Composite Fuse Element for Reliable Current Cutoff
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Solution Overview
Problem
Conventional fuse elements with high-melting-point metal materials, such as silver, do not melt at operating temperatures, leading to incomplete fusion, deformation, and increased electrical resistance, making it difficult to achieve a reliable and compact protective element for small electronic devices.
Innovation Solution
A fuse element composed of a composite metal material where a first fusible metal with a higher melt temperature and a second fusible metal with a lower melt temperature are stacked, allowing both to be molten at a reflow temperature, eliminating the need for solder paste and reducing electrical resistance without using high-melting-point metals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-melting-point metal material such as silver is used for the fuse element, then the electrical resistance is reduced, but the metal does not melt at operating temperature leading to incomplete fusion and deformation
Solution Approach 1:
The fuse element uses a composite structure with a core material (low-melting-point metal) and a cladding material (different metal or alloy) with distinct functional properties. The core provides fusibility at operating temperatures while the cladding maintains structural integrity and provides electrical conductivity, resolving the contradiction between melting point and electrical resistance
Solution Approach 2:
The invention changes the material parameters by selecting specific metal combinations with controlled melting points, thermal conductivities, and electrical resistances. The core material has a melting point below the operating temperature range (e.g., 100-300°C) while the cladding material has higher melting point and better electrical properties, allowing the fuse to reliably melt at operational temperatures
2Volume of moving object
If the thickness of the fuse element is reduced to achieve smaller protective elements, then the size and thickness are reduced, but the fusing operation becomes unreliable and excessive time is required
Solution Approach 1:
The composite structure with core and cladding materials allows for optimized thickness distribution. The core material can be made thinner while maintaining reliable fusing because its lower melting point enables complete fusion at lower temperatures and shorter times, compensating for the reduced thickness
Solution Approach 2:
Different parts of the fuse element have different material properties optimized for their specific functions. The core material is designed for rapid melting and complete fusion, while the cladding provides structural support and electrical conductivity. This local differentiation allows thin overall dimensions while maintaining fusing reliability
3Adaptability or versatility
If a lead-free metal composite material is used to comply with RoHS regulations, then chemical substance compliance is improved, but the material requires careful control of melting and fusion characteristics
Solution Approach 1:
The lead-free composite material combines a low-melting-point lead-free metal (such as tin-based alloy) as the core with a cladding material that provides structural integrity. This composite structure enables compliance with RoHS regulations while maintaining controllable melting and fusion characteristics through careful selection of material compositions and thickness ratios
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 enables reliable current cutoff, prevents deformation, and allows for a more efficient production process by ensuring complete fusion and reducing electrical resistance, thus addressing the limitations of conventional fuse elements.
Implementation Method 1
some of an element of the first fusible metal is molten at a reflow temperature, the second fusible metal has a lower melt temperature than the first fusible metal, and at least some of an element of the second fusible metal is molten at the reflow temperature
Implementation Method 2
the protective element has a resistive element that generates heat by a signal current
Data Source
AI summary
A protective element includes an insulating substrate, a plurality of electrodes provided on the insulating substrate, a fuse element electrically connected to any electrode of the plurality of electrodes, and a heat generation element provided on the insulating substrate for heating and fusing the fuse element. The fuse element contains a composite metal material in which a first fusible metal and a second fusible metal are stacked, some of a component of the first fusible metal being dissolved at a joint working temperature, the second fusible metal being lower in melt temperature than the first fusible metal, at least some of a component of the second fusible metal being molten at the joint working temperature.