Overcurrent protection element

Abstract

A kind of overcurrent protection element includes a first electrode layer, a second electrode layer and a PTC material layer arranged therebetween. The PTC material layer includes a polymer matrix, a conductive ceramic filler, a carbon-containing conductive filler, and an internal filler. The polymer matrix includes a fluorine-containing polymer with a melting point higher than 150℃. The internal filler is selected from any one of aluminum nitride, silicon carbide, zirconium oxide, boron nitride, graphene, aluminum oxide, or a mixture of any of the above materials, and the volume percentage of the internal filler is 2-10%. The overcurrent protection element can inhibit the negative temperature coefficient effect after the element triggers, and has high withstand current and high withstand power.

Description

Technical Field

[0001] This invention relates to an overcurrent protection element, and more specifically, to an overcurrent protection element that suppresses the negative temperature coefficient (NTC) effect after element triggering. Background Technology

[0002] Conductive composite materials with a positive temperature coefficient (PTC) exhibit a sensitive resistance response to temperature changes, making them suitable for use as current sensing elements. They are currently widely used in overcurrent protection components and circuit components. Because PTC conductive composite materials maintain extremely low resistance at normal temperatures, circuits or batteries can operate normally. However, when an overcurrent or overtemperature event occurs in the circuit or battery, its resistance will instantly increase to a high resistance state (at least 10 ohms). 4 (Above Ω), which is called a trip, and the excessive current is reversed to cancel it out, so as to protect the battery or circuit components.

[0003] Overcurrent protection elements consist of a PTC material layer and electrodes adhered to both sides. The PTC material layer comprises a polymer substrate and conductive fillers uniformly dispersed within the polymer substrate. Overcurrent protection elements used in high-temperature environments typically use fluorinated polymers as the polymer substrate. Simultaneously, to achieve low resistance, conductive ceramic powder can be used as the conductive filler. Because the mixture of conductive ceramic powder and fluorinated polymers readily produces hydrofluoric acid at high temperatures, magnesium hydroxide (Mg(OH)2) is generally added to prevent the generation of hydrofluoric acid and its impact on element characteristics. However, such a PTC material layer system, comprising fluorinated polymers, conductive ceramic powder, and magnesium hydroxide, exhibits a negative temperature coefficient effect after element trip; that is, after element trip, the resistance gradually decreases as the temperature gradually increases, making it impossible for the element to completely interrupt the current.

[0004] Furthermore, modern handheld electronic products increasingly demand thinness and lightness, placing stricter constraints on the size and thickness of active and passive components. However, as the top surface area of ​​the PTC material layer shrinks, the component's resistance increases, and its voltage withstand capability decreases. Consequently, overcurrent protection components can no longer withstand high currents and high power. Moreover, as the thickness of the PTC material layer decreases, the component's voltage withstand capability becomes insufficient. Clearly, small-sized overcurrent protection components are prone to burnout in practical applications.

[0005] In summary, conventional overcurrent protection components must suppress the NTC effect after triggering, withstand large currents and high power, and maintain sufficient voltage resistance to meet the requirements for application in high-temperature environments. Summary of the Invention

[0006] This invention provides an overcurrent protection element. By introducing fluorinated polymer, conductive ceramic filler, carbon-containing conductive filler, and internal filler, the NTC effect after element triggering can be effectively suppressed, and the overcurrent protection element's current-carrying capacity, power-carrying capacity, and voltage withstand characteristics can be increased. Furthermore, the reduction in element size does not lead to an increase in volume resistivity, making it ideal for applications in miniaturized electronic products. Therefore, the overcurrent protection element of this invention can be used in environments prone to high temperatures.

[0007] According to an embodiment of the present invention, an overcurrent protection element includes a first electrode layer, a second electrode layer, and a PTC material layer stacked therebetween. The PTC material layer has a volume resistivity of less than 0.05 Ω·cm and comprises a polymer substrate, a conductive ceramic filler, a carbon-containing conductive filler, and an inner filler. The polymer substrate comprises a fluorinated polymer with a melting point higher than 150°C, and the volume percentage of the polymer substrate is 45-60%. The conductive ceramic filler is dispersed in the polymer substrate, and the volume percentage of the conductive ceramic filler is 40-45%, with a volume resistivity of less than 500 μΩ·cm. The carbon-containing conductive filler is dispersed in the polymer substrate, and the volume percentage of the carbon-containing conductive filler is 0.5-5%. The inner filler is selected from any one of aluminum nitride, silicon carbide, zirconium oxide, boron nitride, graphene, alumina, or any mixture of the above materials, and the volume percentage of the inner filler is 2-10%. The overcurrent protection element has a current-to-area ratio of 0.215–0.26 A / mm² at 25°C. 2 The overcurrent protection element has a power handling capacity ratio of 5.1–6.5 W / mm² at 25°C. 2 .

[0008] In one embodiment, the value obtained by dividing the resistance value R_164℃ of the overcurrent protection element at 164℃ by the resistance value R_200℃ at 200℃ is defined as the resistance retention rate R. ％ The resistance retention rate R of the overcurrent protection element ％ The range is 2 to 10.

[0009] In one embodiment, the internal filler comprises boron nitride, and the resistivity retention rate R ％ Less than 5.

[0010] In one embodiment, the fluorinated polymer comprises at least one of polydifluoroethylene, polytetrafluoroethylene, polyfluorinated vinylidene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, perfluoroalkyl oxygen-modified tetrafluoroethylene, poly(chlorotrifluorotetrafluoroethylene), difluoroethylene-tetrafluoroethylene polymer, tetrafluoroethylene-perfluoromethylenedioxane copolymer, difluoroethylene-hexafluoropropylene copolymer, and difluoroethylene-hexafluoropropylene-tetrafluoroethylene trimer.

[0011] In one embodiment, the conductive ceramic filler is selected from at least one of tungsten carbide, titanium carbide, vanadium carbide, zirconium carbide, niobium carbide, tantalum carbide, molybdenum carbide, hafnium carbide, titanium boride, vanadium boride, zirconium boride, niobium boride, molybdenum boride, hafnium boride, or zirconium nitride.

[0012] In one embodiment, the overcurrent protection element can withstand 100 cycles of a 24V and 50A cycle life test without burning out.

[0013] In one embodiment, the top-view area of ​​the PTC material layer is 20–35 mm². 2 The thickness is 0.3 to 0.7 mm.

[0014] In one embodiment, the volume resistivity ρ_R1 max of the overcurrent protection element after one trigger is 0.026 to 0.033 Ω·cm.

[0015] The overcurrent protection element of this invention uses a fluorinated polymer, providing a suitable application for high-temperature environments. By using a specific ratio of polymer substrate, conductive ceramic filler, carbon-containing conductive filler, and internal filler, the NTC effect after element triggering can be suppressed simultaneously, achieving high current handling capacity, high power handling capacity, and high voltage withstand capability (≥24V). The size of the overcurrent protection element is reduced, but the volume resistivity does not increase, making it ideal for applications in miniaturized electronic products. Attached Figure Description

[0016] Figure 1 This invention illustrates an overcurrent protection element according to an embodiment of the present invention;

[0017] Figure 2 show Figure 1 Top view of the overcurrent protection element; and

[0018] Figure 3 Displays the resistance value-temperature curve of the overcurrent protection element.

[0019] The reference numerals in the attached figures are explained as follows:

[0020] 10 Overcurrent Protection Components

[0021] 11 PTC material layer

[0022] 12 First Electrode Layer

[0023] 13 Second electrode layer Detailed Implementation

[0024] To make the above and other technical contents, features and advantages of the present invention more apparent and understandable, relevant embodiments are provided below, and detailed descriptions are given in conjunction with the accompanying drawings.

[0025] Table 1 shows the formulation composition of each example (E1-E8) and comparative example (C1-C2) as a volume percentage. In the polymer substrate, polyvinylidene fluoride (PVDF) with a melting point of 165°C was selected. Product 761A comprises 40-50% of the volume of the PTC material layer; the polytetrafluoroethylene (PTFE) used is DuPont Zonyl ether with a melting point of 315℃. TMThe PTFE MP1000 product comprises 5.5% of the PTC material layer by volume. The conductive fillers in E1-E8 and C1-C2 all contain tungsten carbide (WC) and carbon black. Tungsten carbide is chosen to reduce the component's resistance; therefore, it must have a high volume percentage, comprising 40-45% of the PTC material layer. To improve the component's voltage withstand characteristics and increase its electrical stability, the conductive fillers in E1-E8 and C1-C2 may also contain a small amount of carbon black, comprising 4% of the PTC material layer by volume. In addition, E1 to E6 each added an inner filler, specifically aluminum nitride (AlN), silicon carbide (SiC), zirconium oxide (ZrO2), boron nitride (BN), graphene, and alumina (Al2O3) as inner fillers, respectively, accounting for 2.5% of the volume percentage of the PTC material layer. Compared to E4, Examples E7 and E8 increased the boron nitride (BN) content, increasing it to 5.6% and 8.6% of the volume percentage of the PTC material layer, respectively. C1 used magnesium hydroxide (Mg(OH)2), a common filler in conventional overcurrent protection elements, accounting for 2.5% of the volume percentage of the PTC material layer. C2 only used tungsten carbide and carbon black as conductive fillers, without adding any inner filler. In other words, in this experiment, tungsten carbide (WC) and carbon black are used as conductive fillers, while other added conductive or non-conductive fillers are defined as inner fillers. For example, the inner filler of Comparative Example C1 is magnesium hydroxide (Mg(OH)2), which is used as a flame retardant in conventional overcurrent protection elements.

[0026] Table 1 (Volume percentage, vol%)

[0027]

[0028]

[0029] The materials for each example and comparative example in Table 1 were added to a twin-screw mixer manufactured by HAAKE Corporation and mixed in the indicated volume percentages. The mixing temperature was set at 215°C, the premixing time was 3 minutes, and the mixing time was 15 minutes. The resulting conductive polymer was then hot-pressed at 210°C and 150 kg / cm². 2 The pressure is used to press it into a thin sheet. This sheet is then cut into squares approximately 20 cm x 20 cm, and pressed using a hot press at 210°C and 150 kg / cm². 2The pressure forces two nickel-plated copper foils to adhere to both sides of the thin sheet, and finally, a punch press is used to stamp out multiple PTC wafers, thus forming the overcurrent protection element described in this invention. In one embodiment, the overcurrent protection element 10 of this invention is as follows: Figure 1 As shown, Figure 2 Tie Figure 1 The above view shows the overcurrent protection element 10. The overcurrent protection element 10 includes a PTC material layer 11 composed of the conductive polymer and a first electrode layer 12 and a second electrode layer 13 composed of nickel-plated copper foil. The area "A×B" of the overcurrent protection element 10 is equal to the area of ​​the PTC material layer 11. In Examples E1-E8 and Comparative Examples C1-C2 of Table 1, the length "A" of the overcurrent protection element 10 is 7 mm and the width "B" is 5 mm, therefore the area is 35 mm². 2 The rectangular structure has a PTC material layer 11 with a thickness controlled at 0.7 mm.

[0030] In one embodiment, solder paste can be applied to the outer surfaces of the first and second electrode layers 12 and 13. Two copper electrode sheets with a thickness of 0.5 mm are placed on the solder paste on the outer surfaces of the first and second electrode layers 12 and 13 as external electrodes. The assembled component can then be reflowed at 300°C to obtain an axial-type or radial-lead type PTC component. Alternatively, notches can be etched into the first and second electrode layers 12 and 13 using relevant processes, followed by the fabrication of an insulating layer, an outer electrode layer, and vertical vias to form a surface-mount device (SMD) type PTC component.

[0031] After the PTC wafers with the above different formulations were irradiated with a light dose of 50 kJ (the light dose can be adjusted as needed and is not a limitation of this invention), the following resistance measurements were performed: (1) initial resistance value Ri; (2) resistance value R1 max after one trigger; (3) resistance value R_164℃ at 164℃; and (4) resistance value R_200℃ at 200℃. For each test sample, based on the above four resistance values ​​(R) and the thickness (L) and area (A) of the PTC material layer, and according to the resistance formula R=ρ×L / A, the corresponding volume resistivity ρ and ρ_R1 max can be calculated respectively and recorded in Table 2 below. In addition, R_164℃ / R_200℃ is calculated and defined as the resistance retention rate R. ％ (Resistance RetentionRatio), which is R ％=R_164℃ / R_200℃, to evaluate the degree of resistance decrease of the component at 200℃ relative to the resistance at 164℃. Here, 164℃ is the highest resistance point after one triggering operation when magnesium hydroxide is used as the internal filler. Figure 3 As shown. Ideally, as long as the resistance maintenance ratio is less than or equal to 1, there is no problem with the NTC effect after the component is triggered. The higher the resistance maintenance ratio, the more severe the NTC effect problem after the component is triggered.

[0032] Table 2

[0033]

[0034] Table 2 shows that Examples E1 to E8, using a high proportion of tungsten carbide (WC) and an appropriate proportion of carbon black, can achieve a volume resistivity ρ of less than 0.05 Ω·cm. Because Examples E1 to E8 use aluminum nitride (AlN), silicon carbide (SiC), zirconium oxide (ZrO2), boron nitride (BN), graphene, and alumina (Al2O3) as internal fillers, all of which have the technical effect of suppressing the NTC effect after element triggering, the resistance retention rate (R) of Examples E1 to E8 is high. ％ The resistance retention rate (R = 164℃ / 200℃) was 2-10, which was lower than that of comparative examples C1-C2. Furthermore, the test results showed that boron nitride (BN) and graphene had better suppression effects, especially boron nitride (BN), which had a better suppression effect than graphene. Further comparisons were made with E4, E7, and E8, which also had boron nitride (BN) added as an internal filler. The test results showed that the higher the amount of boron nitride (BN) added, the better the suppression effect, i.e., the resistance retention rate R... ％ The smaller the values ​​of E4, E7, and E8, the higher the resistance retention rate R can be. ％ The resistance drops to less than 5, or even less than 4 or less than 3. C1 uses magnesium hydroxide (Mg(OH)2), which is used in traditional overcurrent protection components, and the NTC effect is significant after the component is triggered. C2 only uses tungsten carbide and carbon black as conductive fillers, without adding any internal fillers, and also has the problem of a sharp drop in resistance value after the component is triggered.

[0035] See Figure 3 It displays the resistance-temperature curve (RT curve) of the overcurrent protection element. Figure 3The three curves in the table represent the RT curves using magnesium hydroxide (Mg(OH)2) or boron nitride (BN) as internal fillers, and without internal fillers, respectively. The PTC material formulations are shown as C1, E4, and C2 in Table 1. The horizontal axis represents temperature in Celsius (°C), and the vertical axis represents the resistance value on a logarithmic scale (Ω). Because the polymers used in C1, E4, and C2 are all fluorinated polymers, such as PVDF and PTFE with melting points greater than 150°C, the trip temperature of the overcurrent protection element is approximately 150–160°C. For C1 with magnesium hydroxide as internal filler and C2 without internal filler, there is a significant NTC effect after element triggering, meaning the slope of the curve after element triggering is relatively steep. In contrast, for E4 with boron nitride as internal filler, the NTC effect after element triggering is suppressed, meaning the slope of the RT curve after element triggering is relatively gentle.

[0036] According to the present invention, the internal filler can be aluminum nitride (AlN), silicon carbide (SiC), zirconium oxide (ZrO2), boron nitride (BN), graphene, aluminum oxide (Al2O3) or any mixture of the above materials, and its volume percentage in the PTC material layer is 2 to 10%, for example 4%, 6% or 8%, all of which have the technical effect of suppressing the NTC effect after the element is triggered.

[0037] As can also be seen from Examples E1 to E8 in Table 2, although the top-view area of ​​the PTC material layer is reduced to 7mm × 5mm = 35mm 2 Furthermore, with the thickness controlled at 0.7 mm, the resistance value of the overcurrent protection element did not increase. Specifically, after one triggering, the volume resistivity (i.e., ρ_R1 max) of the overcurrent protection element is 0.026–0.033 Ω·cm, for example, 0.028 Ω·cm, 0.030 Ω·cm, or 0.032 Ω·cm. In practical applications, the top-view area of ​​the PTC material layer of this invention can be 20–35 mm². 2 (e.g., 25mm) 2 Or 30mm 2 A thickness of 0.3–0.7 mm (e.g., 0.4 mm, 0.5 mm, or 0.6 mm) will not cause an increase in the volume resistivity of the overcurrent protection element.

[0038] In addition, five PTC chips from E1 to E8 and C1 to C2 were selected as samples for voltage withstand and power handling capability verification. The following measurements were performed on the PTC chips: (1) trigger current I-trip@25℃ at 25℃; and (2) cycle life test at 24V, 50A for 100 cycles (on: 10 seconds; off: 60 seconds), where each cycle represents one trigger and recovery process. Based on the trigger current and component area, the trigger current value per unit area (A / mm²) can be calculated. 2 ), and the power per unit area (W / mm²) 2 Trigger current per unit area (A / mm²) 2 This is equivalent to the current that can be withheld per unit area (A / mm²). 2 Table 3 shows the test results for each of the embodiments E1 to E8 and comparative examples C1 to C2.

[0039] Table 3

[0040]

[0041] As shown in Table 3, the overcurrent protection elements in Examples E1 to E8 used appropriate internal fillers, and the ratio of the current that the overcurrent protection element could withstand at 25°C to its area was 0.215–0.26 A / mm². 2 All of them can pass 100 cycles of 24V and 50A cycle life testing without burning out. Furthermore, the overcurrent protection elements of Examples E1 to E8 have a power-to-area ratio of 5.1 to 6.5 W / mm² at 25°C. 2 Comparative Example C1, while possessing a similar current-to-area ratio to E1-E8 and passing the cycle life test with a good power-to-area ratio, suffers from the NTC effect after triggering due to the use of magnesium hydroxide (Mg(OH)2) as the internal filler, as mentioned above. Comparative Example C2, lacking a suitable internal filler, failed the cycle life test and burned out during the test.

[0042] In summary, the polymer used in the PTC material layer of the overcurrent protection element of this invention is a fluorinated polymer with a volume percentage of 45-60%, or for example, 47%, 50%, 53%, 56%, or 59%; the conductive ceramic filler can be, for example, tungsten carbide (WC), with a volume percentage of 40-45%, or for example, 41%, 43%, or 44%; the carbon-containing conductive filler can be, for example, carbon black, with a volume percentage of 0.5-5%, or for example, 1%, 2%, or 4%; the internal filler can be aluminum nitride (AlN), silicon carbide (SiC), zirconium oxide (ZrO2), boron nitride (BN), graphene, alumina (Al2O3), or any mixture of the above materials, with a volume percentage of 2-10%, or for example, 4%, 6%, or 8%. Therefore, the overcurrent protection element of this invention can suppress the NTC effect after element triggering, such as the resistance maintenance rate R. ％ The current-to-area ratio at 25°C is 0.215–0.26 A / mm², ranging from 2 to 10. 2 For example, 0.22A / mm 2 0.23A / mm 2 0.24A / mm 2 Or 0.25A / mm 2 It can withstand 24V and 50A cycle tests without burning out, while also achieving excellent electrical characteristics such as high voltage resistance, high current handling capacity per unit area, and high power handling capacity per unit area. Because the component's voltage resistance can be increased to 24V, the power handling capacity per unit area is also increased to 5.1–6.5 W / mm². 2 , such as 5.5W / mm 2 Or 6W / mm 2 Furthermore, the top-view area of ​​the PTC material layer is reduced to 20–35 mm. 2 (e.g., 25mm) 2 Or 30mm 2 With a thickness of 0.3–0.7 mm (e.g., 0.4 mm, 0.5 mm, or 0.6 mm), after the element is triggered once, the volume resistivity (i.e., ρ_R1 max) of the overcurrent protection element is 0.026–0.033 Ω·cm, for example, 0.028 Ω·cm, 0.030 Ω·cm, or 0.032 Ω·cm, and the volume resistivity does not increase.

[0043] The overcurrent protection element of this invention is used in high-temperature environments, so the fluorinated polymer system is preferably selected with a melting point greater than 150°C. The fluorinated polymer added in this invention is not limited to PVDF and PTFE; other fluorinated polymers with similar properties and melting points higher than 150°C are also covered by this invention. Examples include: polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (PETFE), perfluoroalkoxy modified tetrafluoroethylenes (PFA), poly(chlorotri-fluorotetrafluoroethylene) (PCTFE), vinylide-tetrafluoroethylene copolymer (VF-2-TFE), poly(vinylidene fluoride), tetrafluoroethylene-perfluorodioxole copolymers, and vinylide-hexafluoropropylene copolymers. Fluorinated polymers with different melting points can be selected, such as vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, etc. Due to the characteristics of different melting points, a smoother resistance-temperature curve (RT curve) can be obtained, improving the stability of cycle life testing and better voltage withstand characteristics.

[0044] The conductive ceramic filler is not limited to tin carbide (WC) and can be selected from metal carbides, metal borides, or metal nitrides with a volume resistivity of less than 500 μΩ·cm. For example: titanium carbide (TiC), vanadium carbide (VC), zirconium carbide (ZrC), niobium carbide (NbC), tantalum carbide (TaC), molybdenum carbide (MoC), hafnium carbide (HfC), titanium boride (TiB2), vanadium boride (VB2), zirconium boride (ZrB2), niobium boride (NbB2), molybdenum boride (MoB2), hafnium boride (HfB2), or zirconium nitride (ZrN).

[0045] The overcurrent protection element described in this invention can suppress the NTC effect after element triggering, while achieving excellent electrical characteristics such as high voltage resistance, high current withstand capability per unit area, and high power withstand capability per unit area. It can withstand harsh high-temperature environments and is suitable for high-temperature overcurrent protection applications. In addition, the size of the overcurrent protection element is reduced, but the volume resistivity does not increase, making it very suitable for applications in miniaturized electronic products.

Claims

1. An overcurrent protection element, comprising: First electrode layer; A second electrode layer; as well as A PTC material layer is stacked between the first electrode layer and the second electrode layer, and its volume resistivity is less than 0.05 Ω·cm. The PTC material layer comprises: A polymer substrate comprising a fluorinated polymer with a melting point above 150°C, wherein the volume percentage of the polymer substrate is 45-60%. A conductive ceramic filler is dispersed in the polymer substrate, the volume percentage of the conductive ceramic filler is 40-45%, and its volume resistivity is less than 500µΩ·cm. A carbon-containing conductive filler is dispersed in the polymer matrix, wherein the volume percentage of the carbon-containing conductive filler is 0.5% to 5%; and An internal filler, selected from aluminum nitride, silicon carbide, zirconium oxide, boron nitride, graphene, alumina, or any mixture of the above materials, wherein the internal filler comprises 2-10% by volume; wherein the overcurrent protection element has a ratio of the current-carrying capacity at 25°C to the area of 0.215 to 0.26 A / mm 2 ; wherein the overcurrent protection element has a ratio of the withstanding power at 25°C to the area of 5.1 to 6.5 W / mm 2 ; The resistance value R_164℃ of the overcurrent protection element divided by the resistance value R_200℃ at 200℃ is defined as the resistance value maintenance rate R%. The resistance value maintenance rate R% of the overcurrent protection element is 2~10.

2. The overcurrent protection element according to claim 1, wherein the internal filler comprises boron nitride, and the resistance retention rate R % Less than 5.

3. The overcurrent protection element according to claim 1, wherein the fluorinated polymer comprises at least one of polydifluoroethylene, polytetrafluoroethylene, polyfluorinated vinylidene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, perfluorocarbon oxygen-modified tetrafluoroethylene, poly(chlorotrifluorotetrafluoroethylene), difluoroethylene-tetrafluoroethylene polymer, tetrafluoroethylene-perfluoromethylenedioxane copolymer, difluoroethylene-hexafluoropropylene copolymer, and difluoroethylene-hexafluoropropylene-tetrafluoroethylene trimer.

4. The overcurrent protection element according to claim 1, wherein the conductive ceramic filler is selected from at least one of tungsten carbide, titanium carbide, vanadium carbide, zirconium carbide, niobium carbide, tantalum carbide, molybdenum carbide, hafnium carbide, titanium boride, vanadium boride, zirconium boride, niobium boride, molybdenum boride, hafnium boride, or zirconium nitride.

5. The overcurrent protection element according to claim 1, wherein the overcurrent protection element can withstand 100 cycles of a 24V and 50A cycle life test without burning out.

6. The overcurrent protection element according to claim 1, wherein the top-view area of ​​the PTC material layer is 20~35mm². 2 The thickness is 0.3~0.7mm.

7. The overcurrent protection element according to claim 6, wherein the volume resistivity ρ_R1 max of the overcurrent protection element after one trigger is 0.026~0.033Ω·cm.

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