Solid Electrolytic Capacitor Dummy Layer for ESR Stability
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Solution Overview
Problem
The existing methods for producing solid electrolytic capacitors result in changes in equivalent series resistance (ESR) due to delamination caused by the difference in coefficient of linear expansion between the substrate and external electrodes during heat treatment, leading to inconsistent performance before and after reflow.
Innovation Solution
Incorporating a dummy layer not contributing to the capacitor's capacity between the capacitor element laminate and the insulating substrate, which remains delaminated without affecting the ESR, thereby maintaining consistent ESR levels before and after reflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a substrate is used for precise alignment during stacking, then manufacturing precision is improved, but the substrate causes delamination during heat treatment due to coefficient of linear expansion difference, worsening reliability
Solution Approach 1:
The capacitor element laminate is segmented into multiple functional layers: a first layer with valve-action metal substrate for alignment, a second layer with electrode lead-out, and a dummy layer. This segmentation allows the alignment function to be separated from the heat-resistant function, resolving the contradiction between manufacturing precision and reliability.
Solution Approach 2:
A dummy layer is introduced as an intermediary between the capacitor element laminate and the insulating substrate. This dummy layer acts as a buffer that absorbs thermal stress during heat treatment, preventing delamination of the functional layers while maintaining the alignment function of the substrate.
2Manufacturing precision
If the substrate is kept on the bottom for alignment, then manufacturing precision is improved, but ESR changes occur during reflow due to delamination, worsening product consistency
Solution Approach 1:
The laminate is segmented into functional layers (valve-action metal substrate layer, electrode lead-out layer) and a dummy layer. This allows the alignment function to be isolated to specific layers while protecting the ESR-critical interfaces from thermal stress-induced delamination.
Solution Approach 2:
The dummy layer serves as a thermal buffer between the capacitor element laminate and the insulating substrate, absorbing expansion stresses during reflow and preventing delamination that would otherwise change ESR values.
3Reliability
If a dummy layer is added to prevent delamination, then reliability is improved, but device complexity increases
Solution Approach 1:
The dummy layer is extracted as a dedicated functional element with the sole purpose of preventing delamination. By isolating this protective function into a separate layer, the complexity is localized and manageable, while the core capacitor structure remains relatively simple.
Solution Approach 2:
The dummy layer is strategically placed only where thermal stress and delamination risk are highest (between the capacitor element laminate and insulating substrate), rather than adding complexity throughout the entire device. This localized approach minimizes overall device complexity while maximizing reliability improvement.
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 introduction of a dummy layer prevents changes in ESR due to delamination, ensuring that the equivalent series resistance remains stable even after heat treatment, thus enhancing the reliability and performance of the solid electrolytic capacitors.
Implementation Method 1
the difference in coefficient of linear expansion between the substrate and the external electrodes causes delamination of the sheet closest to the substrate
Data Source
AI summary
A solid electrolytic capacitor that includes a resin molding including: a capacitor element laminate, the capacitor element laminate including a first layer and a second layer that are laminated together, the first layer includes a valve-action metal substrate exposed at a first end surface of the resin molding, the second layer includes an electrode lead-out layer exposed at a second end surface of the resin molding; an insulating substrate; and a sealing resin enclosing the capacitor element laminate; a first external electrode on a first end surface of the resin molding and connected to the valve-action metal substrate; a second external electrode on a second end surface of the resin molding and connected to the electrode lead-out layer; and a dummy layer not contributing to a capacity of the capacitor on a main surface of the capacitor element laminate in a lamination direction thereof and adjacent to the insulating substrate.