Multilayer Ceramic Capacitor Void Structure for Crack Control
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Solution Overview
Problem
Multilayer ceramic capacitors face the risk of cracks due to electrostriction-induced stress between deformable inner layer portions and non-deformable outer layer portions under electric fields, which can lead to mechanical displacement and stress.
Innovation Solution
The design incorporates specific ratios of outer layer portion dimensions and voids in the multilayer ceramic capacitor, with outer layer portions on main and lateral surfaces having controlled thickness and void ratios to disperse inverse piezoelectric-induced stress, reducing the risk of cracks while maintaining sufficient electrostatic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If ferroelectric materials with high permittivity are used to increase capacitance, then the electrostatic capacitance is improved, but electrostriction-induced stress and crack risk increase
Solution Approach 1:
The capacitor structure is divided into effective layer portions (with electrode layers) and outer layer portions (without electrode layers). The outer layer portions act as buffer zones that do not experience electrostriction, thereby isolating and reducing the stress transmitted to the overall structure, which prevents cracks while maintaining high capacitance in the effective regions.
Solution Approach 2:
Different regions of the capacitor are designed with different properties: the effective layer portions use ferroelectric materials with high permittivity to maximize capacitance, while the outer layer portions are designed as stress-buffering regions without electrode layers. This local differentiation allows the capacitor to simultaneously achieve high capacitance and crack resistance by optimizing each region for its specific function.
2Reliability
If outer layer portions are added to reduce stress, then crack resistance is improved, but the device complexity increases
Solution Approach 1:
The outer layer portions are merged with the effective layer portions to form a unified multilayer structure. Both layers are created using the same lamination process with dielectric layers, and the outer layers simply extend the dielectric structure without requiring separate components or additional assembly steps, thus reducing complexity while maintaining stress-buffering functionality.
Solution Approach 2:
The outer layer portions serve multiple functions: they act as stress buffers to prevent cracks, provide mechanical support to the structure, and maintain the overall geometric integrity of the capacitor. This multi-functionality allows a single structural modification to address multiple concerns simultaneously, improving reliability without proportionally increasing complexity.
3Reliability
If outer layer portion thickness is increased to disperse stress, then crack resistance is improved, but the electrostatic capacitance decreases
Solution Approach 1:
The thickness of outer layer portions is precisely controlled within the range of 0.02 to 0.05 times the total multilayer body thickness. This parameter optimization ensures that the outer layers are thick enough to provide stress-buffering functionality and prevent cracks, while simultaneously being thin enough to minimize the reduction of effective capacitance-generating regions, thus balancing both requirements.
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 controlled design effectively reduces the risk of cracks and enhances the strength and density of outer layer portions, ensuring stable operation under electric fields without compromising capacitance.
Implementation Method 1
the dielectric material may generate a phenomenon called electrostriction, causing the multilayer body to distort to an extent that corresponds to the magnitude of the applied voltage. This distortion occurs in a direction of electric field and in a direction perpendicular to the direction of electric field, leading to mechanical displacement. The electrostriction may generate a stress inside of the multilayer ceramic capacitor.
Data Source
AI summary
A multilayer ceramic capacitor includes a multilayer body including dielectric layers laminated on each other, inner electrode layers laminated on the dielectric layers, first and second main surfaces, first and second end surfaces, and first and second lateral surfaces, first and second external electrodes on the first and second end surfaces, an inner layer portion in which the inner electrode layers are opposed to each other, outer layer portions on first and second main surface sides and first and second lateral surface sides. Voids are provided in the outer layer portions on the first and second lateral surface sides. A ratio of a total area of the voids relative to an area of the outer layer portion on the first or second lateral surface side in a cross section of the multilayer body is greater than or equal to about 0.02% and less than or equal to about 0.2%.