Solid Electrolytic Capacitor Sealing Gap Airtightness
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Solution Overview
Problem
Conventional solid electrolytic capacitors lack sufficient airtightness, leading to deterioration of capacitor elements due to exposure to external air, especially during thermal processes like reflow, where moisture vaporization causes volume expansion and potential peeling of the exterior member.
Innovation Solution
A solid electrolytic capacitor design featuring a conductive material between capacitor elements, an anode and cathode terminal connected via conductive paste, and a sealing material filling the gap between the cathode terminal and the element stack to prevent air infiltration, with the sealing material containing ceramic particles and a curing catalyst to enhance adhesion and maintain airtightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the exterior member directly covers the element stack and terminals, then the structure is simple, but airtightness is insufficient allowing air infiltration to deteriorate capacitor elements
Solution Approach 1:
A sealing material is introduced as an intermediary substance between the exterior member and the element stack/terminals. This sealing material fills the gap and prevents air infiltration, thereby improving airtightness without requiring a fundamentally different structural approach. The sealing material acts as a mediator that blocks the harmful air path while maintaining the overall simple encapsulated structure.
Solution Approach 2:
The sealing material is applied in the gap space between the exterior member and the component stack, utilizing the radial/dimensional space rather than adding axial length. This fills the void space in another dimension (radially outward from the element stack) to block air paths without significantly increasing the overall device footprint or complexity.
2Reliability
If thermal processes like reflow are performed, then capacitor elements are sintered or activated, but moisture vaporization causes volume expansion and peeling of the exterior member
Solution Approach 1:
The sealing material is applied beforehand to the gap between the exterior member and the element stack before thermal processing. This pre-applied sealing material cushions and absorbs the volume expansion caused by moisture vaporization during reflow, preventing the expansion forces from causing peeling or damage to the exterior member and capacitor elements.
Solution Approach 2:
The sealing material's physical and chemical parameters are specifically selected to accommodate thermal processing. The material is chosen to maintain appropriate viscosity and adhesion properties at elevated temperatures, and its composition is designed to withstand thermal expansion without degrading, thereby maintaining adhesion strength throughout the thermal process.
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 proposed design significantly improves airtightness by creating a longer path for air to reach the capacitor elements, reducing equivalent series resistance (ESR) and maintaining the strength of the sealing material, thus preventing deterioration and maintaining capacitor performance during reliability tests.
Implementation Method 1
at least a part of the gap is filled with a sealing material
Implementation Method 2
The cathode terminal is connected to the cathode part via a conductive paste
Implementation Method 3
the equivalent series resistance (ESR) of the solid electrolytic capacitor is reduced by connecting the cathode parts of the plurality of capacitor elements with a conductive film
Data Source
AI summary
A solid electrolytic capacitor includes an element stack, an anode terminal, a cathode terminal, and an exterior member. The element stack includes a plurality of capacitor elements stacked on each other, and a conductive material interposed between two adjacent capacitor elements in the plurality of capacitor elements. Each of the plurality of capacitor elements includes an anode part and a cathode part, and the conductive material is disposed on the cathode part. The anode terminal is connected to the anode part. The cathode terminal is connected to the cathode part via a conductive paste. The cathode terminal has a facing surface facing a tip end of the element stack with a gap interposed between the facing surface and the tip end, and at least a part of the gap is filled with a sealing material.