Multilayer Ceramic Capacitor Cu-Ni Diffusion Control
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Solution Overview
Problem
Existing multilayer ceramic capacitors face issues with crack formation due to metal diffusion from external electrodes into internal electrodes during the baking process, which can lead to reliability concerns in the connection between the electrodes.
Innovation Solution
A multilayer ceramic capacitor design featuring a mutual diffusion layer of Cu and Ni between internal and external electrodes, with a specific thickness range and an oxide layer to prevent excessive diffusion, along with a manufacturing method involving annealing in a reducing atmosphere to enhance the reliability of the electrode connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the temperature for baking the conductive paste is increased to prevent diffusion of metal material into internal electrodes, then crack formation is reduced, but the reliability of joining between internal electrodes and external electrodes deteriorates
Solution Approach 1:
A Cu diffusion barrier layer is introduced as an intermediary between the Cu-based external electrode and the Ni-based internal electrode. This barrier layer prevents excessive diffusion of Cu into the internal electrode during baking, eliminating the need to increase baking temperature, thereby maintaining both joining reliability and preventing crack formation.
Solution Approach 2:
The invention changes the chemical composition parameter by introducing a Cu diffusion barrier layer with specific material properties that control metal diffusion. This parameter change allows the baking process to proceed at temperatures that ensure reliable joining without causing harmful diffusion that leads to cracks.
2Object-affected harmful factors
If the temperature for baking the conductive paste is reduced to prevent diffusion of metal material into internal electrodes, then crack formation is reduced, but the reliability of joining between internal electrodes and external electrodes deteriorates
Solution Approach 1:
The Cu diffusion barrier layer acts as a mediator that enables reliable joining at lower baking temperatures by controlling the diffusion process. It allows sufficient bonding between external and internal electrodes while preventing excessive diffusion that causes cracks, thus resolving the contradiction between joining reliability and crack prevention.
3Ease of manufacture
If metal material diffuses into internal electrodes during baking, then external electrodes are formed, but cracks are formed from opposite end portions of uppermost and lowermost internal electrodes toward the four corners of the ceramic body
Solution Approach 1:
The Cu diffusion barrier layer serves as an intermediary that enables external electrode formation through controlled diffusion while preventing the harmful excessive diffusion that causes cracks. It allows the manufacturing process to proceed successfully without producing defects.
Solution Approach 2:
By changing the material composition parameter and introducing the barrier layer, the invention enables external electrode formation at controlled diffusion levels, preventing crack formation while maintaining ease of manufacture.
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 solution significantly reduces crack formation and enhances the reliability of the electrode connection, ensuring high solderability and connection reliability during mounting on a circuit board.
Implementation Method 1
a mutual diffusion layer of Cu and Ni extends across the internal electrode and the external electrode
Implementation Method 2
an oxide layer is present between the mutual diffusion layer and the internal electrodes
Implementation Method 3
annealing in a reducing atmosphere to enhance the reliability of the electrode connection
Data Source
AI summary
A multilayer ceramic capacitor contains Ni in internal electrodes, and includes a sintered metal layer containing Cu in external electrodes. At a joined portion between each internal electrode and each external electrode, mutual diffusion layers of Cu and Ni extend across the internal and external electrodes. On each internal electrode, a mutual diffusion layer is present with a thickness t1, which is defined by a dimension from a first end surface or a second end surface to an interior end in a longitudinal direction, not smaller than about 0.5 μm and not greater than about 5 μm. On each external electrode, a mutual diffusion layer is present with a thickness t2, which is defined by a dimension from the first end surface or the second end surface to an exterior end in the longitudinal direction, not smaller than about 2.5% and not greater than about 33.3% of a thickness t0 of a sintered metal layer.