Dielectric Ceramic Moisture Resistance via Alkali Metal Segregation
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Solution Overview
Problem
Laminated ceramic capacitors using dielectric ceramics with alkali metal elements face issues with moisture resistance degradation and sintering aid effectiveness due to alkali metal scattering during firing, leading to reduced insulation resistance over time.
Innovation Solution
Firing the compact and composition containing an alkali metal element together prevents scattering, maintaining fluidity to induce segregation of a secondary phase at the ceramic surface, which acts as a barrier against moisture erosion, enhancing moisture resistance and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If alkali metal element is added as sintering aid, then sintering performance is improved, but alkali metal element scatters during firing reducing effectiveness
Solution Approach 1:
The patent uses a borosilicate glass composition as an intermediary carrier for the alkali metal element. The glass matrix prevents scattering of the alkali metal during firing while still allowing it to function as a sintering aid. The glass composition (containing SiO2, B2O3, and alkali metal oxides) acts as a vehicle that delivers the alkali metal to the ceramic surface where it segregates to form the protective secondary phase, thus resolving the contradiction between maintaining sintering effectiveness and preventing element scattering.
Solution Approach 2:
The patent changes the physical and chemical parameters of the alkali metal delivery system by incorporating it into a borosilicate glass matrix rather than using pure alkali metal compounds. This parameter change (from pure compound to glass composite) fundamentally alters the behavior during firing - the glass softens and flows at firing temperatures, allowing controlled segregation of alkali metal to the surface while preventing uncontrolled scattering, thus maintaining both sintering performance and element retention.
2Volume of moving object
If dielectric ceramic layer thickness is reduced for miniaturization, then capacitor size is reduced, but reliability and moisture resistance degrade
Solution Approach 1:
The patent applies local quality by creating a secondary phase enriched with alkali metal elements specifically at the surface region of the dielectric ceramic. This localized modification (surface enrichment) provides enhanced moisture resistance exactly where it is needed - at the interface with the environment - without requiring changes to the bulk ceramic composition or increasing overall thickness. The surface secondary phase acts as a protective barrier layer while the thin ceramic body maintains miniaturization benefits.
Solution Approach 2:
The patent creates a composite structure consisting of the dielectric ceramic matrix (e.g., (Ca, Sr)(Zr, Ti)O3) combined with a surface secondary phase enriched with alkali metal elements and borosilicate glass components. This composite architecture provides dual functionality: the ceramic matrix provides dielectric properties and mechanical strength, while the surface composite phase provides enhanced moisture resistance, allowing thin-layer capacitors to maintain high reliability.
3Object-affected harmful factors
If conventional dielectric ceramic is used, then initial moisture resistance is acceptable, but insulation resistance degrades after loading test period
Solution Approach 1:
The patent applies preliminary action by forming the protective secondary phase enriched with alkali metal elements and borosilicate glass components on the ceramic surface during the firing process itself, before the capacitor is put into service. This pre-formed protective layer is created in advance to prevent moisture erosion and insulation resistance degradation during subsequent operation, rather than attempting to repair or restore the surface after degradation occurs.
Solution Approach 2:
The patent provides beforehand cushioning against moisture damage by creating a robust surface secondary phase that acts as a buffer or protective barrier. This cushioning layer, enriched with alkali metal elements and borosilicate glass, is designed to absorb and resist moisture attack, protecting the underlying dielectric ceramic from erosion and preventing insulation resistance degradation over extended operational periods.
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
The method results in a highly moisture-resistant dielectric ceramic with improved reliability, preventing characteristic degradation after moisture resistance loading tests, enabling small-sized, high-capacity laminated ceramic capacitors with stable performance.
Implementation Method 1
the firing induces segregation of a secondary phase at the surface of the dielectric ceramic to improve the moisture resistance of the dielectric ceramic
Implementation Method 2
The fluidity of the sintering aid in the compact is maintained to induce segregation of the secondary phase at the surface of the ceramic
Data Source
AI summary
A highly moisture resistant dielectric ceramic is prepared by providing a compact containing a dielectric ceramic component powder and a second powder including a compound containing an alkali metal element, and firing the compact and a second composition containing an alkali metal element at the same time. A laminated ceramic capacitor using the dielectric ceramic is described.