Multilayer Ceramic Capacitor with Graded Rare-Earth Concentration
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Solution Overview
Problem
Multilayer ceramic capacitors face issues with rare-earth element concentration at ceramic boundaries, leading to reduced resistance to elution in water-soluble fluxes and residual stress, causing structural defects and reliability concerns.
Innovation Solution
A multilayer ceramic capacitor design with a perovskite-type compound-based structure, where the inner layers have a higher rare-earth element concentration than the outer layers, and a specific Mn concentration gradient, inhibiting elution while maintaining electrical characteristics and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If rare-earth elements are added to stabilize temperature characteristics and ensure high-temperature load life, then reliability is improved, but resistance to elution in water-soluble flux is reduced
Solution Approach 1:
The patent applies local quality by creating distinct compositional zones within the ceramic layers. The inner layer portions contain higher rare-earth element concentrations (0.1-1.0 atom%) for reliability, while the outer layer portions contain lower concentrations (0.03-0.3 atom%) for elution resistance. This spatial differentiation of material properties resolves the contradiction between needing rare-earth elements for stability and avoiding them for elution resistance.
Solution Approach 2:
The patent segments the ceramic layers into inner layer portions and outer layer portions with different rare-earth element concentrations. This segmentation allows each zone to fulfill its specific function: the inner layers provide thermal stability and reliability, while the outer layers provide resistance to flux elution during soldering processes.
2Stability of the object's composition
If rare-earth elements concentrate at ceramic boundaries, then temperature characteristics are stabilized, but structural defects occur due to embrittlement from elution
Solution Approach 1:
The patent creates a compositional gradient where rare-earth elements are concentrated in the inner layer portions (away from boundaries) rather than at the ceramic boundaries themselves. This local quality differentiation maintains temperature stability while preventing the embrittlement that occurs when rare-earth elements concentrate at boundaries and are subsequently eluted during soldering.
Solution Approach 2:
The patent provides beforehand cushioning by designing the outer layer portions with lower rare-earth element concentrations before the soldering process occurs. This preventive design protects against future elution damage and structural defects by ensuring that the outer layers, which are most exposed to flux during mounting, have reduced susceptibility to acid attack.
3Strength
If outer layer portions receive high residual stress, then inner electrodes are supported, but elution of components causes embrittlement and structural defects
Solution Approach 1:
The patent applies local quality by differentiating the rare-earth element content between inner and outer layer portions. The outer layer portions have optimized lower concentrations (0.03-0.3 atom%) that provide sufficient mechanical support for the inner electrodes while simultaneously offering enhanced resistance to flux elution, preventing the embrittlement and structural defects that would otherwise occur under high residual stress conditions.
Data Source
AI summary
A multilayer ceramic capacitor includes a ceramic main body including an inner layer portion including third ceramic layers and a plurality of inner electrodes arranged at interfaces between the third ceramic layers, and first and second outer layer portions respectively including first and second ceramic layers, the first and second ceramic layers being arranged vertically so as to sandwich the inner layer portion. The third ceramic layers and the first and second outer layer portions contain a perovskite-type compound represented by ABO3 where A contains one or more of Ba, Sr, and Ca, B contains one or more of Ti, Zr, and Hf, and O represents oxygen) as a main component. Where a rare-earth element concentration (CR) in the third ceramic layers is compared to a rare-earth element concentration (Cr) in outermost layer portions including at least outermost surfaces of the first and second outer layer portions, CR>Cr (inclusive of Cr=0).