Closed-loop electroosmotic microchannel cooling system for VLSI circuits

The increasing heat generation rates in VLSI circuits motivate research on compact cooling technologies with low thermal resistance. This paper develops a closed-loop two-phase microchannel cooling system using electroosmotic pumping for the working fluid. The design, fabrication, and open-loop performance of the heat exchanger and pump are summarized. The silicon heat exchanger, which attaches to the test chip (1 cm/sup 2/), achieves junction-fluid resistance near 0.1 K/W using 40 plasma-etched channels with hydraulic diameter of 100 /spl mu/m. The electroosmotic pump, made of an ultrafine porous glass frit with working volume of 1.4 cm/sup 3/, achieves maximum backpressure and flowrate of 160 kPa and 7 ml/min, respectively, using 1 mM buffered de-ionized water as working fluid. The closed-loop system removes 38 W with pump power of 2 W and junction-ambient thermal resistance near 2.5 K/W. Further research is expected to strongly reduce the thermal resistance for a given heating power by optimizing the saturation temperature, increasing the pump flowrate, eliminating the thermal grease, and optimizing the heat exchanger dimensions.     

Thin-film persistent current switch

We have developed a fast, low power heat switch for switching a niobium thin film between the normal and superconducting state. The sputtered niobium film (400 nm thick, 100 /spl mu/m wide) has a critical current density of 5/spl times/10/sup 10/ Am/sup -2/. Switching is produced by joule heating a small section of the niobium film with a titanium thin-film resistor. With the heat switch in vacuum, the minimum heater power needed to switch to the normal state was 4.5/spl times/10/sup -5/ W. A simple three-dimensional thermal model shows that the minimum power is primarily determined by the thermal conductivity of the substrate. We have achieved response times less than 10/sup -6/ s.     

高导热挠性铝基覆铜板用环氧胶粘剂的研究

采用高导热填料球形氧化铝填充环氧胶粘剂,并添加了适量离子捕捉剂有效地控制有害离子的离子迁移,利用该胶粘剂粘接铝箔和铜箔制备成挠性铝基覆铜板。文章中探讨了环氧胶粘剂的热固化温度和时间、球形氧化铝含量对胶膜热导率的影响,通过显微镜测试了导热填料在胶粘剂中的分散均匀性,最后确定最优配方制备出一种综合性能优异的挠性铝基覆铜板。     

Micro heat pipes in low temperature cofire ceramic (LTCC) substrates

With projected power densities above 100 W/cm/sup 2/ for devices, new methods for thermal management from the heat generation at the die to heat removal to the ambient must be addressed. By integrating micro heat pipes directly within the ceramic substrate, effective thermal conductivity for spreading heat in both radial and axial directions was achieved. New materials and processes were developed to fabricate the unique components required to handle high thermal loads. Enhanced thermal vias to minimize the thermal impedance through the ceramic in the evaporator and condenser sections were developed, increasing the effective thermal conductivity from 2.63 to near 250 W/m-/spl deg/C. The use of an organic insert fabricated into the desired complex shape using rapid prototyping methods, coupled with the viscoelastic flow of the low temperature cofire ceramic (LTCC) during lamination, allowed complex shapes to be developed while ensuring uniform green tape density during lamination prior to tape firing. Large cavities, three-dimensional fine structures and porous wicks for capillary 3-D flow have been utilized to fabricate the heat pipes. Heat pipes and spreaders, utilizing water as the working fluid, have been demonstrated operating with power densities in excess of 300 W/cm/sup 2/.     

Power transistors fabricated using isotopically purified silicon (/sup 28/Si)

It is well known that isotopic purification of group IV elements can lead to substantial increases in thermal conductivity due to reduced scattering of the phonons. The magnitude of the increase in thermal conductivity depends on the level of isotopic purification, the chemical purity, as well as the test temperature. For isotopically pure silicon (/sup 28/Si) thermal conductivity improvements as high as sixfold at 20 K and 10%-60% at room temperature have been reported. Device heating during operation results in degradation of performance and reliability (electromigration, gate oxide wearout, thermal runaway). In this letter, we discuss the thermal performance of packaged RF LDMOS power transistors fabricated using /sup 28/Si. A novel technique allows the cost effective deployment of this material in integrated circuit manufacturing. A clear reduction of about 5/spl deg/C-7/spl deg/C in transistor average temperature and a corresponding 5%-10% decrease in overall packaged device thermal resistance is consistently measured by infrared microscopy in devices fabricated using /sup 28/Si over natural silicon.     

Analysis of heat generation and thermal lensing in erbium 3-/spl mu/m lasers

The influence of energy-transfer upconversion (ETU) between neighboring ions in the upper and lower laser levels of erbium 3-/spl mu/m continuous-wave lasers on heat generation and thermal lensing is investigated. It is shown that the multiphonon relaxations following each ETU process generate significant heat dissipation in the crystal. This undesired effect is an unavoidable consequence of the efficient energy recycling by ETU in erbium 3-/spl mu/m crystal lasers, but is further enhanced under nonlasing conditions. Similar mechanisms may affect future erbium 3-/spl mu/m fiber lasers. In a three-dimensional finite-element calculation, excitation densities, upconversion rates, heat generation, temperature profiles, and thermal lensing are calculated for a LiYF/sub 4/:Er/sup 3+/ 3-/spl mu/m laser. In the chosen example, the fraction of the absorbed pump power converted to heat is 40% under lasing and 72% under nonlasing conditions. The heat generation in a LiYF/sub 4/:Er/sup 3+/ 3-/spl mu/m laser is 1.7 and the thermal-lens power up to 2.2 times larger than in a LiYF/sub 4/:Nd/sup 3+/ 1-/spl mu/m laser under equivalent pump conditions, thus, also putting a higher risk of rod fracture on the erbium system.     

高散热性能TGV转接板

随着玻璃通孔(TGV)转接板在微波系统集成中的应用越来越广泛,其微波大功率应用情况下的散热性能成为研究重点。针对TGV转接板高效散热性能的要求,进行TGV散热结构的设计和性能分析。建立TGV转接板封装集成结构的有限元模型,设计TGV转接板铜柱阵列散热结构。通过TGV工艺制作TGV高密度阵列。在4.82~14.47 W功率范围内对TGV转接板的散热性能进行测试,相应的TGV散热结构区域的热流密度为40.03~120.18 W/cm²,测得热阻芯片表面温度高达54.0~126.5℃,低于微波功率芯片最高结温150℃,可以满足大功率微波系统集成高效散热的需求。     

CVD Diamond Sink Application in High Power 3D MCMs

As electronic packages become more compact, run at faster speeds and dissipate more heat, package designers need more effective thermal management materials. CVD diamond, because of its high thermal conductivity, low dielectric loss and its great mechanical strength, is an excellent material for three dimensional （319） multichip modules （MCMs） in the next generation compact high speed computers and high power microwave components. In this paper, we have synthesized a large area freestanding diamond films and substrates, and polished diamond substrates, which make MCMs diamond film sink becomes a reality.     

固化工艺参数对导电胶导电性的影响

用四点探针法的原理设计了一种测试导电胶电阻的新方法。研究了固化温度、时间及导电胶层厚度对导电胶固化后导电性的影响。结果表明:夹具经预热导电胶,在80~140℃固化较好;未预热时在110~150℃固化较好,但固化时间较长;随着导电胶层厚度增加,固化时间和固化后的最低电阻都有一定的增大;最佳的固化效果是固化到电阻变化很微小时停止固化。     

X 波段四通道MMCM 基板设计

低温共烧陶瓷（LTCC）是制作微波多芯片组件（MMCM）基板的理想材料。本文介绍了基于LTCC 工艺的微 波传输线、集成腔体、功分器和散热过孔的设计。对于多通道微波组件,采用带状传输线和腔体结构有利于实现通道 间的高隔离度,集成功分器和浆料电阻有利于实现组件的小型化并可获得较好的微波性能,而矩阵散热过孔可以显著 改善基板导热性能,满足小功耗器件的散热要求。     

Experimental and theoretical characterization of electrical contactin anisotropically conductive adhesive

Electrical conduction through anisotropically conductive adhesive (ACA) is caused by deformation of metal fillers under pressure and heat. In this work, the hardness of the electrical particles under various deformation degrees was determined by nano-indentor measurements and the electrical resistance of the electrical contacts was measured under various deformation degrees. Theoretical model and simulation have been developed for the microscopic mechanism of the electrical conduction through metal fillers in the anisotropically conductive adhesive. By comparing with experimental data it is concluded that the deformation of the metal filler in our ACA is plastic even at rather low external load. Further theoretical simulation reveals two important aspects of the conductance characteristics. The conductance is improved by increasing the external load but the dependence of the conductance on the spatial position of the metal filler becomes stronger. Design and optimization of the ACA with respect to the absolute value of the electric conductance and its dependence on the spatial position of the metal filler are of essential importance for the electronics packaging application of the anisotropically conductive adhesives     

Temperature Dependence of Electrical and Thermal Conductivities of an Epoxy-Based Isotropic Conductive Adhesive

The temperature dependence of the transport properties, including electrical and thermal conductivities, of a practical isotropic conductive adhesive (ICA) including an epoxy-based binder was investigated in order to comprehensively evaluate the physical changes induced during exposure to elevated temperatures. The ICA specimens were cured and post-annealed under various conditions in order to clarify the effect of curing state of the adhesive binder on the electrical resistivity. The electrical resistivity at ambient temperature tends to decrease with increasing curing temperature, even if the samples exhibit full conversion. In addition, an annealing effect, resulting in a deviation from a linear relationship in the temperature dependence of resistivity, can be induced during the heating process experienced during resistivity measurements. However, the ICA specimens exhibited similar values for the temperature coefficient of resistivity (TCR), regardless of the curing and post-annealing conditions in the temperature range where the annealing effect is rarely induced, although the thermal history of the specimens significantly influences the absolute values of electrical resistivity. The temperature dependence of the thermal conductivity is almost accounted for by the decrease in the contribution of conducting electrons in the temperature range below the glass-transition temperature, T _g.     

A novel approach to stabilize contact resistance of electrically conductive adhesives on lead-free alloy surfaces

Electrically conductive adhesive (ECA) is an alternative for the toxic lead-based solders. However, unstable electrical conductivity has long been a haunting problem. Galvanic corrosion at the ECA/pad interface has recently been found to be the major mechanism for this decay. Applying a more active metal or alloy on a dissimilar metal couple in contact can prohibit galvanic corrosion. In this study, powders of aluminum, magnesium, zinc, and two aluminum alloys were added in an ECA and applied on five pad surfaces. The aging of the bulk resistivity and contact resistance of the ECA/metal surface pairs were studied. The two alloys significantly suppressed the increase of the contact resistance on all tested metal surfaces.     

脉动微波循环注热开采煤层气数值模拟

为获取脉动微波循环加热条件下低渗透储层煤层气运移采出规律,文中综合运用多孔介质传热学、电磁学、渗流力学、岩石力学等相关理论,建立低渗透储层煤层气微波注热开采过程渗流电磁-热-流-固多物理场耦合数学模型,结合COMSOL Multiphysics有限元分析软件进行了脉动微波循环加热过程煤层气运移采出规律的数值模拟,获取了...     

激光填丝钎焊温度场数值模拟仿真研究

为提高车身顶板和侧板之间激光填丝钎焊的质量,研究钎焊热传导规律,建立了镀锌钢板卷边对接模型、CuSi3为钎料进行数值模拟仿真分析,考虑材料热物理属性、相变潜热以及热对流等问题的前提下采用双椭球激光热源模型进行热分析.探究了激光填丝钎焊温度随时间的变化规律,不同区域对温度的敏感程度以及不同功率下焊接熔池的温度场分布,为激...     

碳纤维复合材料电导率-温度特性测量及其在预测雷击热效应中的应用

飞机的碳纤维复合材料（carbon fiber reinforced polymer,CFRP）蒙皮在遭受雷击时将经受急剧的温升效应,对材料电导率造成重要影响,而这一影响又反作用于焦耳热产生过程.文章通过直接加热和电加热两类实验分别测量了ZT7H/5229D碳纤维/树脂层合板在升降温过程中的电导率温度特性;开展了脉冲大电流试验,测量了模拟雷击情况下材料表面的瞬时温度.将实测的电导率温度参数应用到仿真模型中,仿真分析了脉冲注入实验的瞬时温度,结果表明:两类实验的电导率温度特性有着良好的一致性,CFRP在升降温过程中的回滞环现象、热解及基体热固性变化,会影响加温前后及升降温过程中的电导率;基于实验测量规律的仿真模型能够更准确预测雷电流注入时CFRP的温度场.     

Thermal analysis of a channel containing multiple heated obstacles with localized heat generations

This paper studies conjugate heat transfer for two-dimensional, developing flows over an array of multiple rectangular obstacles with localized heat generations. The paper focuses on the spatial distributions of Nusselt number and temperature along the solid/fluid interface, as well as the maximum temperature of the obstacles. The results are compared to uniform heat generation configuration to validate the approach of approximating the local heat generation as uniform. A finite element technique is utilized to solve the governing equations, along with boundary conditions for a wide range of Reynolds numbers and obstacles' thermal conductivities. At certain conditions, the numerical results showed that the uniform heat generation approach could lead to a significant analysis error. When the obstacles' thermal conductivity and Reynolds number are low, the uniform heat generation approach becomes invalid. The average Nusselt number and maximum temperature of the obstacles for the localized heat generation configuration are fully documented.     

微波芯片元件的导电胶粘接工艺与应用

导电胶常用于微波组件的组装过程,其粘接强度、导电、导热和韧性等性能指标严重影响其应用范围.分析了导电胶的国内外情况和主要性能参数,总结了混合微电路对导电胶应用的指标要求.通过微波芯片元件粘接工艺过程,分析了导电胶的固化工艺与粘接强度和玻璃化转变温度的关系、胶层厚度与热阻的关系、胶点位置和大小与粘片位置控制等方面的影响关系.测试结果显示,经导电胶粘接的芯片元件的电性能和粘接强度等指标均满足设计和使用要求,产品具有较好的可靠性和一致性.     

Thermal stability investigations of AlGaN/GaN HEMTs with various high work function gate metal designs

The operation of high power RF transistor generates a huge amount of heat and thermal effect is a major consideration for improving the efficiency of power transistors. AlGaN/GaN high electron mobility transistors (HEMTs) on silicon substrates have been studied extensively because of their high thermal conductivity. This study comprehensively investigates the DC, low frequency noise, microwave and RF power performance of Al_0.27Ga_0.73N/GaN HEMTs on silicon substrates at temperatures from room temperature to 100 °C using high work function metals such as palladium (Pd) and iridium (Ir) gate metals. Although the conventional Ni gate exhibited a good metal work function with AlGaN, which is beneficial for increasing the Schottky barrier height of HEMTs, the diffusion of Ni metal toward the AlGaN and GaN layers influences the DC and RF stability of the device at high temperatures or over long-term operation. Pd and Ir exhibited less diffusion at high temperature than Ni, resulting in less degradation of device characteristics after high temperature operation.