Comparison between piezoelectric method and ultrasonic signal analysis for crack detection in type II multilayer ceramic capacitors

In this paper we present a comparison between two non-destructive techniques for crack detection in MLCCs. First, if a type II MLCC is biased with a DC field, the capacitor becomes temporarily ‘poled’ and can act as a transducer. This is induced by a residual piezoelectric effect used in the impedance spectroscopy method. Second, we used a scanning ultrasonic system working in the 10–100 MHz frequency bandwidth. To understand the ultrasonic signature, we used time-of-flight (TOF) detection with short-time Fourier transform (STFT) analysis to determine the depth and nature of defects with high accuracy. An application of digital signal processing to the characterization of defects is presented for a lot of MLCCs with cracks defects. For comparison, the same lot was tested with the piezoelectric method. The two techniques are closely correlated. © 1998 John Wiley & Sons, Ltd.     

Modeling Stress Responses of Multilayer Capacitors Using Varying Termination Geometries

Environmental regulations and increasingly challenging design objectives have prompted the search for alternative materials in microelectronics. Employing these materials alters the reliability profile and performance characteristics of the electronic components into which they are integrated. This article explores how mechanical stresses impact the reliability of ceramic dielectric bodies of multilayer ceramic capacitors (MLCCs) when the material, shape, and thickness of the MLCC terminations were varied. The termination material, termination geometry, and thickness of the ceramic were varied. Results were obtained using finite element analysis, and a reliability model was developed and validated. A preliminary investigation indicated a relationship between the selection of materials used for capacitor termination and the emergence of cracks. Stresses that occurred when boards were subjected to conditions including cyclic bending, vibrations, temperature cycling, and high-g loading correlated to the appearance of cracks on the bottom of the capacitor in proximity to the termination.     

A study of ceramic addition in end termination of multilayer ceramics capacitors with cofiring process

The silver paste with ceramics addition as end termination was performed on multilayer ceramic capacitors (MLCC) based on ZnO–B₂O₃ + Zn_0.95Mg_0.05TiO₃ + 0.25TiO₂ ceramic (ZnBO-ZMT′) with Ag95–Pd05 internal electrodes. A green sheet was prepared by tape casting using the ZnBO-ZMT′ powders. Ag95–Pd05 was attached on the green sheet as an internal electrode. After lamination, the green chips were pre-sintered at 800 °C for 1 h, then samples were dipped the external electrodes and were cofired together at 900 °C for 2 h. There is no extra curing process, so the production cost may be cut down and thermal shock of the MLCCs may be reduced. To improve the mismatch between end termination and dielectric body during sintering, the silver paste with different amounts of ceramics, e.g., 20, 30 and 40 wt.%, was added in this study. The mechanical and electrical properties of the MLCCs were investigated subsequently. The results showed that end termination with 40 wt.% ceramic addition has good performances on mechanical properties of MLCC, but equivalent series resistance (ESR) is a little bit higher compared to end termination with 20 and 30 wt.% ceramic addition.     

The preparation of copper fine particle paste and its application as the inner electrode material of a multilayered ceramic capacitor

Well size-controlled copper fine particles (diameter: 100-300?nm) were used as the inner electrode material of multilayered ceramic capacitors (MLCCs). The particles were dispersed in terpineol to form a printing paste with 50?wt% copper particles. The MLCC precursor modules prepared by the layer-by-layer printing of copper and BaTiO(3) particles were cosintered. Detailed observation of the particles, paste, and MLCCs before and after sintering was carried out by electron microscopy. The sintering temperature of Cu-MLCC was as low as 960?°C. The permittivity of these MLCCs was successfully measured with the copper inner layers.     

基于循环经济概念下的废弃电路板的再利用

运用循环经济原理,讨论了废弃电路板回收利用的必要性和可行性,并对现有废弃电路板资源化技术进行了分析比较,得出机械-物理处理法是回收利用电路板的最佳选择.针对国外废弃电路板的机械回收利用现状,提出了在国内开展废弃电路板资源化、无害化处理研究的一些建议.     

Finite element analysis of advanced multilayer capacitors

We establish a systematic methodology to design and analyse electromagnetic components such as advanced multilayer ceramic capacitors (MLCCs) using the finite element (FE) method. We employ a coupled formulation to compute the interaction between the electric and magnetic fields. Unlike a linear distribution of current assumed in the circuit model, an accurate electrostatic solution to model the entire advanced MLCCs (4 × 4 × 27 = 432 cells) is presented. The FE solution is used to compute the lumped parameters for a range of frequencies. These lumped parameters are then used to compute the parasitic elements of the MLCCs. We introduce two algorithms to efficiently analyse the behaviour of a capacitor with changing frequency. The lower frequency (much below the self‐resonant frequency of the capacitor) algorithm separates the effect of the electric and magnetic fields and reduces the computational effort required to solve the FE problem, whereas, the high‐frequency algorithm couples the effect between the electric and the magnetic fields. We use these algorithms in conjunction with a new multiple scale technique to effectively determine the small values of R, L and C in MLCCs. The formulation, the implementation, and the numerical results demonstrate the efficacy of the present FE formulation and establish a systematic methodology to design and analyse advanced electromagnetic components. Copyright © 2003 John Wiley & Sons, Ltd.     

Current sensor in PCB technology

A novel DC/AC current sensor works on the fluxgate principle. The core in the form of a 7/10-mm ring made of electrodeposited permalloy is sandwiched in the middle of a printed circuit board (PCB), whereas the sensor excitation winding is also integrated in the copper layers of the PCB. To lower the sensor power consumption, the excitation winding was tuned by a parallel capacitor. The peak-peak/rms ratio of 5.2 was achieved for the excitation frequency of 25 kHz. The open-loop sensor has 100-mV/A sensitivity; the characteristics have a linearity error of 10% and hysteresis below 0.1% in the 1-A range.     

Quantifying shrinkage cracking in fiber reinforced concrete using the ring test

Tensile stress can develop in concrete when rest raint prevents the concrete from shrinking freely in response to drying, chemical reaction, or temperature reduction. When these tensile stresses exceed the tensile strength of the concrete, visible cracking may be expected to occur. While several test methods have been developed to assess a material's potential for early-age shrinkage cracking, this paper describes the use of the ‘ring-test’ for assessing the performance of a fiber reinforced concrete. An equation is presented that enables the residual stress that develops in the concrete ring specimen to be estimated. This expression is used to approximate the stress that is transferred across a crack. It is shown that for conventional fiber reinforced concrete (i.e., the mixtures described in this paper) the pre-peak mechanical properties (elastic modulus, splitting tensile strength and free shrinkage) are not influenced greatly by the addition of fibers. Rather, fibers appear to influence shrinkage-cracking behavior only after the crack begins to open. To better understand the role of fibers in mitigating early-age shrinkage cracking passive acoustic emission testing was used. Acoustic emission measurements indicate microcracking due to the heterogenous nature of the concrete and the presence of moisture gradients. The acoustic emission results highlight how a single crack begins to form into a visible crack. Finally, an approach is presented for estimating crack-width based on the strain data measured from the ring test. The role of the specimen geometry is discussed for comparing the ring test with field applications.     

Performance and characterization of new micromachined high-frequency linear arrays

A new approach for fabricating high frequency (> 20 MHz) linear array transducers, based on laser micromachining, has been developed. A 30 MHz, 64-element, 74-microm pitch, linear array design is presented. The performance of the device is demonstrated by comparing electrical and acoustic measurements with analytical, equivalent circuit, and finite-element analysis (FEA) simulations. All FEA results for array performance have been generated using one global set of material parameters. Each fabricated array has been integrated onto a flex circuit for ease of handling, and the flex has been integrated onto a custom printed circuit board test card for ease of testing. For a fully assembled array, with an acoustic lens, the center frequency was 28.7 MHz with a one-way -3 dB and -6 dB bandwidth of 59% and 83%, respectively, and a -20 dB pulse width of -99 ns. The per-element peak acoustic power, for a +/- 30 V single cycle pulse, measured at the 10 mm focal length of the lens was 590 kPa with a -6 dB directivity span of about 30 degrees. The worst-case total cross talk of the combined array and flex assembly is for nearest neighboring elements and was measured to have an average level -40 dB across the -6 dB bandwidth of the device. Any significant deviation from simulation can be explained through limitations in apparatus calibration and in device packaging.     

片式化高压电容器的内电极结构及优化

耐高压片式化多层陶瓷电容器(MLCC)要求其内电极具有特殊的结构以保证产品的可靠性。本文对比了普通MLCC和高压MLCC的内电极结构，用有限元方法对两种ML—CC中若干典型位置的电场分布进行了分析，从电学角度对高压MLCC中内电极结构尺寸进行了优化，建立了高压MLCC内电极结构尺寸和所选用陶瓷介质材料的电学性能、MLCC的额定工作电压等参数之间的关系，这对中、高压MLCC的设计和制造具有指导意义。     

Experience with the use of the acoustic emission technique for monitoring scale failure in wet and dry environments

Abstract

A brief survey of the acoustic emission technique for monitoring scale cracking and failure on 2.25–24% Cr steels in wet and dry environments is given. A number of acoustic emission test rigs are described. Some of the more simple test rigs are used for testing small oxidation coupons during isothermal oxidation. More sophisticated rigs have been used for testing full size heat exchanger tubes during thermal cycling.

Most acoustic emission measurements in a wet environment come from testing at temperatures below 650°C. There are examples from Alloy 800 and thermal barrier coatings that were tested at higher temperatures, 900°C and 1100°C, respectively. Through the years acoustic emission tests have been performed in dry air, dry air+10%H₂O, dry air+0.5%SO₂, and Ar+5%H₂+50%H₂O. Consequently, a wide variety of exposure temperatures and atmospheres can be investigated using acoustic emission techniques.

Qualitative acoustic emission results can detect when scale cracking occurs at exposure temperature, where such cracks are produced by growth stress. Acoustic emission signals have been measured during sample cooling, where the signal arises from scale cracking that is caused by the thermal expansion mismatch stress. Measured results have clearly shown that scale cracking caused by both growth stress and thermal expansion mismatch stress are affected by water vapor in the exposure environment. Post-test metallographic investigations show that crack orientation and the oxide scale phases are also affected by the gas composition in the test rig. Additionally the sample mass gain and scale thickness is affected by water vapor content.

Finally, acoustic emission techniques are helpful for understanding the phenomena of breakaway oxidation and spallation/exfoliation.     

HG70钢的焊接性能

HG70钢是一种高强度低合金机械工程用钢。本文研究了焊缝中扩散氢含量与预热温度的关系。通过焊接热影响区最高硬度试验、小铁研试验 ,评估了HG70钢的裂纹敏感性 ,测定了手工焊接接头的力学性能。结果表明 ,HG70钢具有较低的裂纹敏感性 ,其焊接接头具有优良的力学性能     

Solution-based aerosol deposition process for synthesis of multilayer structures

In this paper, we report the progress on 3D aerosol deposition of barium titanate (BTO) based multilayer ceramic capacitors (MLCC) using an automated process. Solution-based aerosol deposition is a promising direct-write method to produce three-dimensional (3D) structures at low temperatures. We utilize the combination of solution-based aerosol process and selective laser sintering (SLS) to develop 3D structures. The MLCC structure was synthesized on silicon substrate consisting of alternate layers of 0.5-1.0 μm thick silver electrode layer and 0.5-2 μm thick BTO ceramic. The effect of incident laser power subsequent to deposition (in the range of 105 mW and 930 mW) was systematically investigated revealing the changes in grain morphology as a function of local sintering. The results of this study are promising for development of on-substrate thin/thick film MLCCs.     

钛酸钡陶瓷电容机械性能的尺寸效应

以粉体粒径为0．3pm～0．7pm的BaTiO3粉体为原料．采用传统陶瓷工艺,研究了微粉尺寸对钛酸钡陶瓷机械性能的影响,从粉体形貌、晶粒形貌、相结构、微观结构、应力变化及最终的机械性能改变等方面分析了纯BaTiO3陶瓷的晶粒尺寸效应。实验中发现,晶粒较小时,陶瓷断裂所需要破坏的晶粒多,由于晶界所占比例大,陶瓷断裂走过的路程长．强内应力为陶瓷结构稳定提供支撑,因此机械强度提高。     

Fracture mechanics analysis of the effect of substrate flexibility on solder joint reliability

Solder joint fatigue failure is a serious reliability concern in area array technologies, such as flip chip and ball grid array packages of integrated-circuit chips. The selection of different substrate materials could affect solder joint thermal fatigue life significantly. The reliability of solder joints in real flip chip assembly with both rigid and compliant substrates was evaluated by the accelerated temperature cycling test and thermal mechanical analysis. The mechanism of substrate flexibility on improving solder joint thermal fatigue lifetime was investigated by fracture mechanics methods. Two different methods (crack tip opening displacement, CTOD and virtual crack closure technique, VCCT) are used to determine the crack tip parameters which are considered as the indices of reliability of solder joints, including the strain energy release rate and phase angle for the different crack lengths and temperatures. It was found that the thermal fatigue lifetime of solder joints in flip chip on flex assembly (FCOF) was much longer than that of flip chip on rigid board assembly (FCOB). The flex substrates could dissipate energy that otherwise would be absorbed by solder joints, that is, substrate flexibility has a great effect on solder joint reliability and the reliability improvement was attributed to flex buckling or bending during thermal cycling.     

Inkjet printed electronics for multifunctional composite structure

Copper nano-ink with a drop-on-demand (DOD) piezoelectric inkjet printing method was introduced. The printed electrodes were thermally sintered to ensure high-quality electrical and mechanical performances. To check the reliability of the printed electrodes on a polymer layer, resistance changes were measured under static loading. The electrodes with various widths and thicknesses were used to find the optimal dimensions. A multifunctional composite laminate which can harvest and store a solar energy was fabricated using printed electrodes. An amorphous silicon solar cell and a thin film solid state lithium-ion battery were adhesively joined and electrically connected to a thin flexible printed circuit board (PCB). Then, the passive components such as resistor and diode were electrically connected to the printed circuit board by silver pasting. The integrated PCB was co-cured with a carbon/epoxy composite laminate by the vacuum bag molding process in an autoclave. The structural and functional performance of the final energy harvesting/storage composite laminate was tested under mechanical loading.     

Acoustic emission waveform characterization of crack origin and mode in fractured and ASR damaged concrete

Different constituents of concrete can have cracking behavior that varies in terms of the acoustic waveform that is generated. Understanding the waveform may provide insight into the source and behavior of a crack that occurs in a cementitious composite. In this study, passive acoustic emission (AE) was used to investigate the waveform properties of the individual components of concrete (i.e., aggregate, paste, and interfacial transition zone (ITZ)). First, acoustic events produced by cracks generated using mechanical loading in a wedge splitting test were detected. It was observed that cracks that occurred through the aggregate have an AE frequency range between 300 kHz and 400 kHz, while cracks that propagated through the matrix (paste and ITZ) have a frequency range between 100 kHz and 300 kHz. Second, tests were performed using samples that were susceptible to alkali silica reaction; and AE and X-ray computed tomography were used to detect cracking. AE events with a frequency range between 300 kHz and 400 kHz were detected at early ages, suggesting the initiation of cracks within reactive aggregate. At later ages, AE events were detected with frequency ranges of 100–300 kHz, indicating crack development and propagation in the matrix.     

HDPE/LDPE/SBS高耐应力开裂复合材料亚微相态-力学性能-流变性能的研究(Ⅰ)

HDPE易受环境的影响产生应力开裂,这限制了其在工业上的应用.本文通过HDPE与SBS,LDPE混合,制得一系列不同组分的高分子合金.分析了其球晶结构和拉伸力学性质并用扫描电镜观察断口形态,并与最终测得的耐环境应力开裂时间进行比较.结果表明,共混体系耐应力开裂性能比纯HDPE有很大提高,而且应力开裂性能与材料的强度和球晶形态密切相关,强度较大且球晶小而不规则者,其耐环境应力开裂性能较好.     

Thermal shock cracking of lithium niobate single crystal

The quantitative estimation of failure stress of a lithium niobate (LN) single crystal due to thermal shock was investigated. Cylindrical test specimens were used in the thermal shock tests. The thermal stress of an LN test specimen under conditions of thermal shock cracking was calculated from a computer program which takes account of the crystal anisotropy, using the surface temperature measured in the thermal shock test. Four-point bending tests were also carried out to examine the relationship between the thermal shock cracking and the failure of a small test specimen due to mechanical load. LN single crystals fractured at the cleavage planes {0 1 1 2} in the thermal shock test and the four-point bending test. Although the failure stress data obtained from both tests obey the Weibull distribution, the Weibull distribution depends not only on specimen size but also on loading type. According to the Weibull distribution of thermal shock test data, if the normal stress σ_n acting on the cleavage planes {0 1 1 2} is lower than 10 MPa, the probability of thermal shock cracking becomes very small — less than 2%. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of particle size in Ni screen printing paste of incompatible polymer binders

Dispersion of nano-sized particles at high solid content has attracted attention in many industrial applications such as printed electronic products. However, the material design and processing heavily depends on experience with little quantitative measure. For fabrication of thinner dielectric layers, Ni size is getting smaller when used as an inner electrode in multilayer chip capacitor (MLCC). In the present study, we investigate the rheological properties and printing performance of the pastes with two different sizes of Ni particles in the same incompatible binder mixtures of ethyl cellulose (EC) and polyvinyl butyral (PVB). The difference in particle size causes different microstructural heterogeneity and highly nonlinear rheological properties upon the external flow field. The printing pattern and the surface profile are also analyzed by confocal images after screen printing. For smaller particle size of Ni, the more heterogeneous microstructure is observed with increasing PVB content, which is evidenced by the screen printing images as well as its rheological behavior. We explain the difference of spatial heterogeneity in terms of different interactions between particle–particle and particle–polymer. This work is believed to contribute to better design of inner electrodes and processing in MLCC manufacturing.