Protective element and battery pack

Abstract

The present invention provides a protective element capable of ensuring insulation after fusing of a fuse element.　This protective element comprises an insulating substrate 2, a heating element 6 provided on the insulating substrate 2, an insulating layer 7 covering the heating element 6, an intermediate electrode 4 provided on the surface of the insulating substrate 2 and electrically connected to the heating element 6, a fuse element 3 mounted on the intermediate electrode 4, and a cap member 5 covering a surface 2a side of the insulating substrate 2. The cap member 5 is a molded article of a resin composition containing an insulating inorganic filler, the insulating inorganic filler is a glass fiber milled fiber, and the resin composition has a glass fiber milled fiber filling amount between 35 wt% and 45 wt%, inclusive.

Description

Protection Element and Battery Pack

[0001] The present technology relates to a protection element that is mounted on a current path and melts a fuse element by heating with a heating element to cut off the current path, and a battery pack using the same. This application claims priority based on Japanese Patent Application No. 2024-188967 filed in Japan on October 28, 2024, and this application is incorporated herein by reference.

[0002] Lithium-ion secondary batteries are batteries with high output and high energy density, and are used in small mobile devices such as notebook computers, mobile phones, and smartphones. In recent years, they have been increasingly adopted in devices that require large capacity, large current, or high voltage, such as power tools, electric bicycles, electric motorcycles, electric vehicles, and household storage batteries.

[0003] However, since this battery uses an organic solvent and there is a risk of ignition and smoke generation when the operating range, such as the body temperature, input / output current, and charging voltage, is exceeded, it is common to incorporate a protection circuit using an electronic circuit and a protection element. As the protection element in the protection circuit, an FET that electrically turns on and off, a thermistor that senses temperature, and a fuse that physically cuts off the circuit are used. Among them, a fuse with a heating element is often used.

[0004] A protection element composed of a fuse with a heating element can, in addition to the function of cutting off with overcurrent like a general current fuse, melt and cut off the fuse element by heating the heating element when an electronic circuit senses an abnormality. Compared with a general current fuse that can only be cut by overcurrent, this protection element has the advantages of quickly cutting off in case of an abnormality, being able to easily set a safety margin circuitously considering battery characteristics, usage conditions, etc., and being able to melt and cut off the fuse element at the intended timing.

[0005] Figure 8 shows an example configuration of a surface-mount type protective element, where (A) is a plan view with the cap member omitted, (B) is a cross-sectional view, and (C) is a bottom view. The protective element 100 shown in Figure 8 comprises an insulating substrate 101, first and second electrodes 102 and 103 formed on the surface of the insulating substrate 101, a heating element 104 formed on the surface of the insulating substrate 101, an insulating layer 105 covering the heating element 104, an intermediate electrode 106 laminated on the insulating layer 105 and connected to the heating element 104, a fuse element 107 which is a fusible conductor mounted via a connecting material 110 made of various tin-based solder pastes across the first electrode 102, the intermediate electrode 106, and the second electrode 103, flux 111 applied on the fuse element 107, and a cap member 112 covering the surface of the insulating substrate 101 on which the fuse element 107 is mounted.

[0006] The first and second electrodes 102 and 103 are terminals connected to the current path of the external circuit to which the protection element 100 is connected, and are connected via castellation to the first and second external connection electrodes 102a and 103a formed on the back surface of the insulating substrate 101, respectively. The protection element 100 is incorporated into a part of the current path formed on the external circuit board by the connection of the first and second external connection electrodes 102a and 103a to connection electrodes provided on the external circuit board to which the protection element 100 is mounted.

[0007] The heating element 104 is a conductive material with relatively high resistance that generates heat when energized, and is made of materials such as nichrome, W, Mo, Ru, or materials containing these materials. The heating element 104 is connected to a heating electrode 108 formed on the surface of the insulating substrate 101. The heating electrode 108 is connected via castellation to a third external connection electrode 108a formed on the back surface of the insulating substrate 101. The protective element 100 is connected to an external power supply provided in the external circuit by the third external connection electrode 108a being connected to a connection electrode provided on the external circuit board on which the protective element 100 is mounted. The heating element 104 is constantly controlled to maintain current flow by a switch element or the like (not shown).

[0008] The heating element 104 is covered with an insulating layer 105 made of glass or the like, and an intermediate electrode 106 is formed on the insulating layer 105, so that it is superimposed on the intermediate electrode 106 via the insulating layer 105. In addition, a fuse element 107 connected between the first and second electrodes 102 and 103 is connected to the intermediate electrode 106 via a connecting material 110.

[0009] As a result, the protective element 100 is thermally connected by the superposition of the heating element 104 and the fuse element 107, and when the heating element 104 generates heat due to the flow of current, it can melt the fuse element 107.

[0010] The fuse element 107 is connected from the first electrode 102 through the intermediate electrode 106 to the second electrode 103, thereby forming part of the current path of the external circuit into which the protection element 100 is incorporated. The fuse element 107 melts due to self-heating (Joule heating) when a current exceeding its rating flows through it. Alternatively, the fuse element 107 melts due to the heat generated by the heating element 104, and the molten conductor condenses on the first and second electrodes 102, 103 and the intermediate electrode 106, causing it to melt. This interrupts the current between the first and second electrodes 102, 103.

[0011] Patent No. 5072796 Patent No. 5876346

[0012] In recent years, with the miniaturization of electronic components, protective elements have also become thinner. As protective elements become thinner, the height and top surface thickness of the cap member 112 are reduced, bringing the top surface of the cap member 112 closer to the fuse element 107. When the fuse element 107 melts and the molten conductor (not shown) condenses on the intermediate electrode 106, it becomes difficult to secure sufficient internal space between the molten conductor and the top surface. Therefore, when the heated fuse element 107 expands into a spherical shape, there is a risk that it will come into contact with the top surface of the cap member 112.

[0013] If the cap member 112 is made of a resin with poor heat resistance, when the fuse element 107 or its molten conductor, heated to a high temperature, comes into contact with the cap member 112, it may melt or deform, causing the cap member 112 to carbonize and form a conductive path, which could make it impossible to guarantee the insulation resistance after the fuse element 107 has blown.

[0014] Therefore, the objective of this technology is to provide a protective element that can ensure the insulation of a fuse element after it has blown, and a battery pack using the same.

[0015] To solve the above-mentioned problems, the protective element according to this technology comprises an insulating substrate, a heating element provided on the insulating substrate, an insulating layer covering the heating element, an intermediate electrode provided on the surface of the insulating substrate and electrically connected to the heating element, a fuse element mounted on the intermediate electrode, and a cap member covering the surface side of the insulating substrate. The cap member is a molded product of a resin composition containing an insulating inorganic filler, the insulating inorganic filler is glass fiber milled fiber, and the resin composition contains 35% by weight or more and 45% by weight or less of the glass fiber milled fiber.

[0016] Furthermore, the battery pack relating to this technology comprises one or more battery cells and a protective element connected to the charge / discharge path of the battery cells and blocking the charge / discharge path, wherein the protective element is the protective element described above.

[0017] According to this technology, by filling the resin composition constituting the cap member with an insulating inorganic filler, the amount of carbon in the resin component that carbonizes can be reduced. This prevents the continuous formation of conductive paths through carbonization via the top surface of the cap member, even when a fuse element or its molten conductor heated to a high temperature comes into contact with the cap member. Therefore, the protective element can maintain high insulation resistance after current interruption.

[0018] Figure 1 shows an example of a protective element to which this technology is applied, where (A) is a plan view of an example protective element with the cap member omitted, (B) is a cross-sectional view of (A) along A-A', and (C) is a bottom view. Figure 2 is a plan view of a protective element in which the fuse element melts due to the heat generated by the heating element, interrupting conductivity between the first and second electrodes, with the cap member omitted. Figure 3 is an external perspective view of the cap member. Figure 4 shows an example of a fuse element, where (A) is an external perspective view of a fuse element with a coating structure having a low-melting-point metal layer as the inner layer and a high-melting-point metal layer as the outer layer, and (B) is an external perspective view of a fuse element with a laminated structure having a low-melting-point metal layer as the lower layer and a high-melting-point metal layer as the upper layer. Figure 5 is a circuit diagram showing an example of the configuration of a battery pack. Figure 6 is a circuit diagram showing an example of the configuration of a protective element. Figure 7 shows a modified protective element, where (A) is a plan view with the cap member omitted, (B) is a cross-sectional view of A-A' shown in (A), and (C) is a bottom view. Figure 8 shows an example configuration of a surface-mount type protective element, where (A) is a plan view with the cap member omitted, (B) is a cross-sectional view, and (C) is a bottom view.

[0019] The protective element and battery pack to which this technology is applied will be described in detail below with reference to the drawings. It should be noted that this technology is not limited to the following embodiments, and various modifications are possible within the scope of the gist of this technology. Furthermore, the drawings are schematic, and the proportions of dimensions may differ from those of reality. Specific dimensions should be determined by referring to the following explanation. It should also be noted that there may be differences in the relationships and proportions of dimensions between different drawings.

[0020] Figure 1 shows an example of a protective element to which this technology is applied, where (A) is a plan view of the protective element 1 according to an example, with the cap member omitted, (B) is a cross-sectional view of (A) along A-A', and (C) is a bottom view. The protective element 1 to which this technology is applied comprises an insulating substrate 2, a heating element 6 provided on the insulating substrate 2, an intermediate electrode 4 provided on the surface 2a of the insulating substrate 2 and electrically connected to the heating element 6, a fuse element 3 mounted on the intermediate electrode 4, and a cap member 5 covering the surface 2a of the insulating substrate 2.

[0021] The cap member 5 is a molded product of a resin composition containing an insulating inorganic filler. This improves heat resistance, reduces the amount of carbon in the resin component that carbonizes, and prevents the continuous formation of conductive paths through carbonization via the top surface 5a of the cap member 5 even when the fuse element 3 or its molten conductor, heated to a high temperature, comes into contact with the cap member 5. Therefore, the protective element 1 can maintain high insulation resistance after current interruption.

[0022] [Flexural Modulus (MPa)] The cap member 5 has a flexural modulus (unit: MPa) of 13,000 MPa or more and 17,000 MPa or less, as specified in ISO 178. The flexural modulus can be seen as an indicator of the heat resistance of the cap member 5. If the flexural modulus is lower than 13,000 MPa, when the fuse element 3 or its molten conductor 3a, heated to a high temperature, comes into contact with the cap member 5, carbonization may occur, forming a conductive path, which may make it impossible to guarantee the insulation resistance after the fuse element 3 has melted. By setting the flexural modulus of the cap member 5 to 13,000 MPa or more, it has excellent heat resistance, and even when the fuse element 3 or its molten conductor 3a, heated to a high temperature, comes into contact with the cap member 5, the formation of a conductive path due to carbonization is suppressed, and high insulation resistance can be maintained. As will be described later, if the flexural modulus exceeds 17,000 MPa, there is a risk of impairing moldability.

[0023] In this technology, a test specimen (length: 80 mm, width: 10 mm, thickness: 4 mm) used for bending tests as defined in ISO 178 is used to represent the top surface covering the surface 2a of the insulating substrate 2 of the cap member 5, and the bending modulus (unit: MPa) is measured by performing a three-point bending test in a room temperature environment. The specific measurement conditions conform to ISO 178.

[0024] [Temperature of Deflection under Load (°C)] Alternatively, the cap member 5 has a temperature of deflection under load (°C) of 270°C or higher and 330°C or lower, as specified in ISO 75. The temperature of deflection under load can also be considered an indicator of the heat resistance of the cap member 5. If the temperature of deflection under load is lower than 270°C, the top surface 5a of the cap member 5 may bend inward due to the heat generated by the heating element 6, causing the heated fuse element 3 and its molten conductor 3a to come into contact with the cap member 5, carbonize, and form a conductive path, which may make it impossible to guarantee the insulation resistance after the fuse element 3 has melted. By setting the temperature of deflection under load of the cap member 5 to 270°C or higher, it is possible to maintain excellent heat resistance, prevent the heated fuse element 3 and its molten conductor 3a from coming into contact with the cap member 5 and forming a conductive path due to carbonization, and maintain high insulation resistance. As will be described later, if the temperature of deflection under load exceeds 330°C, there is a risk of impairing moldability.

[0025] In this technology, a test piece (length: 80 mm, width: 10 mm, thickness: 4 mm) used for measuring the load deflection temperature as specified in ISO 75 is used to represent the top surface 5a covering the surface 2a of the insulating substrate 2 of the cap member 5, and a constant load is applied to cause three-point bending. The temperature is raised at a constant rate, and the temperature (unit: °C) is read when the deflection reaches a specified deflection corresponding to the increment of bending strain. The specific measurement conditions conform to ISO 75.

[0026] The components of the protective element 1 shown in Figure 1 will be described in detail below. The protective element 1 shown in Figure 1 comprises an insulating substrate 2, a first electrode 11 and a second electrode 12 provided on the insulating substrate 2, a heating element 6 provided on the surface 2a of the insulating substrate 2, an insulating layer 7 covering the heating element 6, an intermediate electrode 4 provided between the first electrode 11 and the second electrode 12 on the surface 2a of the insulating substrate 2 and electrically connected to the heating element 6, a fuse element 3 mounted on the surfaces of the first electrode 11, the second electrode 12 and the intermediate electrode 4 and electrically connecting the first electrode 11 and the second electrode 12, and a cap member 5 covering the surface 2a side of the insulating substrate 2.

[0027] The protection element 1 is incorporated into an external circuit, such as a protection circuit for a lithium-ion secondary battery, so that the fuse element 3 forms part of the current path of the external circuit and interrupts the current path by melting due to the heat generated by the heating element 6 (see Figure 2). The protection element 1 also has a maximum current and rated voltage set according to the electronic device being used, and when power exceeding the set value is applied, the fuse element 3 heats up due to the current flow (Joule heating) and melts, thereby interrupting the conduction between the first and second electrodes 11 and 12.

[0028] Figure 2 is a plan view showing the state in the protective element 1 where the fuse element 3 melts due to the heat generated by the heating element 6, and the electrical connection between the first and second electrodes 11 and 12 is interrupted, with the cap member 5 omitted.

[0029] [Insulating Substrate] The insulating substrate 2 is formed from an insulating material such as alumina, glass ceramics, mullite, or zirconia. Alternatively, the insulating substrate 2 may be made from materials used for printed circuit boards, such as glass epoxy substrates or phenolic substrates. In this specification, the side of the insulating substrate 2 on which the fuse element 3 is mounted is referred to as the front surface 2a, and the side opposite to the side on which the fuse element 3 is mounted is referred to as the back surface 2b.

[0030] [First and Second Electrodes] A first electrode 11 and a second electrode 12 are formed on opposite ends of the surface 2a of the insulating substrate 2. The first electrode 11 and the second electrode 12 are each formed by a conductive pattern of Ag, Cu, or an alloy thereof. The first electrode 11 and the second electrode 12 can be formed, for example, by screen printing an Ag paste in a predetermined pattern and then firing it at a predetermined temperature.

[0031] The first electrode 11 is continuous with the first external connection electrode 15 formed on the back surface 2b of the insulating substrate 2 via castellation from the front surface 2a. The second electrode 12 is continuous with the second external connection electrode 16 formed on the back surface 2b of the insulating substrate 2 via castellation from the front surface 2a. In the surface-mount type protection element 1, when the protection element 1 is mounted on an external circuit board, the first and second external connection electrodes 15 and 16 are connected to connection electrodes provided on the external circuit board, thereby incorporating the fuse element 3 into a part of the current path formed on the external circuit board.

[0032] The first and second electrodes 11 and 12 are electrically connected via the fuse element 3, which is mounted on the fuse element 3 via various tin-based solder pastes and other conductive connecting materials 40. Furthermore, as shown in Figure 2, the connection between the first and second electrodes 11 and 12 is interrupted when the heating element 6 generates heat when current is applied, causing the fuse element 3 to melt, or when a large current exceeding the rating flows through the protection element 1, causing the fuse element 3 to melt due to self-heating (Joule heating).

[0033] [Heating Element] The heating element 6 is a conductive material with relatively high resistance that generates heat when current is passed through it, and is made of materials such as nichrome, W, Mo, Ru, or materials containing these. The heating element 6 can be formed by mixing powdered alloys, compositions, or compounds of these materials with a resin binder or the like to make a paste, forming a pattern on the insulating substrate 2 using screen printing technology, and then firing it. As an example, the heating element 6 can be formed by adjusting a mixed paste of ruthenium oxide paste, silver, and glass paste according to a predetermined voltage, forming a film over a predetermined area at a predetermined position on the surface 2a of the insulating substrate 2, and then firing it under appropriate conditions. The shape of the heating element 6 can be designed as appropriate, but as shown in Figure 1, it is preferable to make it substantially rectangular in accordance with the shape of the insulating substrate 2 in order to maximize the heating area.

[0034] Furthermore, the heating element 6 has one end 6a connected to the first lead electrode 17 and the other end 6b connected to the second lead electrode 18. The first lead electrode 17 is led out from the first heating element electrode 8 formed on one side edge of the surface 2a of the insulating substrate 2. The second lead electrode 18 is led out from the second heating element electrode 9 formed on the other side edge of the surface 2a of the insulating substrate 2. The first lead electrode 17 is led out from the first heating element electrode 8 along one end 6a of the heating element 6, and in the protective element 1 shown in Figure 1, it extends along one side edge of the heating element 6 which is formed in a substantially rectangular shape, and the other side edge of the heating element 6 is superimposed on it. Similarly, the second lead electrode 18 is led out from the second heating element electrode 9 along the other end 6b of the heating element 6, and in the protective element 1 shown in Figure 1, it extends along the other side edge of the heating element 6 which is formed in a substantially rectangular shape, and the other side edge of the heating element 6 is superimposed on it.

[0035] [Insulating Layer] The heating element 6, the first lead electrode 17, and the second lead electrode 18 are covered with an insulating layer 7. An intermediate electrode 4 is also formed on the insulating layer 7.

[0036] The insulating layer 7 is intended to protect and insulate the heating element 6. The insulating layer 7 is formed to be thin, for example, 10 to 40 μm thick, in order to efficiently transfer the heat from the heating element 6 to the intermediate electrode 4 and fuse element 3. The insulating layer 7 can be formed, for example, by applying and firing a glass-based paste.

[0037] The first heating element electrode 8 and the second heating element electrode 9 are formed on opposite side edges of the insulating substrate 2, different from the side edges on which the first and second electrodes 11 and 12 are provided. The first heating element electrode 8 is an electrode that serves as a power supply terminal to the heating element 6, and is connected to one end 6a of the heating element 6 via a first lead electrode 17, and is also continuous with a third external connection electrode 10 formed on the back surface 2b of the insulating substrate 2 via castellation. The second heating element electrode 9 is connected to the other end 6b of the heating element 6 via a second lead electrode 18, and is also connected to the intermediate electrode 4.

[0038] The first and second heating element electrodes 8 and 9, the first and second lead electrodes 17 and 18, and the intermediate electrode 4 can be formed by printing and firing a conductive paste such as Ag or Cu, similar to the first and second electrodes 11 and 12. Furthermore, by constructing each of these electrodes formed on the surface 2a of the insulating substrate 2 from the same material, they can be formed in one or more printing and firing steps.

[0039] Furthermore, the first heating element electrode 8 may be provided with a restricting wall (not shown) to prevent the connecting solder provided on the electrodes of the external circuit board connected to the third external connection electrode 10 from melting during reflow mounting, etc., and spreading onto the first heating element electrode 8 via castellation. The first and second electrodes 11 and 12 may also be provided with restricting walls in the same manner. The restricting walls can be formed using insulating materials that do not wettable to solder, such as glass, solder resist, or insulating adhesive, and can be formed on the first heating element electrode 8 or the first and second electrodes 11 and 12 by printing or the like. By providing restricting walls, it is possible to prevent the molten connecting solder from spreading to the first heating element electrode 8 or the first and second electrodes 11 and 12, and to maintain connectivity between the protective element 1 and the external circuit board.

[0040] [Intermediate Electrode] The intermediate electrode 4 is provided between the first and second electrodes 11 and 12 and is the electrode to which the fuse element 3 is connected. The intermediate electrode 4 is formed by a conductive pattern such as Ag or Cu. One end of the intermediate electrode 4 is connected to the other end 6b of the heating element 6 via the second heating element electrode 9 and the second lead-out electrode 18. Also, in the protection element 1 shown in FIG. 1, on the other end side, the intermediate electrode 4 extends on the insulating layer 7 in the region between the first electrode 11 and the second electrode 12 and overlaps the heating element 6 via the insulating layer 7. And the fuse element 3 is connected to the intermediate electrode 4 by a bonding material 40 such as connecting solder.

[0041] The fuse element 3 is mounted across the first and second electrodes 11 and 12 and is melted by self-heating (Joule heat) due to the heat generated by the energization of the heating element 6 or the energization of a current exceeding the rating, thereby cutting off the current path between the first electrode 11 and the second electrode 12. The flux 19 is applied to the fuse element 3 for the purpose of preventing oxidation, improving wettability, and achieving quick fusing. The configuration of the fuse element 3 will be described in detail later.

[0042] Note that the surfaces of the first and second electrodes 11 and 12 and the intermediate electrode 4 may be coated with a film such as Ni / Au plating, Ni / Pd plating, Ni / Pd / Au plating, etc. by a known method such as plating. Thereby, the protection element 1 can prevent the oxidation of the first and second electrodes 11 and 12 and the intermediate electrode 4 and prevent the variation of the rating accompanying the increase in the conduction resistance. Also, when the protection element 1 is subjected to reflow mounting, it is possible to prevent the first and second electrodes 11 and 12 and the intermediate electrode 4 from being melted (solder eaten) due to the melting of the connecting material 40 connecting the fuse element 3.

[0043] [Cap Member] The surface 2a of the insulating substrate 2 on which the fuse element 3 is mounted is covered by a cap member 5. The cap member 5 protects the inside of the protection element 1 and prevents the scattering of the melt generated when the fuse element 3 blows. As shown in FIG. 3, in the protection element 1, a top surface 5a formed in a substantially rectangular shape in plan view according to the shape of the insulating substrate 2 and side walls 5b erected from the four sides of the top surface 5a are provided.

[0044] The cap member 5 is provided on the surface 2a of the insulating substrate 2 and is joined by an adhesive. The shape of the cap member 5 is formed according to the shape of the insulating substrate 2. In the protection element 1 shown in FIG. 1, it is formed in a rectangular shape in plan view. Also, the dimensions of the cap member 5 are defined according to the size of the insulating substrate 2. Along with the miniaturization and low-profile of protection elements in recent years, it is, for example, about 4×3 mm and 0.2 mm thick. Note that the shape and dimensions of the cap member 5 are defined according to the specifications of the protection element and are not limited to those described above.

[0045] As the material of the cap member 5, a resin composition having heat resistance by containing an insulating inorganic filler in an insulating resin material such as various engineering plastics can be used. As the insulating resin material, so-called super engineering plastics such as LCP (liquid crystal polymer) and PPS (polyphenylene sulfite) are suitable. As a commercially available product, for example, UENO LCP manufactured by Ueno Pharmaceutical Co., Ltd. can be used. Examples of the insulating inorganic filler include inorganic fillers such as glass fiber. Among them, glass fiber chopped fiber (fiber length: 3 mm to 6 mm) and glass fiber milled fiber (fiber length: 200 μm or less) are suitable. As a commercially available product, for example, E glass fiber manufactured by Nippon Electric Glass Co., Ltd. can be used. Also, as a commercially available product of super engineering plastic filled with glass fiber, for example, Lapros LCP manufactured by Polyplastics Co., Ltd. can be mentioned.

[0046] The manufacturing method for the cap member 5 is not particularly limited, but it is preferable to manufacture it by injection molding. From the viewpoint of molding a miniaturized and low-profile cap member 5 by injection molding, the shape and amount of filler affect the moldability. In other words, as the amount of fibrous filler increases, the fluidity of the resin composition deteriorates. Also, in order to mold a miniaturized and low-profile cap member 5, it is necessary to fill the mold with the resin composition through a narrow resin channel.

[0047] Therefore, it is necessary to adjust the shape and amount of filler material used to fill the insulating resin material, taking moldability into consideration. As an example, a suitable material is LCP, an insulating resin material, filled with 35 to 45% by weight of glass fiber milled fibers.

[0048] By using such a cap member 5, the protective element 1 can maintain high insulation resistance because, when the fuse element 3 melts, the fuse element 3 and its molten conductor 3a, which are heated to a high temperature, come into contact with the cap member 5 and carbonize, thereby suppressing the formation of conductive paths. In other words, with the miniaturization and reduction of protective elements in recent years, the side wall height of the cap member 5 is short, and when the fuse element 3 melts, the molten conductor 3a expands into a spherical shape and aggregates on the intermediate electrode 4 and the first and second electrodes 11 and 12, so that the molten conductor 3a can come into contact with the top surface 5a.

[0049] [Flexural Modulus (MPa)] Here, the cap member 5 is molded using a resin composition that contains an insulating inorganic filler in an insulating resin material to provide heat resistance, so that the flexural modulus (unit: MPa) specified in ISO 178 is 13,000 MPa or more and 17,000 MPa or less. The flexural modulus can be seen as an indicator of the heat resistance of the cap member 5. If the flexural modulus is low, the fuse element 3 and its molten conductor 3a, when heated to a high temperature, expand spherically on the intermediate electrode 4 and the first and second electrodes 11 and 12 and come into contact with the cap member 5, may carbonize and form a conductive path, which may make it impossible to guarantee the insulation resistance after the fuse element 3 has melted.

[0050] However, with the protective element 1, by filling the insulating resin material with a filler, the flexural modulus of the cap member 5 can be set to 13,000 MPa or more, thereby improving the heat resistance of the cap member 5. Furthermore, by filling with an insulating inorganic filler, the amount of carbon in the resin component that carbonizes can be reduced. Therefore, even when the fuse element 3 or its molten conductor 3a, which has been heated to a high temperature, comes into contact with the cap member 5, it is possible to prevent the continuous formation of conductive paths due to carbonization in the region between the first electrode 11 and the second electrode 12 via the top surface 5a of the cap member 5. Consequently, the protective element 1 can maintain a high insulation resistance between the first and second electrodes 11 and 12 after the current has been interrupted.

[0051] Furthermore, if the insulating inorganic filler is filled to such an extent that the flexural modulus exceeds 17,000 MPa, the fluidity of the resin constituting the cap member 5 will deteriorate, which may impair the moldability when the miniaturized and low-profile cap member 5 is formed by injection molding.

[0052] A test specimen (length: 80 mm, width: 10 mm, thickness: 4 mm) used for bending tests as defined in ISO 178 is used to represent the top surface covering the surface 2a of the insulating substrate 2 of the cap member 5, and the bending modulus (unit: MPa) is measured by performing a three-point bending test in a room temperature environment.

[0053] Other measurement conditions for the flexural modulus are in accordance with ISO 178.

[0054] [Temperature of deflection under load (°C)] Alternatively, the cap member 5 is molded using a resin composition that contains an insulating inorganic filler in an insulating resin material to provide heat resistance, so that the temperature of deflection under load (°C) specified in ISO 75 is 270°C or higher and 330°C or lower. The temperature of deflection under load can also be seen as an indicator of the heat resistance of the cap member 5. If the temperature of deflection under load is low, the top surface 5a of the cap member 5 may bend inward due to the heat generated by the heating element 6, causing the fuse element 3 and its molten conductor 3a, which have been heated to a high temperature, to come into contact with the cap member 5, carbonize, and form a conductive path, which may make it impossible to guarantee the insulation resistance after the fuse element 3 has melted.

[0055] However, with the protective element 1, by filling the insulating resin material with an insulating inorganic filler, the load deflection temperature of the cap member 5 can be set to 270°C or higher, thereby improving the heat resistance of the cap member 5. Furthermore, by filling with an insulating inorganic filler, the amount of carbon in the resin component that carbonizes can be reduced. Therefore, deformation such as warping of the cap member 5 is suppressed, and it is possible to prevent the fuse element 3 and its molten conductor 3a, which are heated to a high temperature, from coming into contact with the cap member 5 and continuously forming conductive paths due to carbonization in the region between the first electrode 11 and the second electrode 12 via the top surface 5a of the cap member 5. Therefore, the protective element 1 can maintain a high insulation resistance between the first and second electrodes 11 and 12 after current interruption.

[0056] Furthermore, if the insulating inorganic filler is filled to such an extent that the load deflection temperature exceeds 330°C, the fluidity of the resin constituting the cap member 5 will deteriorate, which may impair the moldability when the miniaturized and low-profile cap member 5 is formed by injection molding.

[0057] A test specimen (length: 80 mm, width: 10 mm, thickness: 4 mm) used for measuring the load deflection temperature as specified in ISO 75 is used to represent the top surface 5a covering the surface 2a of the insulating substrate 2 of the cap member 5, and a constant load is applied so that it is bent at three points. The temperature is raised at a constant rate, and the temperature (in °C) is read when the deflection reaches the specified deflection corresponding to the increment of bending strain.

[0058] Other measurement conditions for load deflection temperature shall be in accordance with ISO 75.

[0059] Furthermore, when using a high-melting-point material such as ceramic or glass, which has excellent heat resistance, as the material for the cap member 5, melting or deformation of the cap member 5 itself can be prevented. However, because these high-melting-point materials have high thermal conductivity, the heat used to heat and melt the fuse element 3 escapes to the cap member 5, causing a delay in the fuse-cutting operation. However, with the protective element 1, heat resistance can be improved without using a high-thermal-conductivity material, heat dissipation to the cap member 5 is suppressed, and the rapid fuse-cutting performance of the fuse element 3 is not hindered.

[0060] Furthermore, if the protective element 1 is required to be certified by safety standards such as UL (Underwriter's Laboratories) and the characters or marks printed on the cap member 5 must be legible, using a material with low heat resistance for the cap member 5 may result in the requirement not being met. However, with the protective element 1, the cap member 5 can be formed from a material with high heat resistance, thus maintaining the legibility of the printed characters or marks and satisfying the standards of UL and other similar standards.

[0061] Furthermore, the cap member 5 may have a projection (not shown) erected on the inner surface side of the top surface 5a facing the fuse element 3, which holds the flux 19 in a predetermined position. This projection acts as tension when it comes into contact with the flux 19, holding the flux 19 on the fuse element 3.

[0062] [Fuse Element] Next, the detailed configuration of the fuse element 3 will be described. The fuse element 3 is mounted between the first and second electrodes 11 and 12, and melts due to heat generated by the energization of the heating element 6, or due to self-heating (Joule heating) when a current exceeding the rating is passed through it, thereby interrupting the current path between the first electrode 11 and the second electrode 12.

[0063] The fuse element 3 can be any conductive material that melts due to the heat generated by the energization of the heating element 6 or due to an overcurrent condition. For example, SnAgCu-based Pb-free solder, BiPbSn alloy, BiPb alloy, BiSn alloy, SnPb alloy, PbIn alloy, ZnAl alloy, InSn alloy, PbAgSn alloy, etc., can be used.

[0064] Furthermore, the fuse element 3 may be a structure containing a high-melting-point metal and a low-melting-point metal. For example, as shown in Figure 4(A), the fuse element 3 is a covering structure consisting of an inner layer and an outer layer, with a low-melting-point metal layer 13 as the inner layer and a high-melting-point metal layer 14 laminated on the low-melting-point metal layer 13 as the outer layer. The fuse element 3 is connected to the first and second electrodes 11, 12 and the intermediate electrode 4 via a conductive connecting material 40 such as connecting solder.

[0065] The low-melting-point metal layer 13 is preferably solder or a metal mainly composed of Sn, and is a material commonly called "Pb-free solder". The melting point of the low-melting-point metal layer 13 does not necessarily need to be higher than the temperature of the reflow oven, and may melt at around 200°C. The high-melting-point metal layer 14 is a metal layer laminated on the surface of the low-melting-point metal layer 13, and is, for example, a metal mainly composed of Ag or Cu, and has a high melting point that does not melt even when the connection between the first and second electrodes 11, 12 and the intermediate electrode 4 and the fuse element 3 or the mounting of the protection element 1 onto the external circuit board is performed by reflow.

[0066] Such a fuse element 3 can be formed by depositing a high-melting-point metal layer onto a low-melting-point metal foil using plating technology, or by using other well-known lamination or film formation technologies. The fuse element 3 may have a structure in which the entire surface of the low-melting-point metal layer 13 is covered by the high-melting-point metal layer 14, or it may have a structure in which it is covered except for a pair of opposing sides. The fuse element 3 may also have a coated structure in which the high-melting-point metal layer 14 is the inner layer and the low-melting-point metal layer 13 is the outer layer. Furthermore, as shown in Figure 4(B), it may have a two-layer structure in which the lower layer is the low-melting-point metal layer 13 and the upper layer is the high-melting-point metal layer 14. In addition, it can be formed in various configurations, such as a laminated structure with three or more layers in which the low-melting-point metal layer and the high-melting-point metal layer are alternately laminated, or a structure in which an opening is provided in a part of the outer layer to expose a part of the inner layer.

[0067] The fuse element 3 has a coating structure or laminated structure of a low-melting-point metal layer 13 and a high-melting-point metal layer 14, so that even if the reflow temperature exceeds the melting temperature of the low-melting-point metal layer 13, the fuse element 3 can maintain its shape and will not melt. Therefore, the connection between the first and second electrodes 11, 12 and the intermediate electrode 4 and the fuse element 3, and the mounting of the protective element 1 onto the external circuit board can be efficiently performed by reflow. Furthermore, even with reflow, it is possible to prevent fluctuations in melting characteristics, such as the fuse element 3 not melting at a predetermined temperature or melting below a predetermined temperature, due to localized increases or decreases in resistance value caused by deformation of the fuse element 3.

[0068] Furthermore, the fuse element 3 will not melt due to self-heating as long as a predetermined rated current is flowing through it. However, if a current higher than the rated value flows through it, it will melt due to self-heating, interrupting the current path between the first and second electrodes 11 and 12.

[0069] Furthermore, when the heating element 4 is energized and generates heat, it melts, interrupting the current path between the first and second electrodes 11 and 12. At this time, as described above, by setting the flexural modulus of the cap member 5 to 13,000 MPa or higher, it has excellent heat resistance, and even when the fuse element 3 or its molten conductor 3a, which has been heated to a high temperature, comes into contact with the cap member 5, the formation of a conductive path due to carbonization is suppressed, and high insulation resistance can be maintained. Alternatively, by setting the load deflection temperature of the cap member 5 to 270°C or higher, it has excellent heat resistance, and when the fuse element 3 or its molten conductor 3a, which has been heated to a high temperature, comes into contact with the cap member 5, the formation of a conductive path due to carbonization can be prevented, and high insulation resistance can be maintained.

[0070] Furthermore, in the fuse element 3, the molten low-melting-point metal layer 13 melts the high-melting-point metal layer 14 (solder erosion), causing the high-melting-point metal layer 14 to melt at a temperature lower than its melting point. Therefore, the fuse element 3 can be fused and cut in a short time by utilizing the melting action of the low-melting-point metal layer 13 on the high-melting-point metal layer 14. In addition, since the molten conductor 3a of the fuse element 3 is separated by the physical pulling action of the intermediate electrode 4 and the first and second electrodes 11 and 12, the current path between the first and second electrodes 11 and 12 can be quickly and reliably interrupted (Figure 2).

[0071] Furthermore, the fuse element 3 may be configured such that the volume of the low-melting-point metal layer 13 is greater than the volume of the high-melting-point metal layer 14. The fuse element 3 is heated by self-heating due to overcurrent or by the heating element 6, causing the low-melting-point metal to melt and dissolve the high-melting-point metal, thereby enabling rapid melting and fuse-cutting. Therefore, by forming the fuse element 3 with a volume of the low-melting-point metal layer 13 greater than the volume of the high-melting-point metal layer 14, this melting action is promoted, and the connection between the first and second electrodes 11 and 12 can be quickly interrupted.

[0072] Furthermore, in a fuse element 3 constructed by laminating a high-melting-point metal layer 14 onto an inner low-melting-point metal layer 13, the melting temperature can be reduced compared to conventional chip fuses made of high-melting-point metals. Therefore, the fuse element 3 can have a larger cross-sectional area and an improved current rating compared to chip fuses of the same size. In addition, it can be made smaller and thinner than conventional chip fuses with the same current rating, and it has excellent rapid melting properties.

[0073] Furthermore, the fuse element 3 can improve the resistance (pulse resistance) to surges caused by the instantaneous application of abnormally high voltages to the electrical system into which the protection element 1 is incorporated. In other words, the fuse element 3 must not melt even when a current of, for example, 100A flows for several milliseconds. In this regard, since large currents flowing for a very short time flow along the surface of the conductor (skin effect), the fuse element 3 is provided with a high-melting-point metal layer 14 such as Ag plating with low resistance as an outer layer, making it easier for the current applied by the surge to flow and preventing melting due to self-heating. Therefore, the fuse element 3 can significantly improve the resistance to surges compared to conventional fuses made of solder alloy.

[0074] [Manufacturing Process for Protective Element] Next, the manufacturing process for the protective element 1 will be described. The manufacturing process for the protective element 1 includes the steps of forming a heating element 6, a first electrode 11, a second electrode 12, a first heating element electrode 8, a second heating element electrode 9, a first lead electrode 17, a second lead electrode 18, an insulating layer 7, and an intermediate electrode 4 on an insulating substrate 2; connecting a fuse element 3 between the first electrode 11, the intermediate electrode 4, and the second electrode 12; and connecting a cap member 5 to the surface 2a of the insulating substrate 2 on which the fuse element 3 is mounted to cover the substrate surface.

[0075] As described above, the first and second electrodes 11 and 12, the first heating element electrode 8, the second heating element electrode 9, and the first and second lead electrodes 17 and 18 are formed on the surface 2a of the insulating substrate 2 by printing and firing a conductive paste such as Ag or Cu using screen printing technology.

[0076] Furthermore, the heating element 6 is made of nichrome, W, Mo, Ru, or materials containing these materials. These alloys or compositions or compounds are mixed in powder form with a resin binder to form a paste, which is then patterned on the insulating substrate 2 using screen printing technology and fired. An insulating layer 7 is formed on the heating element 6 and the first and second extraction electrodes 17 and 18 by applying a glass-based paste using screen printing technology and firing.

[0077] Furthermore, by printing and firing a conductive paste such as Ag or Cu using screen printing technology, an intermediate electrode 4 is formed extending from the second heating element electrode 9 onto the insulating layer 7. The first and second electrodes 11 and 12, and the intermediate electrode 4 are printed with a conductive connecting material 40 such as connecting solder, and after the fuse element 3 is mounted, they are subjected to a reflow process. This connects the fuse element 3 to the intermediate electrode 4 and the first and second electrodes 11 and 12. Note that when using a laminated fuse element 3 with a low-melting-point metal layer 13 as the lower layer and a high-melting-point metal layer 14 as the upper layer, the low-melting-point metal layer 13 melts at the reflow temperature, allowing the fuse element 3 to be connected to the first and second electrodes 11 and 12, and the intermediate electrode 4, so it is not always necessary to print the conductive connecting material 40.

[0078] Next, flux 19 is applied to the fuse element 3 by screen printing or the like, and then the cap member 5 is connected to the surface 2a of the insulating substrate 2 on which the fuse element 3 is mounted to cover the substrate surface and obtain the protective element 1.

[0079] [Circuit Configuration Example] Such a protection element 1 is used by being incorporated into a circuit in a lithium-ion secondary battery pack 20, for example. As shown in Figure 5, the battery pack 20 has a battery stack 25 consisting of a total of four lithium-ion secondary battery cells 21a to 21d.

[0080] The battery pack 20 includes a battery stack 25, a charge / discharge control circuit 26 that controls the charging and discharging of the battery stack 25, a protection element 1 to which the present invention is applied that shuts off the charge / discharge path when there is an abnormality in the battery stack 25, a detection circuit 27 that detects the voltage of each battery cell 21a to 21d, and a current control element 28 that acts as a switch element that controls the operation of the protection element 1 according to the detection result of the detection circuit 27.

[0081] The battery stack 25 consists of battery cells 21a to 21d connected in series, each requiring control to protect against overcharging and over-discharging. It is detachably connected to the charging device 22 via the positive terminal 20a and negative terminal 20b of the battery pack 20, and a charging voltage is applied from the charging device 22. The battery pack 20, once charged by the charging device 22, can power electronic devices by connecting the positive terminal 20a and negative terminal 20b to these devices.

[0082] The charge / discharge control circuit 26 comprises two current control elements 23a and 23b connected in series in the current path between the battery stack 25 and the charging device 22, and a control unit 24 that controls the operation of these current control elements 23a and 23b. The current control elements 23a and 23b are composed of, for example, field-effect transistors (hereinafter referred to as FETs), and the control unit 24 controls the conduction and interruption of the current path of the battery stack 25 in the charging direction and / or the discharge direction by controlling the gate voltage. The control unit 24 operates by receiving power from the charging device 22, and controls the operation of the current control elements 23a and 23b to interrupt the current path when the battery stack 25 is over-discharged or overcharged, according to the detection result by the detection circuit 27.

[0083] The protection element 1 is connected, for example, to the charge / discharge current path between the battery stack 25 and the charge / discharge control circuit 26, and its operation is controlled by the current control element 28.

[0084] The detection circuit 27 is connected to each battery cell 21a to 21d and detects the voltage value of each battery cell 21a to 21d, supplying each voltage value to the control unit 24 of the charge / discharge control circuit 26. The detection circuit 27 also outputs a control signal to control the current control element 28 when any one of the battery cells 21a to 21d reaches an overcharge voltage or over-discharge voltage.

[0085] The current control element 28 is configured, for example, as an FET, and when the voltage value of the battery cells 21a to 21d exceeds a predetermined over-discharge or overcharge state based on the detection signal output from the detection circuit 27, it activates the protection element 1 to control the charging and discharging current path of the battery stack 25 to be interrupted without the switching operation of the current control elements 23a and 23b.

[0086] The protective element 1 to which the present invention is applied, used in the battery pack 20 having the above configuration, has the circuit configuration shown in Figure 6. Specifically, the protective element 1 has a first external connection electrode 15 connected to the battery stack 25 side and a second external connection electrode 16 connected to the positive terminal 20a side, thereby connecting the fuse element 3 in series on the charge / discharge path of the battery stack 25. In addition, the protective element 1 has a heating element 4 connected to a current control element 28 via a first heating element electrode 8 and a third external connection electrode 10, and the heating element 4 is also connected to the battery stack 25. Thus, one end of the heating element 4 is connected to the fuse element 3 and one end of the battery stack 25 via an intermediate electrode 4, and the other end is connected to the current control element 28 and the other end of the battery stack 25 via a third external connection electrode 10. This forms a power supply path to the heating element 4, whose energization can be controlled by the current control element 28.

[0087] [Operation of the protection element] The heating element 6 is connected to a current control element 28 etc. formed in the external circuit via a third external connection electrode 10 when the protection element 1 is mounted on the external circuit board, and under normal conditions, current flow and heat generation are restricted. When the detection circuit 27 detects an abnormal voltage in any of the battery cells 21a to 21d, it outputs a cutoff signal to the current control element 28. The current control element 28 then controls the current to supply power to the heating element 6. The heating element 6 starts to generate heat when current flows from the battery stack 25.

[0088] The heat from the heating element 6 is transferred to the fuse element 3 via the second heating element electrode 9 and the intermediate electrode 4, and also from the insulating layer 7 to the fuse element 3 via the intermediate electrode 4, causing the fuse element 3 to melt. The molten conductor 3a of the fuse element 3 condenses on the intermediate electrode 4, causing it to melt and break between the first electrode 11 and the second electrode 12 (Figure 2). This effectively blocks the charge and discharge path of the battery pack 20.

[0089] When the fuse element 3 melts, the charge-discharge path of the battery stack 25 is interrupted between the first electrode 11 and the second electrode 12. Also, when the fuse element 3 melts, the heating element 6's power supply path is interrupted, and thus it stops generating heat.

[0090] Furthermore, if an overcurrent exceeding the rated current is passed through the fuse element 3, the protection element 1 will melt due to self-heating, causing a fuse to break between the first electrode 11 and the second electrode 12. This will interrupt the charging and discharging path of the battery pack 20.

[0091] Furthermore, the protective element 1 is formed by incorporating a high-melting-point metal and a low-melting-point metal into the fuse element 3. This allows the low-melting-point metal to melt before the high-melting-point metal, and the fuse element 3 to be blown open in a short time by utilizing the dissolving action of the molten low-melting-point metal on the high-melting-point metal.

[0092] The protective element 1 according to the present invention is not limited to use in lithium-ion secondary battery packs, but can of course be applied to various other applications that require interruption of the current path by an electrical signal.

[0093] [Modified Examples] Next, modified examples of the protective element to which this technology is applied will be described. In the following description, the same components as the protective element 1 described above may be denoted by the same reference numerals and their details may be omitted. Figure 7 shows a modified protective element 30, where (A) is a plan view with the cap member 5 omitted, (B) is a cross-sectional view of A-A' shown in (A), and (C) is a bottom view.

[0094] As shown in Figures 7(A) to 7(C), in the modified protective element 30, a heating element 6, first and second lead electrodes 17 and 18, and an insulating layer 7 covering them are formed on the back surface 2b of the insulating substrate 2 opposite to the front surface 2a. In addition, a first heating element electrode 8, a second heating element electrode 9b on the back surface side, and first and second external connection electrodes 15 and 16 are formed on the back surface 2b of the insulating substrate 2.

[0095] Furthermore, first and second electrodes 11, 12 and an intermediate electrode 4 are formed on the surface 2a of the insulating substrate 2, and a fuse element 3 is mounted on each of these electrodes 11, 12, and 4. In addition, a second heating element electrode 9a on the surface side is formed on the surface 2a of the insulating substrate 2 and is connected to the intermediate electrode 4.

[0096] The first and second electrodes 11 and 12, the intermediate electrode 4, the second heating element electrode 9a on the surface 2a of the insulating substrate 2, the heating element 6, the first and second lead electrodes 17 and 18, the first heating element electrode 8, the second heating element electrode 9b on the back surface 2b of the insulating substrate 2, and the first and second external connection electrodes 15 and 16 can be formed by the same process as described above for the protective element 1.

[0097] The second heating element electrode 9a on the front side and the second heating element electrode 9b on the back side are electrically connected by castellations formed on the side surface of the insulating substrate 2 or by conductive through-holes that penetrate the insulating substrate 2. In other words, the intermediate electrode 4 is electrically and thermally connected to the heating element 6 via the second heating element electrode 9a on the front side and the second heating element electrode 9b on the back side. As a result, the protective element 30 can heat the intermediate electrode 4 when the heating element 6 heats the intermediate electrode 4 through the insulating substrate 2, and the heat from the heating element 6 is transferred to the intermediate electrode 4 via the second heating element electrode 9a on the front side and the second heating element electrode 9b on the back side, which have excellent thermal conductivity, thereby heating and melting the fuse element 3.

[0098] Furthermore, in the protective element 30, the first heating element electrode 8 also serves as an external connection electrode that connects to the electrode of the external circuit board; therefore, the third external connection electrode 10, which is provided in the protective element 1, is not provided in the protective element 30.

[0099] Similar to the protective element 1, the protective element 30 has a surface 2a on which the fuse element 3 of the insulating substrate 2 is mounted, which is covered by a cap member 5. The cap member 5 is made of an insulating resin material containing an insulating inorganic filler to provide heat resistance, so that the flexural modulus (unit: MPa) specified in ISO 178 is 13,000 MPa or more and 17,000 MPa or less, or the temperature of deflection under load (°C) specified in ISO 75 is 270°C or more and 330°C or less.

[0100] Therefore, warping of the top surface 5a of the cap member 5 is prevented, and the amount of carbon in the resin component that carbonizes can be reduced by filling it with the filler material. Even when the fuse element 3 or its molten conductor 3a, which has been heated to a high temperature, comes into contact with the cap member 5, it is possible to prevent the continuous formation of a conductive path due to carbonization in the region between the first electrode 11 and the second electrode 12 via the top surface 5a of the cap member 5. Consequently, the protective element 1 can maintain a high insulation resistance between the first and second electrodes 11 and 12 after the current is interrupted.

[0101] Next, an embodiment of this technology will be described. In this embodiment, samples of protective elements were prepared by varying the amount of filler material used to fill the insulating resin material constituting the cap member. For the cap member used in each sample, the flexural modulus of elasticity was measured in accordance with ISO 178, and the temperature of deflection under load was measured in accordance with ISO 75. In addition, the moldability of the cap member when it is formed by injection molding was evaluated.

[0102] [Confirmation of Filling Amount] The filling amount was measured using a thermogravimetric analyzer. Instrument name: TGA Q500 (TA Instruments) Sample amount: 15-20 mg Method: 30-900 in air 40°C / min 3 min keep

[0103] Measurements taken on samples with a filler content of 30-45% by weight showed that the measured values ​​were within ±2% by weight of the theoretical value, confirming its usefulness as a method for measuring filler content.

[0104] Furthermore, for each protective element sample, a predetermined power was applied to the heating element to perform a fuse element melting test, and the insulation resistance was measured. In addition, it was visually evaluated whether the cap member melted and whether warping occurred on the top surface of the cap member.

[0105] The protective element samples in the examples and comparative examples have the same configuration as protective element 1 described above, measuring 4 × 3 cm in plan view and 0.6 mm in height. The heating element resistance (resistance between the first and second electrodes in the sample before the fuse element melts) is 1 Ω, and the power during heating element operation is 12.3 W.

[0106] [Flexural Modulus] The flexural modulus (unit: MPa) was measured by performing a three-point bending test on a test specimen (length: 80 mm, width: 10 mm, thickness: 4 mm) at room temperature, in accordance with the ISO 178 bending test.

[0107] Other measurement conditions for the flexural modulus conformed to ISO 178.

[0108] [Temperature of Deflection under Load] In accordance with the measurement of temperature of deflection under load specified in ISO 75, a constant load was applied to a test specimen (length: 80 mm, width: 10 mm, thickness: 4 mm) so that it was bent at three points. The temperature was increased at a constant rate, and the temperature (unit: °C) was read when the deflection reached the specified deflection corresponding to the increment of bending strain.

[0109] Other measurement conditions for load deflection temperature conformed to ISO 75.

[0110] [Insulation Resistance] The insulation resistance (Ω) between the first electrode and the second electrode after the fuse element had blown was measured (two-terminal resistance measurement). The insulation resistance value was 1.0 × 10⁻⁶. ５ If it exceeds Ω, it is OK (○), and the insulation resistance value is 1.0 × 10 ５ If the value was less than Ω, it was marked as NG (×). The equipment used for measurement was as follows: Measuring instrument: HIOKI Corporation: DSM-8104 Current: 250V Measurement environment: 60 sec charge, 10 sec measurement

[0111] [Melting of Cap Component] After the heating element was activated, the cap component was visually inspected to see if it had melted. If no melting was observed, it was marked as OK (○), and if melting was observed, it was marked as NG (×).

[0112] [Warping of the cap component] After the heating element was activated, the top surface of the cap component was visually inspected to see if warping had occurred. If no warping was observed, it was marked as OK (○), and if warping was observed, it was marked as NG (×).

[0113] [Moldability of Cap Components] If the cap component could be filled into the mold without any problems even through a narrow channel, it was marked as "manufacturable" (○). If the resin flow was poor and it was difficult to fill the cap into the mold through a narrow channel, it was marked as "difficult to manufacture" (×).

[0114] [Example 1] In Example 1, LCP was used as the insulating resin material for the cap member, and a resin composition containing 40% by weight of glass fiber milled fiber was prepared. The cap member was molded by injection molding of the resin composition. The injection molding temperature (resin temperature) was 360°C.

[0115] [Example 2] In Example 2, LCP was used as the insulating resin material for the cap member, and a resin composition containing 45% by weight of glass fiber milled fiber was prepared. The cap member was molded by injection molding of the resin composition. The injection molding temperature (resin temperature) was 360°C.

[0116] [Example 3] In Example 3, LCP was used as the insulating resin material for the cap member, and a resin composition containing 40% by weight of glass fiber milled fiber was prepared. The cap member was molded by injection molding of the resin composition. The injection molding temperature (resin temperature) was 400°C.

[0117] [Example 4] In Example 4, LCP was used as the insulating resin material for the cap member, and a resin composition containing 30% by weight of glass fiber chopped fibers was prepared. The cap member was molded by injection molding of the resin composition. The injection molding temperature (resin temperature) was 400°C.

[0118] [Example 5] In Example 5, LCP was used as the insulating resin material for the cap member, and a resin composition containing 40% by weight of glass fiber chopped fibers was prepared. The cap member was molded by injection molding of the resin composition. The injection molding temperature (resin temperature) was 400°C.

[0119] [Example 6] In Example 6, LCP was used as the insulating resin material for the cap member, and a resin composition containing 35% by weight of glass fiber milled fiber was prepared. The cap member was molded by injection molding of the resin composition. The injection molding temperature (resin temperature) was 360°C.

[0120] [Comparative Example 1] In Comparative Example 1, LCP was used as the insulating resin material for the cap member, and a resin composition was prepared containing a total of 35% by weight of glass fiber milled fiber and inorganic filler. The cap member was molded by injection molding of the resin composition. The injection molding temperature (resin temperature) was 360°C.

[0121] [Comparative Example 2] In Comparative Example 2, LCP was used as the insulating resin material for the cap member, and a resin composition containing 30% by weight of glass fiber milled fiber was prepared. The cap member was molded by injection molding of the resin composition. The injection molding temperature (resin temperature) was 360°C.

[0122]

[0123] As shown in Table 1, Examples 1 to 3 use glass fiber milled fiber as the inorganic filler to fill the resin composition constituting the cap member, and by setting the amount of glass fiber milled fiber filling to 40% by weight or more and 45% by weight or less, excellent heat resistance is obtained, and no melting or warping of the cap member was observed, and the insulation resistance after the fuse element was blown was 1.0 × 10⁻⁶. ５ The value exceeded Ω. Furthermore, there were no issues with moldability.

[0124] Furthermore, when the flexural modulus (ISO 178) of test specimens of the glass fiber milled fiber-containing resin composition constituting each cap member of Examples 1 to 3 was measured, all were 13,000 or higher, and the temperature of deflection under load (ISO 75 / 1.8 MPa) was 270°C or higher in all cases, indicating excellent heat resistance.

[0125] Examples 4 and 5 use glass fiber chopped fibers as an inorganic filler to fill the resin composition constituting the cap member. By setting the amount of glass fiber chopped fibers to 30% or more and 40% or less by weight, excellent heat resistance is achieved, and no melting or warping of the cap member is observed. The insulation resistance after the fuse element has been blown is also 1.0 × 10⁻⁶. ５ The value exceeded Ω.

[0126] However, in Examples 4 and 5, warping of the cap members was observed, and it was difficult to produce the cap members with the dimensions of these examples by injection molding. Therefore, it is preferable to use glass fiber milled fiber as a filler. Furthermore, when the flexural modulus (ISO 178) was measured for test pieces of the glass fiber chopped fiber-containing resin composition constituting each cap member of Examples 4 and 5, all were 13,000 or higher, but all exceeded 14,000 MPa.

[0127] In Example 6, glass fiber milled fiber was used as the inorganic filler to fill the resin composition constituting the cap member, and the amount of glass fiber milled fiber filled was set to 35 by weight. As a result of the excellent heat resistance, no melting or warping of the cap member was observed, and the insulation resistance after the fuse element was blown was 1.0 × 10⁻⁶. ５ The value exceeded Ω. Furthermore, there were no issues with moldability.

[0128] However, in Example 6, the amount of glass fiber milled fiber filling was somewhat low at 35% by weight, and the load deflection temperature was somewhat low at 270°C, resulting in the observation of melting of the cap member. From this, it can be seen that it is preferable to include 40 to 45% by weight of glass fiber milled fiber as the filler material.

[0129] Comparative Example 1 used a mixture of inorganic filler and glass fiber milled fiber as the inorganic filler material to fill the resin composition constituting the cap member. As a result, the amount of glass fiber milled fiber was insufficient, and the heat resistance was poor. Therefore, although there was no problem with moldability, the insulation resistance after the fuse element was blown was 1.0 × 10⁻⁶. ５ The value did not exceed Ω, and melting and warping of the cap material were also observed.

[0130] Furthermore, when the flexural modulus (ISO 178) and heat deflection temperature (ISO 75) were measured for test specimens of the inorganic filler and glass fiber milled fiber-containing resin composition constituting the cap member of Comparative Example 1, it was found that the flexural modulus (ISO 178) was less than 13,000 and the heat deflection temperature was less than 270°C, indicating poor heat resistance.

[0131] Comparative Example 2 used glass fiber milled fiber as the inorganic filler to fill the resin composition constituting the cap member, but the filling amount was small at 30% by weight, resulting in poor heat resistance. Therefore, although there was no problem with moldability, the insulation resistance after the fuse element was blown was 1.0 × 10⁻⁶. ５ The value did not exceed Ω, and melting and warping of the cap material were also observed.

[0132] Furthermore, when the flexural modulus (ISO 178) and heat deflection temperature (ISO 75) were measured for test specimens of the inorganic filler and glass fiber milled fiber-containing resin composition constituting the cap member of Comparative Example 2, it was found that the flexural modulus (ISO 178) was less than 13,000 and the heat deflection temperature was less than 270°C, indicating poor heat resistance.

[0133] 1 Protective element, 2 Insulating substrate, 2a Front surface, 2b Back surface, 3 Fuse element, 3a Molten conductor, 4 Intermediate electrode, 5 Cap member, 6 Heating element, 6a One end, 6b Other end, 7 Insulating layer, 8 First heating element electrode, 9 Second heating element electrode, 9a Second heating element electrode on the front side, 9b Second heating element electrode on the back side, 10 Third external connection electrode, 11 First electrode, 12 Second electrode, 13 Low melting point metal layer, 14 High melting point metal layer, 15 First external connection electrode, 16 Second external connection electrode, 17 Second lead electrode, 18 Second lead electrode, 19 Flux, 20 Battery pack, 20a Positive terminal, 20b Negative terminal, 21 Battery cell, 22 Charging device, 23 Current control element, 24 Control unit, 25 Battery stack, 26 Charge / discharge control circuit, 27 Detection circuit, 28 current control element, 30 protection element

Claims

1. A protective element comprising: an insulating substrate; a heating element provided on the insulating substrate; an insulating layer covering the heating element; an intermediate electrode provided on the surface of the insulating substrate and electrically connected to the heating element; a fuse element mounted on the intermediate electrode; and a cap member covering the surface side of the insulating substrate, wherein the cap member is a molded article of a resin composition containing an insulating inorganic filler, the insulating inorganic filler is glass fiber milled fiber, and the resin composition contains 35% by weight or more and 45% by weight or less of the glass fiber milled fiber.

2. The protective element according to claim 1, wherein the resin composition contains 40% by weight or more and 45% by weight or less of the glass fiber milled fiber.

3. A protective element comprising: an insulating substrate; a heating element provided on the insulating substrate; an insulating layer covering the heating element; an intermediate electrode provided on the surface of the insulating substrate and electrically connected to the heating element; a fuse element mounted on the intermediate electrode; and a cap member covering the surface side of the insulating substrate, wherein the cap member is a molded article of a resin composition containing an insulating inorganic filler, the insulating inorganic filler is glass fiber chopped fiber, and the resin composition contains 30% by weight or more and 40% by weight or less of the glass fiber chopped fiber.

4. The protective element according to any one of claims 1 to 3, wherein the heating element and the insulating layer are formed on the surface of the insulating substrate on which the fuse element is provided, and the intermediate electrode is laminated on the insulating layer.

5. The protective element according to any one of claims 1 to 3, wherein the heating element and the insulating layer are formed on the back surface of the insulating substrate opposite to the surface on which the fuse element is provided.

6. A battery pack comprising one or more battery cells and a protective element connected to the charge / discharge path of the battery cells and blocking the charge / discharge path, wherein the protective element is the protective element described in any one of claims 1 to 3.

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