Thermal shock resistance of miniaturized multilayer ceramic capacitors

The thermal shock resistance of miniaturized multilayer ceramic capacitors (MLCs), of sizes 0402, 0603, 0805 and 1206, was investigated by comparing the leakage currents before and after thermal shock. It was generally found that smaller capacitors have a higher thermal shock resistance than larger ones. The 0402 MLC possesses a thermal shock resistance in excess of 420 C. The linear interdependence of thermal shock resistance and reciprocal of half thickness, as predicted by conventional thermal shock analysis, was not observed. Instead, the thermal shock resistance of an MLC was found to be inversely proportional to the total area of its ceramic surface. This confirms that pre-existing flaws on the ceramic surface dominate the crack initiation process and are therefore primarily responsible for determining the thermal shock resistance of an MLC.     

High-frequency sintering of multilayer ceramic capacitors

Results of sintering multilayer ceramic capacitors by a high-frequency field are presented. It is shown that half-finished multilayer ceramic capacitors subjected to a high-frequency field are sintered in 5–15 min instead of the several hours taken in the conventional method. Possibilities of using high-frequency fields for sintering ceramic materials and electronic products are discussed.Vitebsk Branch of the Institute of Solid State and Semiconductor Physics, Academy of Sciences of Belarus, Vitebsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 1, pp. 143–145, January–February, 1995.     

Advanced characterization of mechanical properties of multilayer ceramic capacitors

Characterization of the mechanical properties of small components is a significant issue. For the multilayer ceramic capacitor (MLCC), direct loading by conventional facilities is not suitable because of its small size. To date, the standard method used to determine MLCC’s mechanical properties is board flex test; i.e., mounting the capacitor onto a printed circuit board (PCB) and applying bending to the entire system. Failure is defined as cracking or capacitance loss of the MLCC when the mounted PCB is subjected to a specified deflection, and the measurements are usually performed after the test. In this case, characterization of the mechanical properties of MLCCs is qualitative. The purpose of the present study was to quantitatively characterize the mechanical properties of MLCCs. Specifically, the acoustic emission was used to detect cracking of MLCCs during the board flex test. To confirm cracking-induced acoustic emission, telemicroscope was used to perform the in situ observation of cracking. Finite element analyses were also performed to analyze the stress field resulting from the test to compare with the observed cracking path. In addition, nanoindentation was used to explore the mechanical properties of the constituents of MLCCs in the nanoscale. Our work not only allows identification and understanding of the fracture origin, but also provides guidelines in the material design.     

Copper electrodes multilayer ceramic capacitors Part I The dielectric composition

Several sintering aids were tested to lower the CaZrO₃ ceramic sintering temperature. Numerous additions are shown to lower the densification temperature and to promote the dielectric properties with a QF product, an insulating resistivity and a permittivity enhancement, and a lowering of the temperature coefficient . A combination of dopants was tested and optimised, resulting in a low temperature sintering ceramic based on CaZrO₃, LiNO₃, SiO₂ and TiO₂. The samples sintered at 1000°C in oxidising or reducing atmosphere exhibit very attractive properties, with a QF product of nearly 15, 28, a near zero and _i 10¹² · cm. The sintering mechanisms of this ceramic are also debated.     

In situ observation of electrode melting in multilayer ceramic capacitors

In the usage of multilayer ceramic capacitors, we are concerned with the intrinsic dielectric properties of the ceramic and its long-term stability/reliability under external stresses in service conditions. Of equal importance to long-term reliability is the short-term survivability under current (power)-surge conditions. It differs from the ability to withstand voltage surge, which is determined by the dielectric strength of the ceramic. In this paper, we present some observations on sectioned and polished multilayer ceramic capacitors, which were subjected to controlled current-surge test conditions. Capacitors from several vendors were examined. The samples were examinedin situ under an optical microscope while current pulses of varying magnitude were applied at a constant voltage. Subsequently some samples were further examined by scanning electron microscopy. The failure mechanism appeared to be the heat-induced local melting of internal electrodes, which might then lead to a blow-out or charring of the capacitor. In less severe cases, we observed local melting and crack formation in the surrounding ceramic as well. The primary change in capacitor properties was in the degradation of the insulation resistance. In severe cases, this also led to an increase in the dissipation factor.     

CaZrO3 additives to enhance capacitance properties in BaTiO3 ceramic capacitors

The effects on the dielectric properties of BaTiO₃ of addition of CaZrO₃ (0–17 wt%) has been investigated. Dielectric constants ranging between 2500 and 15 500 have been obtained by using commercial grade raw materials with the starting dielectric constant of the undoped BaTiO₃ being 800. The capacitor dielectrics have also been analysed for their electrical properties, crystalline phases and microstructural features.     

Copper electrodes multilayer ceramic capacitors Part II Chips fabrication, optimisation and characterisation

In a companion paper, a ceramic formulation based on CaZrO₃ was developed to decrease the sintering temperature of this oxide. We achieved in obtaining a low sintering temperature ceramic fireable below the copper melting point while maintaining attractive properties whatever the atmosphere used (oxidising or reductive). The present paper deals with the fabrication of the copper electrodes multilayer ceramic capacitors (MLCC) and their optimisation. Several points have been tested to enhance the characteristics of the components. They are based on the precursors origin and the manufacturing process optimisation. These studies result in NPO components with good properties (C 30 pF/5 active layers; = –45 ppm/K; ESR 20 m at 30 MHz; tg < 10 × 10^–4; _i > 10¹² · cm).     

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.     

Non-destructive detection and localization of defects in multilayer ceramic chip capacitors using electromechanical resonances

High reliability multilayer ceramic chip capacitors are necessary for use in surface mounting processes which are more mechanically and thermally severe than the traditional through-hole processes. Moreover, in specific environments, even a small defect can be considered as catastrophic for the working of the electronic circuit or even of the entire system. In order to look for the failures—intrinsic latent defects and those caused by SMT soldering processes—appearing in these components, many techniques of analysis can be used. With this present work, we focus on one technique based on the principle of electromechanical resonances existing in piezoelectric materials under a d.c. bias field. The free correlation between the impedance measurement of the chip under a sufficient voltage allows us to highlight some conclusions concerning the behaviour, the nature of the defects and the long-term reliability of ceramic chip capacitors. This method has the advantage of being non-destructive, rapid, efficient and low-cost.     

Measuring the capacitance of capacitors with large losses

Conclusions The application range of the beating method and similar methods for measuring capacitances with large losses are limited by errors which are inherent in these methods and are due to the loss resistances affecting the measurement results (12).The effect of losses on the capacitance measurements is completely eliminated in measuring circuits with modulated parameters. The utilization of circuits with an external modulation serves to raise the sensitivity of capacitance measurements. The automation of these circuits makes them very promising for designing commercial instruments.Translated from Izmeritel'naya Tekhnika, No. 8, pp. 58–61, August, 1968.     

Failure analysis of miniaturized multilayer ceramic capacitors in surface mount printed circuit board assemblies

New failure analysis results of miniaturized multilayer ceramic capacitors (sizes 0402, 0603, 0805 and 1206) which have been subjected to various degrees of thermal shock up to 450°C by ice-water or dry ice quenching are reported. The thermal shock resistance of 0402 multilayer ceramic capacitors was found to be about 400°C and considerably better than those of the larger ones. Microstructural and layer-by-layer insulation resistance analyses have clearly identified the physical locations responsible for the electrical leakage of defective capacitors. Further, no evidence of silver migration as a dominant failure mechanism has been observed for any of the defective capacitors under usual operating stresses. Comparisons ofI–V characteristics for multilayer ceramic capacitors quenched by ice-water and dry ice confirm that water plays a significant role in causing electrical failure at nominal bias. Comparisons with results obtained from practical surface mount printed circuit board assembly of mobile telephones is discussed. From these, failure mechanisms are proposed to explain the failure of miniaturized multilayer ceramic capacitors under normal service conditions.     

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.     

Mechanical vs. electrical failure mechanisms in high voltage,high energy density multilayer ceramic capacitors

Causes of breakdown, both mechanical and electrical, in high voltage, high energy density, BaTiO₃ capacitors were studied. The flexural strength of the capacitors was 96 MPa. Failure was due to surface defects or pores close to the surfaces of the samples. The dielectric breakdown strength of the samples was 181 kV/cm. The causes of breakdown were either electrode end effects or pores between the dielectric and electrode layers. Weibull statistics were used to determine if there was a correlation between mechanical failure and dielectric breakdown. A strong correlation between the two types of failure was not found in the study, in contrast to earlier studies of single dielectric layer capacitor materials.     

Microstructure and thermal properties of dysprosium and thulium co-doped barium titanate ceramics for high performance multilayer ceramic capacitors

The co-doping characteristics on microstructure and thermal properties of barium titanate (BaTiO₃) were investigated to elucidate formation of core-shell structure by dysprosium (Dy) and thulium (Tm) addition in the BaTiO₃-Dy₂O₃-Tm₂O₃ system. The dielectrics co-doped with 0.7 mol% Dy₂O₃ and 0.3 mol% Tm₂O₃ had the dielectric constant up to 2200 as a function of temperature, which was 30% higher than that of specimen containing only Tm₂O₃ at the room temperature. It could be explained by the fact that the increase of Dy₂O₃ addition contributed to the improvement of dielectric constant. On the other hand, the rapid diffusion rate of Dy³⁺ ions in BaTiO₃ showed an adverse effect on temperature stability caused by destruction of core-shell. As the compensation for shell expansion in BaTiO₃, the reinforcement of the core-shell structure through the addition of Tm₂O₃ was confirmed by TEM-EDS analysis and attributed the temperature coefficient of capacitance (TCC) in a reliability condition (−55 °C to 125 °C, △C = ±15% or less). The enhanced electrical properties and temperature stability could be deduced from the generation of electrons and the formation core-shell structure in co-doped BaTiO₃ system respectively.     

Raman investigation of the ageing of Ni-BaTiO<Subscript>3</Subscript> multilayer ceramic capacitors

Ni-BaTiO₃ multilayer ceramic capacitors (MLCC) have been aged at 121 °C and 100% Relative Humidity for 2,600 h. Raman and energy dispersive spectral measurements have been made on both aged and unaged samples. Raman spectra indicate the presence of a coating of substoichiometric SnO _x (1 < x < 2) in the aged samples. Morphological and elemental changes occurring in the MLCC were examined by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). Preliminary, frequency dependent dielectric measurements indicate that ageing causes a substantial decrease (about 50%) of the capacitance, even if only surfaces are affected by the ageing phenomenon.     

Low firing and high dielectric constant X7R ceramic dielectric for multilayer capacitors based on relaxor and barium titanate composite

A temperature stable ceramic dielectric with a low firing temperature (1130 °C) and a high dielectric constant (3700 to 2600) has been developed by sintering the mixture of precalcined lead-based relaxor and prefired modified barium titanate.This dielectric was confirmed to be a two-phase ceramic composite body, according to X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy and dielectric measurements.A shortcoming of the high dissipation factor in the dielectric has been reduced by incorporating MnO into the barium titanate constituent prior to mixed sintering.This ceramic dielectric meets X7R specifications in the EIA (Electronic Industries Association) standard.     

Supercritical extraction of binder containing poly(vinyl butyral) and dioctyl phthalate from barium titanate–platinum multilayer ceramic capacitors

Supercritical extraction using carbon dioxide was examined for the removal of binder from multilayer ceramic capacitors. The binder contained poly(vinyl butyral) (PVB) and dioctyl phthalate (DOP), and the dielectric and metal electrode materials were barium titanate and platinum, respectively. At 40 MPa of carbon dioxide at 95 °C, approximately 55 wt % of the binder could be removed, and this was mainly the dioctyl phthalate component. The use of entrainers such as 2-propanol, methyl isobutyl ketone, and n-hexane was seen to have negligible effect on the degree of binder removal. The dielectric constant, loss tangent, and breakdown voltage of devices processed by supercritical extraction were similar as compared to devices processed by thermal oxidation alone. Although it was not possible to extract all of the binder with supercritical carbon dioxide, removal of the DOP fraction increases the pore space in the body by a factor of two. Transport model calculations indicate this partial removal of binder mitigates the buildup of pressure in the subsequent thermal processing step and can reduce the processing time for thermal removal of the remaining binder by a factor of 25.     

Oxidation resistance and creep behaviour of a silicon nitride ceramic densified with Y2O3

The corrosion resistance and creep behaviour in air of hot-pressed materials with a composition of 70 Si₃N₄-25 SiO₂-5 Y₂O₃ (mol%) has been studied. Kinetics data and microstructural changes in the 1180 to 1650° C temperature range indicate the presence of two oxidation mechanisms. Between 1180 and 1420° C, the preferential oxidation of the intergranular phase containing nitrogen is interpreted in terms of an inward diffusion of ionic oxygen. At temperatures higher than 1420° C, the degradation of the material is the sum of many processes (solution of silicon nitride, migration of oxygen and yttrium and release of nitrogren) but the diffusion to the nitride-oxide interface of a complex combination of yttrium and nitrogen in the boundary phase seems to be the limiting step. The three-point bending creep is discussed in relation to the evolution of the secondary intergranular phases in an oxidizing environment. The creep deformation is the sum of a viscoelastic component and a diffusional component characterized by the same activation energy (720 kJ mol^–1).