Solid Electrolytic Capacitor Anode Foil Structure for ESR Stability
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Solution Overview
Problem
Solid electrolytic capacitors experience a decrease in electrostatic capacity and increased equivalent series resistance (ESR) due to oxidation and decomposition of the solid electrolyte layer when exposed to high temperatures, particularly during soldering and high-temperature environments, leading to reduced reliability.
Innovation Solution
The anode foil of the solid electrolytic capacitor element includes a porous part with a dense part having lower porosity, reducing air permeability and minimizing air entry, thereby protecting the solid electrolyte layer from deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the anode foil surface is made porous to increase surface area for capacitance, then the electrostatic capacity is improved, but air permeability increases allowing air to enter and cause oxidation and decomposition of the solid electrolyte layer at high temperatures
Solution Approach 1:
The anode foil is designed with non-uniform surface properties: a first region with high surface area (porous structure) for capacitance and a second region with low surface area (smooth structure) for air barrier function. This local differentiation allows the capacitor to simultaneously achieve high electrostatic capacity while preventing air permeation that causes electrolyte degradation at high temperatures.
Solution Approach 2:
The anode foil surface is segmented into functionally distinct regions: a first region providing high surface area for charge storage and a second region providing air tightness. This segmentation resolves the contradiction by assigning different structural characteristics to different zones, allowing the porous structure to provide capacitance without compromising the air barrier property needed to prevent oxidation.
2Ease of manufacture
If the solid electrolyte layer is exposed to high temperatures during soldering, then the capacitor can be mounted, but the solid electrolyte layer undergoes oxidation and decomposition causing decreased reliability
Solution Approach 1:
A protective structure (second region with smooth surface and lower porosity) is prepared in advance on the anode foil before the solid electrolyte layer is formed. This preliminary protective structure prevents air from reaching the electrolyte during subsequent high-temperature soldering processes, thereby maintaining electrolyte stability and reliability without interfering with the mounting process.
Solution Approach 2:
The second region of the anode foil acts as an intermediary barrier between the external environment (air) and the solid electrolyte layer. During high-temperature soldering, this intermediary structure prevents direct contact between air and the electrolyte, thereby protecting the electrolyte from oxidation and decomposition while allowing the capacitor to undergo the necessary thermal processing for mounting.
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 effectively suppresses the decrease in electrostatic capacity and increases in ESR, enhancing the reliability of the capacitor by maintaining the integrity of the solid electrolyte layer under high-temperature conditions.
Implementation Method 1
The dense part has a porosity smaller than a porosity of the porous part
Data Source
AI summary
A solid electrolytic capacitor element includes an anode foil that includes a porous part in a surface layer of the anode foil, a dielectric layer, and a cathode part. The cathode part includes a solid electrolyte layer that covers the at least a part of the dielectric layer and a cathode lead-out layer that covers at least a part of the solid electrolyte layer. The anode foil includes a first part that is a cathode forming part where the solid electrolyte layer is formed and a second part where the solid electrolyte layer is not formed. And the anode foil includes a dense part in the surface layer in at least one of the first part and the second part. The dense part has a porosity smaller than a porosity of the porous part. The second part includes at least an anode part including an end part of the anode foil opposite to the first part.