电子封装基板材料研究进展及发展趋势

基板材料在电子封装中主要起到半导体芯片支撑、散热、保护、绝缘及与外电路互连的作用。随着电子封装技术向着高频高速、多功能、高性能、小体积和高可靠性方向发展,电子封装基板材料在新一代电子封装材料中发挥着越来越重要的作用。科学与工业界对电子封装基板材料提出了更高的要求,同时也促进了电子封装基板材料飞速发展。文章分别针对三大类基板材料:陶瓷基板、复合材料基板和有机基板的特点、发展现状及未来发展趋势进行了阐述。     

打桩船桩架结构强度有限元分析

利用MSC Patran和MSC Nastran对某打桩船进行桩架结构强度有限元分析,校核打桩作业时桩架在倾斜范围内的安全性,并绘制桩架的起重特性曲线.     

一种多芯片封装(MCP)的热仿真设计

集成电路封装热设计的目的在于尽可能地提高封装的散热能力,确保芯片的正常运行。多芯片封装(MCP)可以提高封装的芯片密度,提高处理能力。与传统的单芯片封装相比,由于包含多个热源,多芯片封装的热管理变得更为关键。本文针对一种2维FBGAMCP产品,进行有限元建模仿真,并获得封装的热性能。通过热阻比较的方式,分析了不同的芯片厚度对封装热性能的影响。针对双芯片封装,通过对不同的芯片布局进行建模仿真,获得不同的芯片布局对封装热阻的影响。最后通过封装热阻的比较,对芯片的排列布局进行了优化。分析结果认为芯片厚度对封装热阻的影响并不明显,双芯片在基板中心呈对称排列时封装的热阻最小。     

MSC Nastran优化功能在结构强度设计中的应用

对某型飞机机翼主梁,以MSC Patran、 MSC Nastran为基本工具,对其结构进行优化设计. 优化后的结构重量、梁缘条面积、梁腹板厚度满足工程实际要求;通过有限元分析,翼尖扰度也满足变形要求.     

基于阳极氧化铝基板的圆片级板载芯片封装技术

提出了一种新型基于阳极氧化铝基板的板载芯片（Chip on Board）封装技术。在5 wt.%,30℃的草酸电解液中采用60 V直流电压,制备了0.1 mm厚度的阳极氧化铝基板圆片,铝导线最小线宽、电阻及导线间绝缘电阻分别为35μm、小于1Ω/cm与大于1×1010Ω。在超薄阳极氧化铝基板圆片进行了双层Flash裸芯片堆叠及金丝引线键合,实现了圆片级COB封装,成品率高于93%。最后,将COB单元进行三维堆叠封装,制备了32 Gb Flash模组。因此基于阳极氧化铝基板的板载芯片封装技术具有较大的应用前景。     

2.5D Chiplet封装结构的热应力研究

开展了一种2.5D Chiplet封装结构的热应力研究，形成了一套适用于先进封装的设计理论方法，从而显著提升Chiplet封装性能和降低成本。根据实际生产要求，选择芯片表面应力、底部填充胶应力和封装翘曲三个关键封装性能作为优化目标。首先建立了Chiplet封装模型，采用COMSOL进行有限元仿真，揭示了底部填充胶材料选型、两芯片间底部填充胶高度、塑封料和芯片高度三个参数对上述封装性能的影响规律。然后通过正交试验设计方法获得仿真数据，并基于极差分析法处理相关数据，分析各参数影响因素对优化目标的影响程度，进而获得2.5D Chiplet封装结构的最优参数。最后将优化后Chiplet封装模型通过仿真进行验证，结果表明该封装结构中芯片表面平均应力减小为93%,底部填充胶峰值应力减小为86%,和封装翘曲减低为96%,从而验证了设计的有效性。     

GARTEUR飞机模型的有限元分析及模态参数辨识

对GARTEUR飞机模型利用MSC Nastran软件进行有限元分析,得出模型的固有频率与振型等参数. 在实验数据的基础上,基于频率响应函数的有理分式模型,采用Forsythe正交多项式改善求解性态,自己编写模态参数辨识软件进一步分析该模型,比较两软件计算出来的结果来验证自编软件的有效性、实用性.     

高速芯片封装中多平行传输线的设计与优化

随着封装基板朝着高阶高密度方向发展,其信号完整性问题也日趋严重。为研究高速互连结构中反射、串扰等问题与封装基板类型、设计参数和传输线物理特性的相关性,改进了简单的二线平行耦合模型,采用三维电磁仿真软件构建了新的封装级三平行传输线模型,分析了陶瓷基板与有机基板上的传输线反射和串扰特性,研究了该结构下减小反射系数与串扰噪声的方法。仿真结果表明,封装基板上传输线反射系数S11与阻抗匹配程度相关,受信号线宽、厚度和介质厚度影响较大,且S11最小值在不同频率下匹配的最优线宽也不同,需根据不同信号频率具体选择。近端串扰系数受边缘场作用,与线间距密切相关,远端串扰系数受介质厚度影响较大,在相同条件下,远端串扰噪声一般小于近端串扰,对其评估时需结合基板上信号密度、基板材料特性和介质厚度具体分析。     

汽轮机阀壳强度设计及优化

使用MSC Nastran及MSC Patran有限元软件对典型汽轮机阀壳的高温强度进行计算和分析,对应力集中位置采用线性平均方法估算其应力强度,并与材料强度相比较. 由于压力和温度参数的提高,原模型已不满足设计要求. 通过局部改进设计和优化,使阀壳强度符合设计要求.     

新型埋入式板级封装技术

越来越多的高密度、多功能和小型化需求给封装和基板都带来了新的挑战,很多新的封装技术也应运而生,包括引起众多关注的埋入式封装技术.在本文中,我们首先对埋入封装技术的优势、挑战以及发展现状进行了介绍.然后通过将功能性有源器件埋入到有机基板中的尝试说明了设计、制造和测试埋入式封装这一新兴技术的可行性.制定一个切实可行的解决方案,有利于降低制造成本和市场的产品开发周期.我们提出的这种埋入式板级封装技术,与传统的封装和基板工艺都兼容.此外,本文设计了将功能性的MOSFET有源芯片埋入到有机基板中的板级封装模块结构,对该模块进行了热机械仿真分析,找到了最大应力点,优化了工艺设计.最后,结合传统的基板工艺,制备了埋入式板级封装样品,并完成了埋入式板级封装模块的电阻通断测试和功能测试,验证了该工艺设计的可行性.     

Bounded Queries, Approximations, and the Boolean Hierarchy

This paper investigates nondeterministic bounded query classes in relation to the complexity of NP-hard approximation problems and the Boolean Hierarchy. Nondeterministic bounded query classes turn out be rather suitable for describing the complexity of NP-hard approximation problems. The results in this paper take advantage of this machine-based model to prove that in many cases, NP-approximation problems have the upward collapse property. That is, a reduction between NP-approximation problems of apparently different complexity at a lower level results in a similar reduction at a higher level. For example, if M C reduces to (log n)-approximating M C using many–one reductions, then the Traveling Salesman Problem (TSP) is equivalent to M C under many–one reductions. Several upward collapse theorems are presented in this paper. The proofs of these theorems rely heavily on the machinery provided by the nondeterministic bounded query classes. In fact, these results depend on a surprising connection between the Boolean hierarchy and nondeterministic bounded query classes.     

Instrumented film-insert injection compression molding for lens encapsulation of liquid crystal displays

A film-insert injection compression molding process was introduced to encapsulate cholesteric liquid crystal displays with flexible and rigid lens for full protection of displays to replace the currently used time consuming hand lamination technique. For this purpose, a new interchangeable cavity instrumented hot runner mold was designed and constructed. This complex method was carefully optimized considering challenges arising from an insert multilayer display with +80% liquid crystal content as well as different thermal expansion coefficients between the layers and the lens material as a high potential of delamination and warpage. Concerning the desired physical properties including transparency, low melt viscosity and melting temperature as well as a wide range of hardness grades from soft (flexible) to hard (rigid), three different hardness grades of thermoplastic polyurethanes were found to be the best candidates for this lens application. During proposed lens encapsulation, the pressure changes were evaluated with screw and mold movements using position detection via displacement transducers attached to track the mold closure and screw forward motion. The quality of encapsulation and shrinkage related problems, as well as their elimination, were all discussed. Display substrate material selection criteria for lowered warpage were defined with supporting thermal characterizations. Among the process parameters, tested also by applying the design of experiments with Taguchi method, mold temperature was found to be the most influential parameter on warpage, followed by pin gate opening time, packing pressure, and cooling time.     

All PDMS pneumatic microfinger with bidirectional motion and its application

This paper describes the experimental results on static and dynamic bending motions of all polydimethylsiloxane (PDMS) pneumatic microfinger. The proposed pneumatic microfinger consists of two PDMS diaphragms with different thicknesses or material properties. The microfinger is fabricated through PDMS molding process and the PDMS-to-PDMS bonding process. The out-of-plane motion of the microfinger is achieved by using the pulling force of the inflated actuator diaphragms while the square wave pneumatic force is supplied to the balloon actuators. In the case of the microfinger with different thickness of two diaphragms, the pressure-dependent dual-bending motion of the microfinger is available. The proposed working principle is confirmed from the steady-state bending angle measurement of the two types of the microfingers with different thicknesses of the bottom PDMS layers. While the pneumatic force is less than 20 kPa, the top diaphragm of Type A microfinger is fully inflated and the microfinger moves downward. Around 20 kPa, the bending direction of the microfinger starts to be changed from downward to upward. The microfinger with two types of PDMS films with different mixing ratio of base polymer and curing agent is also proposed for the improvement of the PDMS-to-PDMS bonding strength, the material property change, and the rapid manufacturing process. The microfinger moves only upward because the top PDMS diaphragm with excess of silicon hydride group is relatively stiffer than the bottom PDMS diaphragm with excess of vinyl group. The dynamic bending motion of the single microfinger and the object-lifting motion of the microfinger array are observed to evaluate their performance. The dynamic bending angle of the microfinger with golden air bone length is about 179/spl deg/ at 1 Hz, while the square wave input pressure of 250 kPa is supplied to finger structure.     

Electromagnetic characterization of chiral auxetic metamaterials for EMC applications

A new class of auxetic materials, a hexachiral honeycomb structure with good mechanical properties, is investigated through computer simulation and measurement. The electromagnetic properties for shielding applications are taken into account. This new material shows some interesting EMC properties (e.g. − 40 dB transmittance at 2.4 GHz) and promises better performance using different insertion techniques.     

The analysis of warpage in wafer-level compression molding

Advanced 3D MEMS packaging technologies involving the encapsulation of devices at wafer-level are being developed in order to achieve further minimization and cost reduction of consumer electronic devices. Compression molding using epoxy molding compounds is one technique being considered for wafer-level encapsulation. Excessive out-of-plane deformation has been reported in wafer-level compression molding trials using blank wafers which would negatively impact device reliability and the implementation of successive processes to the molded wafer. This paper presents finite element models of the molded wafer, with and without embedded dies which simulate the observed multi-state warpage characteristics. Molded wafer warpage measurements were also carried out in order to verify the applicability of the small and large deformation theories for layered plates and to verify the finite element model of the molded blank wafer. Possible factors (non-planar mold layer thickness and anisotropic wafer elastic properties) leading to asymmetric warpage in molded blank wafers were also investigated. From the molded wafer model with embedded dies the effects of flip-chip die dimensions and wafer thickness on the out-of-plane deformation together with possible reliability issues were analyzed.

     

钢板仓输料桁架动力特性的有限元分析

应用有限元分析理论对钢板仓输料桁架进行动力分析,得到输料桁架的应力分布和位移变化过程图. 通过分析,能对钢板仓输料桁架的结构设计提供有益的参考.     

Detecting patterns in process data with fractal dimension

In quality control discipline, pattern classification is focused on the detection of unnatural patterns in process data. In this paper, fractal dimension is proposed as a new classifier for pattern classification. Fractal dimension is an index for measuring the complexity of an object. Its applications were found in such diverse fields as manufacturing, material science, medical, and image processing. A method for detecting patterns in process data using the fractal dimension is proposed in this paper. A Monte Carlo study was carried out to study the fractal dimension (D) and the Y-intercept (Y_int) values of process data with patterns of interest. The patterns included in the study are natural pattern, upward linear trend, downward linear trend, cycle, systematic variable, stratification, mixture, upward sudden shift, and downward sudden shift. Based on the results, the approach is effective in detecting such non-periodic patterns as the natural patterns, linear trends (at slope ≥0.2), systematic variable, stratification, mixture, and sudden shifts. For the cyclical pattern, although the D and Y_int-values are not stable, the approach can provide useful information when the period of the cycle is greater than 2 and is less than or equal to half the window size (2N/2). The minor drawbacks of this approach are that it is not sensitive for detecting linear trends with small slope and the slope of the original data is needed to detect the difference between upward and downward linear trends and the difference between upward and downward sudden shifts.     

Processing-microstructure-resulting materials properties of LIGA Ni

Electroplated nickel is the main material used in LIGA technique for fabricating MicroElectroMechanical System (MEMS) components. This paper presents the recent results regarding LIGA Ni material property enhancement at Center for Advanced Microstructures and Devices at Louisiana State University. The methodology of this study is based on the fundamental materials science paradigm that processing and manufacturing determine the microstructure of materials, which results in specific properties, and governs the performance of the structures that are made from these materials. This paper will focus on results in three aspects of our current research efforts, which are: (1) manipulating the plating parameters to tailor deposited Ni microstructures for different grain size distributions that are in the range of tens nanometer in diameters; (2) analyzing the mechanical properties, such as nano-hardness, micro-hardness, and wearing property as the function of LIGA Ni metallurgical microstructures; (3) estimating the corrosion properties of nanocrystalline LIGA Ni.     

Linearization of discrete-time systems by exogenous dynamic feedback

It is shown that a discrete-time system may be linearizable by exogenous dynamic feedback, even if it cannot be linearized by endogenous feedback. This property is completely unexpected and constitutes a fundamental difference with respect to the continuous-time case. The notion of exogenous linearizing output is introduced. It is shown that existence of an exogenous linearizing output is a sufficient condition for dynamic linearizability. Necessary and sufficient conditions for the existence of an exogenous linearizing output are provided. The results of the paper are obtained using transformal operator matrices. The properties of such operators are studied. The theory is applied to the exact discrete-time model of a mobile robot, showing that the above-mentioned property concerns not only academic examples, but also physical systems.     

On the equivalence between global recurrence and the existence of a smooth Lyapunov function for hybrid systems

We study a weak stability property called recurrence for a class of hybrid systems. An open set is recurrent if there are no finite escape times and every complete trajectory eventually reaches the set. Under sufficient regularity properties for the hybrid system we establish that the existence of a smooth, radially unbounded Lyapunov function that decreases along solutions outside an open, bounded set is a necessary and sufficient condition for recurrence of that set. Recurrence of open, bounded sets is robust to sufficiently small state dependent perturbations and this robustness property is crucial for establishing the existence of a Lyapunov function that is smooth. We also highlight some connections between recurrence and other well studied properties like asymptotic stability and ultimate boundedness.