Reliability Of Multilayer Ceramic Capacitors Research Articles

Degradation monitoring of multilayer ceramic capacitors during high accelerated lifetime testing using ultrasound

Multilayer ceramic capacitors (MLCCs) are vital circuitry components where long-term stability at high temperature and fields is critical to device operation. High accelerated lifetime testing (HALT) statistically investigates reliability and lifetime of MLCCs through exposure to temperatures and voltages exceeding normal operating conditions. The long-term reliability of the dielectric layers in MLCCs strongly depends on potential variability in the dielectric microstructure, such as cracking, which can be challenging to detect. Nondestructive ultrasonic evaluation is sensitive to microstructural changes through measurements of wave scattering. This work uses high frequency (100 MHz) focused ultrasonic scattering methods to nondestructively monitor structural and microstructural changes in MLCCs from the pristine to the failed state during HALT to understand structural origins of electrical failure. Printed circuit board mounted MLCCs were electrically and ultrasonically characterized in a pristine state and during various degraded states before and after electrical failure under HALT. Evidence of damage pre-HALT was ultrasonically indicated by high attenuation regions on the ultrasonic maps suggesting that the mounting process may induce damage. The high attenuation regions in the pristine samples evolved throughout HALT indicating that the damage in the pristine state might be the spatial origin of part failure, which underscores the impact and importance of detection of structural defects on the reliability of MLCCs.

Publisher’s Note: “Using highly accelerated life test to study insulation reliability of multi-layer ceramic capacitors sintered at different temperatures” [J. Appl. Phys. 134, 194101 (2023)

Publisher’s Note: “Using highly accelerated life test to study insulation reliability of multi-layer ceramic capacitors sintered at different temperatures” [J. Appl. Phys. 134, 194101 (2023)

Thermal activation energy on electrical degradation process in BaTiO3 based multilayer ceramic capacitors for lifetime reliability

For a high capacitance and high lifetime reliability of multilayer ceramic capacitors for automotive applications, the activation energy on thermal activation process can typically be calculated by using Arrhenius based Prokopowicz–Vaskas equation as a method for lifetime prediction. In this study, it is clearly observed that the activation energy shows to be constant in the range of ~ 1.5 eV for the prototype MLCCs, higher than the activation energy values of ~ 1.0 eV related to the motion or diffusion of oxygen vacancies reported in the previous literature. The activation energy value of ~ 1.5 eV for three prototype MLCCs is close to a half the energy band gap (Eg/2 ≈ 1.6 eV) of BaTiO3 obtained from specific environment, where oxygen vacancies are stabilized by external containment such as the effect of rare earth oxide additives. Due to an obvious difference in activation energy values, it difficult to explain the conduction mechanism for failure by only oxygen vacancy migration. Therefore, the concepts of electronic processes and oxygen vacancy should be considered together to understand conduction mechanism for failure of BaTiO3-based MLCCs in thermal activation processes. It can be useful as an indicator for future MLCC development with high lifetime reliability.

P‐N Junction‐Driven Abnormal Electric Field Distribution in the Degraded Multilayer Ceramic Capacitors

Local electric field distribution in the dielectric layer of BaTiO3‐based multilayer ceramic capacitors (MLCCs) is investigated by Kelvin probe force microscopy before and after highly accelerated life test (HALT) degradation combined with the energy band diagram. An unusual electric field concentration phenomenon is directly visualized near the HALT cathode region in the degraded MLCCs while a reverse voltage is applied. Such abnormal behavior is ascribed to the migration of oxygen vacancies within the dielectric layer during the HALT, leading to the formation of a P‐N junction structure and further a heightened barrier under a reverse bias. As a result, a P‐N junctional model is proposed for understanding local failure mechanism of the degraded MLCCs, which enrich the insights into the insulation resistance degradation and the reliability of MLCCs.

Erratum: “Using highly accelerated life test to study insulation reliability of multi-layer ceramic capacitors sintered at different temperatures” [J. Appl. Phys. 134, 194101 (2023)

Erratum: “Using highly accelerated life test to study insulation reliability of multi-layer ceramic capacitors sintered at different temperatures” [J. Appl. Phys. 134, 194101 (2023)

Using highly accelerated life test to study insulation reliability of multi-layer ceramic capacitors sintered at different temperatures

With the developments of the electronic industry, efforts to achieve high DC insulating reliability are underway to improve the mean time to failure (MTTF) of multilayer ceramic capacitors (MLCCs). However, there are few studies on appropriate measuring methods to evaluate their different reliability characteristics quantificationally. This study measured different reliability characteristics of BaTiO3-based multilayer ceramic capacitors sintered at three different temperatures with highly accelerated life tests (HALTs). Kaplan–Meier survival analysis, two-parameter Weibull fitting, and a new method using a stud genetic algorithm were used to calculate their MTTF in HALT conditions, and the comparison among them was carried out to select a proper fitting way. With the appropriate method, their MTTF at the rated condition was predicted and compared. Their conduction modes were also differentiated to explain their aging sensitivities to temperature and voltage. As a result, a proper way to evaluate the sample’s reliability characteristics with a bathtub curve was established, and the best sintering temperature for capacitance that is also the best for reliability at the rated condition was confirmed. Meanwhile, different conducting models of MLCCs were also proved to be related to their insulation stability.

Direct Observation of Local Dielectric Conductive Paths and Their Dynamics in the Degraded Multilayer Ceramic Capacitors

Scanning thermal microscopy is used to perform direct imaging local conductive path and dynamic behaviors in the degraded multilayer ceramic capacitors (MLCCs) due to the thermal conductivity difference between the dielectric layers and the conductive regions. For local conductive path, its electrical tree dynamic growth behaviors under the dc bias on and off state are clearly obtained in the thermal image. Such phenomena reveal that space–charge‐limited current mechanism dominates in local conductive path region of MLCCs. The results give a strong demonstration of scanning thermal microscopy as a powerful tool for imaging local conductive behavior in MLCCs, which provides us a direct, unique view to clarify local breakdown mechanism and enriches our insights in the insulation resistance degradation and the reliability of MLCCs.

Hydrogen migration in BaTiO3-based dielectrics under high humidity and electric field bias

This study investigates the possibility of hydrogen migration in BaTiO3-based dielectrics to improve the electrical reliability of multi-layer ceramic capacitors under conditions of high temperature, humidity, and electric field bias. It was observed that the deuterium in the dielectric drifted and migrated with the electric field, suggesting that deuterium exists as D+. The activation energy was found to be 0.34 eV, which is lower than that observed in previous studies. This finding offers a better understanding of the mechanism behind the migration of deuterium in a dielectric, which is highly relevant to future research in dielectrics and electronic components.

Scanning Pyroelectric Microscopy of Subsurface Dielectric Failures

Dielectric breakdown is a very important factor determining the reliability of multilayer ceramic capacitors, and its microscopy imaging is still a pending work so far. Here, a high resolution scanning pyroelectric microscopy (SPeM) is developed for direct imaging dielectric failure behavior of multilayer ceramic capacitors (MLCCs) due to the combination of pyroelectric effect and scanning thermal microscopy. Subsurface dielectric‐breakdown regions along the depth profile inside BaTiO3 capacitors are successfully visualized by measuring 2ω‐pyroelectric current via the frequency modulated SPeM. It provides a new approach for exploring subsurface dielectric breakdown microstructures, and for further understanding the underlying physical phenomena inside the MLCCs.

Theoretical and experimental studies of formation and migration of oxygen vacancies in BaMxTi1−xO3 (M = Zr, Ge)

The formation and migration energies of oxygen vacancies in pure BaTiO3, and BaMxTi1−xO3 (M = Zr, Ge) are calculated by first-principles calculations to understand the effect of doping on the reliability of multilayer ceramic capacitors (MLCCs). The formation and migration energies of oxygen vacancies are found to be larger in BaZrxTi1−xO3 than in BaTiO3. This finding could be one of the possible reasons behind the improved reliability of Zr-doped MLCCs materials. On the other hand, by substituting Ge, the migration energy of BaGexTi1−xO3 becomes larger than that of BaTiO3. This is despite the smaller oxygen vacancy formation energy in BaGexTi1−xO3 than in BaTiO3. Even though Zr and Ge are tetravalent in BaMxTi1−xO3, their valence states are different after the formation of oxygen vacancies, providing an explanation for the differences in vacancy formation and migration energies between BaZrxTi1−xO3 and BaGexTi1−xO3. Our theoretical results are further confirmed by experiments on these model systems.

Theoretical and experimental analysis for site preference of rare earth elements in BaTiO 3

Rare earth (RE) elements such as Y, Ho, and Dy are considered to play an important role in the long-term reliability of multilayer ceramic capacitors (MLCCs). Theoretical calculations of the site preference of RE elements in BaTiO 3 are useful tools for understanding this mechanism, especially when the RE elements are co-doped with other additive elements. In this study, the site preference of RE elements doped with and without Mg in BaTiO 3 is investigated by performing first-principles calculations and experiments. The calculation results indicate that the site preference of RE elements is strongly related to their ionic radii. In the simulation of Dy, Dy atoms replace both Ba and Ti atoms without Mg co-doping. On the other hand, when Dy is co-doped with Mg, Dy atoms prefer to occupy the Ba site instead of the Ti site in BaTiO 3. Experiments were also performed to analyze element concentrations in Dy-doped BaTiO 3 with and without Mg co-doping by scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy. The theoretical calculation and experimental measurement agree quite well on the site preference of Dy with and without Mg co-doping. Our theoretical and experimental results reveal the influence of Mg co-doping on the site preference of the RE elements in BaTiO 3.

Prognostics of ceramic capacitor temperature‐humidity‐bias reliability using Mahalanobis distance analysis

Purpose – This paper seeks to present a prognostics approach using the Mahalanobis distance (MD) method to predict the reliability of multilayer ceramic capacitors (MLCCs) in temperature‐humidity‐bias (THB) conditions.Design/methodology/approach – Data collected during THB testing of 96 MLCCs were analyzed using the MD method. In the THB tests, three parameters (capacitance (C), dissipation factor (DF), and insulation resistance (IR)) were monitored in situ. A Mahalanobis space (MS) was formed from the MD values of a set of non‐failed MLCCs. MD values for the remaining MLCCs were compared with an MD threshold. Data for MLCCs which exceeded the threshold were examined using the failure criteria for the individual electrical parameters to identify failures and precursors to failure.Findings – It was found that the MD method provided an ability to detect failures of the capacitors and identify precursors to failure, although the detection rate was not perfect.Research limitations/implications – It was observ...

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.

Residual Stresses in Multilayer Ceramic Capacitors: Measurement and Computation

In this paper, we present a combined experimental and computational study of the thermomechanical reliability of multilayer ceramic capacitors (MLCC’s). We focus on residual stresses introduced into the components during the cooling down step of the sintering process. The technique of microindentation turned out to be a useful method to measure the stresses locally. The computations were done with three-dimensional finite element simulations. We find that the cooling step introduces compressive in-plane stresses in the ceramic layers. There is reasonably good overall agreement between the residual stresses obtained from the indentation experiments and the numerical simulations. Some discrepancies do exist, though, for measurements on cross-sectioned MLCC’s. Possible reasons for the differences are discussed.

97/02272 Reliability of multilayer ceramic capacitors with nickel electrodes

97/02272 Reliability of multilayer ceramic capacitors with nickel electrodes

Reliability of multilayer ceramic capacitors with nickel electrodes

The reliability of multilayer ceramic capacitors (MLCCs) with Ni internal electrodes has been studied trom the viewpoint of partial oxygen pressure ( P O2) during firing. It is shown that the load-life time of the insulation resistance (1R) was prolonged by firing under low Po 2 annealing after firing, and the addition of dopants. It is also shown that the generation of oxygen vacancies led to the degradation of IR. Annealing treatment for the oxidation of the dielectric body accelerates the dielectric aging of MLCCs. It is found that the appropriate control of the P O2 during firing can improve the reliability of MLCCs with Ni electrodes to a level as high as that of MLCCs with precious metal electrodes. Thus, we have developed an MLCC with Ni electrodes that features high reliability and a large capacitance of 10 μF for the Y5V characteristic and 4.7 μF for the X7R characteristic, both in the case of the C3216 (3.2 mm × 1.6 mm × 1.4 mm) form.

Effects of Silver Doping on the Reliability of (Pb0.875 Ba0.125)[(Mg1/3 Nb2/3) 0. 5(Zn1/3 Nb2/3)0.3 Ti0.2] O3 Relaxor Dielectric Ceramics

The reliability of the silver‐doped dielectric ceramic (Pb0.875Ba0.25)0.995[(Mg1/3Nb2/3)0.5(Zn1/3Nb2/3)0.3Ti0.2]O3 was investigated to speculate on the effects of silver diffusion from internal electrodes into dielectric layers on the reliability of multilayer ceramic capacitors (MLCs). The addition of silver into the dielectric ceramic degraded the insulation resistance under humid loading conditions. Scanning transmission electron microscopy (STEM) revealed that a Pb‐rich grain boundary phase exists at triple points of Ag‐doped specimens. The Pb‐rich phase appeared to be PbO by X‐ray photoelectron spectroscopy (XPS). Degradation of insulation resistance was interpreted as a result of silver migration from the anode to the cathode through a grain boundary phase dissolved in water. Although silver diffusion from internal electrode layers in MLCs into dielectric layers was confirmed by STEM, a secondary phase was not observed. Intensive study is needed to clarify the effect of silver diffusion on degradation of insulation resistance of MLCs under humid loading conditions.