Surface-mounted overcurrent protection element

Abstract

A surface-adhesive overcurrent protection element includes at least one PTC material layer, a first conductive layer, a second conductive layer, a first electrode, a second electrode, at least one insulating layer, and a capping layer. The PTC material layer comprises a crystalline polymer and conductive fillers dispersed within the crystalline polymer. The first and second conductive layers are respectively disposed on the first and second surfaces of the PTC material layer. The first and second electrodes are electrically connected to the first and second conductive layers, respectively. An insulating layer is disposed between the first and second electrodes for electrical isolation. The capping layer comprises a fluorinated polymer material and covers the entire outer surface of the surface-adhesive overcurrent protection element.

Description

Technical Field

[0001] This invention relates to a surface-mount (SMD) overcurrent protection element, and more specifically, to a surface-mount overcurrent protection element with good resistance reproducibility. 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 applied 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, their resistance instantly increases to a high resistance state (at least 10 ohms). 4 (Above Ω), also known as trip, which reverses the excessive current to counteract it, thereby protecting the battery or circuit components.

[0003] Taking polymeric PTC materials as an example, carbon black is typically used as a conductive filler, dispersed between crystalline polymer particles. This crystal structure causes the carbon particles to be concentrated in the grain boundaries, where they are packed very tightly, allowing current to flow through these "carbon chains" through the insulating plastic polymer. Under normal room temperature conditions, these polymers contain a considerable number of carbon chains, thus forming conductive channels.

[0004] When an overcurrent causes the component temperature to rise beyond the phase transition temperature (e.g., melting point) of the polymer, the polymer expands, disrupting its crystalline structure and transforming it into an irregular state. This destroys the conductive carbon chain channels, preventing current conduction and causing a sharp increase in resistance—a phenomenon known as "trip."

[0005] When the temperature returns to below its phase transition temperature, the polymer recrystallizes, and the conductive carbon chains reform. However, in practice, due to the incomplete recovery of the expanded polymer, the conductive carbon chains cannot maintain their original conductivity, and therefore the resistance cannot return to its original low value. Furthermore, after multiple triggering cycles, there is a significant increase in resistance, indicating a problem with poor resistance recoverability or reproducibility.

[0006] To address the issue of poor resistance resilience or reproducibility, a common approach in traditional electronic component packaging is to encapsulate the component with an epoxy resin layer to prevent water and oxygen from entering and affecting its electrical characteristics. However, modern handheld electronic products increasingly demand thinness and miniaturization, placing stricter constraints on the size and thickness of active and passive components. Encapsulating an SMD overcurrent protection component with an epoxy resin layer would require a thickness of at least 2mm, which contradicts the trend towards miniaturization in SMD overcurrent protection components. Furthermore, the epoxy resin layer would cover the electrodes and conductive vias (e.g., the terminals) of the SMD overcurrent protection component. Figure 2 The conductive connectors 12 and 12' prevent the SMD overcurrent protection element from being soldered to the Protective Circuit Module (PCM) or circuit board, and solder cannot creep through the conductive vias on the end face. Clearly, using epoxy resin as an encapsulation material is unsuitable for SMD overcurrent protection elements. Even if manufacturers propose solutions to avoid covering the electrodes and conductive vias with epoxy resin layers, such manufacturing processes are extremely cumbersome, complex, and costly.

[0007] Furthermore, epoxy resin has its material limits in terms of water and oxygen blocking capabilities. Modern SMD overcurrent protection components require better encapsulation materials to enable them to have excellent resistance recovery or resistance reproducibility. Summary of the Invention

[0008] This invention provides a surface-mount overcurrent protection element that prevents water and oxygen from entering the element by covering its entire outer surface with a capping layer. Due to the extremely thin capping layer, the surface-mount overcurrent protection element is ideal for miniaturized electronic applications. The solderability of the element to PCMs or circuit boards is not affected by the capping layer. Furthermore, the surface-mount overcurrent protection element of this invention exhibits excellent resistive recovery and high current handling capacity per unit area.

[0009] According to an embodiment of the present invention, a surface-adhesive overcurrent protection element includes at least one PTC material layer, a first conductive layer, a second conductive layer, a first electrode, a second electrode, at least one insulating layer, and a capping layer. The PTC material layer has opposing first and second surfaces, and comprises at least one crystalline polymer and at least one conductive filler dispersed in the crystalline polymer. The first conductive layer is disposed on the first surface, and the second conductive layer is disposed on the second surface. The first electrode is electrically connected to the first conductive layer, and the second electrode is electrically connected to the second conductive layer. At least one insulating layer is disposed between the first and second electrodes to electrically isolate the first and second electrodes. The capping layer comprises a fluorinated polymer material and covers the entire outer surface of the surface-adhesive overcurrent protection element. The capping layer has a 10 2 ~10 5 The thickness of the surface-adhesive overcurrent protection element (nm) and its resistive resilience (R) after 336 hours in a high-temperature and high-humidity environment. ％ Between 0.85 and 1.20, the current-carrying capacity per unit area is 0.65 to 0.80 A / mm². 2 between.

[0010] In one embodiment, the crystalline polymer is selected from: high-density polyethylene, medium-density polyethylene, low-density polyethylene, polyethylene wax, ethylene polymer, polypropylene, polyvinyl chloride, polyvinyl fluoride, ethylene-acrylic acid copolymer, ethylene-acrylic ester copolymer, or copolymer of olefin monomers and ethylene alcohol monomers.

[0011] In one embodiment, the conductive filler is selected from: carbon black, nickel, cobalt, copper, iron, tin, lead, silver, gold, platinum, titanium carbide, tin 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, zirconium nitride, or mixtures, alloys, solid solutions, or core shells of the foregoing.

[0012] In one embodiment, the PTC material layer further includes a non-conductive filler selected from: zinc oxide, antimony oxide, aluminum oxide, silicon oxide, calcium carbonate, magnesium sulfate or barium sulfate, magnesium hydroxide, aluminum hydroxide, calcium hydroxide or barium hydroxide.

[0013] In one embodiment, the first or second conductive layer is copper foil, nickel foil, or nickel-plated copper foil.

[0014] In one embodiment, the first or second conductive layer is a conductive material or conductive composite material manufactured through electroplating, electrolysis, deposition, or plating processes.

[0015] In one embodiment, the insulating layer is made of epoxy resin containing glass fibers.

[0016] In one embodiment, the PTC material layer, the first conductive layer, the second conductive layer, the first electrode, and the second electrode are stacked, and the first or second conductive layer is an inner conductive line relative to the adjacent first or second electrode.

[0017] In one embodiment, the surface-adhesive overcurrent protection element further includes a first conductive connector and a second conductive connector. The first conductive connector includes a conductive through-hole, conductive blind hole, or conductive end face located at one end of the element and extends in a vertical direction to connect the first electrode and the first conductive layer. The second conductive connector includes a conductive through-hole, conductive blind hole, or conductive end face located at the other end of the element and extends in a vertical direction to connect the second electrode and the second conductive layer.

[0018] In one embodiment, the insulating layer has two layers respectively disposed on the surfaces of the first conductive layer and the second conductive layer.

[0019] In one embodiment, the first electrode includes a pair of first electrode layers disposed on the surfaces of insulating layers on the surfaces of the first conductive layer and the second conductive layer, and the second electrode includes a pair of second electrode layers disposed on the surfaces of insulating layers on the surfaces of the first conductive layer and the second conductive layer.

[0020] In one embodiment, the fluorinated polymer material is composed of fluorinated aliphatic polymers, fluorinated vinyl copolymers, fluorinated vinyl-vinyl ether copolymers, fluorocarbon polymers, or mixtures thereof.

[0021] In one embodiment, the fluorinated polymer material can be dissolved in fluorinated ether organic solvents.

[0022] In one embodiment, the fluorinated ether organic solvent is ethyl nonafluoroisobutyl ether, ethyl nonafluorobutyl ether, methyl nonafluoroisobutyl ether, methyl nonafluorobutyl ether, or a mixture thereof.

[0023] In one embodiment, the covering layer further comprises a nanofiller material, which is montmorillonite, silica, alumina, or a mixture thereof.

[0024] In one embodiment, the resistivity R of the surface-adhesive overcurrent protection element after 336 hours in a high-temperature and high-humidity environment of 40°C / 95% is... ％ Between 1.10 and 1.20, the current-carrying capacity per unit area is 0.65 to 0.75 A / mm². 2 between.

[0025] In one embodiment, the resistivity R of the surface-adhesive overcurrent protection element after 336 hours in a high-temperature and high-humidity environment of 65°C / 90% is... ％ Between 1.00 and 1.10, the current-carrying capacity per unit area is 0.65 to 0.75 A / mm². 2 between.

[0026] In one embodiment, the resistivity R of the surface-adhesive overcurrent protection element after 336 hours in a high-temperature and high-humidity environment of 85°C / 85% is... ％ Between 0.85 and 1.00, the current-carrying capacity per unit area is 0.75 to 0.80 A / mm². 2 between.

[0027] The surface-mount overcurrent protection element of this invention uses an extremely thin cover layer to cover the entire outer surface of the element, making it ideal for miniaturized electronic applications. It also prevents water and oxygen from entering the element, thereby providing excellent resistive resilience and high current handling capacity per unit area. Simultaneously, the cover layer does not affect the solderability of the element on PCMs or circuit boards. Attached Figure Description

[0028] Figures 1 to 8 These are schematic diagrams of various embodiments of the surface-adhesive overcurrent protection element of the present invention;

[0029] Figures 9A to 9C This is a schematic diagram of the manufacturing process of a surface-adhesive overcurrent protection element according to an embodiment of the present invention;

[0030] Figure 10 This is a schematic diagram of a surface-adhesive overcurrent protection element with a double-layer PTC material layer according to another embodiment of the present invention; and

[0031] Figure 11 This is a schematic diagram of a surface-adhesive overcurrent protection element according to an embodiment of the present invention after being covered with a covering layer.

[0032] The reference numerals in the attached figures are explained as follows:

[0033] 1-8, 90: Surface-mounted overcurrent protection elements

[0034] 9: Conductive composite material components

[0035] 10: PTC material layer

[0036] 11a: First conductive layer

[0037] 11b: Second conductive layer

[0038] 11c: Third conductive layer

[0039] 11d: Fourth conductive layer

[0040] 12: Conductive connectors

[0041] 12': Conductive connector

[0042] 12a, 12a': Conductive connectors

[0043] 12b, 12b': Conductive connectors

[0044] 13: First electrode

[0045] 13': Second electrode

[0046] 15: Insulation layer

[0047] 16, 16', 21: Etching lines

[0048] 17: Solder resist layer

[0049] 20: Conductive layer

[0050] 40: Copper foil

[0051] 60: Insulation layer

[0052] 71: PTC element

[0053] 131: First electrode layer

[0054] 131': Second electrode layer

[0055] 200: Overlay Detailed Implementation

[0056] 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.

[0057] This invention involves covering the entire periphery (i.e., the entire outer surface) of an SMD overcurrent protection element with a capping layer. The capping layer comprises a fluorinated polymer material that prevents water and oxygen from penetrating the element, thereby giving the element excellent resistance recovery and increasing the current-carrying capacity per unit area (A / mm²). 2 ).

[0058] The surface-adhesive overcurrent protection element applicable to this invention can have various different structures. For example, patent certificate number TWI441200 filed by the applicant on September 6, 2012, patent certificate number TWI433169 filed on April 1, 2014, and patent certificate number TWI581274 filed on July 29, 2016, are all incorporated herein by reference. However, this invention is not limited thereto, and any type of surface-adhesive overcurrent protection element is covered by this invention. The following will use… Figures 1-10 As an example, a surface-adhesive overcurrent protection element applicable to the present invention is described.

[0059] Figure 1This is a schematic diagram of a surface-adhesive overcurrent protection element 1 according to a first embodiment of the present invention, which is used to adhere to the surface of a substrate or circuit board (not shown). A first electrode 13 and a corresponding second electrode 13' are typically located on the same plane. The surface-adhesive overcurrent protection element 1 can be designed to include only one electrode group consisting of the first electrode 13 and the second electrode 13', so that only one specific surface of the surface-adhesive overcurrent protection element 1 is bonded to the substrate surface. This design is typically used where placement in confined spaces is required, and where unidirectional thermal insulation or conduction is necessary. In the surface-adhesive overcurrent protection element 1, the first electrode 13, conductive connector 12, first conductive layer 11a, PTC material layer 10, second conductive layer 11b, conductive connector 12', and second electrode 13' form a conductive path to connect an external component (not shown) and a power source (not shown). An insulating layer 15 is located between the first electrode 13 and the second electrode 13' to electrically isolate the first electrode 13 and the second electrode 13'. The conductive connector 12 can be a conductive through hole or a side-wrap-around conductive end face.

[0060] Figure 2This is a schematic diagram of a surface-adhesive overcurrent protection element 2 according to a second embodiment of the present invention. It is designed with an electrode group consisting of a first electrode layer 131 and a second electrode layer 131' on both its upper and lower surfaces. The first electrode 13 and the second electrode 13' can respectively form a positive and negative electrode group on the upper and lower surfaces of the surface-adhesive overcurrent protection element 2. The surface-adhesive overcurrent protection element 2 can be bonded to the substrate surface using either its upper or lower surface. Because this design has no top or bottom orientation, it is easier to process (e.g., resistor sorting, packaging, and component assembly onto a printed circuit board) without having to consider the orientation of the surface-adhesive overcurrent protection element 2. The insulating layer 15 is used to electrically isolate the first electrode 13 and the second electrode 13'. Specifically, the first conductive layer 11a and the second conductive layer 11b are located on the upper and lower surfaces of the PTC material layer 10, respectively; that is, the PTC material layer 10 is stacked between the first conductive layer 11a and the second conductive layer 11b. The first electrode 13 comprises a first electrode layer 131 including a pair of upper and lower surfaces forming the element 2, and the second electrode comprises a pair of second electrode layers 131' including a pair of upper and lower surfaces forming the element 2. The first electrode layer 131 and the second electrode layer 131' are located on the surface of the insulating layer 15. A first conductive connector 12 connects the pair of first electrode layers 131 and the first conductive layer 11a, and a second conductive connector 12' connects the pair of second electrode layers 131' and the second conductive layer 11b. In summary, the PTC material layer 10, the first conductive layer 11a, the second conductive layer 11b, the first electrode 13, and the second electrode 13' are stacked. The first conductive layer 11a is an inner conductive layer relative to its adjacent first electrode 13 or second electrode 13' (i.e., the upper electrode layers 131 and 131'), and the second conductive layer 11b is also an inner conductive layer relative to its adjacent first electrode 13 or second electrode 13' (i.e., the lower electrode layers 131 and 131').

[0061] Figure 3This is a schematic diagram of a surface-adhesive overcurrent protection element 3 according to a third embodiment of the present invention. The first conductive connector 12 or the second conductive connector 12' can be formed by metal electroplating onto the side of the element, thus creating a side-covered electrical conductor. Typically, the first conductive connector 12 is connected to the first conductive layer 11a and the pair of first electrode layers 131, while the second conductive connector 12' is connected to the second conductive layer 11b and the pair of second electrode layers 131'. In this embodiment, the upper first electrode layer 131 contacts the surface of the first conductive layer 11a. The lower second electrode layer 131' contacts the surface of the second conductive layer 11b. Alternatively, the first conductive connector 12 and the second conductive connector 12' can be designed to connect the electrodes 13, 13' to the conductive layers 11a, 11b by applying solder paste, electroplating, and then reflowing or thermally curing. In this embodiment, the first conductive connector 12 or the second conductive connector 12' can also form micropores, and then form conductive through holes (PTH) or metal filling holes by electroplating the hole walls to form conductive cylinders.

[0062] Figure 4 This is a schematic diagram of a surface-adhesive overcurrent protection element 4 according to a fourth embodiment of the present invention. The first electrode 13 includes a pair of first electrode layers 131, and the second electrode 13' includes a pair of second electrode layers 131'. A first conductive connector 12 connects the pair of first electrode layers 131 and the first conductive layer 11a, and a second conductive connector 12' connects the pair of second electrode layers 131' and the second conductive layer 11b. The first conductive layer 11a is formed by etching, and etching lines 16 (or etched areas) prevent it from short-circuiting with the second electrode 13' and the second conductive connector 12'. Similarly, the second conductive layer 11b is also formed by etching, and etching lines 16' (or etched areas) prevent it from short-circuiting with the first electrode 13 and the first conductive connector 12.

[0063] Figure 5 This is a schematic diagram of the surface-adhesive overcurrent protection element 5 according to the fifth embodiment of the present invention, similar to... Figure 1 As shown, this embodiment relates to an SMD overcurrent protection element with a single-sided electrode. The conductive connector 12 connects the first conductive layer 11a, the third conductive layer 11c, and the first electrode 13 via conductive vias or conductive pillars. The third conductive layer 11c is formed by etching, and it forms electrical isolation from the second conductive layer 11b through etch lines 16' (or etched areas). The second metal foil 11b is connected to the second electrode 13' via the conductive connector 12'. This third conductive layer 11c is attached to the PTC material layer 10 and is on the same plane as the second conductive layer 11b. In one embodiment, the surface of the first conductive layer 11a is covered with a thin insulating layer 15, such as insulating varnish or lettering ink.

[0064] Figure 6 This is a schematic diagram of a surface-adhesive overcurrent protection element 6 according to a sixth embodiment of the present invention. The first electrode 13 includes a pair of first electrode layers 131 located on the upper and lower surfaces of the element 6, while the second electrode 13' includes a pair of second electrode layers 131' located on the upper and lower surfaces of the element 6. A first conductive connector 12 connects the first electrode layer 131, the first conductive layer 11a, and the third conductive layer 11c via conductive holes or conductive pillars. The third conductive layer 11c is formed by etching, and is electrically isolated from the second conductive layer 11b by etching lines 16' (or etching areas). The second conductive connector 12' connects the second electrode layer 131', the second conductive layer 11b, and the fourth conductive layer 11d via conductive holes or conductive pillars. The fourth conductive layer 11d is formed by etching, and is electrically isolated from the first conductive layer 11a by etching lines 16 (or etching areas). Typically, the fourth conductive layer 11d is attached to the PTC material layer 10 and is on the same plane as the first conductive layer 11a.

[0065] Figure 7 This is a schematic diagram of a surface-adhesive overcurrent protection element 7 according to a seventh embodiment of the present invention. The overcurrent protection element 7 includes a PTC element 71, a first conductive connector 12a, a second conductive connector 12a', a first electrode 13, and a second electrode 13'. The PTC element 71 includes a first conductive layer 11a, a second conductive layer 11b, and a PTC material layer 10 stacked between the first conductive layer 11a and the second conductive layer 11b. The first electrode 13 includes a pair of first electrode layers 131 located on the upper and lower surfaces of the element 7, and the second electrode 13' includes a pair of second electrode layers 131' located on the upper and lower surfaces of the element 7. An insulating layer 15 covers the PTC element 7. The conductive connector 12a (e.g., a conductive via or a conductive end face) connects the pair of first electrode layers 13; the conductive connector 12b (e.g., a conductive post or a conductive hole) connects the first conductive layer 11a and the upper first electrode layer 131. A conductive connector 12a' (e.g., a conductive via or a conductive end face) connects the pair of second electrode layers 131', and a conductive connector 12b' (e.g., a conductive post or a conductive hole) connects the second conductive layer 11b and the underlying second electrode layer 131'.

[0066] Figure 8 This is a schematic diagram of the surface-adhesive overcurrent protection element 8 according to the eighth embodiment of the present invention. Similar to... Figure 2The structure differs in that it adds a conductive connector 12b connecting the upper first electrode layer 131 and the first conductive layer 11a, and a conductive connector 12b' connecting the lower second electrode layer 131' and the second conductive layer 11b, thereby increasing heat conduction or heat dissipation. Additionally, if the first electrode layer 131 and the second electrode layer 131' are copper layers, they can be covered with tin layers 132 and 132' to improve soldering performance. An insulating solder resist layer 17 can be provided between the upper and lower first electrode layer 131 and the second electrode layer 131'.

[0067] The following will illustrate the fabrication process of the surface-mount overcurrent protection element of the present invention using an embodiment. Those skilled in the art can also apply substantially the same or similar processes to fabricate the SMD structure of the above embodiment or other SMD elements with slightly different structures.

[0068] The manufacturing process of the surface-adhesive overcurrent protection element of the present invention is illustrated as follows: First, the feed temperature of the batch mixer (Haake-600) is set at 160°C, and the feeding time is 2 minutes. The feeding procedure is to add a certain amount of crystalline polymer, stir for a few seconds, and then add conductive filler. The mixer rotates at 40 rpm. After 3 minutes, the speed is increased to 70 rpm, and mixing continues for 7 minutes before discharge, thus forming a conductive composite material with PTC properties. The conductive composite material is placed symmetrically into a mold with an outer steel plate and a middle thickness of 0.35 mm. A layer of Teflon release cloth is placed on both the top and bottom of the mold. Pre-compression is performed for 3 minutes at a pre-compression pressure of 50 kg / cm². 2 The temperature is 160℃. After venting, pressing is performed for 3 minutes, with the pressing pressure controlled at 100 kg / cm². 2 The temperature was 160℃. The pressing process was then repeated once more to form a PTC composite material layer, with a pressing time of 3 minutes and a pressing pressure controlled at 150 kg / cm². 2 The temperature is 160℃.

[0069] Reference Figure 9A The next step is to cut the PTC composite layer into 20×20cm pieces. 2A square PTC material layer 10 is formed, and then two conductive layers 20 are directly physically contacted on the upper and lower surfaces of the PTC material layer 10, symmetrically covering the surface of the PTC material layer 10 from top to bottom. The two conductive layers 20 can utilize a rough surface with nodular protrusions (not shown) to directly physically contact the PTC material layer 10. In other words, both surfaces of the conductive layer 20 can be smooth, but it is more commonly used that the conductive layer contains one smooth surface and one rough surface, with the rough surface with nodular protrusions serving as the inner surface for direct physical contact with the PTC material layer 10. Afterwards, a special cushioning material such as Teflon release cloth and a stainless steel plate (not shown) are sequentially added to the outer side of the symmetrically covered conductive layers 20 to form a multi-layer structure, and then pressed again for 3 minutes at an operating pressure of 60 kg / cm². 2 The temperature was 180℃. After hot pressing, the multilayer structure was then cold-pressed at room temperature for 5 minutes under the same pressure. After pressing, the sheet-like composite material formed by the two conductive layers 20 and the PTC material layer 10 was removed and then irradiated with 50KGy of γ-rays to form a structure like... Figure 9A The conductive composite material element 9 is shown.

[0070] In one embodiment, the conductive layer 20 on the surface of the conductive composite material element 9 is etched to produce etch lines 21 (see Figure 21). Figure 9B To form a first conductive layer 11a on one surface of the PTC material layer 10 and a second conductive layer 11b on the other surface, an insulating layer 15 (e.g., epoxy resin containing glass fiber, FR-4) is then applied over the etched conductive layers 11a and 11b, and a copper foil 40 is applied over the surface of the insulating layer 15. The process is then carried out at 180°C and 60 kg / cm². 2 After hot pressing under pressure for 30 minutes, the result is as follows: Figure 9B The composite material shown includes a PTC material layer 10.

[0071] Reference Figure 9CNext, the upper and lower copper foils 40 are etched to produce two first electrode layers 131 and two corresponding second electrode layers 131'. Conductive through holes (PTHs) are then formed within these holes using a drilling and electroplating method, resulting in first conductive connectors 12 and second conductive connectors 12'. Specifically, the first electrode 13 includes the pair of first electrode layers 131, and the second electrode 13' includes the pair of second electrode layers 131'. The first conductive connector 12 is electrically connected to the first conductive layer 11a and the first electrode layer 131, while the second conductive connector 12' is electrically connected to the second conductive layer 11b and the second electrode layer 131'. Afterward, an insulating layer 60 (using UV-curable coating) is applied between the first electrode 13 and the second electrode 13' as an insulating coating (i.e., solder resist) between the electrodes 13 and 13', thus forming a PTC substrate. After being cured by ultraviolet light, the PTC board is cut to the size of the surface-adhesive element to be used, thus producing a surface-adhesive overcurrent protection element 90 of the present invention.

[0072] In addition to the above-described embodiments containing a single PTC material layer 10, the present invention also includes surface-adhesive overcurrent protection elements made of PTC material layers 10 with other numbers of layers.

[0073] Figure 10 An example of a surface-adhesive overcurrent protection element comprising two PTC material layers is illustrated. The fabrication process is as follows: First, two conductive composite material elements 9 are taken. The conductive layers 11a and 11b on the surface of the first conductive composite material element 9 are etched to create etching lines. Then, a first insulating layer 15 (in this embodiment, epoxy resin containing glass fiber is used) is applied between the conductive layers 11a and 11b and the etched other conductive composite material element 9. Afterward, a copper foil is applied to the surfaces of both the upper and lower insulating layers 15, and the element is then subjected to a temperature of 180°C and a pressure of 60 kg / cm². 2After hot pressing under pressure for 30 minutes and cooling, a multilayer composite material containing two PTC material layers 10 is obtained. The copper foil is etched to produce two first electrode layers 131 and two corresponding second electrode layers 131'. Specifically, the first electrode 13 includes the pair of first electrode layers 131, and the second electrode 13' includes the pair of second electrode layers 131'. Next, a first conductive connector 12 and a second conductive connector 12' are produced by drilling and electroplating. The first conductive connector 12 is electrically connected to the conductive layer 11a and the pair of first electrode layers 131' in each conductive composite material element 9, while the second conductive connector 12' is electrically connected to the conductive layer 11b and the second electrode layer 131' in each conductive composite material element 9. In one embodiment, a second insulating layer 60 (here, a UV-cured coating) is applied between the first electrode 13 and the second electrode 13' as an insulating coating (i.e., a solder resist layer). After UV curing, the surface-adhesive element is cut to the size of the desired application to produce a surface-adhesive overcurrent protection element containing multiple PTC material layers 10 or multiple PTC elements 9.

[0074] The PTC material layer 10 in the above embodiments comprises a crystalline polymer and conductive fillers dispersed therebetween. The crystalline polymer may be a crystalline polyolefin polymer (e.g., high-density polyethylene, medium-density polyethylene, low-density polyethylene, polyethylene wax, ethylene polymer, polypropylene, polyvinyl chloride, polyvinyl fluoride, copolymers of olefin monomers and acrylic monomers (e.g., ethylene-acrylic acid copolymer, ethylene-acrylic ester copolymer) or copolymers of olefin monomers and vinyl alcohol monomers (e.g., ethylene-vinyl alcohol copolymer), and one or more polymer materials may be selected.

[0075] For example, in the application of safety protection for overcharge of lithium-ion batteries, in order to achieve the purpose of low-temperature protection, the PTC overcurrent protection element must generally be able to trigger a reaction at a low temperature. Therefore, in addition to traditionally low-melting-point crystalline polymers such as low-density polyethylene, the PTC material layer can also be selected. Alternatively, one or more crystalline polymer materials can be used, for example, containing at least one crystalline polymer with a melting point below 115°C. The aforementioned low-density polyethylene can be polymerized using conventional Ziegler-Natta catalysts, Metallocene catalysts, or other catalysts, or it can be copolymerized from ethylene monomers with other monomers such as butene, hexene, octene, acrylic acid, or vinyl acetate. However, sometimes, in order to achieve higher temperature protection or other special purposes, the composition of the PTC material layer may also use high-melting-point crystalline polymer materials, such as polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), polytetrafluoroethylene (PTFE), and polychlorotrifluoroethylene (PCTFE).

[0076] The aforementioned crystalline polymers may also contain functional groups, such as acid groups, anhydride groups, halogen groups, amine groups, unsaturated groups, epoxy groups, alcohol groups, amide groups, metal ions, ester groups, acrylate groups, or salt groups; antioxidants, crosslinking agents, flame retardants, waterproofing agents, or anti-arc agents may also be added to the PTC material layer to enhance the material's polarity, electrical properties, mechanical bonding properties, or other properties, such as water resistance, high temperature resistance, crosslinking, and antioxidant properties.

[0077] The conductive filler can be carbon black, metal powder, or conductive ceramic powder. The metal powder can be selected from nickel, cobalt, copper, iron, tin, lead, silver, gold, platinum, or other metals and their alloys. The conductive ceramic powder can be selected from metal carbides, such as titanium carbide (TiC), tin carbide (WC), vanadium carbide (VC), zirconium carbide (ZrC), niobium carbide (NbC), tantalum carbide (TaC), molybdenum carbide (MoC), and hafnium carbide (HfC); or selected from metal borides, such as titanium boride (TiB2), vanadium boride (VB2), zirconium boride (ZrB2), niobium boride (NbB2), molybdenum boride (MoB2), and hafnium boride (HfB2); or selected from metal nitrides, such as zirconium nitride (ZrN). In other words, the conductive filler of the present invention can be selected from mixtures, alloys, hard alloys, solid solutions, or core-shells formed by physical or chemical means from the aforementioned metals or conductive ceramics.

[0078] The metal powder or conductive ceramic powder used in this invention can exhibit various particle shapes, such as spherical, cubic, flake, polygonal, spiky, rod, coral-like, nodular, grape-like, mushroom-like, and filamentous, with an aspect ratio between 1 and 1000. The shape can be either high-structure or low-structure powder. Generally speaking, high-structure conductive fillers can enhance the resistance reproducibility of PTC materials, while low-structure conductive fillers can enhance the voltage withstand capability of PTC materials.

[0079] In addition, to improve voltage withstand capability, the PTC material layer 10 of this invention may be supplemented with a non-conductive filler. The non-conductive filler is primarily selected from inorganic compounds with flame-retardant or arc-resistant effects (e.g., zinc oxide, antimony oxide, aluminum oxide, silicon oxide, calcium carbonate, magnesium sulfate, or barium sulfate) or compounds containing hydroxyl groups (OH) (e.g., magnesium hydroxide, aluminum hydroxide, calcium hydroxide, or barium hydroxide). The non-conductive filler, being an inorganic compound, also functions to control resistance reproducibility.

[0080] Conductive layers 11a and 11b can be made of metal foil, such as commonly used copper foil, nickel foil, or nickel-plated copper foil. Alternatively, conductive layers 11a and 11b can also be conductive materials or conductive composite materials produced through electroplating, electrolysis, deposition, or coating thickening processes.

[0081] Conductive connectors 12, 12', 12a, and 12a' are primarily made of metallic material and can be one or more cylindrical or partially cylindrical, elliptical or partially elliptical cylindrical, planar, sheet-like, or other shapes and structures. Conductive connectors 12, 12', 12a, and 12a' can be formed within vias, blind vias, or wrapped around all or part of the sides of the component, forming conductive vias, conductive blind vias, or conductive end faces. For SMD overcurrent protection components with only single-sided electrodes, the conductive layer of the uppermost PTC material layer can be completely exposed, or its surface can be covered only with a thin layer of insulating material, such as insulating varnish or lettering ink.

[0082] The insulating layer 15 can be a composite material of epoxy resin and glass fiber, such as FR-4, which can also serve as an adhesive for bonding the conductive layers to the surfaces of the various PTC material layers 10. Besides epoxy resin, other adhesive insulating layers can also be used, such as nylon, polyvinyl acetate, polyester, and polyimide. The insulating layer 60 can typically be made of thermosetting or UV-curing acrylic resin.

[0083] To verify the resistive recovery of the SMD overcurrent protection element covered with a capping layer, the PTC material layer 10 and the conductive composite element 9 were prepared according to the formulation components shown in volume percentage in the examples (E1-E2) and comparative examples (C1-C2) in Table 1 below. Two conductive composite elements 9 were then used to fabricate the following... Figure 10 The image shows a two-layer SMD overcurrent protection element with PTC material. The top-view dimensions of the SMD overcurrent protection element are 12mil × 6mil, and it has two PTC material layers. The calculated area is 3mm × 1.5mm × 2 = 9.0mm². 2 The crystalline polymer used is high-density polyethylene (HDPE), and the conductive filler dispersed in the HDPE is tungsten carbide (WC). For Examples E1-E2, the SMD overcurrent protection element with two layers of PTC material is immersed in a fluorinated polymer solution for approximately one second, then immediately removed and air-dried at room temperature. This forms a covering layer 200 on the entire outer surface of the SMD overcurrent protection element. Figure 11As shown. The fluorinated polymer solution used in Examples E1-E2 includes 10% by weight of fluorinated aliphatic polymer and 90% by weight of ethyl nonafluoroisobutyl ether. In Comparative Examples C1-C2, the SMD overcurrent protection components did not undergo this encapsulation step; therefore, the outer surface of the component was not covered with an encapsulation material layer or a capping layer. In practical applications, the volume percentage of HDPE in the PTC material layer can be 50-60%, and the volume percentage of tungsten carbide can be 40-50%.

[0084] Table 1

[0085] HDPE (vol%) WC (vol%) E1 55.0 45.0 E2 53.7 46.3 C1 55.0 45.0 C2 53.7 46.3

[0086] In one embodiment, the fluorinated polymer solution of the present invention comprises a fluorinated polymer material and a fluorinated ether organic solvent, wherein the weight percentages are 10-20% and 80-90%, respectively. The fluorinated polymer material is soluble in the fluorinated ether organic solvent. The fluorinated polymer material may be a fluorinated aliphatic polymer, a fluorinated vinyl copolymer, a fluorinated vinyl-vinyl ether copolymer, a fluorocarbon polymer, or a mixture thereof. The fluorinated ether organic solvent may be ethyl nonafluoroisobutyl ether, ethyl nonafluorobutyl ether, methyl nonafluoroisobutyl ether, methyl nonafluorobutyl ether, or a mixture thereof.

[0087] In another embodiment, the fluorinated polymer solution may further include a nanofiller material, which also has the technical effect of preventing water and oxygen from entering the SMD overcurrent protection element. The nanofiller material can be montmorillonite, silica, alumina, or a mixture thereof. However, because the nanofiller material cannot dissolve in fluorinated ether organic solvents, its weight percentage cannot be too high. In this embodiment, the weight percentages of the fluorinated polymer material, the fluorinated ether organic solvent, and the nanofiller material in the solution are 10–20%, 70–90%, and 0–10%, respectively.

[0088] Regarding Examples E1 to E2, as described above, the capping layer covers the entire outer surface of the SMD overcurrent protection element. Because the content of the fluorinated polymer material in the fluorinated polymer solution is low, after the fluorinated polymer solution is coated on the entire outer surface of the element, the capping layer formed after solvent evaporation only has a thickness of 10%. 2 ~10 5 A thickness of nm, for example, 10 3 nm or 10 4The capping layer has a thickness of nm. The fluorine atoms in the fluorine-containing polymer are hydrophobic, thus the capping layer can prevent moisture from entering the component; the capping layer also has a certain thickness, thus preventing oxygen from entering the component. Furthermore, when SMD overcurrent protection components are soldered to the circuit board, since the solder is usually composed of tin or its alloy, and the reflow oven temperature is controlled at a high temperature of 150–300°C, the material properties of tin allow tin or its alloy to penetrate through the capping layer under this high-temperature reflow environment. Therefore, the capping layer does not affect the solderability of the component on the circuit board, nor does it affect the solder crawling ability of tin or its alloy in the conductive vias on the component end face. In other words, compared to using epoxy resin as the encapsulation material, the capping layer of this invention has a thinner thickness, making it suitable for miniaturized electronic product applications. Additionally, due to the thickness of the capping layer and the material properties of the fluorine-containing polymer, the capping layer can prevent water and oxygen from entering the SMD overcurrent protection component, while not affecting the soldering of the component to the PCM or circuit board using surface mount technology (SMT).

[0089] For the SMD overcurrent protection components of the above embodiments E1 to E2 covered with a cover layer and comparative examples C1 to C2 not covered with the cover layer, 5 samples were taken respectively, and reflowed twice to solder to the test board. After a thermosetting process at about 150°C for 5 minutes, it is equivalent to the component being tripped 3 times to simulate the maximum number of times the component might be tripped by the customer in order to install the component on the PCM or circuit board. Then the following resistance and trigger current measurements were performed: (1) Initial resistance value R at room temperature before high temperature and high humidity environment (40°C / 95%). bf (2) The resistance value R_96hr@40℃ / 95% after 96 hours in a high temperature and high humidity environment (40℃ / 95%); (3) The resistance value R_336hr@40℃ / 95% after 336 hours in a high temperature and high humidity environment (40℃ / 95%); (4) The trigger current I-trip@25℃ at room temperature after 336 hours in a high temperature and high humidity environment (40℃ / 95%). Record the above values ​​in Table 2 below. In addition, calculate R ％ =(R_336hr@40℃ / 95%) / (R bf ), and R ％ Defined as resistance recovery, this is used to evaluate the component's resistance relative to its initial value R after 336 hours in a high-temperature and high-humidity environment. bf The magnitude of the resistance change. Generally, the resistance of a component gradually increases over time. Therefore, ideally, the smaller the resistivity value, the smaller the increase in the component's resistance. In particular, R... ％=1.0 means that after the component is placed in a high temperature and high humidity environment, the resistance value remains the same as the initial resistance value R. bf The resistance remains exactly the same, meaning there is no increase in resistance. Conversely, the larger the resistance resilience value, the greater the increase in the component's resistance. Furthermore, based on the trigger current I-trip@25℃ and the component area (i.e., 3mm × 1.5mm × 2 = 9.0mm²),... 2 The trigger current value per unit area (A / mm²) can be calculated. 2 ), where the trigger current value per unit area (A / mm²) 2 The current per unit area (A / mm²) used to evaluate the component. 2 Taking E1 as an example, the trigger current per unit area at 25℃ (A / mm²) 2 = I-trip@25℃ / area = 6.17 / 9.0 = 0.69.

[0090] Table 2

[0091]

[0092] E1 and C1 have the same material composition, but the component in E1 has a capping layer while the component in C1 does not. Therefore, the test results of this group of samples (i.e., E1 and C1) can be compared. Table 2 shows the initial resistance value R of the component. bf The value of C1 is greater than that of E1. Furthermore, the resistance values ​​R_96hr@40℃ / 95% after 96 hours in a high-temperature, high-humidity environment, and R_336hr@40℃ / 95% after 336 hours in a high-temperature, high-humidity environment, also show that C1 is greater than E1. As for resistance recovery R... ％ The resistivity of E1 is smaller than that of C1 and closer to 1. That is, after 336 hours in a high-temperature, high-humidity environment, the resistance value of E1 compared to its initial resistance value R... bf It increased by 14.571%, while the resistance value of C1 compared to the initial resistance value R bf It increased by 35.657%. As for the current per unit area, the value of E1 is greater than that of C1.

[0093] E2 and C2 have the same material composition, but the components of E2 have a cover layer, while the components of C2 do not. Their test results are similar to those of the aforementioned groups (i.e., E1 and C1).

[0094] Therefore, by covering the entire outer surface of the SMD overcurrent protection element with a coating layer, water and oxygen can be prevented from entering the element, and the element has a small initial resistance value R. bfIt also has excellent resistive resilience, with the resistance value remaining relatively constant compared to the initial resistance value R. bf The variation is not significant. The cover layer can also increase the current that the component can withstand per unit area.

[0095] In another test verification, the high temperature and high humidity environment was changed to a temperature of 65℃ and a humidity of 90%. Similarly, the resistance and trigger current of the SMD overcurrent protection components E1~E2 and C1~C2 were measured and recorded in Table 3 below. Simultaneously, the resistance recovery R was calculated. ％ Trigger current per unit area (A / mm²) 2 ).

[0096] Table 3

[0097]

[0098] The test results in Table 3 are the same as those in Table 2. That is, the cover layer allows the SMD overcurrent protection element to have a smaller initial resistance value R. bf It also has excellent resistive resilience, with the resistance value remaining relatively constant compared to the initial resistance value R. bf The variation is not significant. The cover layer can also increase the current that the component can withstand per unit area.

[0099] In another test verification, the high temperature and high humidity environment was changed to 85℃ and 85% humidity. Similarly, the resistance and trigger current of the SMD overcurrent protection components E1~E2 and C1~C2 were measured and recorded in Table 4 below. Simultaneously, the resistance recovery R was calculated. ％ Trigger current per unit area (A / mm²) 2 ).

[0100] Table 4

[0101]

[0102] The test results in Table 4 are the same as those in Table 2. That is, the cover layer allows the SMD overcurrent protection element to have a smaller initial resistance value R. bf It also has excellent resistive resilience, with the resistance value remaining relatively constant compared to the initial resistance value R. bf The variation is not significant. The cover layer can also increase the current that the component can withstand per unit area.

[0103] In summary, this invention coats the entire outer surface of an SMD overcurrent protection element with a capping layer. This capping layer is formed by coating the entire outer surface of the element with a fluorinated polymer solution. The fluorinated polymer solution may include a fluorinated polymer material and a fluorinated ether organic solvent, with weight percentages of 10-20% and 80-90%, respectively. Alternatively, the fluorinated polymer solution may include a fluorinated polymer material, a fluorinated ether organic solvent, and a nanofiller material, with weight percentages of 10-20%, 70-90%, and 0-10%, respectively. The fluorinated polymer material is soluble in the fluorinated ether organic solvent. The capping layer has an extremely thin 10... 2 ~10 5 A thickness of nm, for example, 10 3 nm or 10 4 With a thickness of nm, it is ideal for miniaturized electronic applications. Furthermore, the capping layer does not interfere with the soldering of components to PCMs or circuit boards using surface mount technology (SMT). The capping layer prevents water and oxygen from penetrating SMD overcurrent protection components, thus ensuring excellent resistance recovery R. ％ and the current per unit area (A / mm²) 2 In particular, according to the present invention, after 336 hours in a high temperature and high humidity environment, the resistance value is compared with the initial resistance value R. bf The change was not significant. As shown in Table 2, the resistive resilience R of the component after 336 hours in a high-temperature, high-humidity environment of 40℃ / 95% was... ％ Between 1.10 and 1.20, the current-carrying capacity per unit area is 0.65 to 0.75 A / mm². 2 Between. As shown in Table 3, the resistive resilience R of the component after 336 hours in a high-temperature and high-humidity environment of 65℃ / 90% is... ％ Between 1.00 and 1.10, the current-carrying capacity per unit area is 0.65 to 0.75 A / mm². 2 Between. As shown in Table 4, the resistive resilience R of the component after 336 hours in a high-temperature and high-humidity environment of 85℃ / 85% is... ％ Between 0.85 and 1.00, the current-carrying capacity per unit area is 0.75 to 0.80 A / mm². 2 Between. Generally speaking, in actual use, the ambient temperature and humidity will not be more severe than those in Tables 1 to 3. Therefore, in actual use, regardless of the ambient temperature and humidity, the resistive resilience R of the component after 336 hours will be... ％ Between 0.85 and 1.20 (e.g., 0.90, 1.0, or 1.10), the current-carrying capacity per unit area is 0.65 to 0.80 A / mm². 2 Between (e.g., 0.70 or 0.75 A / mm)2 ).

[0104] The SMD overcurrent protection element of this invention, due to being covered by a capping layer, can prevent water and oxygen from entering the element, while achieving excellent resistance recovery and current handling capacity per unit area. The capping layer has a nanoscale thickness, making it ideal for miniaturized electronic applications. At the same time, the capping layer does not affect the solderability of the element on PCMs or circuit boards.

Claims

1. A surface-adhesive overcurrent protection element, comprising: At least one PTC material layer having opposing first and second surfaces, the PTC material layer comprising at least one crystalline polymer and at least one conductive filler dispersed in the crystalline polymer; A first conductive layer is disposed on the first surface; A second conductive layer is disposed on the second surface; A first electrode is electrically connected to the first conductive layer; A second electrode is electrically connected to the second conductive layer; At least one insulating layer is disposed between the first electrode and the second electrode to electrically isolate the first electrode and the second electrode; as well as A cover layer comprising a fluorinated polymer material, and the cover layer covering the entire outer surface of the surface-adhesive overcurrent protection element; The capping layer has a thickness of 102–105 nm; and The surface-adhesive overcurrent protection element exhibits a resistance recovery rate (R%) between 0.85 and 1.20 after 336 hours in a high-temperature and high-humidity environment.

2. The surface-adhesive overcurrent protection element according to claim 1, wherein the crystalline polymer is selected from: high-density polyethylene, medium-density polyethylene, low-density polyethylene, polyethylene wax, ethylene polymer, polypropylene, polyvinyl chloride, polyvinyl fluoride, ethylene-acrylic acid copolymer, ethylene-acrylic ester copolymer, or copolymer of olefin monomers and ethylene alcohol monomers.

3. The surface-adhesive overcurrent protection element according to claim 1, wherein the conductive filler is selected from: carbon black, nickel, cobalt, copper, iron, tin, lead, silver, gold, platinum, titanium carbide, tin 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, zirconium nitride, or mixtures, alloys, solid solutions, or core shells of the foregoing materials.

4. The surface-adhesive overcurrent protection element according to claim 1, wherein the PTC material layer further comprises a non-conductive filler selected from: zinc oxide, antimony oxide, aluminum oxide, silicon oxide, calcium carbonate, magnesium sulfate or barium sulfate, magnesium hydroxide, aluminum hydroxide, calcium hydroxide or barium hydroxide.

5. The surface-adhesive overcurrent protection element according to claim 1, wherein the first conductive layer or the second conductive layer is copper foil, nickel foil, or nickel-plated copper foil.

6. The surface-adhesive overcurrent protection element according to claim 1, wherein the first conductive layer or the second conductive layer is a conductive material or conductive composite material manufactured by electroplating, electrolysis, deposition or plating processes.

7. The surface-adhesive overcurrent protection element according to claim 1, wherein the insulating layer is made of epoxy resin containing glass fibers.

8. The surface-adhesive overcurrent protection element according to claim 1, wherein the PTC material layer, the first conductive layer, the second conductive layer, the first electrode and the second electrode are stacked, and the first or second conductive layer is an inner conductive circuit relative to the adjacent first or second electrode.

9. The surface-adhesive overcurrent protection element according to claim 1, further comprising a first conductive connector and a second conductive connector, the first conductive connector comprising a conductive through-hole, conductive blind hole or conductive end face located at one end of the element, and extending in a vertical direction to connect the first electrode and the first conductive layer; the second conductive connector comprising a conductive through-hole, conductive blind hole or conductive end face located at the other end of the element, and extending in a vertical direction to connect the second electrode and the second conductive layer.

10. The surface-adhesive overcurrent protection element according to claim 1, wherein the insulating layer has two layers respectively disposed on the surfaces of the first conductive layer and the second conductive layer.

11. The surface-adhesive overcurrent protection element according to claim 10, wherein the first electrode comprises a pair of first electrode layers disposed on the surfaces of insulating layers on the surfaces of the first conductive layer and the second conductive layer, and the second electrode comprises a pair of second electrode layers disposed on the surfaces of insulating layers on the surfaces of the first conductive layer and the second conductive layer.

12. The surface-adhesive overcurrent protection element according to claim 1, wherein the fluorinated polymer material is composed of fluorinated aliphatic polymers, fluorinated vinyl copolymers, fluorinated vinyl-vinyl ether copolymers, fluorocarbon polymers, or mixtures thereof.

13. The surface-adhesive overcurrent protection element according to claim 12, wherein the fluorinated polymer material is soluble in fluorinated ether organic solvents.

14. The surface-adhesive overcurrent protection element according to claim 13, wherein the fluorinated ether organic solvent is ethyl nonafluoroisobutyl ether, ethyl nonafluorobutyl ether, methyl nonafluoroisobutyl ether, methyl nonafluorobutyl ether, or a mixture thereof.

15. The surface-adhesive overcurrent protection element according to claim 1, wherein the covering layer further comprises a nanofiller material, the nanofiller material being montmorillonite, silica, alumina, or a mixture thereof.

16. The surface-adhesive overcurrent protection element according to claim 1, wherein the resistivity R% of the element after 336 hours in a high temperature and high humidity environment of 40°C / 95% is between 1.10 and 1.20, and the current withstandable per unit area is between 0.65 and 0.75 A / mm².

17. The surface-adhesive overcurrent protection element according to claim 1, wherein the resistivity R% of the element after 336 hours in a high temperature and high humidity environment of 65°C / 90% is between 1.00 and 1.10, and the current withstandable per unit area is between 0.65 and 0.75 A / mm².

18. The surface-adhesive overcurrent protection element according to claim 1, wherein the resistivity R% of the element after 336 hours in a high temperature and high humidity environment of 85°C / 85% is between 0.85 and 1.00, and the current withstandable per unit area is between 0.75 and 0.80 A / mm2.

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