Low Current Fuse with Electroplated Termination
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Solution Overview
Problem
Existing surface mount fuses do not adequately address the need for devices rated for milli-currents of about 50 milli-amps in packages smaller than 80 mil×50 mil, and there is a lack of solutions for low current fuses that can blow at currents in the range of 0.06 to 0.5 Amps.
Innovation Solution
A low current fuse device is designed in either land grid array (LGA) or surface mount (SMD) configuration, featuring a substrate with an elongated fuse element and integral contact pads, passivation layers, and electroplated conductive electrodes, typically using nickel or copper metal with a thin tantalum layer for adhesion, and encapsulated with polyimide and protective coatings for small form factor and high reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional surface mount fuse designs are used, then the fuse structure is simple and easy to manufacture, but the fuse cannot achieve the required milli-current rating (0.06 to 0.5 Amps) in small packages
Solution Approach 1:
The fuse device is divided into multiple functional layers: substrate layer, fuse element layer, intermediate insulation layers, and terminations layer. Each layer performs a specific function, allowing precise control of electrical characteristics while maintaining manufacturability through standard PCB fabrication processes
Solution Approach 2:
The fuse element is configured as a meandering or serpentine trace pattern on the substrate, increasing the effective resistance path within a small footprint. This dimensional transformation allows achieving high resistance (and thus milli-current rating) without increasing package size
2Area of stationary object
If the fuse package size is reduced to below 80 mil×50 mil, then the device becomes more compact and suitable for modern electronics, but existing fuse designs cannot maintain the required current rating
Solution Approach 1:
The fuse element uses localized material selection with high-resistivity materials (such as nickel-chromium alloy or thin-film metal) in the heating section, while terminations use low-resistivity materials for optimal electrical connection. This local optimization enables precise current rating control in small packages
Solution Approach 2:
The fuse element geometry and material properties are pre-designed during fabrication to have specific resistance values that ensure accurate current rating. The meandering trace pattern and thin-film deposition parameters are predetermined to achieve the required electrical characteristics before the fuse is installed
3Manufacturing precision
If thin film technology is used to achieve precise current rating, then the fuse can blow at specific milli-currents, but the manufacturing process becomes more complex
Solution Approach 1:
The fuse element resistance is precisely controlled by varying thin-film deposition parameters such as material composition (e.g., nickel-chromium ratios), film thickness (controlled to within nanometer precision), and trace geometry. These parameter changes enable accurate current rating without fundamentally changing the manufacturing process
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 provides a compact, reliable fuse device capable of blowing at currents between 0.06 to 0.5 Amps, with dimensions as small as 1 mm×0.5 mm, suitable for surface mounting and offering high resistance to electromigration and corrosion, thus addressing the need for small, high-performance fuses.
Implementation Method 1
a thin film fuse element and a pair of integral contact pads formed therewith at opposed longitudinal ends
Implementation Method 2
a pair of windows are opened through both passivation layers above both of the contact pads, so as to receive conductive electrode material electroplated therethrough
Implementation Method 3
typically using nickel or copper metal with a thin tantalum layer for adhesion
Data Source
AI summary
A multi layer fuse device includes a substrate and an elongated fuse element, having a pair of contact pads formed therewith at opposed longitudinal ends thereof formed on one surface of the substrate. A pair of passivation layers are provided covering the fuse and contact pads. Windows may be opened through both passivation layers above both of the contact pads, and conductive electrode material is electroplated through the windows to contact the contact pads and to extend partially above a top surface of the passivation layers. Exposed electroplated material may be coated with solderable conductive material or a surface mount termination may be provided. Electroplated material may cover a portion of the fuse surface prior to application of the passivation layers and extend to an end of the substrate so that windows are not required.