Surface-Mounted PTC Over-Current Protection Device
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Solution Overview
Problem
Surface-mounted over-current protection devices using carbon black as conductive filler face limitations in hold current due to high resistance, restricting their application in small-sized SMDs, with current devices typically achieving a hold current of 0.16 A/mm2 or less, which is insufficient for many practical applications.
Innovation Solution
A surface-mounted over-current protection device utilizing a PTC material layer with high conductivity metal powder or ceramic powder, combined with a crystalline polymer and non-conductive filler, and a unique module structure with rough-surfaced metal foils to enhance hold current and voltage endurance, allowing for a hold current of 0.16 A/mm2 to 1 A/mm2 per unit area, suitable for small-sized SMDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon black is used as conductive filler in PTC material, then the device can be manufactured with conventional processes, but the resistance is high (resistivity seldom reaches below 0.2 Ω-cm) and hold current is limited to 0.16 A/mm2 or less
Solution Approach 1:
The patent changes the key parameter of conductive filler from carbon black to metal powder or conductive ceramic powder with higher conductivity. This parameter change directly addresses the resistivity limitation, enabling resistivity to reach below 0.2 Ω-cm and hold current to exceed 0.16 A/mm2, thereby resolving the contradiction between manufacturability and electrical performance.
Solution Approach 2:
The patent employs composite materials by combining PTC crystalline polymer with high-conductivity metal powder or conductive ceramic powder fillers. This composite approach maintains the PTC protective function while achieving superior electrical conductivity, allowing the device to overcome the limitations of conventional carbon black-filled materials.
2Area of stationary object
If the covered area of the SMD device is reduced to save space, then the device size is minimized, but the hold current capability is reduced proportionally
Solution Approach 1:
By changing the conductive filler parameter to high-conductivity metal powder or conductive ceramic powder, the patent achieves higher hold current density (exceeding 0.16 A/mm2). This allows smaller covered areas to maintain or achieve the required hold current capability, effectively decoupling device size from current handling capacity.
3Reliability
If multiple PTC layers are stacked to increase hold current, then the hold current capability is improved, but the total height and device complexity increase
Solution Approach 1:
The patent changes the fundamental parameter of conductive filler to achieve superior conductivity in a single layer. This eliminates the need for multiple stacked layers, thereby maintaining low device height while achieving high hold current capability. The single-layer high-performance structure resolves the contradiction between current capability and device compactness.
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 achieves improved resistivity, voltage endurance, and high hold current, enabling the device to handle higher currents while maintaining low resistance, thus overcoming the limitations of traditional devices and reducing production costs by allowing more devices per unit area.
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. Therefore, the over-current will be counterchecked and the objective of protecting the circuit elements or batteries is achieved.
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.