Investigation of electromigration reliability of redistribution lines in wafer-level chip-scale packages

Wafer-level chip-scale packages (WLCSPs) have become subject to the same drive for miniaturization as all electronic packages. The I/O count is increasing and ball pitch is shrinking at the expense of trace pitch and in turn, current densities are increasing. This leads to current crowding and Joule heating in the vicinity of solder joints and under bump metallurgy (UBM) structures where resistance values change significantly. These phenomena are responsible for structural damage of redistribution line (RDL)/UBM and UBM/solder interconnects due to ionic diffusion or electromigration. In this work, sputtered Al and electroplated Cu RDLs were examined and quantified by three-dimensional electrothermal coupling analysis. Results provide a guideline for estimating maximum allowable currents and electromigration lifetime.     

Evaluation of solder joint reliability in flip-chip packages during accelerated testing

The microstructural investigation and thermomechanical reliability evaluation of the Sn-3.0Ag-0.5Cu solder bumped flip-chip package were carried out during the thermal shock test of the package. In the initial reaction, the reaction product between the solder and Cu mini bump of chip side was Cu₆Sn₅ intermetallic compound (IMC) layer, while the two phases which were (Cu,Ni)₆Sn₅ and (Ni,Cu)₃Sn₄ were formed between the solder and electroless Ni-P layer of the package side. The cracks occurred at the corner solder joints after the thermal shocks of 400 cycles. The primary failure mechanism of the solder joints in this type of package was confirmed to be thermally-activated solder fatigue failure. The premature brittle interfacial failure sometimes occurred in the package side, but nearly all of the failed packages showed the occurrence of the typical fatigue cracks. The finite-element analyses were conducted to interpret the failure mechanisms of the packages, and revealed that the cracks were induced by the accumulation of the plastic work and viscoplastic shear strains.     

Effects of deposition conditions of Al and Ti underlayer on electromigration reliability for deep-submicron interconnect metallization

We have studied the effects of Ti underlayer (collimated Ti vs. standard Ti) and Al deposition power (12 KW vs. 6 KW) on the electromigration (EM) lifetime of bottom-Ti/Al-0.5wt.%Cu/Ti/TiN-top stack. The (002) texture of standard Ti (s-Ti) was stronger than that of collimated Ti (c-Ti). The Al stack prepared with s-Ti underlayer, which had the stronger Al (111) texture and more uniform grain size distribution, showed better EM lifetime than the same with c-Ti underlayer, independent of the Al deposition power. The Al stack prepared with an Al deposition power of 6 KW was also found to show better EM lifetime than the same with a 12 KW deposition power, independent of the type of Ti underlayer. Longer deposition time for low power sputtering resulted in the stronger Al (111) texture, larger median grain size, and more uniform Ti−Al reaction layer. Finally, the effects of Ti underlayer and Al deposition power on the EM lifetime of Al-0.5%Cu films could be well explained by the grain size distribution and Al (111) texture, which is closely related to the underlying-Ti (002) texture.     

Reliability test and failure analysis of high power LED packages

A new type application specific light emitting diode (LED) package (ASLP) with freeform polycarbonate lens for street lighting is developed, whose manufacturing processes are compatible with a typical LED packaging process. The reliability test methods and failure criterions from different vendors are reviewed and compared. It is found that test methods and failure criterions are quite different. The rapid reliability assessment standards are urgently needed for the LED industry. 85 ℃/85 RH with 700 mA is used to test our LED modules with three other vendors for 1000 h, showing no visible degradation in optical performance for our modules, with two other vendors showing significant degradation. Some failure analysis methods such as C-SAM, Nano X-ray CT and optical microscope are used for LED packages. Some failure mechanisms such as delaminations and cracks are detected in the LED packages after the accelerated reliability testing. The finite element simulation method is helpful for the failure analysis and design of the reliability of the LED packaging. One example is used to show one currently used module in industry is vulnerable and may not easily pass the harsh thermal cycle testing.     

Reliability test and failure analysis of high power LED packages

A new type application specific light emitting diode(LED) package(ASLP) with freeform polycarbonate lens for street lighting is developed,whose manufacturing processes are compatible with a typical LED packaging process.The reliability test methods and failure criterions from different vendors are reviewed and compared.It is found that test methods and failure criterions are quite different.The rapid reliability assessment standards are urgently needed for the LED industry.85℃/85 RH with 700 mA is used to test our LED modules with three other vendors for 1000 h,showing no visible degradation in optical performance for our modules,with two other vendors showing significant degradation.Some failure analysis methods such as C-SAM,Nano X-ray CT and optical microscope are used for LED packages.Some failure mechanisms such as delaminations and cracks are detected in the LED packages after the accelerated reliability testing.The finite element simulation method is helpful for the failure analysis and design of the reliability of the LED packaging.One example is used to show one currently used module in industry is vulnerable and may not easily pass the harsh thermal cycle testing.     

采用文献比较分析法的软件可靠性影响因素分析

可靠性作为衡量软件质量的重要特性,其定量评估和预测已成为人们关注和研究的焦点。为了较好地衡量软件可靠性建模中的影响因素,引入文献比较分析法作为研究方法,从软件过程的视角出发去分析讨论影响软件可靠性的因素问题。该研究方法首先进行了广泛的文献检索,研究不同学者关于影响软件可靠性的各种观点,随后进行分析整理,最后对其进行分类总结获得影响软件可靠性的过程因素。仿真结果表明。该方法能够获得软件可靠性建模中的主要影响因素,从而为建立软件可靠性早期预测模型提供分析基础。     

Fatigue life evaluation of wire bonds in LED packages using numerical analysis

Reliability of LED packages is evaluated using several tests. When a thermal shock test, which is one of the reliability tests, is conducted, the most common failure mode is wire neck breakage. In order to evaluate the wire bonding reliability of LED packages, performing the thermal shock test is time-consuming. In this paper the wire bonding reliability for LED packages is evaluated by using numerical analysis. A wire bonding lifetime model for the thermal shock test was developed, which is based on Coffin-Manson fatigue law. The model was calibrated from fatigue data of thermal shock tests and volume averaging accumulated plastic strains. The accumulated plastic strains were calculated by using finite element analysis corresponding to the test conditions. The test conditions were changed by silicones, package sizes, wire bonding diameters, heights, and lengths. The calibrated model was used to estimate the number cycle to failure so that the wire bonding reliability for the thermal shock test was evaluated by performing the numerical analysis. Furthermore, we used a response surface methodology to study the relationship between the wire loop and the accumulated plastic strain to determine the optimal wire loop. The plastic strain was a function of diameter, height and length. At the optimal point, the number of cycle to failure for the thermal shock test was suggested using the wire bonding lifetime model.     

基于热-结构耦合的3D-TSV互连结构的应力应变分析

建立了3D-TSV(硅通孔)互连结构三维有限元分析模型,对该模型进行了热-结构耦合条件下的应力应变有限元分析,研究了TSV高度和直径对3D-TSV互连结构温度场分布及应力应变的影响。结果表明:随着TSV高度和直径的增大,3D-TSV叠层芯片封装整体、焊球、间隔层、芯片和TSV及微凸点处的最高温度均逐渐降低,TSV高度和直径的增加在一定程度上有利于降低封装体各部分最高温度;随着TSV高度的增加,TSV及微凸点互连结构内的应力应变呈增大趋势。     

基于电热耦合模型的功率器件结温预测

结温预测对于功率器件的可靠性分析具有重要意义,基于此,提出了一种基于电热耦合模型的功率器件结温预测方法。首先通过Twin Builder软件建立了绝缘栅双极晶体管(IGBT)的行为模型,通过电路仿真的手段获取IGBT的平均功耗为324 W;然后将IGBT的功耗代入有限元仿真模型中得到了IGBT模块温度场分布,最高温度为99.58℃;最后搭建了IGBT模块结温测试平台,将仿真结果与实验数据进行对比,验证温度场计算模型的有效性;并实验对比了IGBT功耗分别为119 W和294 W下的最高结温,得到的温度场计算误差在10%以内,验证了IGBT有限元模型的有效性。     

可靠性管理在电厂的应用与成效分析

水电厂发电具有无污染性,能够为当地居民生产生活提供可靠的电源,为促进水电厂进一步发展,可靠性管理被应用进来,随着它的应用给水电厂发展带来了一定好处.本文将从可靠性管理基本情况入手,分别研究可靠性管理在水电厂中的应用与成效.     

内进化容错模型设计及其可靠性分析

仿照自然界的碳基生物进化过程,在FPGA内部实现了可控的硅基进化。针对电子系统常见的SA故障,提出了基于演化硬件技术的内进化容错模型,通过在FPGA内部装载Microblaze CPU和构建可重配置阵列,实现了演化硬件的片内进化。利用该模型进行了故障容错实验,检验了其有效的故障容错能力,证明该容错方法能够有效提高数字电路的可靠性。     

结构分析技术在行波管可靠性评估中的应用

结构分析是一种重要的元器件可靠性评估方法,可以评估元器件内是否存在潜在的缺陷。行波管结构分析可以为行波管固有质量和固有可靠性的判断提供重要依据。探讨了结构分析技术在行波管可靠性评估中的应用,给出了行波管结构分析的一般试验流程、一般技术流程、分解原则以及典型的结构单元分解,并提出了行波管结构分析中应注意的几个问题。     

Implementation of a chaotic oscillator by designing Chua’s diode with CMOS CFOAs

The implementation of a chaotic oscillator which is based on Chua’s circuit, is presented. Chua’s diode is realized by using current feedback operational amplifiers (CFOAs). Furthermore, it is shown that a CMOS compatible CFOA can be designed by connecting two voltage followers sandwiched between two current mirrors. The proposed implementation is biased at ±1.2 V, and simulated by using SPICE and standard CMOS technology of 0.35 μm. Finally, simulation results are presented to show the sequence of chaotic behaviours for increasing values of the linear resistance. Esteban Tlelo-Cuautle received the B.Sc. degree in electronics engineering from the Technologic Institute of Puebla (ITP) México, in 1993, the M.Sc. and Ph.D. degrees from the National Institute for Astrophysics, Optics and Electronics (INAOE) México, in 1995 and 2000, respectively. In 1995 he joined the Department of Electronics at the ITP. Since 2001 he has been with the Department of Electronics at INAOE, where he is currently a Researcher. He has been member of reviewer-committees for the IEEE Trans. on CAS-I, IEEE Trans. on Education, IEEE Latin-America, Información Tecnológica, SCI Journal, IASTED, and IEEE ISCAS. He is member of IEICE, Senior Member of the IEEE, and his research interest include electronic design automation, modeling and simulation, symbolic analysis, circuit synthesis, and analog and mixed-signal CAD tools. Aarón Gaona-Hernández was born in Puebla, México in 1980. He received his B.Sc. degree from the Faculty of Sciences for Electronics at the Autonomous University of Puebla (BUAP-FCE), in 2005. His research interest include analog IC design and chaotic systems. Joel García-Delgado is with the BUAP-FCE México.     

Analysis of physical properties of III-nitride thin films by nanoindentation

The thin films of undoped GaN, GaN:Si, and Al_0.12Ga_0.88N on sapphire (0001) substrate using nanoindentation are investigated. The Young’s modulus, hardness, and plastic energy of the films were calculated from the loading-unloading curve. The true hardness, maximum shear stress, and degree of elastic recovery are then deduced from the preceding calculated data. In addition, the loading-unloading curve clearly shows the pop-in phenomena, which can be attributed to the dislocation nucleation. To better understand the factors affecting the quality of films produced, the stress-strain relationship, which is able to reflect the quality of the fabricated films, is also analyzed using nanoindentation.     

Analysis of rectangular microstrip patch antenna covered with N-dielectric layers

A generalized spectral Green’s function formulation of N-layer substrate structure is given with three dimension sources, which is a set of closed form formulas. A full-wave analysis model for rectangular microstrip antennas covered with N-dielectric layers has been established by using the above spectral Green’s function. The unknown surface current density on the microstrip patch for such structure is found as a solution of an integral equation. The input VSWR and radiation patterns of the antenna are also obtained. The numerical results have been verified by the experimental results. Partly supported by the Research Item B96(56) of the Ministry of Railways of China     

End‐to‐end security‐reliability analysis of multi‐hop cognitive relaying protocol with TAS/SC‐based primary communication,total interference constraint and asymmetric fading channels

In this paper, we analyze the tradeoff between outage probability (OP) and intercept probability (IP) for a multi‐hop relaying scheme in cognitive radio (CR) networks. In the proposed protocol, a multi‐antenna primary transmitter (PT) communicates with a multi‐antenna primary receiver (PR), using transmit antenna selection (TAS) / selection combining (SC) technique, while a secondary source attempts to transmit its data to a secondary destination via a multi‐hop approach in presence of a secondary eavesdropper. The secondary transmitters such as source and relays have to adjust their transmit power to satisfy total interference constraint given by PR. We consider an asymmetric fading channel model, where the secondary channels are Rician fading, while the remaining ones experience the Rayleigh fading. Moreover, an optimal interference allocation method is proposed to minimize OP of the primary network. For the secondary network, we derive exact expressions of end‐to‐end OP and IP which are verified by Monte Carlo simulations.     

Coupled-field FEM nonlinear dynamics analysis of continuous microsystems by non-incremental approach

This paper deals with numerical prediction of the nonlinear dynamic behaviour of electromechanical continuous microsystems, in presence of large displacements. Finite Element Method (FEM) is applied, by following so-called “sequential” approach, based on the solution in series of coupled electromechanical problem. In spite of tested approaches available in the literature, a “non-incremental” method is developed to enhance the performances of numerical tools. In practice, for microelectrostatic beam actuators, the total voltage may be applied once, in only one step, instead of by small increments. Non-incremental approach is based on two features. A special non-incremental beam element is introduced to deal with so-called geometrical nonlinearity of microbeam, caused by large displacement. It allows computing the total displacement of a cantilever microbeam, by integrating local rotation and axial deformation of cross-section, by avoiding to refer to the assumption of small displacement. Proposed procedure includes a preliminary static nonlinear analysis, to find the equilibrium condition, then a computation of nodal voltages for the deformed shape and of electric load. Equations of motion are integrated in time, by Newmark's method, while at each step, Newton-Raphson approach finds the instantaneous equilibrium, by applying the total voltage, instead of a small incremental value. Results evidenced a fast convergence even for large initial deflection. Moreover, typical peculiarities of nonlinear dynamic system, like softening effect in frequency response and amplitude jumping are observed. The whole proposed approach is currently under experimental validation and improvement to include damping effects, to study the dynamic stability of the microsystem. Eugenio Brusa was born in Turin (Italy) on February 8th, 1969. Graduated aeronautical engineer (1993) and Ph.D. in Design and construction of machines (1997) at Politecnico di Torino (Technical University of Turin). Assistant professor at Politecnico di Torino, Dept. Mechanics, and head of the Spin Test Laboratory from 1998 to 2001, then at Università degli Studi di Udine (2001–2002). On 2002 he appointed Associate professor at Università degli Studi di Udine, chair of Machine Design. Since 2005 is Coordinator of the teaching staff of the Master on Project Management and System Engineering of the University of Udine. Research activity: Design of mechanical structures, rotors and structural mechatronic systems, for space applications (Italian Space Agency, INTAS), cold rolling mills (SKF), active magnetic suspension (ESA subcontract), motorvehicle dynamics (FIAT group) and MEMS. Teaching activity in international courses: TU Delft (2001), TU Helsinki (2003), Int. Centre for Mechanical Sciences CISM (2004), Italy, Université Blaise Pascal, Clermont Ferrand (2005), France. More than 80 scientific publications. Mircea Gh. Munteanu was born in Brasov (Romania), on April 5th, 1946. Graduated Mechanical Engineer (1968) and PhD in Applied Mechanics at Transilvania University of Brasov, Romania. Since 1979 in staff at Stress Analysis and Mechanical Vibrations Dept., Transilvania University of Brasov. Since 1993 full professor of Stress Analysis and Mechanical Vibrations, Transilvania University of Brasov. Invited professor at Università degli Studi di Udine, Italia, in the framework of a grant on microsystem mechanical design. Research activity on static and dynamic FEM analysis of mechanical structures, multi-body systems, precision engineering, microsystem design. More than 100 publications on national and international journals and congresses, several books.     

Noise transfer characteristics and design techniques of a frequency synthesizer

This paper presents an exact method for the loop parameters’ calculation. The noise transfer functions of PLL based synthesizers are derived in the z-domain analysis. Through the comparison of the s-domain model with the z-domain model, we show that the noise peak from inherent sampling behaviors always exists in the loop, and the loop filter with the wide loop bandwidth doesn’t suppress it. Such a noise peak causes instability to the system. A stability limit of the wide loop bandwidth frequency synthesizer is extracted by the behavioral simulation using the z-domain model, which depends on the phase margin and the ratio between the reference frequency and the loop bandwidth.