Evaluation of Residual Stress in a Multilayer Ceramic Capacitor and its Effect on Dielectric Behaviors Under Applied dc Bias Field

The residual stress in a multilayer ceramic capacitor (MLCC) has been evaluated by two-dimensional finite element simulation in combination with X-ray diffraction measurement. It is shown that there is a compressive in-plane stress in the active layers of the MLCC, which increases with increases in the number of dielectric layers when both dielectric layer thickness and electrode thickness are kept constant. A good order of magnitude agreement between the residual stresses obtained from two approaches is found. The ɛ– V response of the MLCC with different number of dielectric layers demonstrates that under a given or no applied field, the dielectric permittivity increases with increasing compressive stress. Additionally, under dc bias field, the higher the compressive in-plane stress existing in the MLCC, the more significant the decrease of the dielectric permittivity. These results can be explained through a phenomenological thermodynamic model, including both elastic and electrostatic energy, based on the Ginsburg–Landau–Devonshire theory.     

Reaction-Controlled Binder Burnout of Ceramic Multilayer Capacitors

Reaction-controlled binder burnout of ceramic multilayer capacitors (CMCs) is conducted in a series of small-scale experiments. the burnout process is followed by monitoring the weight of the CMCs. The observed maximum weight loss rate, obtained with a conventional linear heating process, is used to design a weight-time program for a reaction-controlled process. In this process the actual CMC weight is controlled to closely follow the weight program by means of continuous control with the batch temperature. The advantages of this procedure are discussed. The results of the present study, although being restricted to oxidative burnout of a special product, are thought to be of some use for other ceramic burnout situations. The relevant parts of controller design are discussed together with some comments on scale-up.     

Mechanical Failure Characteristics of Ceramic Multilayer Capacitors

The results of both uniaxial and biaxial flexure as well as toughness testing on actual commercial ceramic capacitor samples are reported. Necessary procedural adjustments are outlined for miniaturizing the applied-moment double-cantilever-beam test to accommodate these small samples. Strength and toughness testing showed that the metal electrodes lowered the fracture toughness and that the metal-ceramic interface was a preferred fracture path for crack propagation parallel to the electrodes. However, toughness did not clearly depend on crack propagation parallel or perpendicular to the electrodes, nor with flexural strengths. Flexural strengths were 0 to 40% lower, with the electrodes perpendicular to the tensile surface vs. parallel to the tensile surface. Fractures initiated from machining (or impact) flaws, or voids of various sizes, shapes, and locations, thus explaining the poor correlation between strength and toughness. Biaxial flexure tests of dielectric specimens of various sizes indicate that such a test could be scaled down and "calibrated" for actual testing of capacitors; e.g., a decrease in strength with increasing specimen thickness to support diameter ratio is indicated.     

Influence of Electroless Nickel Plating on Multilayer Ceramic Capacitors and the Implications for Reliability in Multilayer Ceramic Capacitors

The influence of electroless nickel plating on lead-based relaxor ferroelectric multilayer ceramic capacitors (MLCs) was studied by a comparison experiment. It was found that the influence is related to reactions in the electroless plating. It is proposed that adsorbed hydrogen atoms generated in electroless plating can diffuse into the ceramic bodies of MLCs and undergo some reduction reaction with them, resulting in the failure of electroless nickel plating. The implications for the negative influence of electroplating on MLCs and for the degradation in MLCs are also included, in which much attention is paid to the reduction reaction of hydrogen atoms generated by electrolysis of water.     

Degradation of Multilayer Ceramic Capacitors with Nickel Electrodes

The mechanism of degradation, or IR drop, of BaTiO₃-based Ni-electrode chip capacitors has been studied, with special attention to the microstructure. Degradation occurred mainly at the center of the capacitors. Longer-life capacitors were obtained under conditions of low oxygen partial pressure, 10⁻¹² atm, during sintering, and had larger grain sizes and smaller quantities of grain boundary phase. The existence of oxygen vacancies in the grain boundary phase was confirmed by cathode luminescence measurement. Double layers along the surfaces of the Ni electrodes were also related to the life of the capacitors.     

Electrodeposition Method for Terminals of Multilayer Ceramic Capacitors

A method using a combination of electroless and electrolytic plating was developed to provide an alternative method for forming the end terminals of multilayer ceramic capacitors. Electrodeposited terminals were formed by using electroless copper followed by electrolytic nickel plating. The electrical characteristics of the electrodeposited terminal capacitors were compared with standard capacitors and found to be identical.     

Electrode-Based Causes of Delaminations in Multilayer Ceramic Capacitors

Delaminations are a principal quality problem in the manufacture of multilayer ceramic capacitors (MLC's). They are defined as a separation of the electrode and dielectric layers and can result in electrical shorts and/or life failures. Delaminations originate from many sources in MLC manufacture, but we have identified four which are caused by the electrode. High levels of organic resin in the electrode paste lead to high resin content in dried electrode prints, requiring removal of large amounts of organic residues during burnout, causing delaminations. Catalysis of these organics by the precious metals also causes delaminations from rapid evolution of gas and heat release during burnout. Poor adhesion of the dielectric tape layers to dried electrode prints during MLC buildup can cause "green-state" delaminations which remain through firing. Sintering shrinkage mismatch between the electrode and dielectric layers leads to internal stresses in MLC's, resulting in delaminations. We discuss these electrode-based mechanisms of delamination and the design of electrode pastes which solve these problems.     

Finite-Element Analysis of Ceramic Multilayer Capacitors: Modeling and Electrical Impedance Spectroscopy for a Nondestructive Failure Test

The opportunities are introduced to calculate the electrical, mechanical, and thermal couplings of ceramic multilayer capacitors (MLCs) with the finite-element method. The results may lead to improvements in the production, integration, and operation of MLCs. In this paper, a comparison is given of calculations and measurements of electromechanical resonances in the impedance spectra of MLCs. The simulation of defective capacitors with three different types of assumed faults reveals the changes in the impedance spectra due to these defects. This allows the prediction of flaws in MLCs based on measurement of the impedance spectra.     

Effect of Oxygen Partial Pressure on the Dielectric Properties and Microstructures of Cofired Base-Metal-Electrode Multilayer Ceramic Capacitors

The dielectric properties, dopant distributions, and microstructures of BaTiO₃-based multilayer ceramic capacitors (MLCCs) sintered in H₂–N₂–H₂O atmospheres with     =10^−7.5 Pa (BMX-7.5) and     =10^−9.5 Pa (BMX-9.5) were studied, and the effects of oxygen partial pressures were analyzed. Dielectric measurements showed that BMX-7.5 had a lower dielectric constant at temperatures above 20°C, but a higher dielectric constant at temperatures below 10°C when compared with BMX-9.5. The coexistence of core–shell and core grains was observed in bright field (BF) transmission electron microscopy images in both types of capacitors. Triple-point and grain boundary phases were observed more frequently in BMX-9.5 than in BMX-7.5, and energy-dispersive X-ray spectrometer point-by-point analysis revealed that these second phases contained high concentrations of dopants such as Si, Y, and Ca. The dopant concentration in the shell regions in BMX-7.5 was higher than that in similar regions in BMX-9.5. Smeared and twisted grain boundaries with fringes observed in both types of MLCCs indicated that the shell regions in both samples were formed either by diffusion of foreign ions into BaTiO₃ or by crystallization of grain boundary and triple-point liquid phases. It was deduced that the partial pressure of oxygen in the sintering atmosphere influenced the microstructures, dopant distributions, and core–shell ratios of the grains in these materials.     

Polar Nanoregions and Dielectric Properties of BaTiO3‐Based Y5V Multilayer Ceramic Capacitors

Commercial EIA‐Y5V base‐metal‐electrode multilayer ceramic capacitors (BME‐MLCCs) made of (CaO+ZrO₂)‐doped BaTiO₃ are analyzed for the microstructure and investigated for its relation to dielectric properties. The characteristic diffuse scattering (DS) intensities observed in BaTiO₃ ceramics and the featureless “solid‐solution” grains in Y5V capacitor chips are originated from multiple Ti sites in the dynamic BaTiO₃ structure. The pseudo‐cubic (PC)‐grains retaining the overall cubic (C‐) symmetry metastably at room temperature are embedded with polar nanoregions (PNRs) in the ferroelectric (FE) tetragonal (T‐), and rhombohedral (R‐) phases, as revealed by high‐resolution transmission electron microscopy (HRTEM). The presence of PNRs contributes effectively to large relative permittivity ε_r ≈ 13 200 at 25°C. The FE T‐domains grow from within PC‐grains at the expense of embedded PNRs after prolonged annealing by extending “oxidizing firing” at 950°C in pO₂ = 10^?7 atm. These domains contain less Zr with otherwise homogeneously distributed solutes in PNR‐dispersed PC‐grains. Although preserving the relaxors characteristics, ε_r is reduced to ~11 000 after 12 h, and then to ~9000 after 24 h annealing. The reduction in ε_r is attributed to the annealing‐induced FE T‐domains grown at the expense of PNRs in PC‐grains. The Vögel–Fulcher analysis indicates that Y5V ceramics are in the relaxor FE category, containing PNRs derived from polarization frustration.     

Statistical Determination of Plating Process Variables for Multilayer Ceramic Chip Capacitors

The effects of the following barrier layer plating process variables on reliability of multilayer ceramic chip capacitors are discussed: media type, nickel plating thickness, lead concentration, pH, tin plating current density, number of capacitors, and percent loading of the plating barrel. The dielectric was formulated from a lead magnesium niobate material. Evaluations were done with respect to capacitance, dissipation factor, conductance, dry life (temperature bias) test, solderability (with and without steam aging), and voltage surge test. Several of the in-process variables studied were found to have a statistically significant effect on some of these response variables. The data indicate that the most significant inprocess parameters in the barrier layer process, of those included in this study, are media type and percentage loading of the barrel. Variables of marginal significance are number of capacitors, lead in the bath, and tin plating current density. The other variables had no discernible effect on the response variables studied. The presence of such a large experimental error in life test was a significant outcome of the study and indicates a need for further study on means of obtaining reproducible life-test results after plating.     

Thermo-Mechanical Stresses and Mechanical Reliability of Multilayer Ceramic Capacitors (MLCC)

In this work, the effects of design parameters on the mechanical reliability of multilayer ceramic capacitors (MLCC) are evaluated by a board flex test. Using the finite element method (FEM), thermo-mechanical stresses that accumulated in the ceramic of MLCC during termination firing, soldering, and board flex test are determined by varying design parameters. The calculation results revealed that the sizes of Cu terminations are the parameters that affect the stress the most. The degree of sensitivity of the stress to the dominant parameters depends significantly on the thickness ratio of the MLCC to the board. Based on our investigation, better design rules are proposed and verified experimentally.     

Polarization Response and Thermally Stimulated Depolarization Current of BaTiO3‐based Y5V Ceramic Multilayer Capacitors

Polarization response and thermally stimulated depolarization current (TSDC) of BaTiO₃‐based ceramic multilayer capacitors with Y5V specification were studied. The temperature dependence of dielectric behavior shows that as the dc electric field increases, the polarization response in the whole measurement range (from ?125°C to +350°C) is suppressed. As the temperature rises to about 250°C, dielectric loss significantly increases and has a dependence on dc electric field, due to the leakage behavior at high temperature. According to the hysteresis loops, the calculated electrostatic energy density and energy efficiency are also closely related to polarization‐electric field. Utilizing a fixed measuring polarization condition, two TSDC relaxation peaks are observed and both are associated with oxygen vacancies. It is demonstrated that the weak peak originates from the in‐grain migration of oxygen vacancies and the strong peak with high relaxation temperature is caused by the across grain‐boundary oxygen vacancies. The activation energy estimated for the relaxation of oxygen vacancies across grain boundaries is about 0.78 eV. The main contribution for the leakage behavior is from the across grain‐boundary relaxation of oxygen vacancies. With increasing of temperature and electric field stress, the extrinsic oxygen vacancy defects show more fluent migration, which eventually leads to the resistance degradation and breakdown.     

Effect of Densification Mismatch on Camber Development during Cofiring of Nickel-Based Multilayer Ceramic Capacitors

The development of camber during the cofiring of a two-layered structure of Ni-electrode/BaTiO₃-dielectric as a function of temperature has been investigated. At a given thickness of Ni electrode, less camber and camber rate with increasing thickness of BaTiO₃ dielectric have been observed. This phenomenon is attributed to the densification mismatch between the Ni electrode and the BaTiO₃ dielectric during cofiring. The mathematical analysis of camber development, based on a viscous model, shows significant agreement with experimental observations.     

Dielectric Properties and Microstructures of Ba(Ti,Zr)O3 Multilayer Ceramic Capacitors with Ni Electrodes

The microstructures and dielectric properties of multilayer ceramic capacitors based on reoxidized Ba(Ti_0.88,Zr_0.12)O₃ (BTZ) materials with Ni electrodes were studied using transmission electron microscopy. Dielectric measurements showed that the BTZ materials exhibited frequency relaxation effects. Although X-ray diffraction showed a single pseudocubic phase, split and elongated electron diffraction spots were observed using selected area diffraction (SAD). There were no super-lattice diffraction spots in the SAD pattern. The microstructures of BTZ dielectric materials were observed at dynamical diffraction conditions, and multidomain structures coexisting in one grain were imaged with high contrast. Bright field and centered dark field images revealed the pseudocubic (100) and (110) domain walls had developed in some regions of the same grain with normal ferroelectric macro-domain features, and bend contours and distorted domain walls were seen. Defects with the features of low angle grain boundaries, dislocations, and phase boundaries were also observed. Uneven distribution of internal stress and coexistence of multiphases and multidomains in individual grains were considered to be responsible for the frequency relaxor behavior observed in these materials. A model of the evolution of the microstructures with the decrease of temperature is presented.     

Fractography of Thermal-Shock-Cracked Multilayer Capacitors

Cracking of multilayer ceramic chips due to mechanical and thermal stresses during surface mounting is a major problem. Two types of tests were performed to study the susceptibility of chips for thermal shock cracking. In one test, chips were immersed in molten solder at different temperatures and, after cooling, chips were examined for visible cracks. In another test, chips were mounted on a printed circuit board and, then, wave soldered to simulate the actual usage conditions. After the soldering process, chips were exposed to load humidity conditions and, then, tested for insuiation resistance. Cracked chips from both tests were analyzed by fractographic methods to determine the source of failure. Causes of the defects leading to fracture and their relationship to the processing of multilayer capacitors are discussed. The relative advantages and disadvantages of the two thermal shock test methods in evaluating the integrity of the chips are presented. [Key words: capacitors, multilayer, thermal shock, cracks, fractography.]     

陶瓷电容器的制备工艺概述

简介了新型陶瓷电容器的优点、功能、类型和发展现状及表面层陶瓷电容器、表面层型陶瓷电容器和晶界型陶瓷电容器的产生机理和区别，和影响陶瓷电容器性能的诸多因素，如显微结构、掺杂元素和包覆改性等；回顾了国内外陶瓷电容器的烧成工艺发展历史，如高温一次烧成、低温一次烧成、独石法和激光辐射法等；展望了陶瓷电容器在21世纪的研究和应用前景。     

Finite Element Analysis and Design of Thermal–Mechanical Stresses in Multilayer Ceramic Capacitors

A three‐dimensional finite element model describing the thermal–mechanical stress distribution in multilayer ceramic capacitors (MLCCs) during termination firing, soldering, and bending tests is presented. Numerical results indicate that the thermal residual stresses originating from the soldering process are approximately one‐fifth to half of the magnitude of the flexural stresses at the crack occurrence during the board flex test. The peak tensile stress from numerical simulations correlates with the crack initiation site observed in situ in board flex tests. The effects of inner electrode number, solder wicking height, lateral margin length, and the thickness of nickel in the termination component on mechanical failure during the board flex test are also investigated. Numerical results demonstrate that the maximum tensile stress could be effectively relieved by increasing the length of the lateral margin. In addition, a judicious combination of the solder wicking height and nickel termination thickness can further diminish the peak tensile stress during the board flex test. Finally, better design criteria are also developed by modifying the geometric parameters of MLCCs using Taguchi orthogonal arrays to decrease the peak tensile stresses that occur during board flex tests.     

Interaction of Ag/Pd Metallization with Lead and Bismuth Oxide-Based Fluxes in Multilayer Ceramic Capacitors

An ongoing challenge for future developments in high-performance ceramic multilayer capacitors and integrated ceramics is to reduce the internal electrode cost and thickness without sacrificing yield or reliability. Key to these developments is a thorough understanding of the interactions which occur between flux-sintered dielectrics and low-cost, Ag/Pd electrodes. In this paper we present results on the pahse equilibria of Ag/Pd electrode systems with Bi₂O₃ and PbO fluxes. The conditions under which the bismuth reaction occurs and reactions in the Pd–PbO system are reported. Results show that the equilibrium phases which form depend strongly upon the Ag/Pd ratio and temperature. These phases include PdBi₂O₄, Pd(Bi), PdPbO₂, Pd(Pb), and PbPd₃. The PdBi₂O₄ and PdPbO₂ phases decompose when PdO destabilizes, resulting in a series of reactions which result in oxygen evolution and partial melting of components. The exact phase relations of the Ag/Pd–Bi₂O₃–O₂(air) system and Ag/Pd–PbO–O₂(air) system have been established for the first time and are discussed in terms of their impact on multilayer, cofired structures.