X7R Multilayer Ceramic Capacitors Research Articles

Improved prediction for failure time of multilayer ceramic capacitors (MLCCs): A physics-based machine learning approach

Multilayer ceramic capacitors (MLCC) play a vital role in electronic systems, and their reliability is of critical importance. The ongoing advancement in MLCC manufacturing has improved capacitive volumetric density for both low and high voltage devices; however, concerns about long-term stability under higher fields and temperatures are always a concern, which impact their reliability and lifespan. Consequently, predicting the mean time to failure (MTTF) for MLCCs remains a challenge due to the limitations of existing models. In this study, we develop a physics-based machine learning approach using the eXtreme Gradient Boosting method to predict the MTTF of X7R MLCCs under various temperature and voltage conditions. We employ a transfer learning framework to improve prediction accuracy for test conditions with limited data and to provide predictions for test conditions where no experimental data exists. We compare our model with the conventional Eyring model (EM) and, more recently, the tipping point model (TPM) in terms of accuracy and performance. Our results show that the machine learning model consistently outperforms both the EM and TPM, demonstrating superior accuracy and stability across different conditions. Our model also exhibits a reliable performance for untested voltage and temperature conditions, making it a promising approach for predicting MTTF in MLCCs.

Determining the effect of burn-in process on reliability of X7R multilayer ceramic capacitors

Determining the effect of burn-in process on reliability of X7R multilayer ceramic capacitors

Reliability of X7R Multilayer Ceramic Capacitors During High Accelerated Life Testing (HALT).

Multilayer ceramic capacitors (MLCC) are essential components for determining the reliability of electronic components in terms of time to failure. It is known that the reliability of MLCCs depends on their composition, processing, and operating conditions. In this present work, we analyzed the lifetime of three similar X7R type MLCCs based on BaTiO3 by conducting High Accelerated Life Tests (HALT) at temperatures up to 200 °C at 400 V and 600 V. The results were adjusted to an Arrhenius equation, which is a function of the activation energy (Ea) and a voltage stress exponent (n), in order to predict their time to failure. The values of Ea are in the range of 1–1.45 eV, which has been reported for the thermal failure and dielectric wear out of BaTiO3-based dielectric capacitors. The stress voltage exponent value was in the range of 4–5. Although the Ea can be associated with a failure mechanism, n only gives an indication of the effect of voltage in the tests. It was possible to associate those values with each type of tested MLCC so that their expected life could be estimated in the range of 400–600 V.

Breakdown voltages in ceramic capacitors with cracks

Breakdown voltages in 27 types of virgin and fractured X7R multilayer ceramic capacitors (MLCC) rated to voltages from 6.3 to 100 V have been measured and analyzed to evaluate the effectiveness of the dielectric withstanding voltage (DWV) testing to screen-out defective parts and get more insight into breakdown specifics of MLCCs with cracks. Fractures in the parts were introduced mechanically and by thermal shock stress. To simulate exposure of internal electrodes to environments in fractured parts, breakdown testing was carried out also on cross-sectioned and polished capacitors.

Phase Mixture and Reliability of BaTiO3-Based X7R Multilayer Ceramic Capacitors: X-Ray Diffractometry and Raman Spectroscopy

BaTiO3-based multilayer ceramic capacitors (MLCCs) using Ni base-metal electrodes (BME) exhibiting EIA-X7R dielectric behavior are represented by the characteristic microstructure of core–shell grains. In the present study, the crystalline phase contents in the mixture were determined quantitatively for two groups of experimental BME-MLCCs, one with CaO doping and the other with (CaO+MgO) codoping by Rietveld refinement using the software package TOPAS®. X-ray diffractometry was used for the identification of crystalline phases whose quantities were determined for cubic (C), tetragonal (T), and rhombohedral (R)–BaTiO3. Phase identification was corroborated by Raman spectroscopy where the characteristic phonon vibration modes corresponding to the C-, T-, and R-phase were assigned. It is suggested that the C-phase content, corresponding to the shell grains containing intragranular voids and the shell region of the core–shell grains, and the R-phase content, corresponding to the modulated core region, not only determine the diffusiveness of the temperature coefficient of capacitance curve but also serve as measuring indices for evaluating the resistance of MLCC formulations against dc degradation.

Crystal Symmetry of BaTiO3 Grains in X7R Multilayer Ceramic Capacitors

Convergent beam electron diffraction combined with conventional transmission electron microscopy is used to determine the crystal symmetry, and with energy-dispersive spectrometry (EDS) the microchemistry of BaTiO3 grains in (CaO+MgO)-codoped, EIA-X7R multilayer ceramic capacitors (MLCCs). The point group symmetries of the core–shell grain and the shell grain in MLCCs are analyzed following the procedures reported by Buxton and colleagues. It is found that the point group symmetry of the core region from the type-I and type-II core–shell grains are tetragonal (T ) 4mm and rhombohedral (R) 3m, respectively, with that of the shell region and the shell grain is the cubic (C ) m3m. The dependence of the C-, T-, and R-phases on the oxygen vacancy concentration generated by acceptor dopants, sintered in low oxygen partial pressure ( pO2), is discussed.

Hydrogen-Induced Degradation and Aging of Pb(Mg1/3Nb2/3)O3-Based X7R Multilayer Ceramic Capacitors

Pb(Mg1/3Nb2/3)O3-based X7R multilayer ceramic capacitors (MLCs) were placed in 0.01 M NaOH solution to deposit hydrogen on their termination electrodes through the electrolysis of water. The treatment led to great increases in the dielectric loss and the leakage current of the MLCs, and the dielectric properties of the MLCs also showed a strong aging behavior, with the capacitance and dielectric loss first inceased, and then gradually decreased. It was proposed that hydrogen from the electrolysis of water entered into Pb(Mg1/3Nb2/3)O3 lattice and existed at interstial lattice sites. The observed degradation could be explained by free electrons formed through ionization of interstitial hydrogen. Hydrogen-induced degradation happens in Pb(Mg1/3Nb2/3)O3-based MLCs during electroplating and in service and much attention should be paid to prevent hydrogen-induced degradation in them.

Flex Cracking of Multilayer Ceramic Capacitors Assembled With Pb-Free and Tin–Lead Solders

In this paper, an experimental study was conducted to study susceptibility to flex cracking of multilayer ceramic capacitors (MLCCs), in which a comparison was made between identical samples which were assembled using either Pb-free (Sn3.0Ag0.5Cu) or eutectic tin-lead (Sn37Pb) solder. Flex testing was performed on MLCCs with different sizes (1812 and 0805) and on different dielectric materials (C0G and X7R) obtained from three different manufacturers. Experimental results showed that MLCCs mounted on printed circuit boards (PCBs) with Pb-free solder crack less with board flexing than those mounted on boards with eutectic tin-lead solder. For 1812-size MLCCs assembled with tin-lead solder, the PCB strain at 10% failure ranged between 1700 and 2000 microstrains. The PCB strain at 10% failure for 1812-size MLCCs assembled with Pb-free solder varied between 2300 and 9600 microstrains, depending on the MLCC manufacturer. C0G MLCCs are more resistant to flex cracking than X7R MLCCs. Out of 96 samples tested, none of the C0G MLCCs showed evidence of flex cracking up to the maximum strain level on board of about 137 000 microstrains. In contrast, in the case of X7R MLCCs, from the same manufacturer, assembled with tin-lead solder, 94 out of 96 capacitors failed.

Investigation of ferroelectric phase transition for modified barium titanate in multilayer ceramic capacitors by in situ Raman scattering and dielectric measurement

The ferroelectric phase behaviors of modified BaTiO3 in X7R multilayer ceramic capacitors (MLCCs) were investigated by dielectric measurements and in situ Raman scattering. The in situ thermo-Raman scattering shows that because of a residual stress existing in the MLCCs, the tetragonal to cubic phase transition for modified BaTiO3 in MLCCs takes place over a wide temperature range of 373 K to 473 K, suggesting a diffuse-like characteristic which can be well explained by a modified phenomenological thermodynamic model, while the dielectric measurement indicates that the tetragonal to cubic transition occurs at 393 K. A disagreement exists between the two experimental results. Furthermore, a dc field-induced paraelectric to ferroelectric transition was identified by the two measurement techniques, but their phase-transition mechanisms are different. The dielectric measurement reveals the polar-micro-region to macro-domain transformation in the shell part of the core–shell structure while the in situ Raman scattering shows the cubic to tetragonal transition under a dc bias field.

Vacancy ordering in reduced barium titanate

A crystal structure is proposed for reduced barium titanate, BaTiO3−δ, δ≈0.33, formed during the degradation of Ni–BaTiO3 X7R multilayer ceramic capacitors. High-resolution transmission electron microscopy and selected-area electron diffraction have been used in combination with computer simulations to show that oxygen vacancies accrete on every third pseudocubic {111} plane, resulting in a cell with space group P3m1. Additionally, from electron energy loss spectroscopy, it is proposed that Ti4+ is reduced to Ti3+ as a mechanism of charge compensation within oxygen-deficient octahedra.

Flexure strength of multilayer ceramic capacitors

AbstractThe flexure strength (MOR) of multilayer ceramic (MLC) capacitors has been investigated by three point loading tests, using a specially designed, miniaturised test rig. The starting materials were blanks and MLC capacitors of Z5U and X7R formulations containing different numbers of electrodes and ink laydown concentrations. It was found for blanks that MOR decreased as the specimen thickness increased, while for X7R capacitors the MOR increased with the number of electrodes. Electron microscopy showed major differences in the mode of fracture of Z5U and X7R MLC capacitors. In as fired components the MOR varied with the ink laydown concentration, but in equivalent components which had been terminated and annealed, the flexure strength was uniformly high and independent of ink concentration.

Time dependence of dielectric constants of Pb(Mg 1/3 Nb 2/3 )O 3 -BaTiO 3 -PbTiO 3 ferroelectric ceramics for X7R MLCs

The isothermal ageing behaviour of Pb(Mg1/3Nb2/3)O3-BaTiO3-PbTiO3 ceramics, promising high dielectric (e25°C = 4574) materials for X7R multilayer ceramic capacitors (MLCs) was studied over a wide range of frequencies. During ageing, the dielectric constants and loss tangents decreased linearly with the logarithm of ageing time. The ageing rates were evidently influenced by the test frequencies. The maximum value, within the range 0.1 to 1000 kHz, was about 1.7% per decade (time) and meets the corresponding ageing specifications for X7R ceramic dielectrics.

X7R Multilayer Ceramic Capacitors with Nickel Electrodes

Electrical properties and microstructures of a holmium-doped (Ba1.01Mg0.01)O1.02(Ti0.98Zr0.02)O2 system were studied. Additions of Ho2O3 had little effect in preventing the dielectrics from reducing at high temperature, but the resistivity at low temperature increased with increasing amount of Ho2O3 when treated in oxidizing atmosphere at the cooling stage. From transmission electron micrograph (TEM) observation, it was noted that the microstructure exhibited a grain core-grain shell structure. Newly developed X7R multilayer ceramic capacitors with Ni electrodes revealed highly reliable electrical properties.

A New PLZT Dielectric for Use in Characteristic X7R Multilayer Ceramic Capacitors

A low firing-temperature lanthanum-modified lead-zirconate titanate (PLZT) dielectric has been developed to meet EIA Characteristic X7R specifications. Multilayer ceramic capacitors made from this material were sintered below 1100°C and exhibited the following electrical characteristics: dielectric constant, 2050; dissipation factor at I kHz, 1 Vrms/mil of dielectric 106 \Omega -F, and at + 125°C, 50 V/mil, > 105 \Omega -F. Long-term life test at 2 x rated voltage made very little change in any of the electrical properties.