Solid Electrolytic Capacitor Amorphous Alumina Film
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Solution Overview
Problem
Conventional solid electrolytic capacitors with aluminum anodes are prone to leakage current and short-circuit failure due to mechanical stress and defects in the dielectric oxide film, especially when formed with crystalline alumina, which undergoes volumetric shrinkage during formation.
Innovation Solution
A solid electrolytic capacitor with an aluminum anode featuring a dielectric oxide film formed from amorphous alumina and a plurality of tunnel-shaped etching pits, which helps distribute mechanical stress and reduces defects, is fabricated by etching the aluminum material and immersing it in specific acid solutions for anodic oxidation, applying a voltage at least three times the rated voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the formation voltage for anodic oxidation is increased to improve voltage resistance, then the voltage resistance of the capacitor is improved, but the leakage current increases and short-circuit failure occurs
Solution Approach 1:
The invention changes the chemical composition parameters of the electrolytic solution by adding specific organic acids (adipic acid, azelaic acid) and their salts to the existing inorganic acid solution. This compositional parameter change modifies the anodic oxidation process to form a dielectric oxide film with improved properties that can withstand high formation voltages without developing defects, thus simultaneously achieving high voltage resistance and low leakage current.
2Ease of manufacture
If a dielectric oxide film of crystalline alumina is formed to improve manufacturing process, then the formation process is simpler, but the film develops defects due to volumetric shrinkage during formation
Solution Approach 1:
The invention changes the chemical environment parameters during anodic oxidation by introducing specific organic acids and their salts to the electrolytic solution. This parameter modification controls the crystallization process of alumina, promoting the formation of amorphous alumina instead of crystalline alumina, thereby preventing volumetric shrinkage and defect formation while maintaining process simplicity.
3Productivity
If the anode is subjected to mechanical stress during fabrication steps such as cutting, joining, and rolling-up, then the capacitor can be manufactured, but the dielectric oxide film is injured and defects develop
Solution Approach 1:
The invention performs preliminary action by forming a robust dielectric oxide film of amorphous alumina with enhanced mechanical strength before the anode undergoes mechanical stress during fabrication steps. This pre-formed resilient film can withstand the bending, cutting, and rolling operations without developing defects, enabling successful manufacturing while maintaining reliability.
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 capacitor exhibits reduced leakage current and is less prone to short-circuit failure, maintaining high voltage resistance and electrical characteristics while withstanding mechanical stress during fabrication.
Implementation Method 1
effecting anodic oxidation by immersing the aluminum material in an electrolytic solution containing oxalic acid, phosphoric acid, sulfuric acid or the like
Implementation Method 2
effecting anodic oxidation by immersing the aluminum material in an electrolytic solution containing boric acid, phosphoric acid or like inorganic acid or a salt thereof or in an electrolytic solution containing adipic acid, azelaic acid or like organic acid or a salt thereof and applying a voltage at least three times the rated voltage of the capacitor
Implementation Method 3
forming a plurality of tunnel-shaped etching pits in an aluminum material for use as an anode of the capacitor by etching the aluminum material
Data Source
AI summary
The invention provides a solid electrolytic capacitor wherein the anode has a dielectric oxide film of a structure less susceptible to damage due to mechanical stresses and which is diminished in leakage current and less prone to short-circuiting, and a process for fabricating the capacitor. The capacitor of the invention comprises an anode of aluminum having a dielectric oxide film formed over a surface thereof from amorphous alumina, and is characterized in that a plurality of tunnel-shaped etching pits are formed in the anode. The process of the invention for fabricating the solid electrolytic capacitor includes the steps of forming a plurality of tunnel-shaped etching pits in an aluminum material, effecting anodic oxidation by immersing the aluminum material in an electrolytic solution containing oxalic acid or the like, and effecting anodic oxidation by immersing the aluminum material in an electrolytic solution containing boric acid or like inorganic acid or a salt thereof or containing adipic acid or like organic acid or a salt thereof and applying a voltage at least three times the rated voltage of the capacitor.