Ceramic Electronic Device Electrode Cavity Control
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Solution Overview
Problem
Ceramic electronic devices with Ni internal electrode layers and Cu external electrodes face issues with Cu diffusion into internal electrodes during firing, leading to cavity formation, which degrades humidity resistance, voltage resistance, and reliability due to reduced external electrode thickness.
Innovation Solution
A ceramic electronic device with external electrodes made of a first metal (e.g., Cu) and internal electrodes made of a second metal (e.g., Ni) where the melting point of the second metal is higher, and the diffusion coefficient of the first metal into the second metal is greater, ensuring minimal cavity formation by controlling the molar ratio of the first metal in the internal electrode layers to 10-90%, thereby improving reliability and resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If the thickness of external electrodes is reduced to improve capacity volume density, then the capacity volume density is improved, but the resistance to humidity, resistance to voltage and reliability are degraded due to cavity formation
Solution Approach 1:
The patent changes the chemical composition parameters of the external electrode paste by controlling the content of Cu powder, Cu compound, and organic binder within specific ranges. This parameter optimization reduces excessive Cu diffusion into internal electrodes during firing, minimizing cavity formation while maintaining thin external electrode thickness (15-25 μm), thus improving capacity volume density without sacrificing reliability
Solution Approach 2:
The external electrode uses a composite paste formulation combining Cu powder, Cu compound, and organic binder in specific proportions. This composite material approach allows the electrode to maintain structural integrity and control diffusion behavior during firing, preventing cavity formation even at reduced thickness while achieving high capacity volume density
2Power
If Cu external electrodes are used with Ni internal electrode layers, then the electrical conductivity is improved, but Cu diffuses into internal electrode layers during firing causing cavity formation
Solution Approach 1:
The patent optimizes the chemical composition parameters of the external electrode paste, specifically controlling Cu powder content (70-90 wt%), Cu compound content (5-20 wt%), and organic binder content (5-20 wt%). These parameter changes reduce the diffusion driving force of Cu into Ni internal electrodes during firing, minimizing cavity formation while preserving the high electrical conductivity provided by Cu external electrodes
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 approach effectively reduces cavity formation, enhancing the ceramic electronic device's humidity resistance, voltage resistance, and reliability by maintaining a low concentration difference of the first metal between external and internal electrodes, even at reduced external electrode thicknesses.
Implementation Method 1
a large amount of Cu of the external electrodes diffuse into the internal electrode layers during firing of the external electrodes
Data Source
AI summary
A ceramic electronic device includes: a multilayer chip having a structure in which each of dielectric layers and each of internal electrode layers are alternately stacked; and external electrodes provided on end faces of the multilayer chip, wherein a main component of the external electrodes is a first metal, wherein the internal electrode layers include the first metal and a second metal of which a melting point is higher than that of the first metal, wherein a diffusion coefficient of the first metal with respect to the second metal is larger than that of the second metal with respect to the first metal, wherein a number of a cavity in a range of 10 numbers of the internal electrode layers that are next to each other and are connected to a same external electrode of the first external electrode and the second external electrode is 1 or less.