Multilayer Ceramic Capacitor Three-Layer External Electrode Design
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Solution Overview
Problem
Existing multilayer ceramic capacitors face reliability issues due to reduced external electrode density, leading to poor electrical conductivity and plating failures, especially when attempting to achieve high capacitance by increasing the number of internal electrodes, which results in thicker ceramic bodies and thinner external electrodes prone to plating solution permeation.
Innovation Solution
A multilayer ceramic capacitor design featuring a three-layer external electrode structure, where the first layer is copper-glass, the second layer is glass-only, and the third layer is copper-glass, with the second layer being shorter and wider than the first, ensuring adequate electrical connectivity and plating reliability, and a plating layer is applied to the third layer for enhanced bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of stacked internal electrodes is increased to implement high capacitance, then the capacitance is improved, but the size of the ceramic body increases and the external electrode thickness must be reduced
Solution Approach 1:
The external electrode is divided into three distinct layers: a first copper-glass layer (131a, 132a) for electrical connectivity, a second glass layer (131b, 132b) for density and plating reliability, and a third copper-glass layer (131c, 132c) for final plating surface. This segmentation allows each layer to optimize for its specific function while collectively solving the thickness-capacitance contradiction.
Solution Approach 2:
The external electrode uses composite material composition with copper and glass in specific layers. The copper-glass composite paste provides both electrical conductivity (from copper) and glass-like density characteristics (from glass), enabling thin-film external electrodes to achieve high density without sacrificing conductivity, thus resolving the contradiction between reduced thickness and maintained reliability.
2Productivity
If the thickness of external electrodes is reduced to accommodate high-capacitance designs, then the capacitance-to-size ratio is improved, but reliability problems occur due to permeation of plating solution
Solution Approach 1:
Different regions of the external electrode structure are assigned different material compositions: the first and third layers contain copper for conductivity where needed, while the second layer is glass-dominated for density where plating occurs. This local quality differentiation ensures that each region performs its specific function optimally, preventing plating solution permeation at the plating surface while maintaining conductivity elsewhere.
Solution Approach 2:
The second glass layer acts as an intermediary barrier between the internal electrodes and the plating process. This glass-rich layer provides a dense, non-porous structure that prevents plating solution from permeating into the capacitor structure, while still allowing the copper-containing layers to provide necessary electrical connectivity.
3Volume of stationary object
If the content of glass in external electrodes is increased to improve density, then the density is improved, but electrical conductivity with internal electrodes and plating properties deteriorate
Solution Approach 1:
The external electrode is segmented into layers with different glass contents: the second layer has high glass content (≥60 vol%) for density, while the first and third layers have copper-glass composition for conductivity and plating. This segmentation resolves the contradiction by isolating the high-glass region to where density is critical while preserving copper conductivity in regions requiring electrical connection.
Solution Approach 2:
Different layers are assigned different material qualities: the second layer is optimized for density with high glass content, while the first and third layers are optimized for conductivity and plating with copper-glass composition. This local quality assignment allows the structure to achieve high overall density without sacrificing electrical or plating performance in critical regions.
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 design enhances electrical conductivity and plating reliability, preventing permeation issues while maintaining high capacitance, as demonstrated by test results showing no reliability failures when the second external electrode layer's width is ≥3 μm and glass content is ≥60 vol%, thus addressing the limitations of existing capacitors.
Implementation Method 1
external electrodes formed of copper-glass materials typically used in an existing ultra-thin, ultra-high capacitance multilayer ceramic capacitor may suffer from reliability problems due to the permeation of a plating solution when they are provided as thin films
Data Source
AI summary
A multilayer ceramic capacitor includes a ceramic body including dielectric layers; first and second internal electrodes facing each other while having the dielectric layer disposed therebetween, and alternately exposed to end surfaces of the ceramic body; first and second external electrodes electrically connected to the first and second internal electrodes, wherein each of the first and second external electrodes includes a first external electrode layer formed of material containing copper and glass and extending from an end surface of the ceramic body to portions of main and side surfaces of the ceramic body; a second external electrode layer formed of material containing glass, disposed on the first external electrode layer, and being shorter than the first external electrode layer to expose portion of the first external electrode layer; and a third external electrode layer formed of material containing copper and glass and covering the first and second external electrode layers.