Showing papers in "IEEE Transactions on Components and Packaging Technologies in 2007"

Dense Vertically Aligned Multiwalled Carbon Nanotube Arrays as Thermal Interface Materials

Abstract: Carbon nanotube (CNT) arrays are being considered as thermal interface materials (TIMs). Using a phase sensitive transient thermo-reflectance technique, we measure the thermal conductance of the two interfaces on each side of a vertically aligned CNT array as well as the CNT array itself. We show that the physically bonded interface by van der Waals adhesion has a conductance ~105W/m2K and is the dominant resistance. We also demonstrate that by bonding the free-end CNT tips to a target surface with the help of a thin layer of indium weld, the conductance can be increased to ~106W/m2K making it attractive as a TIM

A Practical Implementation of Silicon Microchannel Coolers for High Power Chips

Abstract: This paper describes a practical implementation of a single-phase Si microchannel cooler designed for cooling very high power chips such as microprocessors. Through the use of multiple heat exchanger zones and optimized cooler fin designs, a unit thermal resistance 10.5 C-mm2 /W from the cooler surface to the inlet water was demonstrated with a fluid pressure drop of <35kPa. Further, cooling of a thermal test chip with a microchannel cooler bonded to it packaged in a single chip module was also demonstrated for a chip power density greater than 300W/cm2. Coolers of this design should be able to cool chips with average power densities of 400W/cm2 or more

Miniature Loop Heat Pipe With Flat Evaporator for Cooling Computer CPU

Abstract: This paper presents an experimental investigation on a copper miniature loop heat pipe (mLHP) with a flat disk shaped evaporator, 30mm in diameter and 10-mm thick, designed for thermal control of computer microprocessors. Tests were conducted with water as the heat transfer fluid. The device was capable of transferring a heat load of 70W through a distance up to 150mm using 2-mm diameter transport lines. For a range of power applied to the evaporator, the system demonstrated very reliable startup and was able to achieve steady state without any symptoms of wick dry-out. Unlike cylindrical evaporators, flat evaporators are easy to attach to the heat source without need of any cylinder-to-plane reducer material at the interface and thus offer very low thermal resistance to the heat acquisition process. In the horizontal configuration, under air cooling, the minimum value for the mLHP thermal resistance is 0.17degC/W with the corresponding evaporator thermal resistance of 0.06degC/W. It is concluded from the outcomes of the current study that a mLHP with flat evaporator geometry can be effectively used for the thermal control of electronic equipment including notebooks with limited space and high heat flux chipsets. The results also confirm the superior heat transfer characteristics of the copper-water configuration in mLHPs

TCPT-2006-096.R2: Micro Scale pin fin Heat Sinks —Parametric Performance Evaluation Study

Abstract: A parametric study of heat transfer and pressure drop associated with forced flow of deionized water over five micro pin fin heat sinks of different spacing, arrangements, and shapes was conducted experimentally. Nusselt numbers and friction factors were obtained over Reynolds numbers ranging from 14 to 720. The thermal and hydraulic results were obtained to evaluate and compare the heat sinks performances at fixed mass flow rate, fixed pressure drop, and fixed pumping power. Two distinct regions of the Nusselt number dependency on the Reynolds number separated by a critical Reynolds number have been identified for unstreamlined pin fin devices while the streamlined device showed no slope change. The effects of spacing, shape of pin fins, and arrangement on friction factor and heat transfer were in agreement with existing literature. The results indicate that utilizing streamlined pin fin heat sinks can significantly enhance the thermal-hydraulic performance of the heat sink, but only at moderate Reynolds numbers.

Thermal Resistance Measurement of LED Package with Multichips

Abstract: Thermal transient measurements of high power GaN-based light-emitting diodes (LEDs) with multichip designs are presented and discussed in the paper. Once transient cooling curve was obtained, the structure function theory was applied to determine the thermal resistance of packages. The total thermal resistance from junction to ambient considering optical power is 19.87 K/W, 10.78 K/W, 6.77 K/W for the one-chip, two-chip and four-chip packages, respectively. The contribution of each component to the total thermal resistance of the package can be determined from the cumulative structure function and differential structure function. The total thermal resistance of multichip packages is found to decrease with the number of chips due to parallel heat dissipation. However, the effect of the number of chips on thermal resistance of package strongly depends on the ratio of partial thermal resistance of chip and that of slug. Therefore, an important thermal design rule for packaging of high power multichip LEDs has been analogized.

A Data Mining Based Approach to Electronic Part Obsolescence Forecasting

Abstract: Many technologies have life cycles that are shorter than the life cycle of the product they are in. Life cycle mismatches caused by the obsolescence of technology (and particularly the obsolescence of electronic parts) results in high sustainment costs for long field life systems, e.g., avionics and military systems. This paper demonstrates the use of data mining based algorithms to augment commercial obsolescence risk databases thus improving their predictive capabilities. The method is a combination of life cycle curve forecasting and the determination of electronic part vendor-specific windows of obsolescence using data mining of historical last-order or last-ship dates. The extended methodology not only enables more accurate obsolescence forecasts but can also generate forecasts for user-specified confidence levels. The methodology has been demonstrated on both individual parts and modules.

Piezoelectric Fans Using Higher Flexural Modes for Electronics Cooling Applications

Abstract: Piezoelectric fans are gaining in popularity as low-power-consumption and low-noise devices for the removal of heat in confined spaces. The performance of piezoelectric fans has been studied by several authors, although primarily at the fundamental resonance mode. In this article the performance of piezoelectric fans operating at the higher resonance modes is studied in detail. Experiments are performed on a number of commercially available piezoelectric fans of varying length. Both finite element modeling and experimental impedance measurements are used to demonstrate that the electromechanical energy conversion (electromechanical coupling factors) in certain modes can be greater than in the first bending mode; however, losses in the piezoceramic are also shown to be higher at those modes. The overall power consumption of the fans is also found to increase with increasing mode number. Detailed flow visualizations are also performed to understand both the transient and steady-state fluid motion around these fans. The results indicate that certain advantages of piezoelectric fan operation at higher resonance modes are offset by increased power consumption and decreased fluid flow

Editorial Software Obsolescence—Complicating the Part and Technology Obsolescence Management Problem

Abstract: As a result of the rapid growth of the electronics industry, many of the electronic parts in products have a procurement life cycle that is significantly shorter than the life cycle of the system they go into. A part becomes obsolete when it is no longer manufactured, either because demand has dropped to low enough levels that manufacturers choose not to continue to make it, or because the materials or technologies necessary to produce it are no longer available. The military refers to this situation as Diminishing Manufacturing Sources and Material Shortages (DMSMS). Avionics and military systems may encounter obsolescence before being fielded and always experience obsolescence problems during their field life, [1]. Today there are a growing number of methodologies, databases and tools that address status, forecasting, risk, mitigation and management of electronic parts obsolescence, [2]. However, the one common attribute of all the methodologies, databases and tools that are in use today, whether reactive, proactive or strategic, is that they focus exclusively on the hardware life cycle. In most complex systems, software life cycle costs (redesign, re-hosting and re-qualification) contribute as much or more to the total life cycle cost as the hardware, and the hardware and software must be concurrently sustained.

Acceleration Factors for Lead-Free Solder Materials

Abstract: In this paper, the acceleration factors for lead-free solder materials are discussed. The focus is on the analytical models proposed by Norris-Landzberg, Pan, and Salmela. As most reliability prediction models are originally created for eutectic SnPb solder material, it is expected that the models must be recalibrated in order to be useful in conjunction with lead-free solder materials. Pan et al. have reparameterized the Norris-Landzberg's model for SnAgCu already earlier. However, the data provided by Syed did not fit very well the reparameterized Norris-Landzberg model. An approach to explain this, and a benchmark of results based on alternative parameter value selections, is presented. The underlying assumptions related to the Norris-Landzberg's model and the applicability of the model in case of lead-free solders is discussed. Finally, an alternative form of Norris-Landzberg's equation is introduced and the fit of the existing experimental data to the proposed model is studied.

Packaging Effect on MEMS Pressure Sensor Performance

Abstract: In this study, the effect of epoxy based molding compound packaging on a micro-electro-mechanical system (MEMS) pressure sensor performance is investigated. A series of experiments were conducted to characterize the MEMS sensor over temperature and pressure changes by measuring output voltage signals. The sensor was modeled by a finite element method to investigate the stress developments. The molding compound was assumed as elastic and viscoelastic material to examine the material modeling effect on the calculation results. The model was verified by comparing the calculated results with experimental data. It was found that the stress induced by the molding compound had significant influence on the sensor performance, and the accuracy of the calculations was highly dependent on the modeling of the molding compound. Based on the results, the mechanism of the stress development and its effect on the sensor signal were discussed

Deformation Behavior of MEMS Gyroscope Sensor Package Subjected to Temperature Change

Abstract: In microelectromechanical system (MEMS) devices, the deformation of MEMS structure caused by packaging induced stress is of great concern since it directly affects the performance of the device. In this paper, deformation behavior of the MEMS gyroscope package subjected to temperature change is investigated using a high-sensitivity moire interferometry. Temperature dependent analyses of warpage and extension/contraction of the package are presented. Analysis of the package reveals that global bending deformation occurs due to the mismatch of the coefficient of thermal expansion between the chip, the molding compound, and the printed circuit board. Detailed global and local deformations of the package by temperature change are investigated, and their effect on the frequency shift of the MEMS gyroscope is studied. It is found that package deformation or package induced stress results in the frequency shift of the MEMS gyroscope structure. In order to increase robustness of the structure against deformation, a "crab-leg" type spring is replaced with a semi-folded spring. The results show that the frequency shift is greatly reduced after applying the semi-folded spring. This frequency shift is within the tolerance limit of the gyroscope sensor in this work

Mini-Contact Enhanced Thermoelectric Cooling of Hot Spots in High Power Devices

Abstract: Cooling hot-spots with high heat flux (e.g., >1000 W/cm2) is becoming one of the most important technical challenge in today's integrated circuit industry. More aggressive thermal solutions, than would be required for uniform heating, are highly desired. Recently, solid state thermoelectric coolers (TECs) have received more attention for hot-spot thermal management. However, present day TECs typically have cooling flux much lower than heat flux in the hot-spots. In this work, we reported an innovative technique-TE Mini-contact-to significantly increase cooling flux of TECs for the application in hot-spot cooling. A chip package featuring a TE Mini-contact cooler integrated with conventional integrated heat spreader and heat sink is designed. The cooling performance of such chip package has been investigated by using a 3-D numeric model. It is found that the cooling in the hot-spot (1250 W/cm2, 400 mum by 400 mum) can be about 19 degC better in the proposed package than that achieved in the conventional chip package without TEC. The effects of trench, die thickness, and TEC misalignment on the cooling of the hot-spot are also discussed.

Thermal Metrology of Silicon Microstructures Using Raman Spectroscopy

Abstract: Thermal metrology of an electrically active silicon heated atomic force microscope cantilever and doped polysilicon microbeams was performed using Raman spectroscopy. The temperature dependence of the Stokes Raman peak location and the Stokes to anti-Stokes intensity ratio calibrated the measurements, and it was possible to assess both temperature and thermal stress behavior with resolution near 1mum. The devices can exceed 400degC with the required power depending upon thermal boundary conditions. Comparing the Stokes shift method to the intensity ratio technique, non-negligible errors in devices with mechanically fixed boundary conditions compared to freely standing structures arise due to thermally induced stress. Experimental values were compared with a finite element model, and were within 9% of the thermal response and 5% of the electrical response across the entire range measured

Electrical Contact Resistance Degradation of a Hot-Switched Simulated Metal MEMS Contact

Abstract: Electrical contact resistance testing was performed by hot-switching a simulated gold-platinum metal microelectromechanical systems contact. The experimental objective was to determine the sensitivity of the contact resistance degradation to current level and environment. The contact resistance increased sharply after 100hot-switched cycles in air. Hot-switching at a reduced current and in nitrogen atmosphere curtailed contact resistance degradation by several orders of magnitude. The mechanism responsible for the resistance degradation was found to be arc-induced decomposition of adsorbed surface contaminants

Performance Improvement of a Power Conversion Module by Liquid Micro-Jet Impingement Cooling

Abstract: Liquid micro-jet array impingement cooling of a power conversion module with 12 power switching devices (six insulated gate bipolar transistors and six diodes) is investigated. The 1200-V/150-A module converts dc input power to variable frequency, variable voltage three-phase ac output to drive a 50HP three-phase induction motor. The silicon devices are attached to a packaging layer [direct bonded copper (DBC)], which in turn is soldered to a metal base plate. DI water micro-jet array impinges on the base plate of the module targeted at the footprint area of the devices. Although the high heat flux cooling capability of liquid impingement is a well-established finding, the impact of its practical implementation in power systems has never been addressed. This paper presents the first one-to-one comparison of liquid micro-jet array impingement cooling (JAIC) with the traditional methods, such as air-cooling over finned heat sink or liquid flow in multi-pass cold plate. Results show that compared to the conventional cooling methods, JAIC can significantly enhance the module output power. If the output power is maintained constant, the device temperature can be reduced drastically by JAIC. Furthermore, jet impingement provides uniform cooling for multiple devices placed over a large area, thereby reducing non-uniformity of temperature among the devices. The reduction in device temperature, both its absolute value and the non-uniformity, implies multi-fold increase in module reliability. The results thus illustrate the importance of efficient thermal management technique for compact and reliable power conversion application

Compact Harmonic Filter Design and Fabrication Using IPD Technology

Abstract: An integrated passive device (IPD) technology has been developed to meet the ever increasing needs of size and cost reduction in radio front-end transceiver module applications. Electromagnetic (EM) simulation was used extensively in the design of the process technology and the optimization of inductor and harmonic filter designs and layouts. Parameters such as inductor shape, inner diameter, metal thickness, metal width, and substrate thickness have been optimized to provide inductors with high quality factors. The technology includes 1) a thick plated gold metal process to reduce resistive loss; 2) MIM capacitors using PECVD SiN dielectric layer; 3) airbridges for inductor underpass and capacitor pick-up; and 4) a 10 mil finished GaAs substrate to improve inductor quality factor. Both lumped element circuit simulations and electromagnetic (EM) simulations have been used in the harmonic filter circuit designs for high accuracy and fast design cycle time. This paper will present the EM simulation calibration and demonstrate the importance of using EM simulation in the filter design in order to achieve first-time success in wafer fabrication. The fabricated IPD devices have insertion loss of 0.5 dB and harmonic rejections of 30dB with die size of 1.42 mm for high band (1710 MHz-1910 MHz) and 1.89 mm for low band (824-915 MHz) harmonic filters.

Predictive Model for Optimized Design Parameters in Flip-Chip Packages and Assemblies

Abstract: An analytical model is developed to predict the out-of- plane deformation and thermal stresses in multilayered thin stacks subjected to temperature. Coefficient of thermal expansion mismatches among the components (chip, substrate, underfill, flip-chip interconnect or C4s) are the driving force for both first and second levels interconnect reliability concerns. Die cracking and underfill delamination are the concerns for the first level interconnects while the ball grid array solder failure is the primary concern for the second level interconnects. Inadvertently, many researchers use the so-called rule of mixture in its effective moduli for the flip chip solder (C4)/underfill layer. In this study, a proper formula for effective moduli of solder (C4)/underfill layer, is presented. The classical lamination theory is used to predict the out-of-plane displacement of the chip substrate structure under temperature variation (DeltaT). The warpage and stresses resulting from the analytical formulation are compared with the 3-D finite element analysis. The study helps to design more reliable components or assemblies with the design parameters being optimized in the early stage of the development using closed form analytical solutions.

Avoiding Counterfeit Electronic Components

Abstract: In today's supply chain environment, electronic equipment manufacturers and Government users must be vigilant in order to avoid counterfeit electronic components. The vast majority of counterfeit cases reported are associated with purchases through independent distributors. The most effective approach to avoiding counterfeit electronic components is to purchase product directly from the original component manufacturer, or from a distributor, reseller or aftermarket supplier who is franchised or authorized by the original manufacturer. Because many components needed to produce and support defense electronics are no longer in current production, independent distributors are often used to fill this gap. While independent distributors provide a necessary function within the electronic component supply chain, they are not all created equal. Electronic equipment manufacturers and Government users need to understand the independent distributor's operations and business processes. When considering purchases through independent distributors, electronic equipment manufacturers and Government users should also apply mitigation methods and strategic approaches, such as those discussed in this paper, to reduce the potential for acquiring counterfeit parts

Compact Models of Dynamic Thermal Networks with Many Heat Sources

Abstract: A novel approach, based both on multipoint moment matching and principal component analysis, is proposed for generating passive compact models of dynamic thermal networks with many heat sources. As main result, the generated passive compact dynamic thermal networks both assure a prescribed accuracy and have a number of elements linearly related to the number of heat sources.

Numerical Study of Interrupted Impinging Jets for Cooling of Electronics

Abstract: The objective of this paper is to present the results of a numerical investigation of the effect of flow pulsations on local, time-averaged Nusselt number of an impinging air jet. The problem was considered to provide inputs to augmenting heat transfer from electronic components. The solution is sought through the FLUENT (Version 6.0) platform. The standard k-epsiv model for turbulence equations and two-layer zonal model in wall function are used in the problem. Pressure-velocity coupling is handled using the SIMPLEC algorithm. The model is first validated against some experimental results available in the literature. A parametric study is carried out to quantify the effect of the pulsating jets. The parameters considered are (1) average jet Reynolds number (5130 < Re < 8560), (2) sine and square wave pulsations, (3) frequencies of pulsations (25 < / <400 Hz), and (4) height of impingement to jet diameter ratios (5 < H/d < 9). In the case of sine wave pulsations, the ratio of root mean square value of the amplitude to the average value (AN) was varied from 18% to 53%. The studies are restricted to a constant wall heat flux condition. Parametric conditions for which enhancement in the time-averaged heat transfer from the surface can be expected are identified.

On The Problem of Using Guard Traces for High Frequency Differential Lines Crosstalk Reduction

Abstract: In this paper, the problem of using guard traces for reducing crosstalk between differential transmission line pairs is investigated, both experimentally and by full-wave electromagnetic (EM) simulations. Different cases of differential lines crosstalk are treated with and without guard trace separation between the differential line pairs. Coated microstrip printed circuit board test structures including thru-reflect-line calibration standards are designed and fabricated on a high frequency laminate material, allowing direct measurement of crosstalk between adjacent differential line pairs in the absence and in the presence of guard traces stitched with vias of regular spacing. The test structures are characterized with mixed-mode scattering parameters using a physical layer test system. Different configurations (of differential line pairs) without guard trace, with floating guard traces (which are terminated and nonterminated) and with a solid guard trace separation are investigated using a High Frequency Structure Simulator (a commercial full-wave 3-D EM simulation tool). The experimental data are compared with the simulation results, and some conclusions and guidelines on the effect of guard traces for alleviating crosstalk between differential transmission lines are presented

Flow Boiling Heat Transfer to a Dielectric Coolant in a Microchannel Heat Sink

Abstract: This paper presents an experimental study of flow boiling heat transfer in a microchannel heat sink. The dielectric fluid Fluorinert FC-77 is used as the boiling liquid after it is fully degassed. The experiments were performed at three flow rates ranging from 30-50ml/min. The heat transfer coefficients, as well as the critical heat flux (CHF), were found to increase with flow rate. Wall temperature measurements at three locations (near the inlet, near the exit, and in the middle of heat sink) reveal that wall dryout first occurs near the exit of the microchannels. The ratio of heat transfer rate under CHF conditions to the limiting evaporation rate was found to decrease with increasing flow rate, asymptotically approaching unity. Predictions from a number of correlations for nucleate boiling heat transfer in the literature are compared against the experimental results to identify those that provide a good match. The results of this work provide guidelines for the thermal design of microchannel heat sinks in two-phase flow

Thermal Characterization of Electronic Packages Using the Nyquist Plot of the Thermal Impedance

Abstract: It will be shown in this contribution that if the thermal impedance Zth(jw)of an electronic package is represented in a Nyquist plot, the curve obtained can be fitted very well to a combination of a few (n) circles, n varying between 2 and a maximum of 5. For each of these circles, it is sufficient to know the radius and the coordinates of the center point or just three parameters. With 3n parameters the entire behavior of the impedance can be represented and consequently, the dynamic behavior as well.

Optimal Pellet Geometries for Thermoelectric Refrigeration

Abstract: For a thermoelectric module (TEM) operating in refrigeration mode, the cooling flux provided by it, its coefficient of performance and its operating voltage per unit footprint are key parameters. They are provided here as a function of the temperatures on both sides of a TEM, current flow through it, electrical contact resistance at its interconnects and the geometry, material properties and packing density of its pellets. The pellet heights which maximize TEM performance (i.e., cooling flux they can accommodate for a specified temperature difference) or efficiency (i.e., coefficient of performance) at a specified performance are derived. Moreover, it is shown how to tune the operating current and voltage of a TEM by adjusting the cross-sectional area of its pellets. The analysis is performed in both the absence and presence of electrical contact resistance at the interconnects in a TEM. Implications of the results are placed in context for representative conditions

A Method of Measuring the Transient Thermal Impedance of Monolithic Bipolar Switched Regulators

Abstract: In the paper, a new electrical method of measuring the transient thermal impedance Z(t) of monolithic switched regulators with a bipolar junction transistor as a switch, is proposed. In the method, based on the cooling curve, the electrical power is dissipated in the considered device operating in the boost converter being their typical (catalogue) application circuit. As a thermally sensitive parameter, the voltage across the body diode is used. The general conception of the method is presented. As an example of the realization of the method, the measuring set for LT1073 operating in the boost converter is described and examined in detail. The correctness of the method was proved by means of the known (standard) electrical method and the infrared method, in the wide range of changes of the power dissipated in the investigated device as well as at various conditions of the device cooling.

Low Profile Integratable Inductor Fabricated Based on LTCC Technology for Microprocessor Power Delivery Applications

Abstract: A novel low profile power inductor suitable for planar integration is designed and fabricated based on low temperature co-fired ceramics technology for microprocessor power delivery applications. The inductor was designed to operate at a switching frequency of 4 to 5MHz, carrying a nominal dc current of 20A with a ripple current of 8 to 10A in a 5-V to 1-V dc-dc converter. The design and fabrication procedure is discussed in this paper, followed by small signal measurement and magnetic characterization results. The inductor was implemented in a prototype converter and the large signal measurement results are presented and its performance evaluated

Semiconductor Manufacturers' Efforts to Improve Trust in the Electronic Part Supply Chain

Abstract: One of the major problem areas in the electronic part supply chain is the issue of counterfeit electronic parts and the risks associated with them. Guidelines are needed for detecting, avoiding, and preventing the use of counterfeits in order to mitigate the risks associated with such parts. As part of this effort, we have identified the role of part manufacturers in building trust in the supply chain. Part manufacturers, as the brand owners and trademark holders, play a critical role in enhancing trust in the electronic part supply chain.

The Corrosion of Electronic Resistors

Abstract: Precision thick chip resistors are used in a variety of different industries, from telecommunications to automotive electronics, and as such can be exposed to mild and aggressive corrosive environments. This paper investigates the corrosion performance of two generic precision thick chip resistors in a controlled corrosive atmosphere consisting of 60degC, 4 ppm H2S and water vapor in purified air. The resistors were exposed in an environmental chamber for periods of 5, 10, 15, 30, and 60 days. Following exposure, the samples were cross sectioned and subjected to surface analysis using microscopy and microanalysis. After the initial stages of exposure, corrosion was observed on only one of the two types of resistors. The corrosion developed because H2S gas and water vapor diffuses through the thin protective organic layer on the resistor, and subsequently reacts with the silver conductor layer. Corrosion was facilitated by poor overlapping of the solder and nickel layer and, in particular the glass binder over the glass overcoat, which allowed silver and sulphur to diffuse along the interface. In addition, this poor overlapping allowed contact between the nickel layer and the silver layer resulting in the development of an electrochemical corrosion cell. The main corrosion products that developed were silver sulfide (Ag2S) and nickel sulphur residue.

Ultra-Fine Pitch Stencil Printing for a Low Cost and Low Temperature Flip-Chip Assembly Process

Abstract: This paper presents the results of a packaging process based on the stencil printing of isotropic conductive adhesives (ICAs) that form the interconnections of flip-chip bonded electronic packages. Ultra-fine pitch (sub-100-mum), low temperature (100degC), and low cost flip-chip assembly is demonstrated. The article details recent advances in electroformed stencil manufacturing that use microengineering techniques to enable stencil fabrication at apertures sizes down to 20mum and pitches as small as 30mum. The current state of the art for stencil printing of ICAs and solder paste is limited between 150-mum and 200-mum pitch. The ICAs-based interconnects considered in this article have been stencil printed successfully down to 50-mum pitch with consistent printing demonstrated at 90-mum pitch size. The structural integrity or the stencil after framing and printing is also investigated through experimentation and computational modeling. The assembly of a flip-chip package based on copper column bumped die and ICA deposits stencil printed at sub-100-mum pitch is described. Computational fluid dynamics modeling of the print performance provides an indicator on the optimum print parameters. Finally, an organic light emitting diode display chip is packaged using this assembly process

Feasibility of an Integrated Self Biased Coplanar Isolator With Barium Ferrite Films

Abstract: The development of passive devices using a ferrite is a major focus of current research for electronic applications in the microwave range (circulators and isolators). Hexagonal ferrite, such as barium ferrite (BaFe12O19 or BaM), which has a large resistivity and high permeability at high frequencies are indeed of great interest for microwave device applications. In this work we developed an integrated and self-biased coplanar isolator using BaM sputtered films. BaM films, 1-36 mum thick, were deposited under optimized conditions by radio frequency magnetron sputtering on alumina substrates. The films were crystallized using a 800degC thermal annealing. Isolators were then realized using patterning of coplanar waveguides (CPW) with standard lift-off technique. The slots and the central width were 300 mum wide and gold was used for the conductor lines. We evaluated the influence of various parameters on the device performances: the magnetic film's thickness, the positioning of the magnetic film (CPW deposited onto the magnetic film or directly on the substrate), the CPW metallic thickness and the polarizing field. As standard design, the CPW were deposited on the top of the magnetic film. At the remanent magnetization (no polarizing field applied), the transmission coefficients then showed a non reciprocal effect, which reached 5.4 dB per cm of line length at 50 GHz for a 26.5 mum thick BaM film. Both the insertion losses and the non-reciprocal effect measured increased with the magnetic film thickness with a saturation effect. In the second design where the CPW is deposited directly on the substrate after a selective etching of the BaM film, we measured that the non reciprocal effect reached higher values for lower BaM thicknesses than for the first design and that the insertion losses also decreased. The interaction between the field lines created by the conductors and the magnetic film was indeed favored in the second case. Finally, we show the tunability of the isolator with the polarizing field.