Surface Mountable Thermistor Heat Conductive Dielectric Layer
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Solution Overview
Problem
Surface mountable thermistors with organic polymer materials face limitations in high temperature environments due to inadequate heat transfer and reduced sensitivity to ambient temperatures, which restricts their ability to increase hold current and protect circuits effectively.
Innovation Solution
Incorporating heat conductive dielectric layers with polymeric insulation matrices and heat conductive fillers, such as zirconium nitride or aluminum nitride, to enhance heat transfer efficiency between electrodes, thereby increasing the thermistor's sensitivity to ambient temperatures and hold current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the device is characterized in high thermal insulation, then the device is not sensitive to ambient temperature, but the sensitivity to ambient temperature is required for over-current protection
Solution Approach 1:
The patent introduces a heat conductive dielectric layer as an intermediary component between the PTC core and the external environment. This layer has high heat conductivity (≥1.0 W/mK) that facilitates heat transfer from the PTC core to the ambient environment, enabling the device to sense ambient temperature changes while maintaining electrical insulation. The dielectric layer acts as a thermal mediator that resolves the contradiction between thermal insulation for electrical isolation and thermal conductivity for temperature sensing.
Solution Approach 2:
The patent changes the thermal parameter of the dielectric layer by selecting materials with specific heat conductivity values (≥1.0 W/mK). This parameter change allows the device to maintain electrical insulation while improving heat transfer capability, thereby enhancing sensitivity to ambient temperature without compromising the over-current protection function.
2Volume of moving object
If the device dimensions are reduced for high density circuit design, then the device can be surface mountable, but the hold current cannot increase due to inferior heat transfer
Solution Approach 1:
The patent applies local quality by concentrating high heat conductivity in specific regions where it is most needed - the dielectric layer surrounding the PTC core and the electrode structures. Rather than requiring the entire device to be large for heat dissipation, the high heat conductivity is localized to the thermal pathways, enabling effective heat transfer from the small PTC core to the external environment, thus maintaining hold current capability in a compact form factor.
3Reliability
If the device is designed for rapid heat transfer, then the hold current increases and sensitivity to ambient temperature improves, but the device complexity increases due to additional heat conductive dielectric layers
Solution Approach 1:
The heat conductive dielectric layer performs multiple functions simultaneously: (1) provides electrical insulation between conductive elements, (2) facilitates heat transfer from the PTC core to the ambient environment, and (3) serves as a structural support matrix for the conductive fillers. By making the dielectric layer multi-functional, the patent achieves rapid heat transfer and improved reliability without proportionally increasing device complexity, as the same component structure accomplishes multiple objectives.
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 improved heat transfer efficiency allows for increased hold current and enhanced sensitivity to ambient temperatures, enabling effective over-current protection and protection in high temperature applications like LED devices and secondary battery protection.
Implementation Method 1
The heat conductive dielectric layer contains polymeric insulation matrix and heat conductive filler, and is disposed between the first electrode and the second electrode. The heat conductivity of heat conductive dielectric layer is between 1.2 W/mK-13 W/mK.
Implementation Method 2
The resistance of PTC conductive composite material remains extremely low at normal temperatures, 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 3
The polymeric material layer exhibits PTC or NTC behavior
Data Source
AI summary
A surface mountable thermistor comprises a resistive device, first and second electrodes, and at least one heat conductive dielectric layer. The resistive device contains first and second electrically conductive members and a polymeric material layer laminated therebetween. The polymeric material layer exhibits PTC or NTC behavior. The polymeric material layer and the first and second electrically conductive members commonly extend in a first direction. The first electrode is electrically coupled to the first electrically conductive member. The second electrode is electrically coupled to the second electrically conductive member and is insulated from the first electrode. The heat conductivity of the first electrode or the second electrode is at least 50 W/mK. The heat conductive dielectric layer comprises polymeric insulation matrix and heat conductive filler, and is disposed between the first electrode and the second electrode. The heat conductivity of heat conductive dielectric layer is between 1.2 W/mK-13 W/mK.