硅通孔间距与形状对热应力的影响

针对常用不同孔间距和形状组合的硅通孔(TSV)叠层封装的热问题,利用有限元软件建立模型,对多热源硅通孔叠层封装进行热循环瞬态分析。基于以上分析,进一步探讨不同孔间距和形状的封装体热应力分布情况,得出孔间距和形状与热应力之间的对应关系。数值算例结果表明,以孔间距为1mm朝下开口梯形圆台模型具有良好的热应力特性。     

3D封装与硅通孔(TSV)技术

随着对芯片集成度以及对电性能要求越来越高,近些年来3D封装发展迅速。其中硅通孔技术(TSV)被认为是实现3D封装的最好选择之一。因此TSV工艺逐渐成为微电子领域的热门话题之一,并且促进着微电子行业进一步向前发展。本文分析了硅通孔技术的优点以及挑战,同时也简单介绍了硅通孔技术的应用。     

高深宽比的TSV制作与填充技术

硅通孔技术是三维集成电路中堆叠芯片实现互连的一种新的技术解决方案。本文介绍了TSV的制作与填充技术,通过优化ICP刻蚀工艺,实现了上口尺寸14.41μm、下口尺寸8.83μm、深度331.0μm、深宽比大于20:1的高深宽比通孔的制作;利用LPCVD工艺在通孔内沉积的重掺杂多晶硅作为电极引线实现电气互连,并对通孔进行了电阻特性的测试,测试结果表明,通孔阻值约为25Ω,通孔互连的电学特性较好。     

基于硅基WLP封装的深孔刻蚀工艺研究

本工作针对硅基晶圆级封装(WLP,Wafer level package)的关键工艺技术——深孔刻蚀工艺进行了研究,通过对掩蔽层材料的选择和图形化工艺研究,制备出满足深孔刻蚀工艺要求的掩蔽层,并采用干法刻蚀设备进行深孔刻蚀和工艺优化,最终制作出工艺指标为:刻蚀深度185μm、深宽比9:1、陡直度90.08°、侧壁粗糙度小于64 nm、选择比46:1的硅深孔样品.该深孔刻蚀工艺可应用于薄膜体声波滤波器(FBAR,Film bulk acoustic resonator)晶圆级封装工艺的硅通孔互联(TSV,Through silicon via)技术中.     

TSV转接板组装工艺对微凸点可靠性的影响

TSV转接板组装工艺过程引起的封装结构翘曲和应力对微凸点可靠性有重要影响。该文采用有限元方法,分析了TSV转接板封装自上至下和自下至上两种组装工艺流程,通过比较工艺应力/应变和翘曲得到较优工艺流程;针对优选工艺流程,分析了不同工艺步微凸点的力学行为,重点关注封装结构中微凸点定位对微凸点可靠性的影响。结果表明:自上至下组装工艺流程较优;微凸点位置设计应尽量避开下填料边缘,当微凸点正好位于TSV上方时,微凸点阵列塑性功密度最低,且分布均匀,微凸点的这种定位设计最为合理。     

硅通孔转接板封装结构多尺度问题的有限元模型

三维硅通孔转接板封装结构中,存在大量的微凸点与微焊球,尺寸相差3个数量级,这种结构多尺度给有限元分析模型的建立带来困难。以板级封装焊锡接点热疲劳寿命的有限元计算为目标,采用均匀化方法将芯片与转接板间的微凸点/下填料层以及转接板与基板间的微焊点/下填料层等效为均匀介质,以解决结构多尺度带来的网格划分困难。在对比分析了几种均匀化方案的基础上,建议在计算三维硅通孔转接板板级封装焊锡接点的热疲劳寿命时,芯片与转接板间的微凸点/下填料层以及转接板与基板间的微焊点/下填料层可采用各自的下填料层替代建模。     

超薄衬底的临时键合／去键合加工

许多手持消费类电子产品（如手机、小唱机、相机、游戏系统等）的生产,需要很薄的（器件）晶片。利用穿硅通孔（TSV）技术可以减少封装容积,增大容量和增加功能。柔性晶片或超薄脆性晶片需要一支撑系统以便在传统设备上进行TSV加工。     

以碳纳米管取代铜TSV芯片效能更好

来自瑞典歌德堡（Gothenburg）的查默斯理工大学（Chalmers University of Technology）的研究人员发现,以碳纳米管来填充采用硅穿孔技术（TSV）连结的3D芯片堆栈,效果会比铜来得更好。     

TSV绝缘层完整性在线测试方法研究

硅通孔(TSV)技术是先进的三维系统级封装(3D SIP)集成技术乃至三维集成电路(3D IC)集成技术的核心.TSV绝缘完整性是决定其电性能和长期可靠性的关键因素,在生产过程中对该特性进行在线(in-line)测试,及早筛除有缺陷的产品晶圆,可以有效降低总生产成本.本文提出在晶圆减薄前,通过探针与相邻两个TSV盲孔顶部接触进行I-V特性测试,得到两孔间漏电流数据,绘成曲线.若所得I-V曲线在电压为7 V～10 V时基本呈线性上升,且漏电流为几十皮安量级,则可初步判断该TSV盲孔对的绝缘完整性合格,可进入下一步工艺流程.若I-V曲线在电压为7V或更低时出现漏电流陡增甚至击穿特性,则可以判断该TSV盲孔对中有一个或两个的绝缘完整性已经受损.通过有限元仿真阐释了测试机理,并进行了试验验证.     

基于差分信号的硅通孔无损缺陷判断与定位

硅通孔(Through Silicon Vias,TSV)技术是三维集成电路的核心技术之一.在TSV加工过程中由于填充不均匀、化学机械剖光不彻底等,会造成过孔的开路、短路等缺陷,进而影响系统性能.高效精准的无损检测方法有利于剔除有缺陷裸片,降低缺陷对系统性能的影响.通过分析差分信号激励时地—信号—信号—地(Ground-Signal-Signal-Ground,GSSG)型TSV的电特性,提炼出缺陷无损检测及定位方法,即利用存在缺陷时差模和共模S参数的特点来判断缺陷类型;利用差模S参数及其对频率的数值导数随缺陷位置变化的特点对缺陷进行定位.此外,还对比了输入分别为单端信号和差分信号时的缺陷判断方法,结果表明基于差分信号的缺陷判断方法在判断对地短路缺陷方面比单端信号更有优势.     

Application of Differential Transform Method to Thermoelastic Problem for Annular Disks of Variable Thickness with Temperature-Dependent Parameters

This article analyzes the one-dimensional steady temperature field and related thermal stresses in an annular disk of variable thickness that has a temperature-dependent heat transfer coefficient and is capable of temperature-dependent internal heat generation. The temperature dependencies of the thermal conductivity, Young’s modulus, and the coefficient of linear thermal expansion of the disk are considered, whereas Poisson’s ratio is assumed to be constant. The differential transform method (DTM) is employed to analyze not only the nonlinear heat conduction but also the resulting thermal stresses. Analytical solutions are developed for the temperature and thermal stresses in the form of simple power series. Numerical calculations are performed for an annular cooling/heating fin of variable thickness. Numerical results show that the sufficiently converged analytical solutions are in good agreement with the solutions obtained by the Adomian decomposition method and give the effects of the temperature-dependent parameters on the temperature and thermal stress profiles in the disk. The DTM is useful as a new analytical method for solving thermoelastic problems for a body with temperature-dependent parameters including material properties.     

Bending of curved sandwich beams

Curved sandwich beams in bending are analyzed with analytical elasticity methods and compared to simple analytical formulae and FEM calculations. Solutions to Airy's stress function in polar co-ordinates are used to obtain the stress distributions in the radial and circumferential directions. Plane stress and plane strain solutions are given with isotropic and orthotropic material models. It is shown that the properties of the core can have a significant influence on the circumferential stresses of the faces, but that the radial stress of the core is nearly constant with varying core properties. The radius of curvature can have a large influence on the circumferential stresses of the faces when the radius of curvature to sandwich thickness ratio is small to moderate. It is shown that simple analytical methods can be utilised to calculate the radial stresses in the core and the circumferential stresses of the faces for beams with large to moderate radii of curvature and thin to moderately thick faces.     

Thermal behavior of an elliptic inhomogeneity surrounded by a compliant interphase layer

Summary This paper examines the thermal behavior of a plane elastic compliant interphase layer surrounding an elliptic inhomogeneity which is embedded within an infinite matrix. To allow continuity of traction but discontinuity of displacements, the compliant interphase is modeled as a spring layer with a vanishing thickness. Furthermore, to obtain the resulting thermal stresses, the complex variable method was used, together with a series solution. A commerical finite element package was used to validate the theoretical predictions. The results reveal that thermal stresses vary with the aspect ratio of the inhomogeneity and the parameterh describing the spring constant of the interphase layer for four different types of inhomogeneous materials: aluminum, copper, gold and silver. In all these cases, the matrix was assumed to be made of silicon and the thermal stresses were assumed to result from a uniform change in temperature.     

Thermal shock analysis and thermo-elastic stress waves in functionally graded thick hollow cylinders using analytical method

Transient stress field and thermo-elastic stress wave propagation are studied in functionally graded thick hollow cylinder under arbitrary thermo-mechanical shock loading, in this article. Thermo-mechanical properties of functionally graded (FG) cylinder are assumed to be temperature independent and vary continuously and smoothly in the radial direction. The governing dynamic equations are analytically solved in temperature and elastic fields. To solve the problem, Laplace transform is used respect to time in all constitutive equations and boundary conditions. At first, temperature field equation analytically solved using Laplace transform and series method. The dynamic behaviors of thermo-elastic stresses are illustrated and discussed for various grading patterns of thermo-mechanical properties in several points across the thickness of FG cylinder. Time history of temperature field and thermal stresses are obtained using the residual theorem and the fast Laplace inverse transform method (FLIT), respectively. Also, the effects of the cylinder thickness and convection heat transfer coefficient on dynamic response of FG cylinder are revealed and discussed. The presented analytical method provides a ground to study the time histories of radial and hoop stresses in FG cylinders with different thickness and various volume fraction exponents. The advantage of this method is its mathematical ability to support simple and complicated mathematical function for the thermo-mechanical boundary conditions. A reasonable agreement can be seen in comparison of obtained results based on the presented analytical method with published data.     

A low temperature processable ternary gallium alloy for via filling application in microelectronic packaging

A low temperature processable ternary gallium alloy is formulated using an appropriate mixture of liquid gallium metal with nickel and copper powders. The processability of this alloy for room temperature via filling application is demonstrated using a stencil print process. A test vehicle is fabricated using a 0.2 mm thick and 300 mm×300 mm stainless steel (SS) panel with laser-drilled vias. Parylene N is deposited on the SS panel and around the inside via walls in order to electrically isolate via filling material from the body of the SS substrate and also making the SS surface non-conductive. Filled vias were examined for electrical isolation from neighboring vias and for electrical continuity in the thickness direction. Results show that the ternary gallium alloy is a good via filling material and can be applied to vias as small as 0.25 mm. It is believed that this novel alloy can also be used for thin film process on related MCM-L (multichip module-laminate) substrates.     

Time-dependent creep stress redistribution analysis of thick-walled functionally graded spheres

Time-dependent creep stress redistribution analysis of thick-walled spheres made of functionally graded material (FGM) subjected to an internal pressure and a uniform temperature field is performed using the method of successive elastic solution. The material creep and mechanical properties through the radial graded direction are assumed to obey a simple power-law variation. Total strains are assumed to be the sum of elastic, thermal and creep strains. Creep strains are time, temperature and stress dependent. Using the equations of equilibrium, compatibility and stress–strain relations a differential equation, containing creep strains, for radial stress are obtained. Ignoring creep strains, a closed-form solution for initial thermoelastic stresses at zero time is presented. It has been found that the material in-homogeneity parameterβ has a substantial effect on thermoelastic stresses. From thermoelastic analysis the material identified by β=2 in which a more uniform shear stress distribution occurs throughout the thickness of the FGM sphere is selected for time-dependent stress redistribution analysis. Using the Prandtl–Reuss relations and Norton’s creep constitutive model, history of stresses and strains are obtained. It has been found that radial stress redistributions are not significant, however, major redistributions occur for circumferential and effective stresses. It has also been concluded that stresses and strains are changing with time at a decreasing rate so that there is a saturation condition beyond which not much change occurs. Indeed after 50 years the solution approaches the steady-state condition.     

Residual stresses in plastics,rapidly cooled from the melt,and their relief by sectioning

A theory for the residual stresses in tempered glass plates has been adapted for the cooling of plastics, which have temperature dependent thermal properties. The theory was checked against experimental residual stress distributions found in quenched polycarbonate sheet, and against the analytical solution for temperature independent properties. The heat transfer coefficient for quenching polycarbonate from 170° C into iced water was found to lie between 1000 and 4000 W m^–2 K. It is known that the cutting of thin sections from a sheet relieves the residual stresses, and this is used for transparent plastics to distinguish between orientation and stress bi-refringence. An elastic stress analysis of the sectioning process showed that the section width must be less than 20% of the sheet thickness for the residual stresses to be reduced to 5% of their original values.     

Thermal stresses of asphalt pavement under dependence of material characteristics on reference temperature

This thesis presents an analytical study of thermal stresses of asphalt pavement under dependence of material characteristics on reference temperature. In the analysis, flexible pavement is regarded as a multi-layered elastic half-space axisymmetrical system. Firstly, thermo-elastic theory is used to describe thermal stresses of a multi-layered system, while the temperature-dependent material characteristics are considered. Then Laplace transformation and Hankel transformation with respect to time and radial, respectively, are utilized for thermo-elastic equations of equilibrium. In addition, the transfer matrix method is applied to derive general solutions for the multi-layered problem. Finally, the resulting formulation is applied to calculate thermal stresses in the low temperature cracking problem of asphalt pavement. Thermal stress is calculated and compared with the case that material characteristics are supposed to be constant to show the remarkable impact of temperature-dependent material characteristics on thermal stresses of asphalt pavement.     

早龄期混凝土路面板非线性温度场下温度应力的计算

给出了一种早龄期混凝土路面板非线性温度场下温度应力的解析计算方法。模型将路面板厚度方向的非线性温度分成平均温度、线性温度和非线性温度三个分项,每一分项温度引起应力分别计算,最终总应力为三部分应力的叠加。此外,由于徐变对温度应力发展具有很大影响,因此该文也对混凝土徐变对板内温度应力的影响进行了分析。模型预测结果表明:在非线性温度分布下,温度应力沿板厚也是非线性分布的,温度变化产生的最大温度应力可能出现在路面板厚度方向的任何高度上,这依赖于沿板厚方向的温度分布特征。混凝土徐变会显著的降低路面板内的温度应力。     

Reliability study of through-silicon via (TSV) copper filled interconnects

Through-silicon vias (TSVs) have been extensively studied because of their ability to achieve chip stacking for enhanced system performance. The fabrication process is becoming somewhat mature. However, reliability issues need to be addressed in order for an eventual transition from laboratory to production. In our laboratory, vias with tapered sidewalls are formed through a modified Bosch process using deep reactive ion etching (DRIE). Vias are lined with silicon dioxide using plasma enhanced chemical vapor deposition (PECVD) followed by sputter deposited titanium barrier and copper seed layers before filling with a reverse pulse copper electroplating process. Following attachment of the process wafer to a carrier wafer, the process wafer is thinned from the backside by a combination of mechanical methods and reactive ion etching (RIE). Fabricated vias are subjected to thermal cycling with temperatures ranging from − 25 °C to 125 °C. For via chains, erratic changes in resistance upon temperature cycling indicated a problem with the wire bonds used to connect the sample to the test fixture. Test methods were modified to avoid wire bonding and form the basis of reliability studies presented in this paper. TSVs are shown to be stable with small increases in measured resistance for 200 cycles. In addition, small changes in resistance are observed when vias are held at elevated temperatures for extended periods of time.