Surface Mountable Over-Current Protection Device with Low Resistivity PTC
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Solution Overview
Problem
Current surface mountable over-current protection devices using carbon black as conductive filler are limited by low hold current per unit area due to high resistance, which is insufficient for modern mobile applications requiring higher current handling.
Innovation Solution
Incorporating a PTC material layer with crystalline polymer and conductive filler of low resistivity, along with an efficient heat dissipation structure, including metal foils and connecting conductors, to enhance heat dissipation and increase hold current capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon black is used as conductive filler in PTC material, then voltage endurance is maintained, but resistivity remains high (above 0.2 Ω-cm) and hold current per unit area is limited to below 0.16 A/mm²
Solution Approach 1:
The patent uses composite conductive fillers consisting of metal powder (5-30 wt%), conductive ceramic powder (30-70 wt%), and carbon black (5-30 wt%) combined with crystalline polymer matrix. This composite approach leverages the high conductivity of metals, the voltage endurance of ceramics, and the dispersibility of carbon black to achieve both low resistivity (below 0.2 Ω-cm) and high hold current per unit area (above 0.16 A/mm²) simultaneously.
2Quantity of substance
If metal powder or metal carbide is used as conductive filler to increase hold current per PTC area above 0.16 A/mm², then resistivity decreases, but heat dissipation becomes insufficient for achieving hold current per PTC area greater than 1 A/mm²
Solution Approach 1:
The patent optimizes the compositional parameters of the conductive filler mixture, specifically adjusting the ratios of metal powder (5-30 wt%), conductive ceramic powder (30-70 wt%), and carbon black (5-30 wt%) to achieve the desired balance between conductivity and heat dissipation. This parameter optimization enables the PTC material to achieve hold current per PTC area greater than 1 A/mm² while maintaining effective heat dissipation.
3Quantity of substance
If multiple PTC layers are stacked to increase hold current, then device height and structural complexity increase, but hold current per unit covered area remains limited
Solution Approach 1:
The patent changes the fundamental parameter of conductive filler composition and distribution within the PTC material to achieve higher hold current per unit area in single-layer structures. By using optimized composite fillers with specific ratios of metal powder, conductive ceramic powder, and carbon black, the invention achieves hold current per PTC area greater than 1 A/mm², eliminating the need for multi-layer stacking and reducing device complexity.
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 a hold current per unit area greater than 1 A/mm², effectively addressing the limitations of traditional devices by improving heat dissipation and reducing resistivity, thereby supporting higher current handling in compact designs.
Implementation Method 1
the resistance of PTC conductive composite material remains extremely low at normal temperature, so that the circuit or cell can operate normally. However, when an over-current or an over-temperature event occurs in the circuit or cell, the resistance instantaneously increases to a high resistance state
Implementation Method 2
The first connecting conductor and the second connecting conductor have to be capable of effectively dissipating the heat generated by the PTC material layer
Data Source
AI summary
A surface-mountable over-current protection device comprises one PTC material layer, first and second connecting conductors, first and second electrodes and an insulating layer. The PTC material layer has a resistivity less than 0.2 Ω-cm, and comprises crystalline polymer and conductive filler dispersed therein. The first and second connecting conductors are capable of effectively dissipating heat generated from the PTC material layer. The first and second electrodes are electrically connected to first and second surfaces of the PTC material layer through the first and second connecting conductors, respectively. The dissipation factor depending on the ratio of the total area of the electrodes and the conductors to the area of the PTC material layer is greater than 0.6. At 25° C., the value of the hold current of the device divided by the product of the area of the PTC material layer and the number of the PTC material layer is greater than 1A/mm2.