Multilayer Ceramic Capacitor Electrode Ni-Cu Solid Solution
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Solution Overview
Problem
Multilayer ceramic capacitors face issues with insufficient moisture resistance and reduced thermo-mechanical strength due to interdiffusion of Ag—Cu—Ti alloys and Cu platings, leading to unreliable performance.
Innovation Solution
A multilayer ceramic capacitor design featuring a first outer electrode layer with Ni and a second outer electrode layer containing a glass component and Cu, where Ni diffuses into the Cu layer to form a solid solution, enhancing moisture resistance and thermo-mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If plating entirely covers the metal layer, then moisture resistance is improved, but thermo-mechanical strength decreases due to interdiffusion at the center-side end
Solution Approach 1:
The outer electrode is divided into two distinct layers: a metal layer (first outer electrode layer) and a plating layer (second outer electrode layer). This segmentation allows the metal layer to provide strong bonding to the multilayer body while the plating layer provides moisture resistance, preventing the interdiffusion problem that occurs when plating entirely covers the metal layer.
Solution Approach 2:
The plating layer is designed to cover only specific regions of the metal layer - specifically the end-face-side end and portions near edges - rather than entirely covering the metal layer. This local coverage strategy provides moisture resistance at critical areas while avoiding interdiffusion at the center-side end, thereby maintaining thermo-mechanical strength.
2Strength
If interdiffusion of Ag-Cu-Ti alloy and Cu plating occurs, then bonding strength is improved, but moisture resistance becomes insufficient
Solution Approach 1:
The outer electrode structure is segmented into a metal layer and a plating layer, where the metal layer (containing Ag-Cu-Ti alloy) provides strong bonding to the multilayer body, and the plating layer (containing Cu) provides moisture resistance. This segmentation prevents harmful interdiffusion while maintaining both bonding strength and moisture resistance.
Solution Approach 2:
The metal layer acts as an intermediary between the multilayer body and the plating layer. It provides strong bonding to the multilayer body while the plating layer provides moisture resistance, creating a functional gradient that resolves the contradiction between bonding strength and moisture resistance.
3Reliability
If Ni diffuses into Cu layer, then moisture resistance is enhanced, but layer structure becomes complex
Solution Approach 1:
The patent controls the diffusion of Ni into the Cu layer by adjusting diffusion parameters such as temperature, time, and concentration gradients. This controlled diffusion enhances moisture resistance through the formation of a Ni-Cu intermetallic layer while maintaining a relatively simple two-layer structure, avoiding excessive structural complexity.
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 Ni—Cu solid solution improves moisture resistance and maintains high thermo-mechanical strength, making the capacitor more reliable and resistant to environmental stresses.
Implementation Method 1
Ni of the first outer electrode layer is diffused in the second outer electrode layer and is dissolved in Cu of the second outer electrode layer to define a solid solution
Data Source
AI summary
In a multilayer ceramic capacitor, each outer electrode includes a first outer electrode layer that contains Ni and that is disposed on each main surface of a multilayer body and a second outer electrode layer that contains a glass component and Cu and that covers one end portion of the first outer electrode layer which is closer to an end surface of the multilayer body, the first and second outer electrode layers are joined together in a region including an edge shared by the main surface and the end surface, the other end portion of the first outer electrode layer is exposed from the second outer electrode layer, and Ni of the first outer electrode layer is diffused in the second outer electrode layer and is dissolved in Cu of the second outer electrode layer to define a solid solution in the region including the edge.