Surface-Mounted PTC Over-Current Protection Device
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current surface-mounted over-current protection devices using carbon black as conductive filler have limited hold current due to high resistance, restricting their performance and area efficiency, especially in small-sized SMDs, where the hold current per unit area is below 0.16 A/mm2.
Innovation Solution
A surface-mounted over-current protection device utilizing high conductivity metal powders or conductive ceramic powders within a PTC material layer, combined with metal foils having rough surfaces for enhanced contact, and insulated layers for bonding, achieving a hold current per unit area between 0.16 A/mm2 and 0.40 A/mm2, and improved voltage endurance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If carbon black is used as conductive filler in PTC material, then the device structure is simple and manufacturing is easy, but the hold current is limited due to high resistance (resistivity seldom reaches below 0.2 Ω-cm)
Solution Approach 1:
The patent changes the key parameter of conductive filler from carbon black to metal powder (such as nickel, copper, or aluminum powder with particle size of 0.01-30 μm). This parameter change reduces the resistivity of the PTC material to below 0.2 Ω-cm, thereby increasing the hold current capability while maintaining manufacturing simplicity through conventional mixing and molding processes
Solution Approach 2:
The patent creates a composite PTC material consisting of crystalline polymer matrix combined with metal powder conductive filler. This composite structure achieves both low resistivity (high conductivity) and maintains the PTC effect, resolving the contradiction between ease of manufacture and hold current performance
2Area of moving object
If the covered area of the SMD device is reduced to make it smaller, then the device size decreases, but the hold current per unit area is limited to below 0.16 A/mm2 due to resistance limitations
Solution Approach 1:
By changing the conductive filler parameter to metal powder with higher conductivity, the patent achieves hold current per unit area of 0.16-0.40 A/mm2, which is 3-8 times higher than conventional carbon black filled devices. This allows significant reduction in covered area while maintaining or improving hold current performance
Solution Approach 2:
The patent preemptively addresses the resistance limitation by selecting metal powder filler before device fabrication, preventing the hold current per unit area limitation from occurring in the first place, thereby enabling smaller device sizes without sacrificing performance
3Reliability
If multiple PTC layers are stacked to increase hold current, then the hold current increases, but the total height and device complexity increase
Solution Approach 1:
The patent changes the fundamental parameter of conductive filler to metal powder, which provides such high conductivity that a single layer achieves hold current densities of 0.16-0.40 A/mm2. This eliminates the need for multiple stacked layers, thereby reducing device complexity and total height while maintaining high hold current
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 higher hold currents and voltage endurance, allowing for smaller device sizes with enhanced performance, reducing production costs and overcoming the limitations of traditional devices.
Implementation Method 1
the resistance of the PTC device will immediately increase at least ten thousand times (over 104 ohm) to a high resistance state
Implementation Method 2
Each of the first and the second metal foils uses a rough surface with plural nodules to physically contact the PTC material layer
Data Source
AI summary
A surface-mounted over-current protection device with positive temperature coefficient (PTC) behavior is disclosed. The surface-mounted over-current protection device comprises a first metal foil, a second metal foil corresponding to the first metal foil, a PTC material layer stacked between the first metal foil and the second metal foil, a first metal electrode, a first metal conductor electrically connecting the first metal foil to the first metal electrode, a second metal electrode corresponding to the first metal electrode, a second metal conductor electrically connecting the second metal foil to the second metal electrode, and at least one insulated layer to electrically insulate the first metal electrode from the second metal electrode. The surface-mounted over-current protection device, at 25° C., indicates that a hold current thereof divided by the product of a covered area thereof and the number of the conductive composite module is at least 0.16 A/mm2.