Solid Electrolytic Capacitor Blocking Layer for Silver Migration
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Solution Overview
Problem
Solid electrolytic capacitors face reliability issues due to delamination caused by thermomechanical stresses and silver migration, leading to increased ESR and leakage current, particularly during surface mount technology (SMT) processes and exposure to humidity.
Innovation Solution
Incorporating a blocking layer, preferably a hydrophobic or carbon-based layer, between the cathode and the metal plated layer, along with a nickel plated metal layer, to inhibit metal ion migration and maintain low ESR, which reduces ESR shift and improves humidity resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a metal filled layer is used to conduct current from the lead frame to the cathode, then high conductivity is achieved, but silver migration occurs leading to increased leakage current and reliability issues
Solution Approach 1:
A blocking layer is introduced as an intermediary between the metal filled layer and the cathode. This blocking layer prevents direct contact between silver and the cathode, thereby stopping silver migration while still allowing electrical conduction to occur through the layered structure.
Solution Approach 2:
The capacitor employs a composite structure combining multiple materials: the metal filled layer (silver in polymer/resin matrix) for conductivity, and the blocking layer (hydrophobic or carbon-based) for migration prevention. This composite approach allows simultaneous achievement of high conductivity and silver migration resistance.
2Ease of manufacture
If the resin in the metal filled layer is degraded to allow solder wetting, then solderability is improved, but excessive degradation causes silver leeching resulting in poor connection
Solution Approach 1:
The blocking layer serves as a protective intermediary that prevents silver from leaching out during the soldering process. This allows the resin to be adequately degraded for solder wetting without causing silver loss, as the blocking layer intercepts and contains the silver.
Solution Approach 2:
The patent controls the thermal stability parameters of the resin and the properties of the blocking layer to achieve optimal balance. By adjusting these parameters, the resin degrades sufficiently for solder wetting while the blocking layer prevents excessive silver leeching, maintaining connection integrity.
3Ease of manufacture
If electroplating is performed on water based graphite coatings and silver paint coatings, then metal layer formation is achieved, but diffusion of plating electrolyte through the hydrophilic and porous conductive layer causes high leakage current and electrical shorts
Solution Approach 1:
The blocking layer acts as a mediator between the porous conductive layer and the plated metal layer. It prevents plating electrolyte from diffusing through the hydrophilic and porous conductive layer to the anode, thereby eliminating leakage current and electrical shorts while still allowing metal layer formation.
4Productivity
If thermomechanical stresses occur during assembly and board mounting, then capacitor assembly is completed, but delamination of layers occurs causing reliability issues
Solution Approach 1:
The patent uses composite material structures with carefully selected material combinations and interfaces. The blocking layer is specifically designed to be compatible with both the metal filled layer and the plated metal layer, creating strong interfacial bonds that resist delamination under thermomechanical stresses during assembly and board mounting.
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 solution effectively reduces ESR shift and leakage current, enhancing the reliability and environmental resistance of solid electrolytic capacitors by preventing metal ion migration and maintaining low electrical resistance.
Implementation Method 1
Incorporating a blocking layer, preferably a hydrophobic or carbon-based layer, between the cathode and the metal plated layer
Implementation Method 2
to inhibit metal ion migration and maintain low ESR
Implementation Method 3
a nickel plated metal layer, to inhibit metal ion migration and maintain low ESR
Implementation Method 4
An important feature of the solid cathode electrolyte is that it can be made more resistive by exposure to high temperatures. This feature allows the capacitor to heal leakage sites by Joule heating.
Data Source
AI summary
A capacitor with an anode, a dielectric on the anode and a cathode on the dielectric. A blocking layer is on the cathode. A metal filled layer is on said blocking layer and a plated layer is on the metal filled layer.