks
Authors: Iyengar Madhusudan , Bar-Cohen Avram
Published: January 2011

The substantial material stream, and energy consumption, associated with the cooling of desktop computers, servers, routers, and power electronic modules contribute significantly to the depletion of key resources. To reduce this severe environmental impact, while meeting the thermal management requirements of these components and systems, it is essential that a minimum energy, design-for-manufacturability approach be followed in the design and commercialization of such air-cooled heat sinks. In this paper, a design-for-manufacturability methodology (DFM) is combined with a least-energy optimization methodology, using the total Coefficient of Performance (COPT), to identify practical low energy designs and existing gaps in manufacturing capability that prevent the attainment of the ideal minimum energy solutions. The COPT methodology relates the heat sink cooling capability to the invested fan pumping work and the thermodynamic work required to manufacture and assemble the heat sink and seeks to maximize the thermal energy that can be extracted from a specified space, while minimizing the material and energy consumed in the fabrication and operation of the specified heat sink. This combined methodology was applied to aluminum, copper, and magnesium as potential heat sink materials for a fixed input work of 20 kWh, and for three different duty cycles, namely, sporadic (1500 h), periodic (6000 h), and continuous (26208 h), respectively. The results presented herein, are derived for heat sinks on a 10 cm by 10 cm isothermal base, and 5 cm fin height, operating at an excess temperature of 25 K relative to the inlet air. The thermo-fluid analysis of the forced convection rectangular plate-fin array has been carried out using a well-validated semi-analytical model. The energy-optimal aluminum, copper and magnesium designs are compared to draw quantitative and qualitative conclusions.
Subcooled Flow Boiling in Mini and Micro Channel: Contribution Toward High Heat Flux Cooling Technology for Electronics
Authors: Nomura Tomoyuki , Shustov Michael V. , Suzuki Koichi , Hong Chungpyo , Kuzma-Kichta Yury A.
Published: January 2011

Subcooled flow boiling has been investigated for horizontal mini and micro channels of which hydraulic diameters are 1mm and 150μm, respectively for high heat flux cooling in electronics. The heating surface is 1mm in width and 10mm in length for the mini channel. Eleven micro grooving are made on the copper heating block of 5.25mm×5.25mm. Aqueous solutions of ethanol, 10% and 50% in mass concentration, are used as boiling liquid for the micro channel. Microbubble emission boiling (MEB) of water is generated at liquid subcooling of 40K in the mini channel as same cases of conventional macro channels and the maximum heat flux obtained is a 10MW/m2 at liquid velocity of 1m/s (1000kg/m2s). However, the boiling turns to film boiling at low liquid velocity, 0.3m/s (300kg/m2s) for an example. In subcooled boiling of aqueous solutions, the heat flux becomes small for the lower ethanol concentration. The critical heat fluxes are well agreed with the existing theories and the maximum heat fluxes are higher than CHF. However, no micro bubble emission boiling is observed in subcooled flow boiling of mini channels and the CHF is considerably smaller than the existing theories. It is difficult to generate MEB for micro channels with heating surface of large thermal capacity because the coalescing bubbles formed on the heating surface are filled up in the channel and the liquid vapor exchange is disturbed.
Peridynamic Theory for Simulation of Failure Mechanisms in Electronic Packages
Authors: Oterkus Erkan , Agwai Abigail , Guven Ibrahim , Madenci Erdogan
Published: January 2011

Peridynamic theory is employed to investigate crack propagation in a multi-layer thin-film structure of electronic packages and in single layer graphene sheets. A brief description of this non-local theory is presented. Crack propagation path in patterned multilayer thin-film structures predicted by the peridynamic theory is compared against measurements from cross-sectional nanoindentation experiments. Single layer graphene sheet simulation results are compared to molecular dynamic simulations.
Cooling Control Using by Emulsified Heat Transfer Medium
Authors: Yamasaki Hiroshi , Suzuki Kei , Ohashi Atsushi , Ujiie Yasushige
Published: January 2011

Experimental study has been conducted on the heat transfer coefficient control using by the water and silicone oil emulsions. The focus is mainly paid on the effect on the heat transfer of the ambient emulsion temperature, water content and the stirring conditions. Heat transfer on an electrically heated horizontal Pt wire was measured. It is concluded that there is the transition point in the heat transfer coefficient, which is just above the boiling point of emulsified component of water. This may be the potentially useful method for the cooling control. The mechanism of heat transfer of the emulsions has been discussed and revealed for fundamental and practical points of view.
Thermal-Structural Performance of Orthotropic Pin Fin Applications
Authors: Arif Abul Fazal M. , Zubair Syed M.
Published: January 2011

Thermally conductive composites as compared to metals have reduced density, decreased corrosion, oxidation, and chemical resistance, as well as adjustable properties to fit a given application. However, there are several challenges that need to be addressed before they can be successfully utilized in heat sink design. The interface between the device and thermal product that is used to cool it is an important factor in the thermal network designs of microelectronics cooling. Depending on the thermal interface conditions and material properties, the contact pressure and thermal stress level can attain undesirable values. In this paper, we investigate the effect of thermal interface between the fin and base plate on thermalstructural behavior of heat sinks. A coupled-field (thermal-structural) analysis using finite element method is performed to predict temperature as well as stress fields in the region of interface. In addition temperature and heat transfer rate predictions is supported through analytical results. Effect of various interface properties (such as air gap with rough surface and gaps filled with interface material) on the resulting thermal-structural response of the pin fin is investigated with respect to four interface materials combinations.
Numerical Solutions of Poisson Equation by the CIP-Basis Set Method
Authors: Shibata Daisuke , Utsumi Takayuki
Published: January 2011

An accurate and reliable real space method for the ab initio calculation of electronic-structures of materials has been desired. Historically, the most popular method in this field has been the Plane Wave method. However, because the basis functions of the Plane Wave method are not local in real space, it is inefficient to represent the highly localized inner-shell electron state and it generally give rise to a large dense potential matrix which is difficult to deal with. Moreover, it is not suitable for parallel computers, because it requires Fourier transformations. These limitations of the Plane Wave method have led to the development of various real space methods including finite difference method and finite element method, and studies are still in progress. Recently, we have proposed a new numerical method, the CIP-Basis Set (CIP-BS) method [1], by generalizing the concept of the Constrained Interpolation Profile (CIP) method from the viewpoint of the basis set. This method uses a simple polynomial basis set that is easily extendable to any desired higher-order accuracy. The interpolating profile is chosen so that the sub-grid scale solution approaches the local real solution by the constraints from the spatial derivative of the original equation. Thus the solution even on the sub-grid scale becomes consistent with the master equation. By increasing the order of the polynomial, this solution quickly converges. The governing equations are unambiguously discretized into matrix form equations requiring the residuals to be orthogonal to the basis functions via the same procedure as the Galerkin method. We have already demonstrated that the method can be applied to calculations of the band structures for crystals with pseudopotentials. It has been certified that the method gives accurate solutions in the very coarse meshes and the errors converge rapidly when meshes are refined. Although, we have dealt with problems in which potentials are represented analytically, in Kohn-Sham equation the potential is obtained by solving Poisson equation, where the charge density is determined by using wave functions. In this paper, we present the CIP-BS method gives accurate solutions for Poisson equation. Therefore, we believe that the method would be a promising method for solving self-consistent eigenvalue problems in real space.
Evaluation of the Accuracy of Out-of-Plane Normal Stress Detection Using Novel Piezoresistive CMOS Sensors
Authors: Lemke Benjamin , Baskaran Rajashree , Paul Oliver
Published: January 2011

This paper discusses the measurement opportunities arising from a novel piezoresistance sensor featuring vertical currents. Temperature-compensated measurements of a sum of the three normal stress components including the vertical normal stress, are presented. In specific applications with sensors located at free surfaces where the vertical normal stress component vanishes, a combination of this temperature-compensated measurement and a pseudo-Hall measurement yields the individual in-plane normal stresses. Furthermore, the temperature-uncompensated extraction of the vertical normal stress component is discussed with respect to the new measurement possibilities provided by the presented sensor. A sensitivity analysis illustrates the influence of individual uncertainty sources to the overall uncertainty of the measurement. Based on these results possible improvements in stress detection are suggested.
A Real-Time Data Center Airflow and Energy Assessment Tool
Authors: Zhang Xuanhang Simon , VanGilder James W. , Healey Christopher M.
Published: January 2011

A tool has been created to provide a simple assessment of airflow and energy management in an existing data center. Calculations are based on a well-mixed model of the data equivalent to the assumption that there is one effective rack and one effective cooling unit. The Air Distribution Effectiveness (ADE) index is proposed as a performance metric. For a given facility layout, ADE is a fixed number and is independent of IT load and cooler airflow. Therefore, ADE may be used as a performance metric and also to estimate rack inlet temperatures under various alternative cooler-airflow and rack-load scenarios. The tool described here may be used to determine how cooler airflow may be reduced or the chilled-water temperature may be increased to reduce data center energy consumption. The total net savings includes possible IT server fan speed (power) increases in response to inlet temperatures reaching a critical threshold value. This paper details the methods used in the software tool and shows example applications.
Sources of Fatigue in Random-Vibration Durability of Surface Mount Interconnects
Authors: Zhou Y. , Al-Bassyiouni M. , Dasgupta A.
Published: January 2011

The transient response of a PBGA256 assembly to random excitation is explored with quasi-static and transient finite element analysis, as well as with experiments. The quasi-static approximation is based on the first modal contribution to the measured PWB response. The dynamic prediction for solder strain and resulting damage accumulation rate are found to be significantly larger than in the quasi-static approximation. The quasi-static model is clearly missing additional stress drivers such as the dynamic movement of the component relative to the PWB and higher resonant modes of PWB flexure. The dynamic mode of the component is verified in this paper with two accelerometers placed on the component and on the PWB. Investigation of the higher modes of the PWB is deferred to a future study.
Improving Flow Circulation in Heat Sinks Using Quadrupole Vortices
Authors: Dake Timothy J. , Majdalani Joseph
Published: January 2011

In this paper, we show that improved air circulation above a heat sink is possible using thin winglet-type vortex generators that can be passively retrofitted to an existing unit. By mounting these vortex generators on the leading edge of heat sink fins, pairs of counter-rotating vortices are induced within the interfin spacing. The vortices disturb the boundary layers and serve to mix the air in the interfin channel. The devices we have designed are passive and can be added to existing systems using a simple clip-on mechanism. In this study, several designs are experimentally investigated for the purpose of identifying the optimal configuration that will be most conducive to flow enhancement and, therefore, heat transfer augmentation. Using the typical operational range of air velocities for PCs, routers and servers, an experimental simulation of the interfin channel reveals that certain vortex generators, when placed upstream, can outperform others in their ability to fill the channel with pairs of strong vortices. Multiple pairs can also be generated to further accentuate the heat transfer using dual vortex generators. A description of the specific shapes is furnished here along with particulars of the performance study. By control and manipulation of the vortices, our results suggest the possibility of optimizing the generator design. Experimentation was conducted in two phases. The first phase is a study of the ability to generate and control vortices within the fin channel. This aspect was simulated using a Lexan mock-up of the fin channel that permits introduction of glycerin smoke to visualize the shape, size, strength and structure of the vortices. The clear Lexan permitted viewing of the vortices by passing a red planar laser through the apparatus. The second phase involved using the optimization data gained in the first phase to generate vortices in an actual heat sink fitted with thermocouples to measure the temperatures at various points during heating.
A Capability to Model Crack Initiation and Growth in Solder Joints
Authors: Neilsen Mike , Vianco Paul , Kilgo Alice , Holm Elizabeth
Published: January 2011

A new capability to model both crack initiation and growth in eutectic Sn-Pb solder joints was developed and implemented into finite element analysis codes. Two significant developments were needed to create this new capability. First, an ability to accelerate the simulations such that the effects of hundreds or thousands of thermal cycles could be modeled in a reasonable amount of time was needed. This was accomplished by applying a user prescribed acceleration factor to specific terms in the solder model’s damage evolution equation; then, the damage generated by an acceleration factor of cycles could be captured by the numerical simulation of a single thermal cycle. Second, an ability to capture the geometric effects of crack initiation and growth was needed. This was accomplished by replacing material in finite elements that had met the cracking failure criterion with very flexible elastic material. This diffuse crack modeling approach with local finite elements is known to generate mesh-dependent solutions. However, mesh refinement studies revealed that for thermal mechanical fatigue simulations, the mesh dependency is small and has a small effect on predictions for cycles to generate an electrical open. The new crack modeling approach will be described. Finally, crack predictions are compared with experimental observations.
Fracture Life Evaluation of Cu-Cored Solder Joint in BGA Package
Authors: Tanie Hisashi , Chiwata Nobuhiko , Wakano Motoki , Fujiyoshi Masaru , Itabashi Takeyuki
Published: January 2011

A Cu-cored solder joint has an accurate height, a low thermal resistance, and a low electric resistance. However, the fracture mechanism of Cu-cored solder joints has yet to be clarified, and thus the fracture life cannot be predicted. We evaluated the fracture life of Cu-cored solder joints by using our molten-solder-shape analysis and crack-propagation analysis methods. Our molten-solder-shape analysis is based on the moving-particle semi-implicit (MPS) method. In the MPS method, a continuum is expressed as an assembly of particles. In contrast to finite element analysis (FEA), the MPS method can easily express a large deformation and any geometric topology changes, because the continuum does not need to be divided into elements. Using our molten-solder-shape analysis, we could calculate the shapes of Cu-cored solder after the reflow process. Our crack-propagation analysis has a feature where a crack initiation point and the crack propagation paths are automatically calculated and where the fracture life is quantitatively evaluated using FEA. Using our crack-propagation analysis, we could analyze the fracture mechanism of Cu-cored solder joints. By combining our molten-solder-shape and crack-propagation analyses, we could evaluate the fracture life of Cu-cored solder joints in a ball grid array package. As a result, we found that the fracture life of Cu-cored solder joints is longer than that of conventional joints. The height of a joint is one of the reasons for the improved fracture life. Since the height of a Cu-cored solder joint is controlled by the size of the core ball, the height is larger and more highly accurate than that in conventional joints. Accordingly, the solder strain and strain variation are decreased. Joint stiffness is the second reason for the improved fracture life. Cu is harder than solder, so the joint stiffness of a Cu-cored joint is greater than that of conventional joints. Accordingly, the displacement of a joint is decreased. The crack-propagation behavior is the third reason for the improved fracture life. In a conventional solder joint, a solder crack only propagates near the interface of the solder and the land. In a Cu-cored solder joint, a solder crack not only propagates near the interface of the solder and the land, but also at the interface of the solder and core ball. The crack-propagation life is longer than that in a conventional joint due to crack-path scattering. We found that the fracture life of Cu-cored solder joints is improved by using these mechanisms.
Enhancement of Condensation Heat Transfer in Micro Systems
Authors: Tokunaga Atsushi , Nagayama Gyoko , Tsuruta Takaharu
Published: January 2011

Thermal management becomes a serious concern in computer system. CPU chips are placed into small spaces with difficulty in heat diffusion. This promotes many challenges in the field of thermal management of electronics to maintain the desirable operating temperature. In order to realize the enhancement of dissipation of high heat flux from electronic components, a lot of investigations have been carried out on new cooling technology using phase change phenomena. Since the micro condenser is required in the cooling system, we are directing our attention to the enhancement of condensation heat transfer in the micro system. This study focuses on high performance of dropwise condensation heat transfer due to its small conduction resistance. In the micro systems, the interface phenomena play an important role in heat transfer. We have done dropwise condensation experiments in a high vacuum chamber system to get precise information about the vapor-liquid interface transport phenomena. Surface temperature transients are measured directly with the thin film thermocouples fabricated on the condensing surface.
Thermal Imaging of Two-Phase Coooled Microgap Channel Wall
Authors: Sheehan Jessica , Kim Dae Whan , Bar-Cohen Avram
Published: January 2011

The forced flow of dielectric liquids, undergoing phase change while flowing in a narrow channel formed between chips or a chip and a passive cover, is a promising candidate for the thermal management of high heat flux semiconductor devices. These microgap configurations provide direct contact — and hence highly efficient cooling — between a chemically-inert, dielectric liquid and the back surface of an active electronic component. However, the two-phase flow phenomena that establish the upper bound on the cooling capability of such microgap coolers are only poorly understood. In the present study, IR images of the heated surface of a two-phase microgap channel, 260 μm × 30 mm × 34mm, are obtained, through a sapphire window on the opposing wall of the channel Corrections are made for the reflection and absorption of IR radiation by the two-phase mixture flowing in the channel. Previously undetected spatial and temporal temperature variations, approaching 20 K, were observed on the surface of the microgap channel for heat fluxes of 3.2 W/cm2 and FC-72 mass flux of 35 kg/m2s. The frequency and amplitude of the observed temperature variations appear to reflect the complexity of the prevailing thermal transport phenomena and may provide evidence of local dryout in high quality annular flow in miniature channels.
The Numerical Study for the Thermal Characteristics of 3D Vertical Stacked Die Packages
Authors: Yu Chih-Kuang , Hsieh Ming-Che , Liu Chun-Kai , Dai Ming-Ji , Tain Ra-Min
Published: January 2011

In this study, the thermal simulations of 3 dimensional IC packages base on 4-layer vertical stacked die (bare die on bare die) with TSV (through silicon vias) and micro-bumps structure are conducted. The thermal models by finite volume method are developed for different geometrical parameters (TSV, micro-bumps distribution arrangement and spacer thickness) and material property (thermal conductivity of spacer). The thermal performance and the heat transfer mechanism for the stacked die package are analyzed for optimizing the geometrical and material parameters. Not only the temperature distributions but also the junction temperature and thermal resistances in 4-layer stacked die package with different multi-die power configurations are shown and discussed.
Reliability Assessment for Printed Circuit Board in Lead-Free Process
Authors: Huang Chien-Yi , Ku Chen-Liang , Hsieh Hao-Chun , Chien Tzu-Min , Huang Hui-Hua
Published: January 2011

This study aimed to explore Printed Circuit Board (PCB) failure mechanism and recommend appropriate material and handling process for the boards used in lead-free assembly process. In this study, the most stringent conditions in Printed Circuit Board Assembly (PCBA) process was used for various base-materials of PCB, such as Tg, and curing agent. In addition, thermal shock testing at 0∼100°C for 900 cycles was employed to simulate PCB performance during field service. Cross-section analysis was implemented to identify failure modes. Finally, the PCB moisture absorption property was evaluated by exposing the boards in a temperature/humidity chamber at 28°C and 60% RH, that was the worst condition in PCBA production environment. Results indicated that Tg had significant influence to the PCB quality, high Tg materials performs better. During multiple reflow process verification, cross section analysis of high Tg material indicated that Dicy material appear delamination even no electrical failure occurred. As for thermal shock test, high Tg material (either with Dicy or Phenolic curing agent) survived after 900 shock cycles. Also, moisture uptake in assembly environment, even at the worst scenario of 28°C and 60% RH for 120 hours, had not caused any PCB delamination.
Hygro-Mechanical Analysis of LCD Panels
Authors: Ikeda Toru , Mizutani Tomonori , Miyazaki Noriyuki
Published: January 2011

Liquid crystal displays (LCDs) are getting larger, and the homogeneity of an LCD panel is becoming very important for the quality of the display. Inhomogeneity in an LCD panel can be caused by inhomogeneity of its materials and the defective production process, warpage of the panel due to changes in the temperature and humidity, and so on. In this study, we developed a scheme of hygro-mechanical analysis to reduce the warpage of an LCD. First, we measured the diffusion coefficients and Henry’s law coefficients of the respective components of an LCD using a thermo-gravimetric analyzer (TGA) under controlled humidity. We then measured the coefficients of moisture expansion (CME) of the componenets using a humidity-controlled thermo-mechanical analyzer (TMA). We analyzed the hygro-mechanical deformations of the respective components, a polarizing plate and an LCD panel using the finite element method (FEM) with measured diffusion coefficients, Henry’s law coefficients and the CMEs of the respective components. The analyzed deformations of the respective components corresponded quantitatively with the deformations measured experimentally. However, the analyzed deformation of the polarizing plate did not correspond with the measured deformation perfectly. A polarizing plate is made by sandwiching a polarizer by two sheets of protective film; the effect of the thin boundary layer between the polarizer and its protecting film was ignored in this analysis. The effect of this boundary layer on the diffusion of moisture may have caused the difference between the analysis and the measurement. The expected warpage of the analyzed LCD corresponded qualitatively with the measured warpage. In LCD panels, glass plates and polarizing plates are bonded using pressure-sensitive adhesive. Slippage between the glass plates and the polarizing plates may occur during the deformation of an LCD. We investigated the warpage of LCDs with two types of protecting film and different directions of polarizing plates using the developed technique of FEM analysis.
Phase Growth Process of Sn-3.0Ag-0.5Cu Solder Joints Under Mechanical Cyclic Loading at the Same Temperature
Authors: Nakano Hiroyuki , Ejiri Yasuhiro , Mori Takao , Sayama Toshihiko , Takayanagi Takeshi , Okamoto Yoshiyuki
Published: January 2011

In order to improve the reliability of electronic devices, it is important to evaluate the thermal fatigue crack initiation lifetime of Sn-3.0Ag-0.5Cu solder joints. The phase growth parameter has been shown to be useful in estimating the thermal fatigue crack initiation lifetime of Sn-3.0Ag-0.5Cu solder joints through thermal cyclic tests. The phase growth parameter is affected by both temperature and the strain induced by the mismatch between the thermal expansion of a chip and substrate. A study of the influence of this strain on the phase growth process is important in estimating lifetime. In a previous paper, mechanical cyclic loading tests using a mini-lap joint type shear specimen at a temperature of 125°C were performed in order to evaluate the influence of the strain in Sn-3.0Ag-0.5Cu solder joints on the phase growth parameter. Moreover, an elastic-plastic-creep analysis of the solder joints under mechanical cyclic loading was carried out using a finite element method. Consequently, it was confirmed that the phase growth parameter of Sn-3.0Ag-0.5Cu solder joints was in good agreement with the creep strain. While the strain distribution in the solder joint of a mini-lap joint type specimen is nearly uniform, strain concentration exists in the actual solder joint. Therefore, in this paper, in order to clarify the phase growth process in the solder joint, which exhibits strain concentration at the joint end, a detailed finite element analysis of a mini-lap joint type specimen was performed, and the strain in the neighborhood of the joint corner was examined. The corrected increment for the phase growth parameter at the strain concentration occurrence zone is in good agreement with the master curve obtained by the thermal cycle tests of the PCB specimen. It is clear that the crack initiation life time can be evaluated using the increment of the phase growth parameter at the strain concentration occurrence zone, as same as for a PCB specimen. The phase growth parameter is considered to be the evaluation parameter corresponding to creep strain.
Thermal Shock and Drop Test Behaviour of Area Array Packages in Forward and Backward Compatible Assemblies
Authors: Chheda Bankeem V. , Sakthivelan Sathishkumar , Ramkumar S. Manian , Ghaffarian Reza
Published: January 2011

With lead-free implementation it is important to examine the behaviour of the solder joint at the component level and at the board level. Assembly related issues along with component reliability are the main focus of this experimental research. This experimental study aims to evaluate the mechanical integrity of solder joints comprising of both lead-free and SnPb alloys. Lead-free and SnPb solder pastes were used to assemble the components. This will allow us to check the forward and the backward compatibility of the solder alloys. The test vehicle considered for this study contained a variety of components such as ultra chip scale package (UCSP192), package on package (PoP), plastic ball grid array (PBGA-676 & 1156), very thin chip array BGA (CVBGA432), thin small outline package (TSOP-40 & 48), dual row micro-lead frame (DRMLF), micro-lead frame (MLF-36 & 72), and chip resistors (0201, 0402, 0603). The scope of this paper is limited to the performance evaluation for area array packages only. Solder ball alloy for the area array packages included SAC 305, SAC405, SAC105, SnAg and SnPb. Three different PCB surface finishes, electroless nickel immersion gold (ENIG), SnPb hot air solder level (HASL), and immersion silver (ImAg) were used. Different solder ball alloys and surface finish combinations provided good comparison data for investigating the assembly performance. The PCB assemblies were subjected to mechanical shock test in the as-soldered condition and also after 200 and 500 thermal shock cycles at −55 to 125°C. For the mechanical shock test, the assemblies were subjected to 30 drops from a height of 3 ft, generating an average G force of 485N. After each drop the components were checked for the continuity of the total daisy chain. The number of drops for the first failure was used in analyzing the performance of the components for various combinations. Since each component had many independent daisy chains, the failure of the individual daisy chains was later used in determining the location of the failure and how it progressed. Two sets of test vehicles were assembled. One set comprised of components with lead-free solder balls of different composition (SAC305, SAC405, SAC105, SnAg) and the other set comprised of components with lead-free solder balls and SnPb solder balls (SAC305, SAC405, SnPb). This mix of alloy composition provided adequate data for comparison. It was critical to optimize the process in order to enable the melting of the mix of alloys. The area array package performance was evaluated when assembled with lead-free and SnPb solder paste. Some of the assemblies were cross-sectioned after the tests and the microstructure of the solder joint was analyzed to study the possible cause for assembly failure.