bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment of the Cold-Wire Resistance Thermometer for High-Speed Turbomachinery Applications
Authors: De´nos R. , Sieverding C. H.
Published: May 2010

The paper first describes the fundamentals of cold-wire resistance thermometry. The transfer functions with and without wire-prong heat conduction effects are discussed and a new method for the description of complicated transfer functions describing both the prongs and wire frequency response is proposed. The experimental part of the paper starts with an investigation of the transfer function of various probes differing by the wire diameter, the l/d ratio, and the wire-prong connection using two simple methods: (1) electrical heating of the wire by a sine current and (2) a temperature step test consisting in injecting the probe into a hot air stream. The first test provides information on the wire response, whereas the second serves to study wire prong heat conduction effect. The tests cover a wide range of velocities and densities. A frequency bandwidth of 2 kHz is obtained with a 2.5 μm wire probe at an air velocity of 200 m/s at atmospheric pressure. A numerical compensation system allows us to extend the use of this probe to much higher frequencies. Finally, the probe is mounted onto a wheel in a high-speed rotating test rig allowing probe traverses through a stationary hot air jet at rotational speeds up to 5000 rpm with the probe positioned at a radius of 0.380 m. The probe signal is transmitted via an opto-electronic data transmission system. It is demonstrated that using the numerical compensation method, it is possible to reconstruct the hot jet temperature profile at frequencies up to 6 kHz.
Measurement and Computation of Heat Transfer in High-Pressure Compressor Drum Geometries With Axial Throughflow
Authors: Long C. A. , Morse A. P. , Tucker P. G.
Published: May 2010

This paper makes comparisons between CFD computations and experimental measurements of heat transfer for the axial throughflow of cooling air in a high-pressure compressor spool rig and a plane cavity rig. The heat transfer measurements are produced using fluxmeters and by the conduction solution method from surface temperature measurements. Numerical predictions are made by solving the Navier–Stokes equations in a full three-dimensional, time-dependent form using the finite-volume method. Convergence is accelerated using a multigrid algorithm and turbulence modeled using a simple mixing length formulation. Notwithstanding systematic differences between the measurements and the computations, the level of agreement can be regarded as promising in view of the acknowledged uncertainties in the experimental data, the limitations of the turbulence model and, perhaps more importantly, the modest grid densities used for the computations.
Transient Heat Transfer Experiments in a Linear Cascade Via an Insertion Mechanism Using the Liquid Crystal Technique
Authors: Hoffs A. , Bo¨lcs A. , Harasgama S. P.
Published: May 2010

An insertion mechanism for a linear cascade allowing the displacement of one measurement airfoil to conduct transient heat transfer experiments is introduced. A basic feature of the system is its capability to work in a continuously running tunnel driven by a compressor at steady-state conditions. The experiment is initiated by pulling the measurement airfoil very rapidly through the sidewalls of the cascade by means of a pneumatic cylinder. Heat transfer measurements were obtained on a turbine airfoil at different exit Mach numbers up to M = 0.8 and exit Reynolds numbers up to Re = 1.2E6. The transient liquid crystal method was used applying a digital image processing system capable of recording and storing the optical signal in real time. Comparisons were performed with measurements conducted in the same test facility using the naphthalene sublimation technique as well as thin film gages. Calculations were made with a two-dimensional boundary layer code.
Laminar Forced Convection Flow Past an In-Line Elliptical Cylinder Array With Inclination
Authors: Alawadhi Esam M.
Published: May 2010

Laminar forced convection flow past an in-line elliptical cylinder array with inclination is simulated using the finite element method. The inclination of the elliptical cylinders is increased with the number of the cylinder in the array, 0 deg for the first cylinder and 90 deg for the last cylinder. The global objective of this research is to enhance the heat transfer out of the cylinders. A parametric study of heat exchanges between the cylinders and flow (expressed by the Nusselt number) is reported for Reynolds numbers between 125 and 1000, while the Prandtl number is fixed at 0.71. The results are compared with an elliptical cylinder array without inclination to assess the heat transfer enhancement. The problem is solved as transient, and a vortex shedding phenomenon is reported. The results indicated that the Reynolds number has a significant effect on the heat transfer out of the cylinders, and the inclination of the elliptical cylinders enhances heat transfer rate up to 238.59%, but pressure drop is increased as high as 700%. Also, skin-friction coefficient along the five cylinders’ perimeter, plots of the velocity flow field, and temperature contours are presented.
New Bio-Inspired, Multiphase Forced Convection Cooling by ABS Plastic or Encapsulated Paraffin Beads
Authors: Hassanipour Fatemeh , Lage José L.
Published: May 2010

Preliminary experimental results of forced convection by octadecane paraffin (encapsulating phase-change material (EPCM)) particles, acrylonitrile butadiene styrene plastic particles, or by clear (of particulates) water flowing through a heated parallel-plates channel are reported. The objective is to investigate the mixing effect of the particles vis-à-vis the latent heat effect. The particle concentration is kept at 3% in volume. The results, in terms of surface-averaged channel temperature and heat transfer coefficient for different fluid speed and heat-flux, indicate the mixing effect to account from 19% to 68% of the heat transfer enhancement produced by using EPCM particles. Hence particle mixing, even at a very low particle concentration, is an effective convection mechanism.
Analysis of Microheat Pipes With Axial Conduction in the Solid Wall
Authors: Hung Yew Mun , Tio Kek-Kiong
Published: May 2010

A one-dimensional, steady-state model of a triangular microheat pipe (MHP) is developed, with the main purpose of investigating the thermal effects of the solid wall on the heat transport capacity of an MHP. The energy equation of the solid wall is solved analytically to obtain the axial temperature distribution, the average of which over the entire length of the MHP is simply its operating temperature. Next, the liquid phase is coupled with the solid wall by a heat transfer coefficient. Then, the continuity, momentum, and energy equations of the liquid and vapor phases are, together with the Young–Laplace equation, solved numerically to yield the heat and fluid flow characteristics of the MHP. The heat transport capacity and the associated optimal charge level of the working fluid are predicted for different operating conditions. Comparison between the models with and without a solid wall reveals that the presence of the solid wall induces a change in the phase change heat transport by the working fluid, besides facilitating axial heat conduction in the solid wall. The analysis also highlights the effects of the thickness and thermal conductivity of the solid wall on its axial temperature distribution. Finally, while the contribution of the thermal effects of the solid wall on the heat transport capacity of the MHP is usually not dominant, it is, nevertheless, not negligible either.
Enhancement of Saturation Boiling of PF-5060 on Microporous Copper Dendrite Surfaces
Authors: El-Genk Mohamed S. , Ali Amir F.
Published: May 2010

Experiments are performed to investigate saturation boiling of degassed PF-5060 dielectric liquid on microporous copper dendrite surface layers deposited on 10×10 mm2 Cu substrates. The electrochemically deposited surface layers are of different thicknesses (145.6 μm, 46.3 μm, and 33.1 μm). The thickest layer gives the best results: the saturation CHF of 25.27 W/cm2 occurs at a surface superheat of only 2.9 K and the maximum nucleate boiling heat transfer coefficient, hMNB, near the end of the fully developed nucleate boiling region, is 8.76 W/cm2 K. In addition, nucleate boiling ensues at a surface temperature slightly above saturation (<0.5 K), with no temperature excursion. The temperature excursions before initiating boiling on the 46.3 μm and 33.1 μm thick Cu nanodendrite surface layers are small (3.7 K and 6 K), corresponding to surface temperatures of ∼55.1°C and 57.4°C, respectively. These temperatures are much lower than recommended (85°C) for reliable operation of most silicon electronics and central processor units.
The Onset of Convection in a Layer of Cellular Porous Material: Effect of Temperature-Dependent Conductivity Arising From Radiative Transfer
Authors: Nield D. A. , Kuznetsov A. V.
Published: May 2010

The onset of convection in a horizontal layer of a cellular porous material heated from below is investigated. The problem is formulated as a combined conductive-convective-radiative problem in which radiative heat transfer is treated as a diffusion process. The problem is relevant to cellular foams formed from plastics, ceramics, and metals. It is shown that the variation of conductivity with temperature above that of the cold boundary leads to an increase in the critical Rayleigh number (based on the conductivity of the fluid at that boundary temperature) and an increase in the critical wave number. On the other hand, the critical Rayleigh number based on the conductivity at the mean temperature decreases with increase in the thermal variation parameter if the radiative contribution to the effective conductivity is sufficiently large compared with the nonradiative component.
Analysis on Acoustic Emission Produced by Strength Test of Bio-Ceramics: Dependency of AE Parameters on the Material Property
Authors: Nakayama Mitusyuki , Suzuki Hideto
Published: May 2010

Recently, advanced material used as a bio-ceramic is developed. These materials have one of the important features that characteristics of biocompatibility are improved considerably. However, these advanced materials include some problems that the strength of bio-ceramics decreases in accordance with improvement of biocompatibility. In this paper, it is the main purpose to accurate the acoustic emission characteristics of bio-ceramics on the breaking test, which has never been discussed enough. Therefore, AE parameters are calculated with the wave form of AE signal emitted on the breaking test. Next, the relation between AE parameters and material property of bio-ceramics are discussed in order to accurate the effectiveness of micro-structure elements to mechanical characteristics. As a result, it is found that AE parameters have remarkable dependence on micro-structure element in the body of bio-ceramics. Consequently, it is clarified that the acoustic emission method gives good agreement with the mechanical characteristics.
The Role of Fin Geometry in Heat Sink Performance
Authors: Khan Waqar A. , Culham J. R. , Yovanovich M. M.
Published: May 2010

The following study will examine the effect on overall thermal/fluid performance associated with different fin geometries, including, rectangular plates as well as square, circular and elliptical pin fins. The use of EGM allows the combined effect of thermal resistance and pressure drop to be assessed through the simultaneous interaction with the heat sink. A general expression for the entropy generation rate is obtained by using the conservations equations for mass, energy, and entropy. The formulation for the dimensionless entropy generation rate is developed in terms of dimensionless variables, including the aspect ratio, Reynolds number, Nusselt number and the drag coefficient. Selected fin geometries are examined for the minimum entropy generation rate corresponding to different parameters including axis ratio, aspect ratio, and approach velocity. The results clearly indicate that the preferred fin profile is very dependent on these parameters.
Effects of Localized Heat Generations Due to the Color Conversion in Phosphor Particles and Layers of High Brightness Light Emitting Diodes
Authors: Arik Mehmet , Weaver Stanton , Becker Charles , Hsing Michael , Srivastava Alok
Published: May 2010

The efficiency and reliability of the solid-state lighting devices strongly depend on successful thermal management. Light emitting diodes, LEDs, a strong candidate for the next generation general illumination applications are of interest. Typical white LEDs start with either blue or near UV light generated by the active quantum layers. The light is guided through a transparent encapsulant filled with micron sized phosphor particles. The phosphor particles up-convert the short wavelength light to desired colors, producing white light. Due to low quantum efficiency, during the conversion, localized heating of small particles occurs. Experimental results with high brightness LED packages showed that there is significant light output reduction. Idealized numerical models through Finite element technique were created to evaluate the effects of localized heat generations at particles and layers. Results showed that as small as a 3 mW heat generation on a 20 μm diameter spherical phosphor particle might lead to excessive temperatures which can be a major source of light output degradation and reliability concern for high brightness LEDs.
Chip in Polymer: 3D Integration of Active Circuitry in Polymeric Substrate
Authors: Jung Erik , Wojakowski Dirk , Neumann Alexander , Ostmann Andreas , Aschenbrenner Rolf , Reichl Herbert
Published: May 2010

The demand to miniaturize products especially for mobile applications and autonomous systems is continuing to drive the evolution of electronic products and manufacturing methods. One key to miniaturization developed in the past was the use of unpackaged, bare dice. Saving the volume and weight of the package, significant reduction in footprint was achieved. A next step conceived to further the miniaturization is the integration of functions on miniaturized subsystems, i.e. System-in-Package (SiP), in contrast to a full silicon integration (System-on-Chip, SoC). Here, use of recent manufacturing methods allows to merge the SiP approach with a volumetric integration. Up to now, most of the systems make use of single- or double-sided populated system carriers. Embedding of passive components was a first step forward. A new challenge is to incorporate not only passive components, but as well active circuitry (IC’s) and the necessary thermal management. Ultra thin chips (i.e. silicon dies thinned down to <50μm total thickness) lend themselves to reach these goals. Chips with that thickness can be embedded in the dielectric layers of modern laminate PCB’s. Micro via technology allows to contact the embedded chip to the outer faces of the system circuitry. As a ultimate goal for microsystem integration, the embedding of optical and fluidical system components can be envisioned. This paper presents the first attempts to embed thin silicon dies in to polymeric system carriers. The aspects of embedding and making the electrical contact as well as the thermal management are highlighted. To reach the goal of a vertically stackable “box-of-bricks” type of ultra thin (UT) package, thin silicon chips are embedded and interconnected on a peripheral UT-CSP.
Crack Area Analysis of SnPb and SnAg Solder Joints in Plastic Ball Grid Array Packages From Dye Penetration Studies
Authors: Park Changyoung , Dias Filho Jose Marcio , Kim Donghyun , Mawer Andrew , Masada Glenn Y. , Moon Tess J.
Published: May 2010

Crack growth in solder joints caused by thermal cycling is a critical issue for reliability in electronic packages. This study presents experimental data on crack growth in SnPb and SnAg solder joints of 357-joint PBGA packages attached to PWBs and subjected to 30-minute, 0°C to 100°C temperature cycles. The board assemblies were exposed to three process conditions upon exiting the solder reflow furnace—air cooled to room temperature, quenched at 0°C, and aged at 150°C (SnPb) or 160°C (SnAg) for 1008 hours—prior to the accelerated thermal cycle testing. At scheduled intervals, the packages were dye-penetrated, removed from the board, and the joint crack areas in several regions measured. The experimental data and statistical analysis of 9000 joints show that SnAg solder joints have half the crack areas of their SnPb counterparts for all regions, cycles and aging conditions. For both solders, the joints located under the die edge have the largest cracks of any region, and the three adjacent joints at each of the four corners under the die edge are the joints most likely to have the largest crack areas. Comparing aging conditions, the differences in the means of % crack area for SnPb packages were not statistically different, but for SnAg packages, the aged joints had 50% smaller crack areas than non-aged joints (air and quench).
Vibration Fatigue Test of Surface Mount Electronic Components
Authors: Wong T. E. , Fenger H. S.
Published: May 2010

The objectives of the present studies are to design and test representative commercial off-the-shelf plastic encapsulated microcircuits, including various types of ball grid array (BGA) components, chip scale package, flip chip, lead flat pack, and leadless capacitor, over military random vibration levels. The approach is to demonstrate the solder joint reliability performance of these components through the design of an electrical daisy-chain pattern printed wiring board (PWB) assembly test vehicle (TV), in which the design and manufacturing variables are included. The three variables, including BGA underfilled materials, solder pad sizes on PWB, and BGA rework, with each having either two or three levels of variation are used to address test criteria and to construct 14 different types of TV configurations. All TV configurations are then subjected to random vibration tests while continuously monitoring solder joint integrity. Based on the measured results, a destructive physical analysis is then conducted to further isolate the failure locations and determine the failure mechanisms of the solder joints. Test results indicate that the 352-pin tape BGA and 600-pin super BGA are more susceptible to failure than plastic BGAs under the same conditions, and that the use of underfilled materials appears to improve the life expectancy of all the components. The stiffer packages of tape BGA and super BGA, which have copper heat spreaders, may account for higher BGA solder joint stress/strain during random vibration tests. Test data also shows that only a limited number of electrical opening are observed. This indicates that the test modules are robust enough to survive the random vibration inputs. One possible reason is that the test modules are very stiff, whose 1st mode of natural frequency is about 550 Hz. Therefore, the curvature changes of the test modules are minimal, which resulted in smaller relative motion between the package and the PWB, and less solder joint stresses. All these test results are recommended to be used for calibrating BGA solder joint vibration fatigue life prediction models, which will be presented in other publications.
Thermal and Physical Characterization and Curing Kinetics Study of a Novel Curable Fillet Forming Ball Attach Flux for Improvement of Solder Joint Reliability on Ball Grid Array Packages
Authors: Chandran Dennis Prem Kumar , He Yi , Gan Eng Chiang
Published: May 2010

This paper concentrates on the characterization of a novel curable fillet forming ball attach flux. This polymer based material is expected to improve 2nd level interconnet solder joint reliability on ball grid array packages. The evaluations reported in this paper consist of the characterization of their physical and thermal properties. With the understanding of the materials physical properties, the failing mechanism, and material robustness can be predicted.
Design of Micro-Arrayed Thin Film Thermocouples (TFTC)
Authors: Park Jong-Jin , Taya Minoru
Published: May 2010

We designed the thin film thermocouples (TFTC) made by T-type (Copper-Constantan) thermocouple arrays in order to measure temperature distribution at higher spatial resolutions. This sensor consists of a few different layers; silicon wafer, thin aluminum nitride (AlN) layer, and thin film thermocouple layers. The thickness of the thin aluminum nitride (AlN) layer is 100nm and the layer is located between silicon wafer and thin film thermocouples to construct an electrical insulator and thermal conductor. T-type (Copper-Constantan) thermocouples are deposited on the aluminum nitride (AlN) layer over the silicon wafer and the copper thickness and constantan thickness are 50nm, repectively. The sensor area is 10mm × 10mm, and has 10 × 10 junction arrays, and each junction has 100μm × 100μm surface area. According to the measured data, electrical resistivitives of thin films are almost 5 times greater than those of bulk materials. This is based on the comparison of thermal simulation and measured data of 1-D heat conduction in steady state. Seebeck coefficients between copper bulk material and constantan thin film are calculated and the weight factor is defined due to Seebeck coefficient mismatches of bulk materials and thin films. Thermal simulation of 2-dimensional heat conduction in steady state calculated by finite element analysis and compared with the measured data, resulting in a good agreement between simulations and measured data.
Analysis of ACF Contact Resistance
Authors: Constable J. H.
Published: May 2010

An analysis of the electrical resistance of an anisotropic conducting film (ACF) bond is presented. The electrical circuit for the bond resistance is divided into its different geometric regions for analysis. While the analysis of the resistance resulting from the bond pads is more complex than other regions because of the multiple random contact points, it is argued that the formula developed by Greenwood gives an adequate estimate of this contribution. A comparison is made of this estimate with evaluations in the literature, and the importance of the disagreement between methods is discussed. The magnitude of the contact resistance between the contact pad and particle (including film and constriction resistance), and the resistance of the deformed particle, are still contentious issues, and evidence is presented addressing this issue. In all previous reported results, excluding the author’s, the implicit assumption is that the apparent physical area of contact between the deformed particle and the bond pad is equal to the real area of electrical contact. This work reinforces the author’s contention that the electrical contact area is only a small fraction of the mechanical contact area, just as it is in separable contacts. A calculation is presented that evaluates the effect of electrically heating the ACF bond in order to separate the contact resistance from the remaining bulk resistance of the interconnect. In this technique, the small metal asperities (a-spots) on the surface of the apparent contact region are preferentially electrically heated due to their much higher current density, which in turn changes the resistance of the a-spot. Previous calculations of this effect have been carried out only for conductors that obey the Wiedemann-Franz law, and calculations in this work have extended the results to materials used in ACF bonds that depart significantly from the Wiedemann-Franz law. Further, it is argued that the observed larger than expected contact resistance in ACA bonds is likely due to a high resistivity temperature independent film resistance.
Prediction of Electromigration Failure in Passivated Polycrystalline Line Considering Passivation Thickness
Authors: Sasagawa Kazuhiko , Hasegawa Masataka , Yoshida Naoki , Saka Masumi , Abe´ Hiroyuki
Published: May 2010

It is known that the lifetime of the passivated metal line varies depending on kind and thickness of the passivation layer. The appropriate consideration of the effect of passivation on electromigration damage makes it possible to evaluate the reliability of the metal line with choosing kind or thickness of the passivation. This paper is focused on the effect of passivation thickness on the failure prediction. The failure prediction considering the passivation thickness is shown. First, the film characteristic constants depending on the passivation thickness are experimentally determined in the lines with three kinds of passivation thickness. Next, by extrapolating the obtained dependencies, the characteristic constants are determined to predict the lifetime of the line covered with the thicker passivation than that employed in the experiment, and the lifetime is predicted by the reliability evaluation method based on the numerical simulation.
Newly Developed Real Time Monitoring System for Ionic Migration by Means of Quartz Crystal Microbalance (QCM) and Electrochemical Impedance Spectroscopy (EIS)
Authors: Yoshihara Sachio
Published: May 2010

Micro-fabricated or Nano-fabricated Printed Circuit Boards (PCB) using environmental friendly materials and processes will be desirable candidates for future electronic packaging technologies. To investigate the ionic migration for thus developed PCB, quite new measurement method has been developed by the authors, which enables real time monitoring of the growth process of ionic migration using QCM (Quartz Crystal Microbalance) and Electrochemical Impedance Spectroscopy (EIS). First part of this research has focused on the QCM method and EIS to study the process of ion migration (hereinafter we call it simply “migration”) in various types of lead-free solder plating and the effects of the reflow (Heat treatments) processing and flux residue of soldering processes. In addition, we investigated the anodic dissolution characteristics of the elements in each type of solder alloy by measuring the current-potential curves in 0.1 kmol m−3 KNO3 solution. When using Sn-3.5 mass%Ag solder plating, reflow processing segregate the stable compound Ag3Sn layer and Sn layer. The Sn layer selectively promotes the anodic dissolution reaction, increasing the occurrence of migration. When using Sn-9 mass%Zn solder plating, the Sn effectively prevents the excessive dissolution reaction of Zn. However, since reflow processing causes each element to separate out, reflow processing lessens the effectiveness of Sn, thus promoting the occurrence of migration. The flux processing of lead-free solders suppresses anodic dissolution and effectively prevents the occurrence of migration. However, with Sn-9 mass%Zn, the lowered adhesion between the flux film and the electrodes is a factor in speeding the growth of migration. The ionic migration of lead free solder in severe NOx circumstance will be commented. Next, electric reliability of the newly developed copper printed boards by NEDO project (L/S = 4/6, 8/12, 12/16 μ□) using polyimide as the substrate have been evaluated under 85 °C, 85%RH. The generation of the migration was tested by conventional time dependence of current under bias of 5.0 V. The progress of the migration could be investigated by EIS (Cole-Cole plots of the impedance). The degradation of the diameter of the impedance loop suggested the intimation of migrations. Finally, in order to establish the micro-fabricated printed circuit boards, “semi-additive” process will be one of the candidates. The process involves the copper etching processes by use of FeCl3 or CuCl2 aqueous solution. But even after the cleansing of such etched substrate, some residue of the iron or copper contaminants will affect the electric reliability of the boards. Such effects have been evaluated by the QCM method. The obtained results suggested that scarce residue of iron contaminants will diminish the reliability rather than residue of copper contaminants.
Through-Hole Drilling Condition of FR-4 Printed Wiring Boards Based on Preventing Ion Migration
Authors: Aoyama Eiichi , Nobe Hiromichi , Ikuta Tadayuki , Katayama Tsutao , Hirogaki Toshiki , Inoue Hisahiro , Yamauchi Katsutoshi
Published: May 2010

In the printed wiring board manufacturing sector, methods have been developed to improve the circuit packaging density. A problem has emerged in that the quality of drilled through hole is deteriorating in the smaller diameter drilling of printed wiring boards (PWBs) with high packaging density, because the insulation is insufficient among through-holes after plating in finer circuit pattern. Thus, we have attracted attention to occurrence of delamination in the glass cloth around the drilled hole of FR-4 type PWBs, because it is considered that the poor insulation among through holes is caused by ion migration along the delamination of glass cloth. In the drilling hole to GFRP, Damage occurs from the drilled hole wall to the inside of material by peeling off between layers, it is defined as delamination in this study. In the present report, we describe the influence of drilling conditions on the width of delamination of glass cloth around the drilled hole. First, we made the FR-4 type PWBs (thickness 0.2 mm) reinforced by five kinds of glass cloths. We carried out the drilling experiments (spindle speed 33000rpm and feed rate 0.01–0.06 mm/rev) for these PWBs with diameter 0.4 mm drill tools. Second, we researched the relationship between delamination width and relative hole position for the glass cloth thickness by image processing method. As a result, we demonstrate two important factors (the feed rate conditions in drilling and the thickness of glass cloth at drilled hole wall) to prevent the delamination of glass cloth. The practical formula is proposed to predict the delamination width around the drilled hole by a multivariate analysis method.
Quality Estimating Model Based on Temperature of Hole Bottom in Laser Drilling of Blind Holes
Authors: Aoyama Eiichi , Kondou Hisaya , Minagi Ryu , Katayama Tsutao , Hirogaki Toshiki , Inoue Hisahiro
Published: May 2010

The printed wiring board (PWB) has becomes relatively smaller due to the downsizing of electric devices. Higher densification has been advanced by the circuit formation of multi-layer PWBs in the current manufacturing of these boards. In current manufacturing of multi-layer printed wiring boards, a method frequently used is to laminate the core with insulating resin as build-up layers. Microvia drilling using laser technology has become the prevailing method of machining smaller blind via holes. Aramid fiber reinforced plastic (AFRP) is considered suitable material for the build-up layers, because it is efficient in laser drilling. However, heat damage in the hole has been a problem because the laser drilling cause a heat damage to the PWB materials. The poor hole quality, such as the carbonization of the resin and the peel around circuit copper foil/core material, causes decrease in the reliability of circuit connections. In the present report, first, we took multi layer PWB-reinforced by aramid unwoven cloth, and measured the temperature distribution of the circuit copper foil during laser drilling using a thermocouple. Second, we proposed a heat input prediction model using a finite element method (FEM), considering the change of laser absorption of the circuit copper foil surface. Finally, we carried out a thermal stress analysis based on the temperature distribution, and confirmed the efficiency of this analysis. As a result, the calculated temperatures by this model, considering the variation of the absorption of foil surface during laser drilling, are in good agreement with the experimental temperatures. It is confirmed that this model is effective in estimating the temperatures and thermal stresses in the bottom copper foil during laser drilling of the build-up layers.
Experimental Analysis of Compressive Stresses in ACF Flip Chip Joint and Its Influence on ACF Joint Reliability
Authors: Kwon Woon-Seong , Paik Kyung-Wook
Published: May 2010

This paper presents the mechanical contribution of shrinkage stress in a bonding process to electrical conduction establishment and reliability of ACF joint. The conduction establishment and reliability of ACF joint strongly depend on joint clamping force related with the thermal and mechanical properties of ACF. Therefore, it is important to understand the effect of ACF shrinkage stresses on the conduction establishment and reliability. In this study, thermal and mechanical properties of ACF materials were investigated during and after thermal reaction. The important mechanical mechanism of ACF conduction for good bonding quality and reliability is the joint clamping force developed during curing and cooling-down process of ACFs. Based on thermo-mechanical properties involved in ACF thermal reaction, the build-up behavior of thermally induced shrinkage stress during curing and cooling-down processes of ACF materials was experimentally investigated. It was experimentally shown that the shrinkage stresses of ACF materials are strongly dependent on material properties such as modulus, CTE and Tg. Moreover, it was evident that in temperature aging test, ACF joint reliability was affected by compressive stress. These results indicate that shrinkage stress, developed by the thermal reaction of ACFs, is the important parameter to the electrical conduction establishment and reliability of interconnects using ACF material.
Packaging Friendly Parallel Optical Transceivers
Authors: Wang Xiaoqing , Kiamilev Fouad , Papen George , Ekman Jeremy , Gui Ping , Haney Mike , Deroba Joseph , McFadden Michael , Kuznia Charles
Published: May 2010

High-density, small spot size, and high power consumption have imposed both a technical and an economic challenge on optoelectronic (OE) packaging. Device non-uniformity and dynamic operating environments cause device performance variations, especially in applications where large OE arrays are employed. We describe our work to explore the opportunities in transceiver circuit design to relax optical alignment requirements, provide efficient thermal management, and allow dynamic variation within the optical system. Our approach focuses on a built-in power negotiation algorithm, which is developed to dynamically optimize the power consumption of optical links based on the bit error rate (BER) of each optical link. This algorithm can be executed as the system is powered up or during normal system operation if the link is idle or a change has been made. It converges to an optimal setting for each vertical cavity surface emitting lasers (VCSEL) that has the minimum power consumption for a given target BER. The intelligence of the dynamic power optimization provides the system with the capability of compensating for the potential variations in the system and therefore, relaxing the packaging requirements. We implement this algorithm in a 0.5μm CMOS silicon-on-insulator (SOI) chipset and develop parallel optical transceivers based on VCSELs and photodetectors to demonstrate the benefit of our approach. We build a field programmable gate arrays (FPGA) based test bed where both fiber optic and free-space optical interconnects are used for communications between two chips. Test results show that the algorithm is able to find the optimum power setting for all VCSELs despite varied light attenuation in optical path.
Microwave Imaging of Conductivity Distribution of Silicon Wafers
Authors: Ju Yang , Saka Masumi , Abe´ Hiroyuki
Published: May 2010

Conductivity of silicon wafers was measured using the amplitude of the reflection coefficient of a microwave signal. A network analyzer was used to generate the microwave signal fed to a sensor and to measure the amplitude of the reflection coefficient. An open-ended coaxial line sensor was used to increase the spatial resolution and the sensitivity of the measurement. By microwave imaging, the distribution of the conductivity of a silicon wafer was mapped.
Effect of Ni Coating Over Cu Ball on the Microstructure of Flip Chip Joints With Cu-Cored Solder Balls
Authors: Shohji Ikuo , Shiratori Yuji , Yoshida Hiroshi , Mizukami Masahiko , Ichida Akira
Published: May 2010

Effect of Ni coating over the Cu core of Cu-cored Sn-5mass%Ag balls was investigated on the microstructures of flip chip joints with Ni/Au plated Cu pads after reflow soldering and the subsequent heat exposure at 423 K. For joints using Cu-cored Sn-5Ag balls with Ni coating over the Cu core, a Ni-Sn reaction layer forms at the Cu core/Sn-5Ag interface. A similar Ni-Sn reaction layer forms at the interface between the Sn-5Ag solder and the Ni/Au plated Cu pad. Although the Ni-Sn reaction layers grow with increasing the thermal exposure time, the growth rate is slower than that of a Cu-Sn reaction layer formed at the Cu core/Sn-5Ag interface in the joint with the Cu-cored Sn-5Ag ball without Ni coating over the Cu core.
A Research of Actuators for Micromirror Control
Authors: Mamiya Hiroki , Ishikawa Koji , Yu Qiang
Published: May 2010

In this paper, a new thermal actuator for micromirror control with very low operating voltage is described. The actuator consists of three straight polysilicon cantilever arms and a polysilicon winding arm that is inherently twisted due to stress-induced bending. Controlling heat generating positions in those arms, the actuator shows both torsional and vertical motions. Mechanical-electro-thermal FEM simulation results show that the actuator has more than a 1.11 degree twisting angle and a 2.31 μm vertical displacement. In order to enhance torsional motion, design optimization is carried out by using a response surface method called the statistical design support system. After optimization, the total twisting angle improves to 2.05 degrees which is enough to actuate micromirrors for optical beam adjusting, switching and attenuating.
Controlled S-Parameters on Multi-Layer Package
Authors: Chen Nansen , Chiang Kevin , Wang Y. P. , Hsiao C. S.
Published: May 2010

Multilayer packages are extensively used and designed in high-speed and wireless applications. An approach to achieve the controlled S-parameters with 15% less degradation than the original multilayer package design at 5 GHz was presented. The substrate dimension budget was determined to meet the manufacturing capability using 3-D full wave simulator. Controlling the return loss is the domination of the overall controlled S-parameters.
Thermodynamic Assessment of Sn-Co-Cu Lead-Free Solder Alloy
Authors: Liu Libin , Andersson Cristina , Liu Johan , Chan Y. C.
Published: May 2010

To select a lead-free solder system, factors such as eutectic/peritectic point, electron negativity, abundance, cost, toxicity of elements, world production capacity, segregation during solidification, possibility to form low melting phases with Pb, among others must be carefully considered. On the basis of thorough analysis of binary phase diagrams of Sn-X-systems (X represents other elements) and the properties of the element X, the Sn-Co-Cu eutectic ternary alloy system has been chosen as a new lead-free solder candidate. In order to find the eutectic point for the Sn-Co-Cu system, the Sn-Co binary system was thoroughly assessed with CALPHAD (CALculation of PHAse Diagram) methods. The ternary phase diagram of Sn-Co-Cu system was extrapolated with the assessed thermodynamic parameters of Sn-Co, Sn-Cu, and Co-Cu system. The eutectic point for L–Sn2Co+(Sn)+Cu6Sn5 is 224.4°C and 0.37%Co and 0.68%Cu and 98.95%Sn.
Analysis of the Micro-Mechanical Properties in Aged Lead-Free, Fine Pitch Flip Chip Joints
Authors: Liu Changqing , Conway Paul , Li Dezhi , Hendriksen Michael
Published: May 2010

This research seeks to characterize the micro-mechanical behavior of Sn-Ag-Cu solder bumps/joints generated by fine feature flip chip fabrication and assembly processes. The bumps used for characterization were produced by stencil deposition of solder paste onto an electroless Nickel UBM, followed by a bump-forming reflow soldering process and the final assembly joints were then achieved by a subsequent reflow of die onto a fine feature Printed Circuit Board (PCB). The bumps and joints were aged at either 80°C or 150°C for up to 1.5 months and then analyzed by means of micro-shear testing and nano-indentation techniques. The shear test of the aged bumps showed a slight increase in shear strength after an initial period of aging (∼ 50h) as compared to as-manufactured bumps, but a decrease after longer aging (e.g. 440 h). A brittle Ag3Sn phase formed as large lamellae in the solder and along the interface between the Cu on the PCB during the initial aging, and is attributed to the increase of shear strength, along with the refinement of the bump microstructure. However, as the time of aging extended, the solder bumps were softened due to grain growth and re-crystallization. It was found that the formation of brittle phases in the solder and along the interfaces caused localized stress concentration, which can significantly affect joint reliability. In addition, Nano-testing identified a lamellar Au-rich structure, formed in the solder and interface of the solder/PCB in the joints after the aging process. These are believed to be detrimental to joint reliability.
An Investigation of Spray Cooling Thermal Management for Semiconductor Burn-In
Authors: Cader T. , Tolman B. , Tilton C. , Harris M. C.
Published: May 2010

Semiconductor logic burn-in is a process during which potentially large quantities of devices are subjected to elevated temperatures and voltages in order to accelerate latent reliability defects and processing problems to failure prior to customer delivery. During burn-in, there is typically a large variation in the device power levels as well as a product-specific maximum burn-in temperature. Such variations result in a wide device temperature distribution (i.e., device temperature spread), which lowers the median allowable device temperature for the lot. Burn-in time is directly related to the median device temperature, in the sense that the lower the median temperature, the longer the required burn-in time. An optimum thermal management solution is one that is reliable, low-cost, enables a high median device temperature, and maximizes device throughput. Current thermal solutions include forced convection air-cooling, single-phase liquid-cooled heat sinks, and thermoelectric coolers. Some of the solutions employ thermal interface materials, as well as an active thermal control scheme for minimization of device temperature spread. All current solutions also employ an engage mechanism that places the thermal solution in contact with the device under test (DUT). The thermal solution at each DUT is typically gimbaled in an effort to ensure uniform contact pressure between the cooling head and device. The present study deals with the application of direct spray cooling of semiconductor devices undergoing burn-in: this approach negates the need for an actuation mechanism and thermal interface material, is capable of reduced junction temperature spread via active thermal control, and results in reduced across device temperature “gradients”. A spray cooled burn-in slot level prototype was built to accommodate single burn-in boards for bare DUTs as well as small and large lidded DUTs. The solution was investigated primarily for thermal capability and device-to-device junction temperature spread, but results were also obtained for on-DUT thermal “gradients”. For the specific test conditions selected, the heat flux removal capability demonstrated was 146W/cm2 for the bare DUT, 136W/cm2 for the small lidded DUT, and 63W/cm2 for the large lidded DUT. For each DUT investigated, and through the use of active flow control, the device temperature spread between two devices running at a 50% difference in power levels was shown to be less than 1°C.
8CH AWG Multi/Demultiplexer With MEMS Variable Optical Attenuator
Authors: Ishikawa K. , Yu Q.
Published: May 2010

An integrated arrayed waveguide grating multi/demultiplexer (AWG) with a micro-electro-mechanical systems (MEMS) based variable optical attenuator (VOA) is reported. The device consists of an AWG based on silica and a MEMS-VOA chip. The MEMS chip includes 100 μm × 100 μm polysilicon shutter plates coated with gold and electrostatic comb-drive actuators. The MEMS chip is interposed in a trench located in the middle of the I/O waveguides of the AWG to tune the optical transmitting power intensity through the waveguides continuously. The MEMS-VOA shutters have more than a 10 μm displacement. Using those shutters, 30 dB optical contrast from 5 dB at the transmit state to 35 dB at the isolation state is achieved. The obtained attenuation contrast is greater than that of a conventional waveguide-based Mach-Zehnder interferometer VOA and sufficient to adjust and equalize the optical signal power in the wavelength division multiplexing (WDM) network systems.
The Effect of Multiple Reflow Times on Lead-Free Solder Joint Microstructure
Authors: Nurmi Sami T. , Sundelin Janne J. , Ristolainen Eero O. , Lepisto¨ Toivo K.
Published: May 2010

As environmental issues are raising more interest and are becoming crucial factors in all parts of the world, more and more environmental-friendly electronics products are emerging. Usually this means the introduction of products with lead-free solders. However, the reliability of lead-free solders is still a serious concern despite the vast research done in this field. This paper will describe the interconnect reliability of three kinds of solder joints respectively prepared with lead-free solder paste and lead-free PBGA components, lead-free solder paste and tin-lead-silver PBGA components, and tin-lead solder paste and tin-lead-silver PBGA components. Lead-free and tin-lead solders were composed of eutectic tin-silver-copper and tin-lead, respectively. In addition, the study also presents the effect of multiple reflow times. The study focuses on the microstructures of different assemblies. The particular interest is on the assemblies soldered with lead-free solder paste and tin-lead-silver PBGA components, since the SnPbAg solder on the bumps of the PBGA components were exposed to the reflow profile meant for the lead-free SnAgCu solder. Thus, these SnPbAg solder bumps were in the molten state almost twice as long as the rest of the solders. This had a notable effect on the reliability of these solder joints as we will be showing later in this paper. The test boards were temperature-cycled for 2500 cycles between −40 and +125°C (a 30-minute cycle). PBGA solder joint failures were monitored with a real time monitoring system. Optical and scanning electron microscopy was used to inspect the broken solder joints and their microstructure. The results of tests indicate that the number of reflow times can significantly affect the lifetime of PBGA solder joints. The most notable changes can be seen in the solder joints made with tin-lead-silver PBGA components and tin-silver-copper solder paste soldered with a lead-free reflow profile. The general trend was that the reliability of the solder joints increased in proportion to the number of reflow times. Mainly two factors are believed to have the major effect on the reliability of PBGA solder joints, voids, and microstructural changes in solder.
Design Optimization of Via Transitions for Broadband Applications
Authors: Lu Albert Chee W. , Fan Wei , Wai Lai L. , Jin Lin , Low Lee A.
Published: May 2010

This paper describes the two key aspects of via transition optimization methodology: impedance matching and power plane resonance suppression. Ground vias are used to improve the impedance mismatch caused by the via transition and the optimal location of the ground vias at the same time helps to suppress the resonance caused by the cavity effect of the power plane pair. Full-wave electromagnetic simulations were carried out to demonstrate that via transition optimization is able achieve resonance-free high bandwidth operation. Optimal use of ground vias will not only enhance impedance matching but also significantly suppress suppression due to power plane resonance. Test vehicle characterizations were also carried out to demonstrate the impact of ground vias and power plane resonance characteristics on signal integrity.