三维存储器模块热分析技术的研究

随着3D封装密度的加大,单位体积的热容量增加,对3D封装的热分析与热设计技术就显得越来越重要了.针对某3D SRAM模块,对其结构特点和工作方式进行了分析,通过Ansys有限元仿真工具对模块内部温度场进行了仿真,并与实验数据进行了对比,为3D SRAM模块的可靠性设计提供了有利的技术支持.     

A Review of Experimental and Computational Advances in Thermal Boundary Conductance and Nanoscale Thermal Transport across Solid Interfaces

Interfacial thermal resistance is the primary impediment to heat flow in materials and devices as characteristic lengths become comparable to the mean‐free paths of the energy carriers. This thermal boundary conductance across solid interfaces at the nanoscale can affect a plethora of applications. The recent experimental and computational advances that have led to significant atomistic insights into the nanoscopic thermal transport mechanisms at interfaces between various types of materials are summarized. The authors focus on discussions of works that have pushed the limits to interfacial heat transfer and drastically increased the understanding of thermal boundary conductance on the atomic and nanometer scales near solid/solid interfaces. Specifically, the role of localized interfacial modes on the energy conversion processes occurring at interfaces is emphasized in this review. The authors also focus on experiments and computational works that have challenged the traditionally used phonon gas models in interpreting the physical mechanisms driving interfacial energy transport. Finally, the authors discuss the future directions and avenues of research that can further the knowledge of heat transfer across systems with broken symmetries.     

Development of 3-D Stack Package Using Silicon Interposer for High-Power Application

Stacking of many functional chips in a 3-D stack package leads to high heat dissipation. Therefore, a new platform technology is required to assemble chips vertically and remove the heat effectively. A 3-D stacked package with silicon interposers was developed to integrate one ASIC and two memory chips in a package. Electrical connections in the silicon interposer were formed by through silicon via. Silicon interposer has much high thermal conductivity than organic interposer, therefore the package thermal resistance is lower. Thermal performances of the 3-D package were analyzed and thermal enhancements like thermal via, thermal bridging were evaluated. The designed package showed 5 times lesser thermal resistance compared to a similar package with organic substrate. An additional silicon heat spreader was designed and attached to the package for high power application. Thermal analysis was performed to optimize package thermal performances and experimental validation was carried out. The designed 3-D stack package is suitable for 20 W application.     

Disk-shaped miniature heat pipe (DMHP) with radiating micro grooves for a TO can laser diode package

A mounting base integrated with disk-shaped miniature heat pipe (DMHP) is designed for laser diode TO can package in the present study. The heat spreading performance of the disk-shaped miniature heat pipe is also presented. The present mounting base is made of aluminum (6061 T6) other than the conventional TO can package with oxygen free copper. The mounting base shows different thermal resistance with different working fluid charge volume. By optimizing the working fluid charge volume, the thermal resistance of the present mounting base will become lower than the conventional base with an oxygen free copper disk for TO can package. Moreover, this novel design can be manufactured on a massive scale and the fabrication cost can thus be effectively reduced.     

Reliability experiments of sintered silver based interconnections by accelerated isothermal bending tests

Integration of more functionality and smaller chips into decreasing package volume leads to increasing heat generation. In addition, the use of new compound semiconductors like SiC and GaN require a high thermal conductivity of the interconnect materials. One of the promising solutions is a layer of sintered silver between semiconductor and substrate. The advantages compared to conventional solders are significant. A higher thermal and electrical conductivity in combination with a higher duty temperature due to a higher melting point should enhance the reliability of the package. However, even as the large scale commercial usage of the material has been started by the industry recently, many important details of the mechanical properties and the reliability behavior are still unknown. While the thermal properties could be characterized relatively easy and are quite repeatable and stable, the mechanical properties - important for the reliability - are extremely process-dependent and wide-spreading. The hunt for lowest feasible sintering process parameters - such as temperature, time and especially pressure - even amplify that behavior and led to an impasse in some cases. Also their failure mechanisms, to be identified in lifetime investigations, are yet unknown as well as their stability and predictability. In order to enable prolonged function of these interfaces, thermo-mechanical reliability has to be assured. Within this paper, we show the status of silver sintering and the problems regarding mechanical material characterization found in literature. Additionally, we present a guideline for the mechanical acceleration of reliability experiments by isothermal bending tests. Finally a proof of concept by failure analysis will be presented.     

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

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.     

All Channels Open — Multimodal Human/Computer Interfaces

As the use of information technology becomes more and more pervasive in people's everyday life, the need for effective human/computer interfaces becomes ever greater. In many cases it will be the usability of a service which is more important than the number of technical features offered. Current computer interfaces are counter-intuitive and require too much learning. Although it is true that humans can adapt remarkably well in some cases, e.g. seven-year olds who can surf the net with ease while their parents are unsure how to operate a mouse, the proliferation of different computer systems in all aspects of life demands that interfaces become easier to use.     

Characterization of interfacial thermal resistance by acoustic micrography imaging

In high-power electronics modules, the heat generated by the power devices is transferred to the ambient environment by attaching a heat spreader to the semiconductor package to ensure efficient thermal management. Typical attachment materials introduce interfaces and/or interlayers of finite thickness. Using a scanning acoustic microscope (SAM), a non-destructive inspection tool, we can detect the cracks, voiding, porosity, coplanarity and delamination in the interface layer, which correlate to the measured thermal resistance of an interface. This investigation would result in optimizing the bonding process of the selected interface material, minimizing the void-content to ensure enhanced thermal management of power modules.     

Effect of Hygrothermal Aging on Interfacial Reliability of Silicon/Underfill/FR-4 Assembly

The reliability issues have been converted to the underfill adjacent interfaces since the introduction of the underfill to flip chip package in 1990's. Both thermal cycling and hygrothermal conditioning severely attack the interfaces to de- laminate. The moisture migrating into the underfill decreases the adhesion strength, swells to deform the assembly, and weakens the mechanical and thermal properties of the material. In this study, interfacial reliability of a silicon/underfill/FR-4 assembly exposed at 85degC/85%RH was studied using moire interferometry and micro-digital image speckle correlation (mu-DiSC) techniques. A thermal aging study was simultaneously performed to understand the long-term reliability of the assembly. The results showed that the thermal aging relieved the stresses induced by hygrothermal swelling mismatch between dissimilar materials involved, whereas increased the strains induced by hygrothermal swelling. It indicated the time effect is not negligible when the assembly is subjected to the moisture conditioning, otherwise, the deformation induced by the swelling could be overestimated. The mu-DiSC technique was applied to measure the critical interfacial fracture toughness of the silicon/underfill interface. The results showed that the moisture could significantly reduce the interfacial strength due to the break of hydrogen bonding. By combining the moire and mu-DiSC results, it was concluded that the hygrothermal loading could increase the possibility of interfacial delamination in a flip chip package. Finally, the morphologies of the fractured surface were studied with the aid of scanning electron microscope. Remarkable changes of the failure mode were observed.     

封装中的界面热应力分析

随着电子封装集成度的不断提高,集成电路的功率容量和发热量也越来越高,封装体内就产生了越来越多的温度分布以及热应力问题。文章建立了基板-粘结层-硅芯片热应力分析有限元模型,利用有限元法分析了芯片/基板的热应力分布,封装体的几何结构参数对应力的影响,重点讨论了芯片与粘结层界面上和基板与粘结层界面上的层间应力分布     

Thermal performance impacts of heat spreading lids on flip chip packages: With and without heat sinks

Heat spreading lids on a flip chip package can provide many thermal and mechanical advantages. Major drawbacks are higher module costs and potentially poorer thermal performance with a heat sink. This study compares thermal performance of direct lid attach (DLA) and bare die flip chip packages and addresses the roles of interface resistance and lid thickness. The IBM SLC^TM package is tested and modeled. JEDEC standard wind tunnel tests as well as CFD models are used for analysis. The study reveals that the DLA design without additional heat sinking can provide significantly better thermal performance compared to the bare die package, depending on package size and airflow rate. With a heat sink the performance of the lidded package can be superior or inferior depending on interface resistance, lid design and the standard used for comparison.     

Colouring by numbers-the use of video look-up tables

Colour has become important in many graphics applications because it increases visual appeal, simplifies data interpretation and increases the amount of information that can be displayed. By means of a look-up table, a graphics package can display a selection from an immense variety of colours even using relatively limited memory space. The use of these video look-up tables is discussed     

Thermal design of a broadband communication system with detailed modeling of TBGA packages

This paper presents a thermal modeling of a broadband network communication box partitioned into two stacked modules. A printed circuit board (PCB) is inside each module where an array of 16 tape ball grid array (TBGA) packages is surface mounted to the PCB. The TBGA package dissipates 6 W power each. In addition, 12 W of power is dissipated from four plastic ball grid array (PBGA) packages on the PCB. Pin-fin heat sinks are attached to the TBGA packages using silica-filled epoxy to enhance heat dissipation. Pin-fin heat sinks are also attached to the PBGA packages. Two exhaust fans are mounted at the flow exit to draw ambient air into the system at approximately 200 linear feet per minute (LFM) of velocity. The full Navier–Stokes equations for airflow are solved to simulate the forced convection cooling in the electronic module. Buoyancy effect was considered in the numerical model by incorporating Boussinesq-approximation. The TBGA packages are modeled in detail in order to obtain the package junction temperatures for system reliability evaluation and thermal design optimization. Detailed models of the attached pin-fin heat sinks and the epoxy interfaces are also utilized in this study. Compact heat sink model composed of a base plate and a resistance fluid volume is applied to model heat dissipation from the heat sinks attached to the four PBGA packages. System fan curve is used to simulate the fan operating conditions. The effect of changing system thermal design on the TBGA package junction temperatures as well as the hydraulic operating conditions of the system fans are examined and reported herein. The effect of radiation heat transfer is also examined. The importance of detailed modeling of the high power TBGA packages is demonstrated in this study. Simulation results were compared with JEDEC thermal test data under similar conditions of airflow.     

Computer-aided design/drafting on personal computers

In the past few years, Computer-Aided Drafting (CAD) capabilities have become available on personal computer systems. The popularity of personal computer-based (PC-based) CAD is not only due to low cost but also ease of use; improved accuracy over manual drafting; cleaner, more professional output; and the ease of making changes, all of which aid creative expression. This paper gives a brief overview of typical PC-based CAD hardware and software configurations, how much they cost, the capabilities of such systems, and a discussion of points to consider in selecting a PC-based software package.     

功率电子封装技术及确定其热阻的实现方法研究

随着用户对功率电子散热效果要求的提高，早先在功率封装上附加散热片的方法实现起来很困难。本文在介绍了功率电子器件的工艺技术后，详细地讨论了封装技术对功率电子的重大影响，并以热增强型封装、热插片封装为例，描述了功率封装的动、静态特性，并给出了计算热阻的处理步骤和测量电路，具有一定的参考价值。     

3D MCM组件产品热分析技术研究

三维多芯片组件(3D MCM-Three Dimension Multi-Chip Module)是近几年正在发展的一种电子封装技术。在3DMCM封装中,随着芯片封装密度的增加,对其热分析与热设计技术就显得越来越重要了。文章利用有限元方法,通过Ansys软件工具对某静态存储器组件(3DMCM模块)内部温度场进行了模拟仿真,并与实验数据进行了对比,获得了很好的分析效果,为3DMCM的可靠性设计提供了技术支持。     

功率电子封装技术及确定其热阻的实现方法研究

随着用户对功率电子散热效果要求的提高，早先在功率封装上附加散热片的方法实现起来很困难。本文在介绍了功率电子器件的工艺技术后，详细地讨论了封装技术对功率电子的重大影响，并以热增强型封装、热插片封装为例，描述了功率封装的动、静态特性，并给出了计算热阻的处理步骤和测量电路，具有一定的参考价值。     

集成电路封装基板过孔电学仿真技术研究

随着集成电路设计技术及工艺技术的发展,元器件的工作频率越来越高,对微电子封装技术的要求也越来越严格。目前,BGA与MCM作为逐渐普及的封装形式,其基板上都有大量的过孔,在高频时必须考虑过孔寄生参数对芯片电性能的影响,特别是针对于射频电子和高速数字IC。文章以CBGA基板过孔为例,通过有限元方法初步探讨了不同参数的过孔其寄生参数RLC的变化趋势。并以其中一组寄生参数分析了对某理想放大器电路输出波形造成的过冲与畸变等影响。     

球栅阵列——更适合多端子LSI的表面安装式封装

塑封球栅阵列（ＢＧＡ）是一种新型表面安装多端子型ＬＳＩ封装。与塑封四方扁平封装（ＱＦＰ）相比，前者外形更小，设备与操作较为简单，可靠性也有所提高。ＢＧＡ替代ＱＦＰ的尝试从美国开始，并正在各国展开     

High density packaging technology ultra thin package & new tab package

As electronic devices become more highly integrated, the demand for small, high pin count packages has been increasing. We have developed two new types of IC packages in response to this demand. One is an ultra thin small outline package (TSOP) which has been reduced in size from the standard SOP and the other, which uses Tape Automated Bonding (TAB) technology, is a super thin, high pin count TAB in cap (T.I.C.) package. In this paper, we present these packages and their features along with the technologies used to improve package reliability and TAB. Thin packages are vulnerable to high humidity exposure, especially after heat shock.1 The following items were therefore investigated in order to improve humidity resistance: (1) The molding compound thermal stress, (2) Water absorption into the molding compound and its effect on package cracking during solder dipping, (3) Chip attach pad area and its affect on package cracking, (4) Adhesion between molding resin and chip attach pad and its affect on humidity resistance. With the improvements made as a result of these investigations, the reliability of the new thin packages is similar to that of the standard thicker plastic packages.