bluuebunny/crossref_metadata_2025 huggingface dataset:
Ceramic Resistors and Capacitors Embedded in Organic Printed Wiring Boards
Authors: Borland William , Felten John J. , Dellis Lynne E. , Ferguson Saul , Majumdar Diptarka , Jones Alton B. , Lux Mark S. , Traylor Richard R. , Doyle Marc
Published: July 2013

Combining thick-film and printed wiring board processes allows thick-film ceramic resistors and capacitors to be embedded in printed wiring boards (PWB). The resistor materials are based on lanthanum boride and cover the range of 10 ohm/square to 10 Kohm/square resistivities. The capacitor material is based on doped barium titanate. Both systems are designed to be “thick-film” printed on copper foil in the locations desired in the circuit and the foil is then fired in nitrogen at 900°C to form the ceramic component on the copper foil. The foil is then laminated, component face down, to FR4 using standard prepreg. The inner layer is then etched to reveal the components in a FR4 matrix. The resistors can be trimmed to tight tolerance at this stage and the components tested. The inner layer can then be laminated into a multilayer PWB. The process is described and the influence of board design, PWB processing and materials are presented and discussed. Examples of circuits using embedded thick-film passives are shown and results of reliability studies are presented.
A Novel Electronics Cooling System Using Water Heat Pipes Under Freezing Conditions
Authors: Suzuki Osamu , Nishihara Atsuo
Published: July 2013

A novel electronics cooling system that uses water heat pipes under an ambient temperature range from −30°C to 40°C has been developed. The system consists of several water heat pipes, air-cooled fins, and a metal block. The heat pipes are separated into two groups according to the thermal resistance of their fins. One set of heat pipes, which have fins with higher thermal resistance, operates under an ambient temperature range from −30°C to 40°C. The other set, which have lower resistance, operates from 0°C to 40°C. A prediction model based on the frozen-startup limitation of a single heat pipe was first devised and experimentally verified. Then, a prediction model for the whole-system was formulated according to the former model. The whole-system model was used to design a prototype cooling system, and it was confirmed that the prototype has a suitable cooling performance for an environmentally friendly electronics cooling system.
Fluid Flow and Thermal Characteristics for a Microchannel Heat Sink Subject to an Impinging Jet
Authors: Jang Seok Pil , Kim Sung Jin
Published: July 2013

In the present study fluid flow and heat transfer characteristics of a microchannel heat sink subject to an impinging jet are experimentally investigated. In order to evaluate the cooling performance of a microchannel heat sink subject to an impinging jet under the fixed pumping power condition, the pressure drop across a microchannel heat sink and temperature distributions at the base of it are measured. Especially, a micro-thermal sensor array is manufactured with simple and convenient microfabrication processes to measure temperature distributions at the base of the heat sink accurately. Based on these experimental results, we suggest a correlation for the pressure drop across a microchannel heat sink subject to an impinging jet as well as a correlation for the thermal resistance of that. In addition, we show that the cooling performance of a microchannel heat sink subject to an impinging jet is superior to that of the microchannel heat sink subject to a parallel flow.
A Package for Thermal Compensation of Fiber Bragg Gratings
Authors: Howlett Alison L. , Vandeperre Luc J. , Clegg William J.
Published: July 2013

A new package for thermally compensating a fiber Bragg grating, which requires less accuracy in positioning the fiber onto the device, is discussed. Experiments show that it can reduce the shift in reflected wavelength from 1575 pm to 78 pm for a temperature change of 120 K. The deformation of the package showed no hysteresis, and the effective thermal compensation is repeatable over many cycles. Furthermore the package also has the potential to give non-linear thermal compensation for fiber Bragg gratings.
Numerical Simulation of Conjugate Heat Transfer From Multiple Electronic Module Packages Cooled by Air
Authors: Yoshino Hideo , Fujii Motoo , Zhang Xing , Behnia Masud
Published: July 2013

This paper reports on the numerical simulation of conjugate heat transfer from multiple electronic module packages (45 × 45 × 2.4 mm) on a printed circuit board placed in a duct. The dimensions of the modules are the same as a single module package previously studied. In the series arrangement, two module packages are installed on the center of the printed circuit board along the airflow direction. In the parallel arrangement, two and/or four module packages are installed normal to the airflow direction. In the numerical simulations, the interval between the module packages was varied and three values were considered (45, 22.5 and 9 mm). The variation of the printed circuit board thermal conductivity was also considered and 0.3, 3 and 20 W/m/K were used with the mean velocity in the duct also at three different values (0.33, 0.67 and 1 m/s). In order to derive a non-dimensional correlation from the numerical results, the concept of the effective heat transfer area previously used for a single module package was used for the multiple module packages. For the series arrangement, the effects of the interval on the effective heat transfer area are relatively low, and the numerical results can be summarized with the same correlation obtained from the single module package. On the other hand, the effective heat transfer area for the parallel arrangement is strongly affected by the parallel interval and the thermal conductivity of printed circuit board. When the interval increases, the temperature of the module packages greatly reduces as the thermal conductivity of the printed circuit board increases.
Thermal Design and Packaging of a Prototype Refrigeration Cooling System for CMOS-Based MCMs
Authors: Wei Jie , Kubo Hideo , Ishimine Junichi
Published: July 2013

Thermal design and packaging strategy of a prototype dual-loop vapor compression refrigeration cooling system, developed as a pilot model for thermal management of high performance CMOS based MCMs, is introduced in this paper. The cooling system was comprised of two separated refrigeration units providing low temperature cooling via a dual-path cooling module (evaporator) mounted on a CPU-MCM package. Cooling capacity for each refrigeration unit was controlled ranging from 250W to 2500W with a refrigerant evaporating temperature at −25 degree centigrade. The CPU-MCM mounted with the refrigeration cooling module was packaged on a system board assembly, together with other electronic devices. The assembly was accommodated into a dew-point control box where two dewpoint control units were operating in a redundancy to remove moisture and keep a dew temperature inside the box below −30 degree centigrade for completely preventing from condensation. Cooling redundancy was provided by both the refrigeration units and dual-path cooling module. The cooling module was redundant in that two sets of refrigerant passages were staggered within a thin copper plate, where each set was connected to a separated refrigeration unit. Apart from the robust system and steady operation, the configuration and operation mode also provided the cooling system a high power efficiency and much shortened starting time. Numerical simulations were also performed for investigating airflow and thermal characteristics, in a system board level inside the dew-point control box. Detailed predictions of airflow and temperature distributions were significantly helpful for improving and verifying practical system designs.
Thermal Management of Transient Power Spikes in Electronics: Phase Change Energy Storage or Copper Heat Sinks??
Authors: Krishnan Shankar , Garimella Suresh V.
Published: July 2013

A transient thermal analysis is performed to investigate thermal control of power semiconductors using phase change materials, and to compare the performance of this approach to that of copper heat sinks. Both the melting of the phase change material under a transient power spike input, as well as the resolidification process, are considered. Phase change materials of different kinds (paraffin waxes and metallic alloys) are considered, with and without the use of thermal conductivity enhancers. Simple expressions for the melt depth, melting time and temperature distribution are presented in terms of the dimensions of the heat sink and the thermophysical properties of the phase change material, to aid in the design of passive thermal control systems. The simplified analytical expressions are verified against more complex numerical simulations, and are shown to be excellent tools for design calculations. The suppression of junction temperatures achieved by the use of phase change materials when compared to the performance with copper heat sinks is illustrated. Merits of employing phase change materials for pulsed power electronics cooling applications are discussed.
Effect of Percolation on Equivalent Thermal Conductivity of Insulating Layer in Insulated Metal Substrates
Authors: Monden Kenji
Published: July 2013

An insulated metal substrate (IMS) is a circuit board comprising an insulating layer on a metal base plate. The insulating layer is made from epoxy resin incorporating dense inorganic fillers with high thermal conductivity. Because the substrates have high thermal conductivity, they are used in applications where electric parts generate intense heat, such as inverters, amplifiers, motor drivers and so on. It is expected that the insulating layer has higher thermal conductivity as the use of an IMS is expanded. Therefore, the influence of percolation on the equivalent thermal conductivity of an insulating layer is considered. The effect of the volume fraction of inorganic filler on the equivalent thermal conductivity of insulating layer in IMS is experimentally investigated. The equivalent thermal conductivity of insulating layer as a function of volume fraction of filler is estimated by FEM and Monte Carlo technique together. The acquired value of percolation threshold volume fraction is the same grade as the previous reported value. Based on these experimental and numerical results, an effective thermal conductivity of a filler which contains surrounding interfacial region is evaluated. The effective thermal conductivity of an irregular filler is presumed smaller than that of a spherical filler. It is noted that the control of filler size and shape is important for the formation of high thermal conductivity of an insulating layer. In addition, an improved equation for the equivalent thermal conductivity of insulating layer in IMS is proposed. The predictive values from the equation for insulating layer in an improved IMS agree with experimental results.
Thermal Management of Airbourne Early Warning and Electronic Warfare Systems Using Foam Metal Fins
Authors: Klein John , Gilchrist George , Karanik Jim , Arcas Noe , Yurman Richard , Whiteside James , Shields Bill , Bartilucci Tony
Published: July 2013

This program, addresses the need for thermal management of increasingly powerful and densely packaged electronic devices. Open-celled foams and lattice structures offer the promise of much improved heat transfer between the coolant and the solid structure of the lattice compared to traditional finned heat exchangers. The focus of this program is to evaluate integration of foam and lattice materials as heat exchanger cores and as electronic racks. The potential benefits of this approach include reduction in the volume and weight of the heat exchanger core and/or device junction temperature as well as direct attach cooling of high power electronics. To begin we have selected two major applications, a liquid cooling system heat exchanger, and avionics rack cooling. There is little data on foam metal heat transfer in the regime we anticipate for aircraft applications. Our approach begins with the measurement of heat transfer characteristics of compressed foam metals under conditions suitable for aircraft applications. Basic heat transfer data is being obtained for heat removal from a heated surface by “foam metal fins” with air flowing through the foam. Effective heat transfer coefficient and airflow resistance have been measured. The test method and apparatus are briefly described. Results of heat transfer measurements to date are presented. A theoretical model of “foam metal fins” has been developed and is applied for scaling foam metal fins within our test matrix. Using the model we determine the heat transfer coefficient between the air and foam ligaments. These heat transfer coefficients are compared with cylinders in cross flow. We applied our measured heat transfer characteristics to the design, fabrication and verification test of a highly efficient heat exchanger core. A laboratory scale thermal performance demonstration core was sized based on our test results. Initial tests of a single air / liquid heat exchanger core leg validates our core sizing. Our results can also be applied to cooling of individual electronic components as well as cold plates for electronics.
V-PAC: Vertical Packaging for Assembly-Compatible Chip Stacks
Authors: Malba Vincent , Evans Leland B. , Harvey Christopher D. , Bernhardt Anthony F.
Published: July 2013

A new process for making high-density memory stacks which are completely compatible with typical electronic assembly techniques is presented. The process uses PECVD-SiO2 passivation, laser direct-writing, electrodeposited photoresist, and metal electroplating to form a reroute pattern extending from the input/output (I/O) pads on top of the chip directly onto the chip sidewalls. With the I/O available for interconnection on the side of the chip, four memory chips are stacked together with one silicon reroute chip. A high-temperature compatible anisotropically conductive adhesive is used to connect a flex circuit to the sidewall I/O pads of the memory chips and the reroute die. The reroute die’s sidewall pads connect to a pattern on the die surface which redistributes the I/O for connection to a leadframe. The lead frame is epoxied to the reroute die, and wirebonded to complete the electrical connection. The leadframe/stack assembly is then encapsulated with an epoxy potting compound, and the leads are formed and trimmed, creating a chip stack which is indistinguishable from a standard IC package.
Automatic Generation and Validation of Compact Network Models for a Fine Pitch BGA Package
Authors: Nagulapally Manoj , Zhao Sam Ziqun
Published: July 2013

A methodology for automatically generating compact thermal network models of increasing complexity, for use in numerical simulations of general semiconductor integrated circuit (IC) packages is presented. The method is based on the multi-grid agglomeration of the underlying mesh used in the finite volume discretization of the energy conservation equation of the package. The method is applied to a 196-pin fine pitch ball grid array (FBGA) package. Various network topologies and the corresponding network conductances were automatically extracted for this package. These networks were then used in computational fluid dynamics (CFD) simulations for a range of boundary conditions corresponding to single-phase natural and forced convective cooling. Results show good agreement with the detailed package simulations.
Control of a Laboratory-Based Thermal Management System
Authors: McKinney Mark H. , Wall Charles
Published: July 2013

In a laboratory environment, flexible, accurate and reliable thermal management is critical to successful analysis and testing of a single package IC device under test (DUT). As next generation electronic components approach a heat flux of 200W/cm2, the control aspects of the thermal management system become even more critical. Utilizing advanced vapor-compression refrigeration technology in conjunction with PID control algorithms, accurate thermal management of a DUT is achieved. In order to accurately control the temperature, the control system monitors case (TC), evaporator (TE), or internal junction (TJ) temperature and employs real time pulse width modulation control of refrigerant flow to achieve accurate control to less than ±3°C. The system also includes the capability to monitor the actual power supplied to the DUT and is capable of control up to a thermal load of 200W. This paper presents the requirements for and the design of the thermal control system utilized in a high heat-flux, laboratory-based thermal management system.
Design Optimization of Off-Chip Inductors
Authors: Jin Lin , Lu Albert Chee W. , Wai Lai L. , Fan Wei , Tan Aik Chong , Chan Kai Chong
Published: July 2013

A solution space design methodology is presented for optimization of off-chip inductors. The analysis has been performed for an advanced wafer level redistribution manufacturing process. Electromagnetic simulations were performed to extract the characteristics of different inductor designs. It was observed that the design optimization should be tuned to the operating frequency.
Rugged Portable Grayscale Optical Correlator for Onboard Automatic Target Recognition Applications
Authors: Chao Tien-Hsin , Reyes George , Zhou Hanying
Published: July 2013

Jet Propulsion Laboratory (JPL) has developed, for the first time, a matchbox-size compact grayscale optical correlator (GOC). In this paper, we will report the recent development of a prototype 512 × 512 GOC utilizing a new miniature ferroelectric liquid crystal spatial light modulator (FLCSLM) with a 7-micron pixel pitch. We will discuss recent progress in the design and packaging technology to achieve a rugged portable GOC module to enable the real-time onboard applications of this miniature GOC. Experimental demonstration of ATR applications using this new GOC will be presented.
Raised Floor Computer Data Center: Effect on Rack Inlet Temperatures When Adjacent Racks Are Removed
Authors: Schmidt Roger , Cruz Ethan
Published: July 2013

This paper focuses on the effect on inlet rack air temperatures when adjacent racks are removed. Only the above floor (raised floor) flow and temperature distributions were analyzed for various air flowrates exhausting from the perforated tiles and the rack. A Computational Fluid Dynamic (CFD) model was generated for the room with electronic equipment installed on a raised floor with particular focus on the effects on rack inlet temperatures of these high powered racks. The baseline case was with forty racks of data processing (DP) equipment arranged in rows in a data center cooled by chilled air exhausting from perforated floor tiles. The chilled air was provided by four A/C units placed inside a room 12.1 m wide × 13.4 m long. Since the arrangement of the racks in the data center was symmetric only one-half of the data center was modeled. To see the effect of missing racks adjacent to high powered racks various configurations were analyzed. The numerical modeling was performed using a commercially available finite control volume computer code called Flotherm (Trademark of Flomerics, Inc.). The flow was modeled using the k-e turbulence model. Results are displayed to provide some guidance on the design and layout of a data center.
Raised Floor Computer Data Center: Effect of Rack Inlet Temperatures When Rack Flowrates Are Reduced
Authors: Schmidt Roger , Cruz Ethan
Published: July 2013

This paper focuses on the effect on inlet rack air temperatures when rack flowrates are reduced. Reduced flowrates for the same heat loads results in higher air temperature differences across the rack and thereby higher air temperatures exiting the rack. The effect of the higher rack exhaust temperatures on the inlet rack air temperatures is the focus of this investigation. Only the above floor (raised floor) flow and temperature distributions were analyzed for a range of rack flowrates and with various flowrates exhausting from the perforated tiles. A Computational Fluid Dynamic (CFD) model was generated for the room with electronic equipment installed on a raised floor with particular focus on the effects on rack inlet temperatures of these high powered racks. Fourty racks of data processing (DP) equipment were arranged in rows in a data center cooled by chilled air exhausting from perforated floor tiles. The chilled air was provided by four A/C units placed inside a room 12.1 m wide × 13.4 m long. Since the arrangement of the racks in the data center was symmetric only one-half of the data center was modeled. The numerical modeling was performed using a commercially available finite control volume computer code called Flotherm (Trademark of Flomerics, Inc.). The flow was modeled using the k-e turbulence model. Results are displayed to provide some guidance on the design and layout of a data center.
Embedded Passives: A Novel Approach Using Ceramic Thick Film Technology
Authors: Snogren Richard C.
Published: July 2013

This paper is an in depth presentation of a novel approach for design and manufacturing processes to embed ceramic thick film resistors and discrete capacitors into circuit board substrates. These robust materials are available in a wide range of values. Embedded passives, i.e., resistors and capacitors built right into the printed circuit board substrate will be the next pivotal technology for the PCB industry, preceded by the plated thru hole in the 50s, and microvias in the 90s. Key drivers are performance, miniaturization, and cost. The average cell phone has 445 SMT passive components at a 25:1 ratio to ICs. Embedding many of these will improve performance, enable more functionality and reduce cost per function. Embedded passives are not limited to cell phones, many other applications will benefit from improved performance. Several materials are commercially available today and many new materials are in development.
Insertion of HDI and Grid Array Technologies Into Military/Space Applications
Authors: Keller Jerry D.
Published: July 2013

As with the commercial market, Military/Aerospace electronic packaging has similar needs to develop smaller/lighter/ higher performance electronics. This need has required the use of High Density Interconnect (HDI) circuit boards and Grid Array components (ball and column) in rugged environment applications such as military and space. This discussion will cover the technology study program conducted by Honeywell Defense and Space Electronics Systems on the mechanical durability of HDI (High Density Interconnect) and Grid Array component packaging and its application into “Hi Rel” aerospace programs.
Effect of Manifold Design on Flow Distribution in Parallel Micro-Channels
Authors: Webb Ralph L.
Published: July 2013

Gas or liquid flow in multiple, parallel micro-channels is of interest for Micro-Electro-Mechanical Systems (MEMS) cooling applications. The published data for friction in 10-to-400μm hydraulic diameter, single micro-channels show good agreement with the conventional equations in the laminar and turbulent regimes. However, investigators of flow in multiple, parallel micro-channels in the same range of channel sizes report significantly different results. They report significant disagreement with the conventional equations and argue that transition occurs at Reynolds numbers as small as 200, dependent on the channel shape. This paper proposes that the apparent discrepancies of friction in multiple micro-channels can be attributed to flow mal-distribution. Flow mal-distribution is expected in multi-channels, because of manufacturing tolerances and poor manifold design. It can be minimized by proper header design and better manufacturing tolerances.
Benchmark Heat Transfer Data for Micro-Structured Surfaces for Immersion Cooled Microelectronics
Authors: Nimkar Nitesh D. , Bhavnani Sushil H. , Jaeger Richard C.
Published: July 2013

Pool boiling from a surface featuring micro-pyramidal re-entrant cavities (mouth size 40 μm) etched in silicon, on a glass substrate, was studied. All experiments were conducted in the dielectric fluid FC-72 at one atmosphere. The heat sink is designed to eliminate spreading through the substrate, and back heat loss. Experimentation showed that the critical heat flux was 12.8 W/cm2. A high speed camera (400fps) was used to record and quantify the effect of heat flux on departure diameter and bubble emission frequency. Both departure diameter and frequency showed an increasing trend with heat flux. Comparison with existing literature are also presented.
Experiments and Modeling of the Hydraulic Resistance of In-Line Square Pin Fin Heat Sinks With Top By-Pass Flow
Authors: Urdaneta Mario , Ortega Alfonso , Westphal Russel V.
Published: July 2013

Extensive experiments were performed aimed at obtaining physical insight into the behavior of in-line pin fin heat sinks with pins of square cross-section. Detailed pressure measurements were made inside an array of square pins in order to isolate the inlet, developing, fully developed, and exit static pressure distributions as a function of row number. With this as background data, overall pressure drop was measured for a self-consistent set of aluminum heat sinks in side inlet side exit flow, with top clearance only. Pin heights of 12.5 mm, 17.5 mm, and 22.5 mm, pin pitch of 3.4 mm to 6.33 mm, and pin thickness of 1.5 mm, 2 mm and 2.5mm were evaluated. Base dimensions were kept fixed at 25 × 25 mm. In total, 20 aluminum heat sinks were evaluated. A “two-branch by-pass model” was developed, by allowing inviscid acceleration of the flow in the bypass section, and using pressure loss coefficients obtained under no bypass conditions in the heat sink section. The experimental data compared well to the proposed hydraulic models. Measurements in the array of pins showed that full development of the flow occurs after nine rows, thus indicating that none of the heat sinks tested could be characterized as fully-developed.
Effect of the Thermostatic Expansion Valve Characteristics on the Stability of a Refrigeration System: Part II
Authors: Kulkarni Amit , Agonafer Dereje , Schmidt Roger
Published: July 2013

The combination of increased power dissipation and increased packaging density has led to substantial increases in chip and module heat flux in high-end computers. The challenge has been to limit the rise in chip temperature. In the past virtually all-commercial computers were designed to operate at temperatures above the ambient. However researchers have identified the advantages of operating electronics at low temperatures. The current research focuses on IBM’s mainframe, which uses a conventional refrigeration system to maintain chip temperatures below that of comparable air-cooled systems, but well above cryogenic temperatures. An experimental bench was built to study the effect of variation of evaporator outlet superheat on system performance. Three different types of thermostatic expansion valves were tested in order to verify that the bulb size and bulb location have significant effect on the transient behavior of the system. Bulbs of each of the three thermostatic expansion valves were mounted at five different locations on the suction line. It was observed that the overall system stability increases as we move closer to the evaporator exit. It was also observed that there exists a region in the suction line at which the superheat variation is the least and placing the bulb at this region gives maximum stable operation of the system. This region can be defined as the minimum stable superheat point. Tests were conducted at five different load conditions 1000W, 750W, 500W, 250W and no load condition. It was observed that the system was the most stable at full load condition for all three types of valves and system stability consistently decreased as the load was decreased.
Orientation-Independent Atomization Heat Transfer Cell for Thermal Management of Microelectronics
Authors: Heffington Samuel N. , Glezer Ari
Published: July 2013

This paper describes a new gravity-independent version of a two-phase cooling, closed heat transfer cell, similar to a thermosyphon. The cooling method is based upon a Vibration-Induced Droplet Atomization, or VIDA, process that can generate small liquid droplets inside a closed cell and propel them onto a heated surface. The VIDA technique involves the violent break-up of a liquid film into a shower of droplets by vibrating a piezoelectric actuator and accelerating the liquid film at resonant conditions. A piezoelectric diaphragm pump is used to supply a constant stream of liquid to the VIDA atomizer enabling gravity-independent operation. The atomized secondary droplets continually coat the heated surface with a thin liquid film that evaporates. The resulting vapor is condensed on internal surfaces of the heat transfer cell as well as the liquid working fluid. The condensed liquid is collected and returned to the atomizing driver by the piezoelectric diaphragm pump. A small-scale gravity independent VIDA atomizer generating spherical droplets of relatively uniform diameter and having sufficient momentum to reach the remotely located heated source has been constructed. Initial test data described in this study include the operating characteristics of the VIDA spray and heat transfer capabilities. Heat dissipation levels as high as 195 W have been measured from an evaporation surface held below 120°C at atmospheric pressure.
Thermal Issues in Next Generation Integrated Circuits
Authors: Gurrum Siva , Suman Shivesh , Joshi Yogendra , Fedorov Andrei
Published: July 2013

Effective cooling of electronic chips is crucial for reliability and performance of electronic devices. Steadily increasing power dissipation in both devices and interconnects motivate the investigation of chip-centric thermal management as opposed to traditional package-centric solutions. In this work, we explore the fundamental limits for heat removal from a model chip for various configurations. Temperature rise when the chip is embedded in an infinite solid is computed for different thermal conductivities of the medium to pin down the best that can be achieved with conduction based thermal management. Next, a chip attached to a spreader plate with convection boundary condition on top was considered. A brief review of interface thermal resistances and partitioning of overall thermal resistance is presented for current generation microprocessors. Based upon the analysis it is concluded that far-term cooling solutions might necessitate integration with chip/interconnect-stack to meet the challenges. In addition, this would require concurrent thermal and electrical design/fabrication of future high-performance microprocessors.
Characterizing Bulk Thermal Conductivity and Interface Contact Resistance Effects of Thermal Interface Materials in Electronic Cooling Applications
Authors: Gektin Vadim , Ankireddi Sai , Jones Jim , Pecavar Stan , Hundt Paul
Published: July 2013

Thermal Interface Materials (TIMs) are used as thermally conducting media to carry away the heat dissipated by an energy source (e.g. active circuitry on a silicon die). Thermal properties of these interface materials, specified on vendor datasheets, are obtained under conditions that rarely, if at all, represent real life environment. As such, they do not accurately portray the material thermal performance during a field operation. Furthermore, a thermal engineer has no a priori knowledge of how large, in addition to the bulk thermal resistance, the interface contact resistances are, and, hence, how much each influences the cooling strategy. In view of these issues, there exists a need for these materials/interfaces to be characterized experimentally through a series of controlled tests before starting on a thermal design. In this study we present one such characterization for a candidate thermal interface material used in an electronic cooling application. In a controlled test environment, package junction-to-case, Rjc, resistance measurements were obtained for various bondline thicknesses (BLTs) of an interface material over a range of die sizes. These measurements were then curve-fitted to obtain numerical models for the measured thermal resistance for a given die size. Based on the BLT and the associated thermal resistance, the bulk thermal conductivity of the TIM and the interface contact resistance were determined, using the approach described in the paper. The results of this study permit sensitivity analyses of BLT and its effect on thermal performance for future applications, and provide the ability to extrapolate the results obtained for the given die size to a different die size. The suggested methodology presents a readily adaptable approach for the characterization of TIMs and interface/contact resistances in the industry.
Design Optimization of a Router Board Using Computational Fluid Dynamics
Authors: Dake Timothy J. , Majdalani Joseph , Narasimhan Susheela
Published: July 2013

The cooling of boards and components in telecommunication chassis is becoming progressively more challenging as the power dissipation of the components increases. The internet market is demanding higher speeds and the internet gear makers try to accommodate the increasing demand of the consumer. Hence there are situations where the power requirement for one rack unit of the chassis is reaching 500–600 W currently and expected to reach about 800–1000 W in 1–2 years. The power dissipations on components are currently in the vicinity of approximately 60–80 W and expected to reach roughly 100–120 W in the near future. This paper presents a design effort wherein a chassis has been analyzed and designed for a cooling capacity on the order of 600 W for the board to the extent that one is able to cool about 80 W for the ASICs and other components on the board.
Use of Plastic Commercial Off-the-Shelf (COTS) Microcircuits for Space Applications
Authors: Gerke R. David , Shapiro Andrew A. , Agawal Shri , Peters David M. , Sandor Michael A.
Published: July 2013

Commercial-off-the-shelf (COTS) plastic encapsulated microcircuits (PEM) are candidate-packaging technologies for spacecraft due to their enhanced performance, lower weight and lower cost. Much of the electronics used in space applications would be considered obsolete by everyday standards. This is primarily due the cost and time required for full space qualification. In order to gain the performance available in today’s electronics, COTS PEMs offer a viable path. PEMs can weigh half as much as their counter part ceramic packages. A lighter package results in a smaller overall payload for the same board functionality, a concern of critical importance for space missions because the payload mass dictates the launch vehicle requirements. Costs can be potentially reduced by using screening, accelerated testing or partial qualification techniques to complement the existing commercial qualification as well as by the reduced package materials costs. Assessing the risk associated with potentially lower reliability devices, engineers within the commercial and aerospace industries are using trade-off and risk analysis to aid in reducing spacecraft system cost while increasing performance and maintaining high reliability. In this paper we will outline the issues facing the use of COTS PEMs for spaceflight hardware from the aspect of both the electronic active devices as well as their packages. Finally, we will provide some guidelines for their use.
RF System-on-Package (SOP) Development for Compact Low Cost Wireless Front-End Systems
Authors: Tentzeris M. , Laskar J.
Published: July 2013

This paper presents the development of RF System-on-Package (SOP) architectures for compact and low cost wireless radio front-end systems. A novel 3D integration approach for SOP-based solutions for wireless communication applications is proposed and utilized for the implementation of a C band Wireless LAN (WLAN) RF front-end module by means of stacking LTCC substrates using μBGA technology. LTCC designs of high-performance multilayer embedded bandpass filters and novel stacked cavity-backed patch antennas are also reported. In addition, the fabrication of very high Q-factor inductors and embedded filter in organic substrates demonstrate the satisfactory performance of multilayer organic packages. The well known full-wave numerical techniques of FDTD and MRTD are used for the modeling of adjacent lines crosstalk, of the Q-factor of embedded passives and for the accurate simulation of MEMS structures.
Behavior of Suction Caissons Measured in Laboratory Pullout Tests
Authors: Luke Adam M. , Rauch Alan F. , Olson Roy E. , Mecham Elliott C.
Published: July 2013

Laboratory experiments are being conducted to study the behavior of suction casissons used for deep offshore moorings. Tests with a 100-mm diameter by 910-mm long caisson prototype, which is installed using dead weight or suction, are performed in a 1.1-m thick deposit of normally consolidated kaolinite. Instrumentation is used to record displacements, axial forces, and pore water pressures (at five locations along the interior and exterior surfaces of the caisson) during extraction of the caisson. Axial pullout tests have been conducted on caissons inserted using dead weight only or dead weight plus suction pressure, on caissons pulled with a vented or sealed top cap, and with rapid (undrained) versus slow (drained) pullout. Measured pullout capacities are interpreted in terms of the weight of extracted soil, side resistance on the caisson walls, and the reverse end bearing capacity at the tip.
Reliability Analysis of FRP Laminated Plates With Initial Imperfection
Authors: Chen Jianqiao , Wang Xiangyang , Luo Cheng
Published: July 2013

In this paper, a probabilistic progressive failure analysis method is applied to estimating the reliability of a simply supported laminated composite plate with an initial imperfection under bi-axial compression load. The initial imperfection and the strength parameters are considered as random variables. Ply-level failure probability is evaluated by the first order reliability method (FORM) together with the Tsai-Wu strength criterion and Tan criterion. Current stresses in the laminated structure are calculated by classical lamination theory with the stiffness being modified based on the last step ply failure. Probabilistieally dominant ply-level failure sequences leading to overall system failure are identified by branch and bound method. The system failure probability is estimated through the union of significant failure sequences. A numerical example is presented to demonstrate the methodology proposed. Parameter studies show that the deviation of the initial imperfection and strength parameters largely influence the system reliability.
The Limit Pressure for a Cracked Branch Junction and Comparison With a Cracked Plain Cylinder
Authors: Lee K. S. , Moreton D. N. , Bouchard P. J. , Moffat D. G.
Published: July 2013

The limit load of structures that contain defects may be determined using standard limit load solutions for simple components or by employing Finite Element (FE) procedures for more complex structures. This work considers the case of a pressurised piping branch junction (D/T = 20, d/D = 0.5, t/T = 1) which contains two axial through-wall cracks, symmetrically extending from each crotch corner at the crown of the junction. The structure is idealised as a plain cylinder containing a single axial defect with three proposed definitions of an equivalent crack length. Such a cracked cylinder can be analysed using a standard limit load solution or by FE analysis. The three crack length definitions used are the distance between the two outer crack tips, the sum of the two crack lengths and the length of one of the cracks. Estimates of branch junction limit pressures have been obtained by FE analysis using ABAQUS for a range of crack lengths. These are compared with the theoretical solutions for an equivalent plain cylinder of the run pipe dimensions containing a single crack whose length has been defined in each of the above ways.
Justification of the Use of Liquid Nitrogen to Make Ice-Plugs in Carbon-Manganese Steel Pipes for Maintenance Purposes in Nuclear Plants
Authors: Messelier-Gouze Clarisse , Bre´zillon Christian , Tubiana Andre´ , Rousseau Gilles
Published: July 2013

During maintenance operations in nuclear power plants, it is sometimes necessary to isolate temporarily sections of pipes. When no other mechanical device is available (floodgates, valves), the freeze sealing technique can be used. With a heat-exchanger surrounding a portion of the pipe and filled with liquid Nitrogen (−196°C), the water contained in the pipe is frozen, resulting in an ice-plug. During these operations, stresses of thermal origin are generated in the pipes, due to the thermal amplitude between the initial temperature of the pipes (40°C), and the coolant (−196°C). This is why it is necessary to study the resistance of the structure, in particular towards brittle fracture in case of the presence of a small defect in the material. The main purpose of this study, is to evaluate the maximum size of a defect acceptable, without leading to rupture of the structure while freezing. In order to reach this aim, a freezing test has been performed, and the measuresd temperatures on the surface of the tube have been used to conduct thermal and mechanical calculations. In places of maximum load, different defects have been postulated, and their nociviy has been calculated with RSEM simplified methods. This study takes place in the file concerning the justification of the cryogenic technique towards the French Nuclear Safety Authority. The evaluation of the maximum admissible defect is the first step of the demonstration, the second step will consist in studying the possible extensions to other configurations that can be met in a nuclear plant (materials, diameter, thickness), and to make a second ice-plug test in a Carbon-Manganese pipe where the maximum admissible defect has been machined, in order to show that it is resistant to the freezing with liquid Nitrogen.
Simplified Modeling of a PWR Reactor Pressure Vessel Lower Head Failure in the Case of a Severe Accident
Authors: Koundy V. , Durin M. , Nicolas L. , Combescure A.
Published: July 2013

In order to characterize the timing, mode and size of a possible lower head failure (LHF) of the reactor pressure vessel (RPV) in the event of a core meltdown accident, several large-scale LHF experiments were performed under the USNRC/SNL LHF program. The experiments examined lower head failure at high pressures (10 MPa in most cases) and with small throughwall temperature differentials. Another recent USNRC/SNL LHF program, called the OLHF program, has been undertaken in the framework of an OECD project. This was an extension of the first program and dealt with low and moderate pressures (2 MPa to 5 MPa) but with large throughwall temperature differentials. These experiments should lead to a better understanding of the mechanical behavior of the reactor vessel lower head, which is of importance both in severe accident assessment and the definition of accident mitigation strategies. A well-characterized failure of the lower head is of prime importance for the evaluation of the quantity of core material that can escape into the containment, since this defines the initial conditions for all external-vessel events. The large quantity of escaping corium may lead to direct heating of the containment. This is an important severe accident issue because of its potential to cause early containment failure. The experiments also provide data for model development and validation. For our part, as one of the program partners, numerical modeling was performed to simulate these experiments. This paper presents a detailed description of three of our numerical models used for the simulation. The first model is a simplified semi-analytical approach based on the theory of a spherical shell subjected to internal pressure. The two other methods deal with 2D finite element (2D-FE) modeling: one combines the Norton-Bailey creep law with a damage model proposed by Lemaitre-Chaboche while the other uses only a creep failure criterion but takes into account thermo-metallurgical phase transformations. The numerical results are consistent with the experimental measurements. The effect on the numerical results of the multiphase transformation of the shell material and of the two failure criteria used, one involving necking (Conside`re’s criterion) and the other involving creep damage (Lemaitre-Chaboche), is discussed.
Fracture Mechanics Evaluation Considering Thermal Aging Embrittlement
Authors: Chang Yoon-Suk , Jin Tae-Eun
Published: July 2013

Various cast austenitic stainless steels composed of austenite and ferrite phases are used for primary pressure boundary components such as main coolant loop piping, pump casings and so on in old PWRs. However, these components have been known to experience a loss of fracture toughness caused by thermal aging embrittlement, when exposed to reactor operating temperatures over a long period, that may lead to failure. The purpose of this paper is to introduce the major component status, thermal aging embrittlement susceptibility, material property change determination, flaw evaluation methods, case studies considering the thermal aging embrittlement phenomenon and future plan of Korean industry. The tentative results showed that the thermal aging embrittlement is a plausible age-related degradation mechanism, thereby its effects should be managed adequately in order to sustain the integrity of the corresponding components.
The Impact of an Improved Flaw Model on a Pressurized Thermal Shock Evaluation
Authors: Dickson T. L. , Simonen F. A.
Published: July 2013

The current regulations for pressurized thermal shock (PTS) were derived from computational models that were developed in the early-mid 1980s. The computational models utilized in the 1980s conservatively postulated that all fabrication flaws in reactor pressure vessels (RPVs) were inner-surface breaking flaws. It was recognized at that time that flaw-related data had the greatest level of uncertainty of the inputs required for the probabilistic-based PTS evaluations. To reduce this uncertainty, the United States Nuclear Regulatory Commission (USNRC) has in the past few years supported research at Pacific Northwest National Laboratory (PNNL) to perform extensive nondestructive and destructive examination of actual RPV materials. Such measurements have been used to characterize the number, size, and location of flaws in various types of welds and the base metal used to fabricate RPVs. The USNRC initiated a comprehensive project in 1999 to re-evaluate the current PTS regulations. The objective of the PTS Re-evaluation program has been to incorporate advancements and refinements in relevant technologies (associated with the physics of PTS events) that have been developed since the current regulations were derived. There have been significant improvements in the computational models for thermal hydraulics, probabilistic risk assessment (PRA), human reliability analysis (HRA), materials embrittlement effects on fracture toughness, and fracture mechanics methodology. However, the single largest advancement has been the development of a technical basis for the characterization of fabrication-induced flaws. The USNRC PTS-Revaluation program is ongoing and is expected to be completed in 2002. As part of the PTS Re-evaluation program, the updated risk-informed computational methodology as implemented into the FAVOR (Fracture Analysis of Vessels: Oak Ridge) computer code, including the improved PNNL flaw characterization, was recently applied to a domestic commercial pressurized water reactor (PWR). The objective of this paper is to apply the same updated computational methodology to the same PWR, except utilizing the 1980s flaw model, to isolate the impact of the improved PNNL flaw characterization on the PTS analysis results. For this particular PWR, the improved PNNL flaw characterization significantly reduced the frequency of RPV failure, i.e., by between one and two orders of magnitude.