Solid Electrolytic Capacitor Resin Coefficient Thermal Stress
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Solution Overview
Problem
The adhesion between the positive electrode and the positive electrode lead in solid electrolytic capacitors deteriorates when the principal components of these materials differ, leading to an increase in equivalent series resistance (ESR) due to high-temperature loads, such as those encountered during the reflow process.
Innovation Solution
A solid electrolytic capacitor design where the linear expansion coefficient of the resin outer body is greater than those of the positive electrode, positive electrode lead, positive electrode terminal, and negative electrode terminal, enhancing adhesion at interfaces and suppressing ESR increases by applying stress during high-temperature loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a positive electrode lead made of niobium (a valve metal different from tantalum) is used to connect to a tantalum-based positive electrode, then adhesion between the positive electrode and the positive electrode lead is enhanced, but the equivalent series resistance (ESR) increases under high-temperature loads such as during the reflow process
Solution Approach 1:
The patent changes the linear expansion coefficient parameter of the resin outer body to be larger than those of the positive electrode, positive electrode lead, positive electrode terminal, and negative electrode terminal. This parameter change enables the resin outer body to generate beneficial stress during high-temperature loading that enhances adhesion at the positive electrode/positive electrode lead interface and suppresses ESR increases, while maintaining the use of different valve metals (tantalum and niobium) for the positive electrode and positive electrode lead respectively.
2Strength
If the principal components of the positive electrode and positive electrode lead are made different (tantalum and niobium), then adhesion is enhanced, but the risk of leakage currents increases under high-temperature exposure
Solution Approach 1:
The patent modifies the linear expansion coefficient parameter of the resin outer body to be larger than all other components. This creates thermal stress during high-temperature exposure that reinforces the adhesion between the positive electrode and positive electrode lead interface, thereby preventing the formation of voids or delamination that would otherwise lead to leakage currents, while still allowing the use of different valve metals for adhesion enhancement.
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 design effectively enhances adhesion between the positive electrode and the positive electrode lead, and between the terminals and the conductive adhesive, thereby suppressing the increase in ESR after high-temperature exposure and reducing the risk of leakage currents.
Implementation Method 1
a linear expansion coefficient of the resin outer body is larger than all of linear expansion coefficients of the positive electrode, the positive electrode lead, the positive electrode terminal, and the negative electrode terminal
Data Source
AI summary
A solid electrolytic capacitor comprising a capacitor element including a positive electrode which contains tantalum as a principal component and is composed of a porous sintered body, a positive electrode lead which contains niobium as a principal component and has a first end part embedded in the positive electrode and a second end part extending from the positive electrode, a dielectric layer which is disposed on a surface of the positive electrode and a part of a surface of the positive electrode lead, and a negative electrode layer disposed on the dielectric layer; an positive electrode terminal electrically connected to the second end part of the positive electrode lead; a negative electrode terminal electrically connected to the negative electrode layer; and a resin outer body covering the surfaces of the capacitor element, a part of the positive electrode terminal and a part of the negative electrode terminal, wherein a linear expansion coefficient of the resin outer body is larger than all of linear expansion coefficients of the positive electrode, the positive electrode lead, the positive electrode terminal, and the negative electrode terminal.