Laminated Fuse Element With Segmented Current Path
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Solution Overview
Problem
Existing fuse elements face challenges with surface mounting using reflow, low current ratings, and degradation of rapid interruption properties when increasing ratings, and they often require lead-containing solders which are restricted by the RoHS directive.
Innovation Solution
A fuse element with a laminated structure of a low melting point metal layer and a high melting point metal layer, where the low melting point metal layer has a film thickness of 30 μm or more and the high melting point metal layer has a film thickness of 3 μm or more, and the length in the width direction is greater than the length in the conduction direction, along with recesses or through holes to divide the current path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a fuse element is enlarged to increase current rating, then current handling capability is improved, but rapid interruption properties deteriorate
Solution Approach 1:
The fuse element is divided into multiple segments by providing recesses or through holes that partition the current path. This segmentation allows the fuse to blow out in multiple stages, with each segment contributing to rapid current interruption while maintaining the overall current rating. The segmented structure reduces the distance electrons must travel during blowout, enabling faster interruption even at higher current ratings.
2Reliability
If Pb-containing high melting point solder is used to avoid melting during reflow, then mounting reliability is improved, but compliance with RoHS directive deteriorates
Solution Approach 1:
The fuse element employs a composite structure with a low melting point metal layer (30 μm or more) laminated with a high melting point metal layer (3 μm or more). This composite material combines the advantages of both materials: the low melting point layer ensures reliable reflow mounting without requiring Pb-containing solder, while the high melting point layer provides structural integrity and prevents premature blowout during the reflow process. This composition enables Pb-free soldering while maintaining mounting reliability.
3Ease of manufacture
If the low melting point metal layer thickness is increased to 30 μm or more for surface mounting, then ease of mounting is improved, but device size increases
Solution Approach 1:
The fuse element applies local quality by concentrating the low melting point metal layer (30 μm or more) specifically at the regions requiring reliable solder joint formation, while maintaining a thinner overall profile. The high melting point metal layer (3 μm or more) is strategically laminated to provide structural support where needed. This localized application of different material thicknesses and properties enables surface mounting ease without proportionally increasing the overall device volume.
4Speed
If the length in width direction is made greater than length in conduction direction, then rapid blowout properties are improved, but device footprint increases
Solution Approach 1:
The fuse element utilizes dimensional optimization by making the length in the width direction greater than the length in the conduction direction. This dimensional configuration optimizes the blowout path geometry, allowing rapid interruption to propagate efficiently across the width while minimizing the conduction path length. The recesses or through holes are strategically positioned to facilitate this dimensional advantage, enabling fast blowout performance within a compact footprint by exploiting the width dimension more effectively than the conventional conduction direction.
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
Enables surface mounting using reflow, increased ratings for handling large currents, and rapid blowout properties for interrupting current paths, while avoiding the use of lead-containing solders and preventing explosive scattering of the fuse element.
Implementation Method 1
a fuse element which constitutes a current path of a fuse device and blows out due to self-generated heat when a rating-exceeding current flows therethrough
Implementation Method 2
a low melting point metal layer; and a high melting point metal layer laminated on the low melting point metal layer
Data Source
AI summary
A fuse device and a fuse element having excellent rapid blowout properties and excellent insulation properties after blowout even in a size-reduced fuse device are provided. A fuse element constitutes a current path of a fuse device and blows out due to self-generated heat when a rating-exceeding current flows, a length W in a width direction perpendicular to a conduction direction being greater than a total length L in the conduction direction in the fuse element. In particular, the fuse element includes a low melting point metal layer and a high melting point metal layer, the low melting point metal layer eroding the high melting point metal layer when current flows to cause blowout.