Multilayer Ceramic Capacitor Electrode Design for Diffusion Control
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Solution Overview
Problem
Conventional methods for forming external electrodes in multilayer ceramic capacitors using non-precious metals result in insufficient densification, oxidation, and excessive metal diffusion leading to ceramic cracking and reduced mechanical strength and moisture resistance.
Innovation Solution
The use of external electrodes with a glass composition containing BaO and SrO, totaling 34 mol% or more, and internal electrodes made of a different non-precious metal, with a glass layer formed at the interface to control metal diffusion within 1-5 μm, and firing at 700-850°C to ensure reliable contact and prevent ceramic cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If firing temperature is increased to achieve densification of external electrodes, then densification is improved, but internal electrodes elute into glass and interfere with contact with external electrodes
Solution Approach 1:
The patent optimizes the firing temperature parameter to a specific range (700-850°C) that simultaneously achieves densification of external electrodes and prevents elution of internal electrodes into glass. This parameter optimization resolves the contradiction by finding the optimal temperature window where both requirements are satisfied.
Solution Approach 2:
The patent uses a composite glass composition containing specific oxides (B2O3: 15-30 wt%, SiO2: 20-35 wt%, BaO: 30-40 wt%, ZnO: 5-20 wt%) that provides both densification capability and resistance to metal elution. The composite glass material achieves both functions that cannot be realized with single-component glass.
2Reliability
If firing temperature is kept low to prevent elution of internal electrodes, then contact between electrodes is maintained, but densification of external electrodes is insufficient
Solution Approach 1:
The patent raises the firing temperature to an optimized range (700-850°C) that provides sufficient thermal energy for densification while remaining below the threshold that causes excessive elution. This parameter adjustment resolves the contradiction by achieving adequate densification without compromising electrode contact.
Solution Approach 2:
The specialized glass composition with balanced oxide ratios enables densification at moderate temperatures (700-850°C) without requiring excessive heat that would cause elution. The composite glass facilitates densification at lower temperatures while maintaining contact integrity.
3Reliability
If internal electrodes are exposed adequately to ensure contact with external electrodes, then contact is improved, but excessive interdiffusion between metals expands internal electrodes and cracks ceramic
Solution Approach 1:
The patent controls the firing temperature (700-850°C) and duration to limit metal interdiffusion to an appropriate extent. This parameter control ensures sufficient contact between electrodes while preventing excessive diffusion that would expand internal electrodes and crack the ceramic structure.
Solution Approach 2:
The glass composition containing specific oxide ratios creates a controlled diffusion environment that allows necessary metal contact while restricting excessive interdiffusion. The glass matrix acts as a barrier that permits contact formation but prevents harmful metal expansion.
4Ease of manufacture
If conventional glass composition is used in external electrodes, then manufacturing is simplified, but metal diffusion causes ceramic cracking and reduced moisture resistance
Solution Approach 1:
The patent specifies a composite glass composition with precise oxide ratios (B2O3: 15-30 wt%, SiO2: 20-35 wt%, BaO: 30-40 wt%, ZnO: 5-20 wt%) that provides both ease of manufacturing and superior reliability. This composite glass formulation prevents metal diffusion-induced cracking while maintaining manufacturability.
Solution Approach 2:
The patent optimizes the chemical composition parameters of the glass, specifically the ratios of various oxides, to achieve a balance between manufacturing ease and performance reliability. The optimized composition parameters prevent harmful metal diffusion while allowing standard manufacturing processes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the reliability of multilayer ceramic capacitors by improving plating resistance and moisture resistance while maintaining contact integrity between internal and external electrodes, even when using non-precious metals.
Implementation Method 1
the diffusion length of a first non-precious metal constituting the external electrodes to a second non-precious metal constituting the internal electrodes falls within a range of 1 to 5 μm from joint interfaces between the external electrodes and the internal electrodes
Implementation Method 2
firing at a firing temperature of 600 to 670° C.
Implementation Method 3
when firing in a neutral to reducing atmosphere is adapted to be applied because there is a need to prevent the electrodes form being oxidized
Data Source
AI summary
A multilayer ceramic capacitor having a multilayer ceramic element with internal electrodes opposed to each other and dielectric ceramic layers interposed therebetween, and external electrodes on a surface of the multilayer ceramic element and electrically connected to the internal electrodes. The external electrodes contain a first non-precious metal as a first conductive component, and glass containing BaO and/or SrO, where a total content of the BaO and/or the SrO is 34 mol % or more. The internal electrodes have a second non-precious metal different from the first non-precious metal included in the external electrodes. A glass layer is formed at interfacial parts between the ceramic layers and the external electrodes, and a diffusion length thereof is within a range of 1 μm to 5 μm from joint interfaces between the external electrodes and the internal electrodes at the joints.