Flexible Circuit Fuse with Opening for Fast Overcurrent Interruption
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Solution Overview
Problem
Flexible printed circuit boards with fuses face issues of short circuits and delayed current interruption due to heat dissipation and carbonization when the fuse portion is heated, leading to unreliable overcurrent interruption.
Innovation Solution
Incorporating a conductive pattern with a fuse portion having a smaller cross section and strategically placed opening portions on both sides of the fuse portion to reduce heat capacity and accelerate the blowing of the fuse, thereby preventing short circuits and ensuring reliable overcurrent interruption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fuse is mounted on a flexible printed circuit board, then overcurrent protection function is provided, but the number of components and mount steps increases leading to higher costs
Solution Approach 1:
The patent merges the fuse function with the circuit board itself by forming a fuse portion directly on the flexible printed circuit board through conductive pattern deposition. This integration eliminates the need for separate fuse components and their mounting steps, while maintaining overcurrent protection functionality. The fuse portion is created as part of the circuit board structure, combining multiple functions into a single integrated component.
2Reliability
If the cross section of the circuit is reduced to provide fuse function, then overcurrent protection is achieved, but heat dissipation to the base film causes delayed fuse blowing
Solution Approach 1:
The patent applies local quality by creating a fuse portion with reduced cross-sectional area at a specific location on the circuit board. This localized reduction in conductor width increases the current density and heat generation at that specific point, causing the fuse to blow faster when overcurrent occurs. The base film thickness is also reduced at the fuse portion location to minimize heat absorption and accelerate the melting process.
3Reliability
If the fuse portion is heated to blow, then current interruption is achieved, but heat dissipation to the base film causes carbonization and short circuits
Solution Approach 1:
The patent changes the physical parameters of the base film at the fuse portion location, specifically reducing the base film thickness to 1-5 μm. This parameter change reduces the heat capacity and thermal mass of the base film at the fuse location, allowing the fuse portion to reach melting temperature faster before heat dissipation causes carbonization of the base film. The reduced thickness also minimizes the volume of material that can carbonize and cause short circuits.
4Loss of time
If heat dissipation is reduced to accelerate fuse blowing, then current interruption speed is improved, but heat capacity of the surrounding region increases
Solution Approach 1:
The patent segments the base film structure by creating a recessed portion or removing the base film at the fuse location, effectively dividing the continuous base film into separate regions. This segmentation isolates the fuse portion from the bulk base film, reducing the amount of material that can absorb heat. The segmented structure minimizes the heat capacity of the surrounding region while still providing adequate thermal isolation to prevent unwanted heat dissipation paths.
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 suppresses heat dissipation and carbonization, allowing for faster and more reliable interruption of overcurrent, preventing short circuits between the fuse and adjacent wiring.
Implementation Method 1
heat of the fuse portion escapes to the base film to make it difficult for the fuse portion to blow
Implementation Method 2
reducing the heat capacity in a vicinity region to which heat may conduct from the fuse portion
Implementation Method 3
the fuse portion of the base film of the flexible printed circuit board is heated and carbonized
Data Source
AI summary
A flexible printed circuit board according to an aspect of the present invention includes a base film having insulating properties and a conductive pattern laminated to one surface side of the base film. The conductive pattern forms part of a circuit and includes at least one fuse portion having a cross section smaller than the other part. The flexible printed circuit board includes at least one opening passing through front and rear surfaces on at least one of the right and left sides of the fuse portion in a two-dimensional view.