Multilayer Varistor Coating Layout for Humidity Migration Resistance
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Solution Overview
Problem
Multilayer varistors experience surface migration issues in humid environments due to the high-resistivity layer between external electrodes, leading to potential malfunction and reduced reliability.
Innovation Solution
A multilayer varistor design featuring a sintered compact with internal and external electrodes, where the high-resistivity layer consists of a thicker first layer covering planar portions and a thinner second layer covering corner portions, or a layer with higher arithmetic mean surface roughness, to reduce migration and enhance mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If a high-resistivity layer is formed on the sintered compact to reduce plating deposition, then plating deposition is reduced, but migration occurs on the surface of the high-resistivity layer between external electrodes in humid environments
Solution Approach 1:
The patent applies local quality by forming a first high-resistivity layer with greater thickness on planar portions and a second high-resistivity layer with smaller thickness on corner portions. This differential thickness design addresses the specific problem of migration on planar surfaces while maintaining the benefits of reduced plating deposition, resolving the contradiction between plating deposition reduction and migration resistance.
Solution Approach 2:
The high-resistivity layer is segmented into two distinct layers: a first high-resistivity layer covering planar portions and a second high-resistivity layer covering corner portions. This segmentation allows each layer to be optimized for its specific function, with the first layer providing migration resistance and the second layer maintaining overall protective coverage, thereby resolving the technical contradiction.
2Reliability
If the high-resistivity layer is made thicker to prevent migration, then migration resistance improves, but mechanical strength and mounting strength are compromised
Solution Approach 1:
The patent uses local quality to apply different thicknesses of the high-resistivity layer to different areas: the first layer on planar portions is thicker to prevent migration, while the second layer on corner portions is thinner to preserve mechanical strength. This localized approach resolves the contradiction between migration resistance and mechanical strength.
Solution Approach 2:
The patent applies partial action by forming the high-resistivity layer only where needed for migration prevention (primarily on planar portions) rather than uniformly across the entire surface. This partial coverage maintains mechanical strength while providing sufficient migration resistance where it is most critical.
3Ease of manufacture
If a uniform high-resistivity layer is formed on the sintered compact, then manufacturing is simplified, but migration occurs on planar portions between external electrodes
Solution Approach 1:
The patent implements local quality by differentiating the high-resistivity layer into two types based on location: a first layer for planar portions with properties optimized for migration resistance, and a second layer for corner portions with properties optimized for mechanical strength. This resolves the contradiction between manufacturing simplicity and migration resistance by making the manufacturing process location-aware.
Solution Approach 2:
The uniform coating is segmented into two distinct high-resistivity layers with different thicknesses and properties. This segmentation allows the manufacturing process to address the specific needs of different surface areas, preventing migration on planar portions while maintaining overall structural integrity.
Data Source
AI summary
A multilayer varistor according to the present disclosure includes: a sintered compact having, on a surface thereof, at least one planar portion and at least one corner portion; an internal electrode provided inside the sintered compact; a high-resistivity layer arranged to cover the at least one planar portion and the at least one corner portion of the sintered compact at least partially; and an external electrode arranged to cover the high-resistivity layer partially and electrically connected to the internal electrode. The high-resistivity layer includes: a first high-resistivity layer covering the at least one planar portion; and a second high-resistivity layer covering the at least one corner portion. The first high-resistivity layer has a larger average thickness than the second high-resistivity layer.