Solid Electrolytic Capacitor Cathode Coating for Edge Coverage

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Solution Overview

Problem

Existing methods for forming polymer layers in solid electrolytic capacitors fail to provide adequate coverage of edges and corners, leading to reliability issues such as increased residual currents and corrosion, especially under high humidity and temperature conditions.

Innovation Solution

The application of a monophosphonium-counter acid combination as a solution or dispersion in the cathode layer of capacitors improves polymer corner and edge coverage without the drawbacks of polyvalent ionic crosslinkers, such as contamination and viscosity increase.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If an ionic crosslinker solution is applied between conductive polymer dispersion dipping cycles to improve polymer coverage of corners and edges, then coverage is improved, but the crosslinker solution contaminates the conductive polymer dispersion causing viscosity increase or agglomeration

Engineering Contradiction:

Improvepolymer coverageVSAvoiddispersion stability

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent extracts and removes the harmful ionic crosslinker solution from the process, replacing it with a non-ionic alternative that provides crosslinking functionality without causing contamination, viscosity increase, or agglomeration of the conductive polymer dispersion

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces a non-ionic crosslinking agent as an intermediary substance that enables crosslinking between polymer chains without the harmful effects of ionic crosslinkers, serving as a mediator that achieves the desired coverage improvement while maintaining dispersion stability

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If polyvalent ionic crosslinkers are used to improve corner and edge coverage, then coverage is improved, but leakage current increases under high humidity conditions due to dissociation of strong ionic species

Engineering Contradiction:

Improvecorner and edge coverageVSAvoidleakage current

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent changes the chemical parameter of the crosslinking agent from ionic to non-ionic, eliminating the dissociation of strong ionic species that causes increased leakage current under high humidity conditions while maintaining effective corner and edge coverage

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the problematic ionic crosslinker system with a simpler non-ionic alternative that achieves the same coverage improvement without the long-term reliability issues of ionic species migration and corrosion

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Manufacturing precision

If ionic crosslinker solutions are applied to improve polymer coverage, then coverage is improved, but corrosion occurs on aluminum metals due to migration of strong ionic species

Engineering Contradiction:

Improvepolymer coverageVSAvoidmetal corrosion

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful effect of ionic species migration and corrosion into a beneficial outcome by using non-ionic crosslinking agents that eliminate corrosion risks while maintaining the coverage improvement benefits

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

4Reliability

If a water wash step is applied after the conductive polymer layer is dried to remove ionic species, then leakage current is reduced, but delamination of polymer from dielectric occurs and ESR increases

Engineering Contradiction:

Improveleakage currentVSAvoidadhesion

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent applies non-ionic crosslinking agents during the coating process as a preliminary action that prevents the formation of ionic species that would require washing, thereby avoiding delamination and ESR increase while achieving low leakage current

Inventive Principle:

Principle #10Preliminary action

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 monophosphonium-counter acid combination effectively enhances polymer coverage on edges and corners, improving the reliability of capacitors under high humidity and temperature conditions while maintaining low leakage performance.

Implementation Method 1

The effectiveness of the crosslinker is attributed to the presence of multiple cationic functional groups that form a chemical bond, referred to as 'crosslinks', between polymer dispersion particles

Methodology Applied

Scientific EffectChemical bonding (crosslinking): Chemical Bonding

Implementation Method 2

Typical methods for applying conductive polymers onto a dielectric include in situ chemical/electrochemical oxidation polymerization

Methodology Applied

Scientific EffectOxidation polymerization: Oxidation

Data Source

PatentUS12205775B2Process to improve coverage and electrical performance of solid electrolytic capacitors

Publication Date: 2025.01.21 KEMET ELECTRONICS CORP

AI summary

Provided herein is a method for forming a capacitor and an improved capacitor formed by the method. The method comprises providing an anode with an anode lead extending therefrom. A dielectric is formed on the anode thereby forming an anodized anode. A cathode layer is formed over the dielectric wherein the cathode layer is formed by applying a conductive polymer solution or dispersion and applying a primer solution or dispersion comprising a monophosphonium or monosulfonium cation.