3D IC受热载荷作用下的数值模拟

针对基于硅通孔技术的3D IC在工作过程中的受热问题,利用热弹性力学理论建立了三维有限元数值模拟分析模型,对结构进行了热分析,同时探讨了器件由此产生的热应力.计算结果表明,由芯片到底面的热通路为散热的主要通道,其它表面的对流条件对热场分布影响不大;芯片与通孔接触面的边角处有应力集中,在热载荷的长期、交变作用下容易发生开...     

The development of effective model for thermal conduction analysis for 2.5D packaging using TSV interposer

The effective model for the orthotropic TSV (Through Silicon Via) interposer in heat conduction for 2.5D IC integration was proposed in this study. The simple parallel model was used in out-of-plane direction to predict the effective thermal conductivity for the TSV interposer. The in-plane effective thermal conductivity for the interposer was derived on basis of heat balances. By introducing the effective orthotropic thermal parameters, the TSV structures can be ignored in the present effective model. The computations using the effective model for TSV interposer and the 2.5D package with interposer were carried out. The results showed that the accuracy of the effective model was above 95% comparing with the real model including TSV structures when the volume ratio of the electroplating copper and the silicon interposer is smaller than 10%. Using the effective model, the parametric studies on the interposer sizes and the thermal conductivities of different materials in the 2.5D package were conducted with higher efficiency. The results showed that the performance and sizes of EMC (Epoxy Molding Compound) and the package substrate are more important than that of internal underfills in heat dissipation of the package with TSV interposer.     

1D and Q2D thermal resistance analysis of micro channel structure and flat plate heat pipe

Heat pipes and two-phase heat transfer devices are widely used in electronics cooling, and the thermal resistance is a key issue to ensure the system performance and reliability. In this study, the traditional one dimensional (1D) and quasi-two dimensional (Q2D) methods were utilized to analyze the thermal resistance of the previous boiling experiments of evaporator tests with silicon (Si) and copper (Cu) micro channel structures as well as the existing flat-plate heat pipe tests with aluminum micro channels as wick structures. The temperature distributions and variations under different test conditions were collected, and the 1D and Q2D methods were applied to calculate the overall thermal resistance for evaporator tests and heat pipe tests and compared with the experimental data. The results showed that the Q2D method can predict the overall thermal resistance for the evaporator region and the whole heat pipe with a higher accuracy because the spreading resistance was significant and should be considered under small heater area (hot spot) conditions. Detailed distributions of thermal resistance and the calculated errors of each test sample under different heat loads were presented and compared. For present tests, the Q2D method can reach a lower average error (about 10%) and is recommended for calculations. Furthermore, the spreading resistance of Q2D method is further applied to calculate the selected test cases to investigate the wall thickness effects. The spreading resistance of the selected evaporator tests and heat pipe tests may decrease and increase, respectively, as wall thickness increases due to different evaporative heat transfer conditions. The present results demonstrate the applicability of the Q2D methods for both evaporator and heat pipe tests, and the present analyses can be a reference for future thermal management and electronic cooling designs.     

Thermal characteristic of Cu-Cu bonding layer in 3-D integrated circuits stack

Copper (Cu) thermo-compression bonding of wafers can be used to fabricate multi-layer three-dimensional (3-D) integrated circuits (ICs). This work examines the thermal characteristic of the Cu bonding layer and demonstrates experimentally that Cu bonding layer can act as a spreading layer that helps in heat dissipation of bonded 3-D ICs stack more efficiently compared to silicon dioxide bonding layer. The use of Cu bonding layer in a double-layer stack of ICs provides better cooling by as much as 9 °C compared to oxide bonding interface.     

Numerical investigation of characteristics of wick structure and working fluid of U-shape heat pipe for CPU cooling

In the current study, the effects of the wick structures and working fluids characteristics on U-shape heat pipe performance were numerically presented. A two-dimensional FEM simulation was performed on U-shape heat pipe to analyze the temperature and the pressure distributions inside the heat pipe. In order to reduce the pressure arising in the area of the wick to increase heat transport capability at the liquid-wick region, a comparative numerical study was made by using methanol and water as working fluids with sintered powder and screen mesh wicks. The simulation was performed by using ANSYS/FLOTRAN software with heat input of 10 W at forced convection. The results showed that the use of sintered copper powder wick resulted in a small temperature difference between the evaporator and condenser compared to screen mesh wick. The use of screen mesh wick caused a decrease in the pressure drop in liquid-wick region while the use of methanol as working fluid increased the liquid pressure drop.     

Highly doped Si/SiO<Subscript>2</Subscript>/W sandwich structures with an exposed insulator edge: Electrical transport and electroforming

The results are presented of an experimental investigation into electrical transport in Si-SiO₂-W sandwich structures with an exposed insulator edge that include highly doped silicon of either conductivity type, the insulator being about 20 nm thick. Processes occurring before, during, or after electroforming are examined. It is demonstrated that electroforming is possible at either voltage polarity. The finding has made it possible to gain a deeper understanding of electrical transport in the structures considered. This is shown to involve ionic transport, minor electroforming, and major electroforming. Minor electroforming is caused by electron emission from the edge of the W electrode when this is negative. Major electroforming is found to be substantially independent of voltage polarity, silicon conductivity type, or doping level. At the same time, certain parameters of I–V characteristics are shown to be determined by the dopant type and concentration when dealing with electroformed structures.     

适用于大功率光电芯片散热的一体化平板热管

为解决大功率光电芯片散热问题,构造了一种新结构一体化平板热管。利用超轻多孔泡沫金属作为毛细吸液芯,以水、丙酮和乙醇为工质,在不同充液比、加热功率和倾角条件下对新结构热管的热性能进行了研究,结果表明,这种新结构平板热管不仅消除了热管与散热片间的接触热阻,而且使整个散热翅片也处于均温状态,当功率达到380W、热流密度超过445 W/cm2时,热管仍具有较好的均温特性,且热阻较小,可达0.04℃/W。在3种工质中,水是最佳工质选择,且当充液比为30%时具有较好的效果。实验表明,以泡沫金属为吸液芯的新结构一体化平板热管具有很好的传热性能,并扩展了承载大热流密度的能力。     

Investigation of electrical characteristics of memory cells based on self-forming conducting nanostructures in a form of the TiN-SiO2-W open sandwich structure

The results of experimental investigations of electroforming and quasi-static current-voltage (I-V) characteristics of formed TiN-SiO₂-W open sandwich structures in comparison to the Si-SiO₂-W structures are presented. It is shown that similar memory and switching effects, which are associated with self-forming the conducting nanostructures on the surface of the open end of the dielectric film (silicon dioxide) about 20 nm thick, are observed in them. However, the features of the structures with the lower TiN electrode are the noticeably larger current, the lower threshold switching voltage from the low-conducting state into the high-conducting state, and a flatter I–V characteristic at voltages below the threshold one. These features can be explained by the decrease in the spreading resistance from the conducting structure, which is formed during electroforming, into the material of the lower electrode for titanium nitride compared to silicon (their resistivity values differ by a factor of 4) and the lower potential barrier at the TiN-SiO₂ interface compared with the Si-SiO₂ interface. The cell of energy-independent electrically reprogrammable memory with the TiN-SiO₂-W structure possesses the better technical characteristics and manufacturability.     

带有TSV的硅基大功率LED封装技术研究

介绍了一种带有凹槽和硅通孔(through silicon via,TSV)的硅基制备以及晶圆级白光LED的封装方法。针对硅基大功率LED的封装结构建立了热传导模型,并通过有限元软件模拟分析了这种封装形式的散热效果。模拟结果显示,硅基封装满足LED芯片p-n结的温度要求。实验结合半导体制造工艺,在硅基板上完成了凹槽和通孔的制造,实现了LED芯片的有效封装。热阻测试仪测得硅基的热阻为1.068K/W。实验结果证明,这种方法有效实现了低热阻、低成本、高密度的LED芯片封装,是大功率LED封装发展的重要方向。     

充液量对回路热管性能的影响

实验研究了以Cu粉烧结块为吸液芯、Al制太阳花散热器为冷凝器的回路热管(LHP)在不同充液率条件下充入工质为无水乙醇后的启动、温度波动以及热阻等传热性能。Cu粉烧结块吸液芯相对丝网吸收层可以产生更大的毛细力,Al制太阳花散热器可以使整个LHP更轻便,利于不同安装场合的应用。研究结果表明:1)LHP的启动受热负荷大小和充液率共同作用;2)温度波动随功率的增加而变得平缓,而随着充液率的增加,温度波动频率却有所上升;3)充液率影响LHP的热阻变化,最佳充液率为60%。     

Fabrication of 50 nm patterned nickel stamp with hot embossing and electroforming process

Fabrication of imprint stamp is a key issue of nanoimprint lithography. In this study, we attempt to fabricate the nickel imprint stamp using hot embossing lithography and electroforming processes. As small as 50 nm sized patterns of original silicon master were faithfully transferred to polyvinyl chloride (PVC) film. By electroforming on hot embossed PVC film, nickel stamp, which has the same patterns of original silicon master stamp, was successfully fabricated.     

Experimental study of microrectangular groove structure covered with multi mesh layers on performance of flat plate heat pipe for LED lighting module

The paper presents a novel concept for a coronary-stent-like model to solve the problem of compactness between wick and copper mesh, which can enhance the performance of the hybrid structure flat plate heat pipe (FPHP) of LED lighting modules. The various wick structures combine axial rectangular grooved structures, manufactured in aluminum extraction, and the concept of a coronary-stent-like model, which provides a supportive copper mesh and wick structure. In this study, the performance of FPHP was experimentally measured at different inclination angles and heating areas. The axial rectangular groove structure and copper mesh layer structures have different permeabilities and capillary pumping forces, and combining these two structures could be beneficial for pumping the required operational fluid across the axial groove structure and from the condenser to the evaporator under different inclinations of the flat plate heat pipe. The exterior wall temperature of the FPHP was measured to evaluate the thermal resistance and vapor heat transfer coefficient at the condenser and evaporator for 31 × 31 and 10 × 10 mm² heating areas. The experimental result showed that the FPHP has better performance in both the junction temperature of the LED light module and the uniformity of the substructure temperature. The highest FPHP temperature was decreased by 28%, as compared to a commercial substrate. In addition, a 200 W LED light module, running for 9 h with FPHP, maintained luminance at about 2080 lux due to its low thermal resistance and high capillary force.     

The Effects of Si Submounts Containing Cu Thermal Vias on the Heat-Dissipation Characteristics of a High-Power Light-Emitting Diode Package

We investigated the effects of Si submounts containing Cu thermal vias on the heat-dissipation characteristics of a high-power light-emitting diode (LED) package. Simulations were used to determine the optimum conditions for effective heat dissipation from the LED. The optimum thickness of the Si submount containing the Cu thermal vias was 250 μm. The optimum heat flux area ratio between the Si submount and the LED chip was 25. The thermal resistance of an Si submount 250 μm thick and 25 mm² in area was 1.85 K/W without Cu vias. This value decreased to 1.50 K/W on incorporation of the 400-μm-diameter Cu vias. In addition, the total thermal resistance of the LED package structure was improved from 9.7 K/W to 8.3 K/W on incorporation of the 400-μm-diameter Cu vias into the Si submount.     

基于LTCC的微流道散热技术

简要介绍了在低温共烧陶瓷(LTCC)基板中制作微流道结构对电路散热的必要性,建立3种不同结构微流道LTCC基板有限元模型并对其进行了热-流耦合仿真,分别分析不同结构、流体流速及进出口截面对散热性能的影响.基于仿真结果制备实物,实测结果表明14 W/cm2热流密度下最高温升124.3 K,在设定水流流速为0.012 m/...     

Improving thermal performance of miniature heat pipe for notebook PC cooling

A miniature heat pipe (MHP) with woven wire wick was used for cooling a notebook PC. The cross-sectional area of the pipe is reduced by about 30% of the original, when the diameter of the MHP is pressed from 4 to 2 mm for packaging in a notebook PC. In the present study, a test of the MHP has been performed in order to review the thermal performance by varying pressed thickness, total length of MHP, wall thickness, heat flux and inclination angle. New wick types were considered for overcoming low heat transfer limits, which occur when the MHP is pressed to a thin plate. Through a performance test, the limiting thickness of pressing is shown to be within the range of 2–2.5 mm. When the wall thickness of 0.4 mm is reduced to 0.25 mm for minimizing conductive thermal resistance through the wall of heat pipe, the heat transfer limit and thermal resistance of the MHP were improved about 10%. While the thermal resistance of the MHP with central wick type is lower than that of the MHP with circular oven wire wick, the thermal resistance of the MHP with composite wick of woven/straight wire is higher than that of the MHP with circular woven wire wick. From the performance test conducted on the MHP cooling modules with woven wicks, it is seen that the T_jc (junction temperature of the processor) satisfies a demand condition of being between 0 and 100 °C. This shows the stability of the MHP as a cooling system of notebook PCs.     

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。     

Characterization of flip chip bonded structure with Cu ABL power bumps

Power distribution in both 2D and 3D integrated circuit (IC) devices becomes one of the key challenges in device scaling, because the on-chip power dissipation becomes significantly severe and causes thermal reliability issues. In this study, the process solution to resolve the on-chip power dissipation by improving power distribution was investigated through newly designed power bumps called ABL (advanced bump layer) bumps. Rectangular-shaped Cu ABL bumps were fabricated and bonded on Si substrate using flip chip bonding process. The bump height difference in signal and ABL power bumps, bonding interface, and electrical resistivity of flip chip bonded structure were evaluated. The lowest electrical resistivity of Cu ABL bump system was estimated to be 3.3E−8 Ω m. The process feasibility of flip chip bonded structure with Cu ABL bumps has been demonstrated.     

芯片散热微通道仿生拓扑结构研究

为提升高热流密度芯片的散热能力,借鉴自然界中众多具有优良传质传热特性的网络拓扑,设计了多种仿生微通道拓扑结构.利用数值模拟方法,分析了不同拓扑结构的散热效果及压降特性,结果表明不同拓扑结构的散热能力存在一定差异,且芯片热流密度越高差异越明显.对数值分析中综合性能优秀的蜘蛛网结构的散热特性进行了理论分析,并通过3D打印加工了微通道散热器,测试表明其散热能力和压降相对现有平直微通道均有明显提高.     

LED灯具散热结构温度分布计算模型及验证

以通过热传导流入肋片热量与通过空气与肋片间的对流所散出的热量相等作为条件,分别讨论翅片串接与翅片并接两种情形,以热流传递的连续性作为关联条件,并通过结构基座的温差及翅片顶端的热流为零这一求解条件,推导出了整个散热结构的温度计算求解方程。并以某型铝制散热结构作为分析对象,通过实验与仿真得到了该型散热结构关键节点的温度数值,并与计算值进行了对比,验证了所构建的计算模型的正确性。     

Thermal Stability Improvement of Vertical Conducting Green Resonant-Cavity Light-Emitting Diodes on Copper Substrates

Green light vertical-conducting resonant-cavity light-emitting diodes (RCLEDs) have been fabricated on a Cu substrate by the combination of laser lift-off and plating techniques. The structure of the RCLED/Cu is consisted of the InGaN-GaN multiple-quantum-well active layer between three layers of the dielectric TiO-SiO distributed Bragg reflector as a top mirror and an Al metal layer as a bottom mirror. It was found that the RCLED with Cu substrate presents superior thermal dissipation and a stable electroluminescence emission peak wavelength (507 nm) under a high injection current. It is attributed to the Cu substrate providing a good heat sink and effectively reducing the junction temperature.