bluuebunny/crossref_metadata_2025 huggingface dataset:
Desktop NC Machine Tool With Abilities of Compliant Motion and Stick-Slip Motion
Authors: Nagata Fusaomi , Tani Shintaro , Mizobuchi Takanori , Hase Tetsuo , Haga Zenku , Watanabe Keigo
Published: January 2011

In this paper, a new desktop NC machine tool, which has abilities of compliant motion and stick-slip motion, is first presented for finishing small metallic molds with curved surface. The NC machine tool consists of three single-axis robots with a high position resolution of 1μm. A thin wood stick tool is attached to the tip of the z-axis. The tool tip has a small ball-end shape. The control system is composed of a force feedback loop, position feedback loop and position feedforward loop. The force feedback loop controls the polishing force consisting of tool contact force and kinetic friction forces. The position feedback loop controls the position in pick feed direction, e.g., z-direction. The position feedforward loop leads the tool tip along a desired trajectory called cutter location data (CL data). The CL data are generated from the main-processor of a CAM system. The proposed NC machine tool has realized a compliant motion required for the surface following control along a spiral path. In order to improve the finishing performance, a small stick-slip motion control strategy is further added to the control system. The small stick-slip motion is orthogonally generated to the direction of the tool moving direction. Generally, the stick-slip motion is an undesirable phenomenon and should be eliminated in precision machineries. However, the proposed NC machine tool employs a small stick-slip motion to improve the finishing quality. The effectiveness of the NC machine tool was examined through an actual finishing test of a LED lens mold with a diameter of 4 mm. It was observed that the undesirable cusps can be removed uniformly. And, it was confirmed from the results that the proposed finishing strategy by using the stick-slip motion control is effective to achieve a higher quality surface like a mirror finishing.
Development of 6mil Copper Wire Bonding for Replacing 10–15mil Aluminum Wire
Authors: Jiang Yingwei , Sun Ronglu , Wang Sonder , Tan Kenny , Yu Youmin , Chen Weimin , Wei Xiao
Published: January 2011

In IC package assembly, copper (Cu) wire bonding is a developing alternative interconnection technology for its advantages of more cost saving and better mechanical and electrical characteristics than gold (Au) and aluminum (Al) wires. This paper discusses experimental development of 6mil Cu wire bonding on ASM wire bonder to replace 15mil Al wire in a power IC package. It covers wire and tool selection, wire bonding process development, wire bonding integrity inspection and reliability study. The wire and tool selection includes wire type, capillary and wire bonder. The process development focuses on two crucial stages, Free Air Ball (FAB) formation and bonding process window development. DOE approach is introduced into the process development. The experimental studies show that flow rate of forming gas is a key factor to form the qualified FAB and a workable process window is established. Wire pull and ball shear tests are conducted to measure wire bonding strength of the built samples based on the criteria of JEDEC. Meanwhile, crater test and Zygo’s 3-D measurement are carried out to inspect any risk of underlying metal integrity in die before reliability tests. The data discloses that sufficient Al bond pad thickness is needed to avoid underlying metal damage during bonding process. The results of the two reliability tests, High Temperature Baking (HTB) and Pre-Condition (PC) & Temperature Cycle (TC), show that Cu/AL IMC growth is slow and accordingly lifetime of product may significantly extend. The overall result of the study finally indicates that with current thermosonic ball bonder, 6mil Cu wire is feasible to replace heavy 10–15mil Al wire in power package assembly.
Thermal Modeling of Snap-In Type Electrolytic Capacitors in Electronic Equipment
Authors: Koizumi Katsuhiro , Ishizuka Masaru , Nakagawa Shinji
Published: January 2011

The electrolytic capacitor is one of the most important components for the thermal analysis of electronic equipment. To predict component and system temperatures, the thermal flow simulation technique has been applied to thermal design in the development phase of electronic equipment. In this study, we examined a compact modeling method for electrolytic capacitors in order to simulate thermal flow based on the computational fluid dynamics (CFD) code. To obtain fundamental data for the thermal modeling method, first, we conducted experiments to identify the major thermal path of electrolytic capacitors in actual electronic equipment by using a switch mode power supply unit. Next, to verify the validity of the thermal model, a benchmark experiment was conducted to obtain actual measurement data of the temperature rise of electrolytic capacitors under various operating conditions. The thermal model of the electrolytic capacitor was presented based on the CFD code, which is a commercially available thermal flow simulation tool. In this paper, we describe in particular the snap-in type electrolytic capacitor.
Fast Thermal Analysis of Vertically Integrated Circuits (3-D ICs) Using Power Blurring Method
Authors: Park Je-Hyoung , Shakouri Ali , Kang Sung-Mo
Published: January 2011

CMOS VLSI technology has been facing various technical challenges as the feature sizes scale down. To overcome the challenges imposed by the shrink of the conventional on-chip interconnect system in IC chips, alternative interconnect technologies are being developed: one of them is three dimensional chips (3D ICs). Even though 3D IC technology is a promising solution for interconnect bottlenecks, thermal issues can be exacerbated. Thermal-aware design and optimization will be more critical in 3D IC technology than conventional planar IC technology, and hence accurate temperature profiles of each active layer will become very important. In 3D ICs, temperature profile of one layer depends not only on its own power dissipation but also on the heat transferred from other layers. Thus, thermal considerations for 3D ICs need to be done in a holistic manner even if each layer can be designed and fabricated individually. Conventional grid-based temperature computation methods are accurate but are computationally expensive, especially for 3D ICs. To increase computational efficiency, we developed a matrix convolution technique, called Power Blurring (PB) for 3D ICs. The temperature resulting from any arbitrary power dissipation in each layer of the 3D chip can be computed quickly. The PB method has been validated against commercial FEA software, ANSYS. Our method yields good results with maximum error less than 2% for various case studies and reduces the computation time by a factor of ∼ 60. The additional advantage is the possibility to evaluate different power dissipation profiles without the need to re-mesh the whole 3D chip structure.
Integrating an Electronics Component Database Into a Thermal Design Tool
Authors: Loney Patrick
Published: January 2011

When developing a thermal model of a highly populated electronics board, a significant amount of time and effort is needed to track the thermal characteristics of all the dissipating components. In business sectors where multiple boards are thermally designed and analyzed each year, developing a components database and integrating it into the analysis tool will save time and ensure that consistent values are used in every design. With an “in tool” component database, multiple advantages are achieved. Once a component is entered into the database, the component information can be accessed in subsequent designs that employ the component. All engineers doing thermal design have access to the database. Once the thermal characteristics of a component are agreed upon, consistency across all boards is maintained. Additionally, values for each component in the database can be automatically brought into the analysis tool. By making a computer program develop the model of the component, human error is removed. The database tracks all major thermal aspects of a component. This includes the maximum junction temperature, Theta JC (case to junction resistance), leg/pin configuration (size, length, number, conductivity), and board to case gap thickness. Optional values can include top side cooling resistance, performance temperature limits, manufacturer, datasheet web address, and even an entry to identify the configuring engineer.
Effect of Design Parameters on Thermo-Mechanical Stresses in 3D ICS
Authors: Ladani Leila J.
Published: January 2011

Solid Liquid Inter-diffusion (SLID) bonds have been recently utilized to fabricate 3-dimensional integrated circuits (3D ICs). Introduction of this new technology in the production of electronic devices has enabled the electronic industry to produce super high density interconnects and vertical integration of ICs without manufacturing and environmental limitations of conventional solder interconnects. The properties of these bonds however are completely different from conventional solder joints. This manuscript presents a microstructural characterization of these bonds. This analysis shows that the bond mostly consist of intermetallic material, therefore may not behave visco-plastically under thermo-mechanical loading. A numerical experiment is conducted to evaluate the effect of design parameters such as underfill properties, die thickness, interconnect size and substrate thickness on stress level in SLID bonds and copper interconnects. A finite element model was built for all the treatments of the experiment and von mises stress at the copper interconnects and SLID bonds were obtained from finite element. Statistical analysis of the results was conducted to determine the main effects of selected parameters. This analysis shows that die and substrate thicknesses and underfill stiffness are the most influential factors among the selected parameters on stress on copper interconnects. Main effect results for stress analysis in SLID bonds using finite element shows that die thickness and underfill stiffness are the most influential factors in defining stress at SLID bonds. Both factors show higher stress at higher levels.
Effects of Enhanced Surface Inclination on Pool Boiling of a Dielectric Fluid
Authors: Chien Liang-Han , Lee Shu-Che
Published: January 2011

The manuscript presents an experimental study of inclination and pin-finned surfaces on nucleate boiling in FC-72 of saturated 50°C. The orientation angle of test surface from horizontal plane was varied from 0° (upper surface) to 90° (vertical surface). The boiling surfaces include a plain surface, a straight surface (C-0.2-0.5) and a pin-finned surface (P-0.2-0.5), whose fin width, fin height, and fin gap are 0.2mm, 0.5mm and 0.2mm. The effect of the surface inclination angle is notable at the increasing heat flux tests, while no marked effect is observed at the decreasing heat flux tests. With 10K superheat, the straight fin surface(C-0.2-0.5) and pin-finned surface (P-0.2-0.5) enhanced the boiling performance by approximately 6.7 and 7.5 folds, respectively. The enhancement is attributed to the increased surface area, the increased nucleation sites and the proper fin and gap widths.
An Improved Network Model for Determining the Effective Thermal Conductivity of Particulate Thermal Interface Materials
Authors: Dan Bo , Kanuparthi Sasanka , Subbarayan Ganesh , Sammakia Bahgat G.
Published: January 2011

Thermal Interface Materials (TIMs) are particulate composite materials widely used in the microelectronics industry to reduce the thermal resistance between the device and heat sink. Predictive modeling using fundamental physical principles is critical to developing new TIMs since it can be used to quantify the effect of particle volume fraction and arrangements on the effective thermal conductivity. The existing analytical descriptions of thermal transport in particulate systems do not accurately account for the effect of inter-particle interactions, especially in the intermediate volume fractions of 30%–80%. An efficient Random Network Model (RNM) that captures the near-percolation transport in these particle-filled systems, taking into account the inter-particle interactions and random size distributions, was previously developed by the authors. The RNM is computationally efficient compared to full field simulations and was demonstrated to match to within 5% of the full field simulations and to within 15% of the experimentally measured values. The RNM approach uses a cylindrical region to approximate the thermal transport within the filler particles and to capture the inter-particle interactions. This approximation is less accurate when the polydispersivity of the particulate system increases. In the present paper, a novel semi-spherical approximation to the conductance of the fillers is presented as an alternative to the cylindrical region approximation used earlier. The new semi-spherical model is compared to the cylindrical model in two and three dimensions. In two dimensions, the semi-spherical model and the cylindrical model were compared with Finite Element Model (FEM) results. The comparison showed that the temperature distribution of the semi-spherical model matched more closely to the FEM model than the temperature distribution of the cylinder model when the radius ratio of the two particles increases. In three dimension microstructures, the semi-spherical model and the cylindrical model were compared under various volume fractions. The comparison showed that thermal conductivities of the semi-spherical model were always higher than thermal conductivities of the cylindrical model and were in better agreement with existing experimental data for particulate TIMs at 58% volume loading.
High Performance Flip Chip Package With Higher Mountability and Longer Interconnect Life
Authors: Katsurayama Satoru , Tohmyoh Hironori , Saka Masumi
Published: January 2011

Generally, underfill material is adopted for encapsulation of flip chip package. And, the role of the underfill materials has become important day by day due to variant requirements for higher reliability of flip chip package. Also lower warpage gives higher mount-ability of the flip chip package and the small changes in the warpage of the package during the thermal cycle mitigate the stress working at the bump/substrate interface and bump/chip interface. Therefore, controlling the warpage of the flip chip package becomes very important problem for enhancing the performance of the package, i.e., the higher mount-ability and longer interconnect life. In this study, the effect of physical properties of underfill materials and substrates on the warpage behavior and the interconnect reliability of the flip chip package is reported. It was found from the experiments that the selection of an underfill and a substrate gave the highest interconnect reliability for the bump bonds. In addition to control the warpage behavior of the package during assembly, by selecting the suitable underfill material and substrate, the flip chip package with lower warpage and higher interconnect reliability can be realized.
Coupled Electro-Thermal Simulation of MOSFETs
Authors: Ni Chunjian , Aksamija Zlatan , Murthy Jayathi Y. , Ravaioli Umberto
Published: January 2011

Thermal transport in metal-oxide-semiconductor field effect transistors (MOSFETs) due to electron-phonon scattering is simulated using phonon generation rates obtained from an electron Monte Carlo device simulation. The device simulation accounts for a full band description of both electrons and phonons considering 22 types of electron-phonon scattering events. Detailed profiles of phonon emission/absorption rates in the physical and momentum spaces are generated and are used in a MOSFET thermal transport simulation with a recently-developed anisotropic relaxation time model based on the Boltzmann transport equation (BTE). Comparisons with a Fourier conduction model reveal that the anisotropic heat conduction model predicts higher maximum temperatures because it accounts for the bottlenecks in phonon scattering pathways. Heat fluxes leaving the boundaries associated with different phonon polarizations and frequencies are also examined to reveal the main modes responsible for transport. It is found that though the majority of the heat generation is in the optical modes, the heat generated in the acoustic modes is not negligible. The modes primarily responsible for the transport of heat are found to be medium-to-high frequency acoustic phonon modes.
Effect on Inlet Vent Porosity on Fan Characteristic Performance for Electronics Cooling
Authors: Fukue Takashi , Koizumi Katsuhiro , Ishizuka Masaru , Nakagawa Shinji
Published: January 2011

Critical fan performance metric such as characteristic output curves and maximum flow rates are affected by various environmental conditions where cooling fans are installed. This paper describes the relationship between the fan performance and configuration factors such as the flow inlet porosity of electronic enclosure, the flow obstacles which imitate high-density packages and narrow flow area configurations. We installed a test enclosure in front of a test fan and measured P-Q curves of the test fan, which were operated in the enclosure. The experiments, it was observed that the pressure difference was increased in the enclosure by the effects of a wall. We installed a perforated plate in front of the fan as an obstacle and investigated how this changed the P-Q curve. In general, addition of the perforated plate in front of the fan decreased the characteristic output of the fan. On the other hand, the flow rate by the fan supply was decreased by the existence of the narrow inlet or obstacles. When an opening area in front of a fan became smaller than double of the fan flow area, the flow rate was significantly decreased. In addition, it was observed that the maximum flow rate depended on the opening area ratio. Finally, a model for predicting flow rates decreases by the enclosure inlet and obstacles was proposed.
Angular Offset Splicing of Polarization Maintained (PANDA) Optical Fibers in an Electronics Manufacturing Environment
Authors: Kulkarni Rohan , Srihari Krishnaswami
Published: January 2011

Panda fibers are used in applications where polarized light is required as an input. Panda fibers do not polarize the light passed through them but maintain the polarization of the incident light. The focus of this research endeavor is restricted to the angular offset splicing process of Polarization Maintaining (PM) panda fibers during optoelectronic assembly. In the splicing process, two or more fiber ends are fused together using a high electric discharge in such a manner that a minimum amount of losses are introduced [1]. However, in this particular research effort, angular offset was used to perform the splicing of panda fibers. Angular displacement is not desired during the splicing of panda fibers as it introduces losses due to phase changes that are caused because of the misalignment of stress rods. This study observes the effects of angular displacement on the splice loss. This paper focuses on the angular offset splicing of Panda fibers. The objective of the study was to observe the effect of angular displacement on the splice loss during the angular offset splicing process for panda fibers and outline the splicing parameters that have a significant impact on the splice loss. A design of experiments (DOE) approach has been used to perform the splicing. Even though the splicer provides a loss estimate, a real time splice loss measurement set up using a power meter and source was used to measure the actual loss. Offset distance, target loss and angular displacement were the factors selected for experimentation. Experiments were conducted using the aforementioned parameters. An effort has been made to obtain ‘best’ combination values for the significant parameters that can be used for production in an Electronic Manufacturing Services (EMS) provider’s environment.
An Optimization Design for a MEMS Fabricated Jet Impingement Cooling Device
Authors: Won Yoon Jin , Lee Jae ho , Wang Evelyn N. , Goodson Kenneth E. , Kenny Thomas W.
Published: January 2011

This paper discusses a novel design for cooling microprocessors using micro fabricated water impinging jet on a hot surface in contact with an electronic device. The goal is to achieve enhanced heat transfer from the exposed surface, especially at localized “hot spot” regions, with minimum pressure drop to achieve the flow rate necessary. The proposed methodology is used to analyse cooling performance in our test structures, get temperature data, and extract heat transfer coefficient from the model. Based on this analysis with various design, optimisation of these design parameters will be studied to improve designs of liquid jet impingement for electronic cooling.
A Molecular Dynamics Study of Thermal Conductivity in Nanocomposites via the Phonon Wave Packet Method
Authors: Tian Zhiting , Kim Sang , Sun Ying , White Bruce
Published: January 2011

The phonon wave packet technique is used in conjunction with the molecular dynamics simulations to directly observe phonon scattering at material interfaces. The phonon transmission coefficient of nanocomposites is examined as a function of the defect size, thin film thickness, orientation of interface to the heat flow direction. To generalize the results based on phonons in a narrow frequency range and at normal incidence, the effective thermal conductivity of the same nanocomposite structure is calculated using non-equilibrium molecular dynamics simulations for model nanocomposites formed by two mass-mismatched Ar-like solids and heterogeneous Si-SiCO2 systems. The results are compared with the modified effective medium formulation for nanocomposites.
Effect of Thermal Contact Resistance on Optimum Mini-Contact TEC Cooling of On-Chip Hot Spots
Authors: Litvinovitch Viatcheslav , Bar-Cohen Avram
Published: January 2011

Shrinking feature size and increasing transistor density, combined with the high performance demanded from next-generation microprocessors and other electronic components, have lead to the emergence of severe on-chip “hot spots,” with heat fluxes approaching — and at times exceeding — 1 kW/cm2. The cost-effective thermal management of such chips requires the introduction and refinement of novel cooling techniques. Mini-contact enhanced, miniaturized thermoelectric coolers (TECs) have been shown to be a viable approach for the remediation of on-chip hot spots, but their performance is constrained by the thermal resistance introduced by the attachment of this thermal management device. This paper uses a detailed finite-element package-level model to examine the parasitic effects of the thermal contact resistance (at the interfaces of the mini-contact and TEC) on the cooling efficacy of this thermal solution. Particular attention is devoted to the deleterious effect of contact resistance on the thermoelectric leg height and the mini-contact size required to achieve the greatest hot spot temperature reduction on the chip. Data from experiments with TECs (with a leg height of 130 μm) combined with several sizes of mini-contact pads, are used to validate the modeling approach and the overall conclusions.
Remaining Useful-Life Based on Damage Pre-Cursors for Leadfree Electronics Subjected to Multiple Thermal-Environments
Authors: Lall Pradeep , Vaidya Rahul , More Vikrant , Suhling Jeff , Goebel Kai
Published: January 2011

Electronic assemblies deployed in harsh environments may be subjected to multiple thermal environments during the use-life of the equipment. Often the equipment may not have any macro-indicators of damage such as cracks or delamination. Quantification of thermal environments during use-life is often not feasible because of the data-capture and storage requirements, and the overhead on core-system functionality. There is need for tools and techniques to quantify damage in deployed systems in absence of macro-indicators of damage without knowledge of prior stress history. The presented PHM framework is targeted towards high reliability applications such as avionic and space systems. In this paper, Sn3.0Ag0.5Cu alloy packages have been subjected to multiple thermal cycling environments including −55 to 125C and 0 to 100C. Assemblies investigated include area-array packages soldered on FR4 printed circuit cards. The methodology involves the use of condition monitoring devices, for gathering data on damage pre-cursors at periodic intervals. Damage-state interrogation technique has been developed based on the Levenberg-Marquardt Algorithm in conjunction with the microstructural damage evolution proxies. The presented technique is applicable to electronic assemblies which have been deployed on one thermal environment, then withdrawn from service and targeted for redeployment in a different thermal environment. Test cases have been presented to demonstrate the viability of the technique for assessment of prior damage, operational readiness and residual life for assemblies exposed to multiple thermo-mechanical environments. Prognosticated prior damage and the residual life show good correlation with experimental data, demonstrating the validity of the presented technique for multiple thermo-mechanical environments.
Assessment of Alpha Emissivity of Packaging Materials and Method to Improve the Measurement Accuracy
Authors: Su Peng , Wong Rick , Wen Shi-Jie , Li Li
Published: January 2011

Alpha emission from packaging materials is one of the major contributors for soft errors. Because of these materials’ immediate contact or close proximity to active areas of the silicon, even small increase in alpha emissivity may have significant impact on the performance of the device. In this work, we present the analytical steps to identify materials and manufacturing steps that caused high soft error rates for flip chip devices. We will also present some experimental results to highlight the impact of assembly process control. The results from these studies suggest that to minimize the impact of alpha emission from packaging materials, material set selection and assembly process control must be addressed simultaneously to ensure robust device performance.
Mechanical Design Optimization of a Package on Package
Authors: Menon Abhilash R. , Lakhkar Nikhil , Karajgikar Saket , Agonafer Dereje
Published: January 2011

In the past decade, compact components such as Chip Scale Packages and flip chips were the work horses of miniaturization. However, emerging applications are now demanding even higher packaging density. In order to fulfill this requirement, three dimensional packaging was evolved. Advantages of three dimensional packaging structure include minimal conductor length and eliminate speed limiting inter chip interconnects. In order to reduce signal delays and to increase heat dissipation, lot of solutions like through silicon vias, thermal vias, stacking were implemented. Stacked packages are finding applications ranging from high-end servers to mobility products. Most common applications of stacked packages include high performance memory, DRAM, logic-memory stack, system in a package etc. Stacked packages can be package-on-package or die stacked (with several dice inside the same casing) or both. The thermo-mechanical design of package on package is very complex and often requires elaborate models and analysis with considerable CPU time. In this paper we have considered a package with both die stacking and package on package. In the first part of this study we considered a variety of cases resembling the applications that stacked CSP can go into. In this study, we have considered various geometries to optimize the design mechanically in thermo-cycling loading. The optimization function for this study is to minimize the package height without compromising its reliability in terms of thermo-cycles. “Package on package” family of packages is expensive to operate and to fabricate hence a prior simulation of various geometry of interconnects is necessary to understand how the package is going to behave in terms of number of cycles. In this study we have considered different thicknesses of die, die attach, top substrate and bottom substrate to optimize solder joint fatigue life. In this study SAC405 is considered.
Aging Effects on the Mechanical Behavior and Reliability of SAC Alloys
Authors: Zhang Yifei , Cai Zijie , Suhling Jeffrey C. , Lall Pradeep
Published: January 2011

The microstructure, mechanical response, and failure behavior of lead free solder joints in electronic assemblies are constantly evolving when exposed to isothermal aging and/or thermal cycling environments. In our prior work on aging effects, we have demonstrated that the observed material behavior variations of Sn-Ag-Cu (SAC) lead free solders during room temperature aging (25°C) and elevated temperature aging (125°C) were unexpectedly large and universally detrimental to reliability. Such effects for lead free solder materials are especially important for the harsh applications environments present in high performance computing and in automotive, aerospace, and defense applications. However, there has been little work in the literature, and the work that has been done has concentrated on the degradation of solder ball shear strength (e.g. Dage Shear Tester). Current finite element models for solder joint reliability during thermal cycling accelerated life testing are based on traditional solder constitutive and failure models that do not evolve with material aging. Thus, there will be significant errors in the calculations with the new lead free SAC alloys that illustrate dramatic aging phenomena. In the current work, we have extended our previous studies to include a full test matrix of aging temperatures and solder alloys. The effects of aging on mechanical behavior have been examined by performing stress-strain and creep tests on four different SAC alloys (SAC105, SAC205, SAC305, SAC405) that were aged for various durations (0–6 months) at room temperature (25°C), and several elevated temperatures (50, 75, 100, and 125°C). Analogous tests were performed with 63Sn-37Pb eutectic solder samples for comparison purposes. Variations of the mechanical and creep properties (elastic modulus, yield stress, ultimate strength, creep compliance, etc.) were observed and modeled as a function of aging time and aging temperature. In this paper, we report on the creep results. The chosen selection of SAC alloys has allowed us to explore the effects of silver content on aging behavior (we have examined SACN05 with N = 1%, 2%, 3%, and 4% silver; with all alloys containing 0.5% copper). In order to reduce the aging induced degradation of the material behavior of the SAC alloys, we are testing several doped SAC alloys in our ongoing work. These materials include SAC0307-X, SAC105-X, and SAC305-X; where the standard SAC alloys have been modified by the addition of small percentages of one or more additional elements (X). Using dopants (e.g. Bi, In, Ni, La, Mg, Mn, Ce, Co, Ti, etc.) has become widespread to enhance shock/drop reliability, and we have extended this approach to examine the ability of dopants to reduce the effects of aging and extend thermal cycling reliability.
Superior Thermal Interfaces Made by Metallically Anchored Carbon Nanotube Arrays
Authors: Hu Xuejiao , Pan Lawrence S. , Gu Gang , Goodson Kenneth E.
Published: January 2011

Vertically aligned carbon nanotube arrays (CNAs) have received much interest for thermal interface applications due to the extremely high thermal conductivity of carbon nanotubes (CNTs) and the compliant mechanical properties of the CNA film. The challenge has been the big contact thermal resistance between the CNA tips and the opposing surface, which has resulted in the overall thermal performance of CNA TIMs far below expectation. We developed a process to metalize the CNA tips, and then firmly weld the tips to the back side metal of the SiO2/Si substrates using indium solder. We achieved close to 1 mm2K/W total interface thermal resistance (1.4 mm2K/W estimated from infrared thermal microscopy and 1.3±0.3 mm2K/W measured using a 3-omega method) with nearly zero compression pressures. This thermal resistance value is about one order of magnitude smaller than that of the thermal interfaces used for the state-of-the-art microprocessors.
Major Considerations in System-Level Thermal Design of Next-Generation Telecommunications Equipment
Authors: Yuan Lang , Patel Jignesh
Published: January 2011

The thermal management of next-generation telecommunications equipment is becoming more challenging than ever before, thanks to the elevated ambient temperature requirements (up to 65°C) from network carriers, and the thermal limitation of critical components such as optical transceivers (with a max. rating of 85°C). With thousands of watts of heat dissipation from a single shelf, a systematic methodology has to be developed at the planning stage so that every possible means to streamline the thermal management can be integrated into the system-level design. This paper uses a next-generation fiber-optic telecom product as an example to demonstrate the impact of some major mechanical/electrical parameters (such as fan curve, acoustic noise, air filter, copper content of PCB and baffles, etc.) on the thermal performance of the system. Each factor is quantitatively analyzed based on field tests, and good design practices are suggested.
Characterization of Viscoelasticity of Molding Compounds in Time Domain
Authors: Chae Seung-Hyun , Zhao Jie-Hua , Edwards Darvin R. , Ho Paul S.
Published: January 2011

Although polymer-based materials are widely used in microelectronics packaging and viscoelasticity is an intrinsic characteristic of polymers, viscoelastic properties of polymeric materials are often ignored in package stress analyses due to the difficulty of measuring this property. However, it is necessary to consider the viscoelastic behavior when an accurate stress model is required. Viscoelastic properties of materials can be characterized either in the time domain or frequency domain. In this study, stress relaxation experiments were performed on a molding compound in the time domain. Prony series expansion was used to express the material’s relaxation behavior. Thermo-rheologically simple model was assumed to deduce the master curve of relaxation modulus using the time-temperature equivalence assumption. Two methods were compared to determine the Prony pairs and shift factor.
Mechanistic Model for Aging Influenced Steady State Flow Behavior of Sn3.8Ag0.7Cu Solder Alloys
Authors: Mysore K. , Chavali S. , Chan D. , Subbarayan G. , Dutta I. , Gupta V. , Edwards D.
Published: January 2011

Sn3.8Ag0.7 Cu solder alloys age even at ambient temperatures. This significantly affects both microstructure and behavior of these alloys. In this work, aging influences on both are addressed. In particular, we discuss (a) honey comb type microstructure patterns in unaged samples and their subsequent evolution into a coarsened random microstructure at prolonged aging durations (b) aging effects on primary, secondary creep and on a range of applied loads and test temperatures through double lap shear experiments; the results show an increased tendency of aged solders to flow (c) a modified power law creep-plasticity model to predict aging effects on behavior. Possible mechanisms that result in the above behavior are also discussed; they motivate the mechanistic basis for the developed aging-informed behavior model, (d) procedures to compare alloys in terms of aging effects. Steady state creep strains, monotonic plastic strains and unified creep-plasticity theory are also discussed. Aging temperatures of −10 °C, 25°C, 75°C and 125°C, and aging times of 15, 30, 60 and 90 days (at each aging temperature) were selected as different levels of factors in a statistically designed experiment to study aging effects. Test specimens were selected with due pre-test considerations to joint-geometry, associated stress heterogeneity and joint-microstructures.
Characterization of Crack Fronts in a WLCSP Package: Experiments and Models for Application of a Multiscale Fracture Theory
Authors: Chan Dennis , Bhate Dhruv , Subbarayan Ganesh , Nguyen Luu
Published: January 2011

Extensive failure analysis was performed on identical, isothermally cycled wafer-level chip scale packages with Sn3.8wt%0.7wt%Ag (SAC387) solder joints. Packages were periodically removed during the cycling process to observe crack front progression. The packages were dipped in liquid nitrogen to reduce solder ductility and then pried apart. The crack areas were observed under an optical microscope. The average crack areas on the corner and mid-edge joints of the package were measured using an image processing software. 50 packages were characterized from 240 to 7200 cycles at every 240 cycles. An average of 20 solder joints per cycle was observed to estimate the crack length and area. A finite element model of this package was constructed in ABAQUS. The solder interconnects of the model were given full plastic and creep properties. Using the failure analysis data and the finite element model, the material constant value in a previously developed hierarchal fracture model was calibrated for SAC387. The ability of the model to predict non-intuitive failure initiation sites due to the under bump metallurgy (UBM) geometry is demonstrated. The hierarchal fracture process model was inspired by information theory and continuum thermodynamics. It was earlier proposed to capture the length-scale and temporal hierarchy inherent in quasi-static fracture processes. This single parameter model allows for a non-empirical, geometry independent approach to predicting crack growth by relating equivalent inelastic dissipations and a material constant to the probability of fracture at a material point.
Thermal Performance of a Mini Liquid-Cooled Cold Plates for Robot Cooling
Authors: Karng Sarng Woo , Hwang Kyudae , Moon Jongmin , Kim Seo Young
Published: January 2011

Thermal performance for mini water-cooled cold plates covered with non-metallic polycarbonate (PC) is experimentally measured in this study. The mini cold plates are designed to reduce the overall weight of the cooling device for effective heat dissipation from a humanoid robot. The water-cooled cold plate has a 10×10 mm2 of base plate which is made of copper or aluminum. Two different types of enhanced surfaces are considered in the present study: copper pin-finned surface of 0.5×0.5 mm2 area and 1.5 mm high with 0.5 mm fin spacing and aluminum foam-finned surface of 92% porosity and 40 PPI (pores per inch). Heat transfer rates are measured according to the input power and the flow rate of cooling water. The surface temperature of the base plate and the cooling water temperatures at inlet and outlet of each cold plate are measured. From the results, it is found that the copper pin-finned cold plate shows better performance than the aluminum foam-finned cold plate in terms of thermal resistance and pressure drop.
Modeling Nanomechanical Strains in Healthy and Diseased Single-Cells Due to Applied Fluidic Stresses
Authors: Wilson Zachary D. , Kohles Sean S.
Published: January 2011

Advancements in technologies for assessing biomechanics at the cellular level have led to discoveries in the relationship between mechanics and biology (mechanotransduction) and the investigation of cell mechanics as a biomarker for disease [1]. With the recent development of an integrated optical tweezer with micron resolution particle image velocimetry (436 nm spatial resolution), the opportunity to apply controlled multiaxial stresses to suspended single cells is available [2]. A stress analysis was applied to experimental and theoretical flow velocity gradients of suspended cell-sized polystyrene microspheres in microfluidic environments representing the relevant geometry of non-adhered spherical cells as observed for osteoblasts, chondrocytes, and fibroblasts [3]. That analysis identified a very low level of applied stresses available during creeping laminar flow within straight and cross-junction microfluidic channel arrangements with uniform and extensional flows, respectively. As a followup study, the objective here was to apply a range of normal and shear stress profiles in a two-dimensional, computational analysis and estimate the responding cellular strains.
Simultaneous Measurements of Diffusion Coefficient on Cell Membrane by Fluorescence Photobleaching and Single Quantum Dot Tracking Techniques
Authors: Lee Donghee , Lee Jeonghoon , Park Choonho , Kim Jung Kyung
Published: January 2011

The diffusion of biomolecules in plasma membranes is the key mechanism of their transportation. Lipid rafts, which are diffused on a plasma membrane, carry receptors and proteins. Receptors become the passages where viruses invade, and proteins play an important role in signaling and controlling functions of cells. If we know the characteristics of biomolecular motility and structural differences between normal cells and diseased cells, we could find out how to treat the disease. So, it is very important to develop the method which analyzes the dynamic biomolecular movement in the cell membrane.
Effects of an Experimental Drug, Suberoylanilide Hydroxamic Acid (SAHA), on Attachment, Spreading, and Stiffness of Human Breast Cancer Cells on Silicon Substrates
Authors: Strobl Jeannine S. , Nikkhah Mehdi , Rhoades Robert , Agah Masoud
Published: January 2011

We are investigating silicon-based platforms for detection and analysis of breast cancer cells. Attachment and spreading of MDA-MB-231 human metastatic breast cancer cells was compared to that of non-tumorigenic human breast epithelial cells, MCF-10A, and the impact of SAHA (Vorinostat), a histone deacetylase (HDAC) inhibitor, on cell behaviors was ascertained. Our results showed the cancer cells attached to flat silicon and PECVD nitride-coated silicon more efficiently than non-cancer cells, and preferential cancer cell attachment was enhanced by SAHA. Fluorescent immunohistochemistry (IHC) revealed that SAHA stimulated actin stress fiber formation and focal adhesion to the substrates; atomic force microscopy (AFM) showed SAHA increased the cancer cell stiffness. Collectively, SAHA-induced biomechanical changes altered the cell morphology and mode of attachment to flat silicon and to three-dimensional silicon microstructures. This is the first report of the use of AFM to characterize the biomechanical effects of a HDAC inhibitor in cancer cells.
Gold Nanoshell Mediated Heating of Brain Tumors
Authors: Shetty Anil M. , Schwartz Jon A. , Yung Joshua , McNichols Roger J. , Price Roger , Hazle John D. , Stafford R. Jason
Published: January 2011

Primary brain tumors are treated surgically or with stereotactic radiation but often residual positive margins lead to recurrence. While these approaches have success, recurrences have more limited options. These approaches also cause serious functional impairment, and treatment of a recurrent tumor in a previously irradiated or post-surgical fibrosed field is a difficult problem [1]. A controlled minimally invasive alternative is the proposed treatment of nanoshell mediated heating with intratumoral fiber placement to overcome the light penetration limitation of surface illumination.
Development of a Peroxidase Biosensor for the Detection of Endocrine Disrupting Chemicals (EDCs)
Authors: Gonza´lez Camille , Va´zquez Anai´s , Morales Angel , Di´az Liz , Cabrera Carlos R. , Griebenow Kai
Published: January 2011

Endocrine disruptor compounds are able to mimic or antagonize the effects of endogenous hormones. Phenolic compounds are one of the most abundant classes of endocrine disruptors due to their presence in a broad range of chemical manufacturing processes. The detection of such compounds in food, medicine, and the environment (i.e., water) is crucial to ensure their quality. To prevent the noxious effects of endocrine disruptors an efficient monitoring system is required in order for immediate remediation to be activated. The long-term goal of the project is to develop a robust and stable amperometric enzyme based biosensor able to determine the concentration of phenolic endocrine disruptors. This type of biosensor can be useful to monitor endocrine distruptors in biological fluids and environmental samples as for example the spacecraft drinking water, to ensure the health of the astronauts in space.
Poly-Silicon Nanowire FET Chemical Sensor
Authors: Lin Chih-ting , Huang Che-wei , Wang Jui-ching
Published: January 2011

Based on the improvements of the fabrication technologies, the dimension of the device has decreased to tens of nanometer. The nano-technology has become intriguing to integrate semiconductor technologies into bio-related applications. As the consequence, silicon nanowires (Si NWs) have been proposed to detect proteins, DNA, virus, and ions etc. However, few of previous studies consider the possibility to merge with CMOS standard process. In this work, we announced CMOS compatible technique which is used to develop polysilicon nanowire field effect transistor (poly-Si NW FET) as a chemical sensor to address this issue.
Fibrin Networks Sustain Large Extensions Due to Unfolding Proteins
Authors: Purohit Prashant K.
Published: January 2011

Blood clots and thrombi consist primarily of a mesh of branched fibers made of the protein fibrin. We show how these networks give rise to the remarkable extensibility and elasticity of blood clots by determining structural and mechanical properties of the clot at the network, fiber, and molecular levels. The force required to stretch a clot initially rises almost linearly and is accompanied by a dramatic decrease in the clot volume. These macroscopic changes are accompanied by fiber alignment and bundling following forced protein unfolding. We develop constitutive models to integrate observations at spatial scales that span six orders of magnitude and indicate that fibrin clot extensibility and shrinkage are both manifestations of protein unfolding, which is not apparent in other matrix proteins such as collagen.
Electron Transportation Behavior in Single Crystal Silicon Nanowires
Authors: Shih Yu C. , Chen Chuin S. , Lin Chih T. , Wu Kuang C.
Published: January 2011

The electron transport properties of the highly boron-doped <110>-Silicon nanowires were investigated by first principle calculation with nonequilibrium Green’s function. We found that the highly doped silicon nanowires become metallic and the conductance drops as the undoped region increases.
Photothermal Therapy of Glioma in a Mouse Model With Near-Infrared Excited Nanoshells
Authors: Day Emily S. , Zhang Linna , Lewinski Nastassja A. , Thompson Patrick A. , Drezek Rebekah A. , Blaney Susan M. , West Jennifer L.
Published: January 2011

Glioblastoma multiforme is the most common and aggressive primary brain tumor, with median survival of approximately 10 months and only 5% of patients surviving greater than 5 years after treatment (1). Surgery and radiotherapy are the main treatment modalities for primary brain tumors, but the associated risks are high when infiltrative tumors are positioned near sensitive regions in the brain. Nanoshells, nanoparticles characterized by a spherical silica core and a gold shell, may provide the opportunity to treat brain tumors in a minimally invasive manner, reducing the risk associated with treatment. Upon exposure to a near-infrared laser, nanoshells convert light energy into heat that can thermally ablate cancerous cells (2). Targeted photothermal ablation of human glioma and medulloblastoma cells has already been demonstrated with this technique in vitro (3).