Protective element and battery pack

Abstract

The present invention provides a protective element which prevents rapid fusing and dielectric breakdown of a fusible conductor and contributes to thinning of the element.　A protective element 1 comprises: an insulating substrate 2; a first heating element 5 formed on a front surface 2a of the insulating substrate 2; a first heating element electrode 6 connected to the first heating element 5 and serving as an energization terminal of the first heating element 5; a second heating element 7 formed on a back surface 2b of the insulating substrate 2; a second heating element electrode 8 connected to the second heating element 7 and serving as an energization terminal of the second heating element 7; and a fusible conductor 9 provided on the front surface 2a of the insulating substrate 2 and fused by heating. The first heating element electrode 6 or the second heating element electrode 8 can be selected as an energization electrode from an external power supply.

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. 2025-020368 filed in Japan on February 10, 2025, and this application is incorporated herein by reference and is incorporated into this application.

[0002] Conventionally, the spread of secondary batteries such as lithium-ion batteries has been expanding. However, these secondary batteries have a high energy density and may use organic solvents in the electrolyte, accompanied by the risks of heat generation and ignition. To prevent this heat generation and ignition, a protection circuit is provided, and the adoption of non-return fuse elements such as SCP has been expanding.

[0003] In addition, due to the high capacity of secondary batteries in recent years, while the main heat generation and ignition used to be on the high voltage side during overcharging, the risk of heat generation and ignition has also increased on the low voltage side during discharging, and there is an increasing need to expand the operating voltage range even for SCP.

[0004] FIG. 12 is a diagram showing a configuration example of a conventional protection element, where (A) is a plan view and (B) is a circuit diagram. The protection element 100 shown in FIG. 12 includes an insulating substrate 103, a first electrode 101 and a second electrode 102 provided on the insulating substrate 103, an intermediate electrode 104 disposed between the first electrode 101 and the second electrode 102, and a soluble conductor 105 disposed from the first electrode 101 to the second electrode 102 to electrically connect between the first electrode 101 and the intermediate electrode 104 and between the second electrode 102 and the intermediate electrode 104. The first electrode 101 is connected to an external connection terminal (not shown) formed on the back surface of the insulating substrate 103. Similarly, the second electrode 102 is connected to an external connection terminal (not shown) formed on the back surface of the insulating substrate 103.

[0005] On the surface of the insulating substrate 103, a heating element 106, an insulating layer 107 covering the heating element 106, a heating element electrode 108 which serves as a power supply terminal to the heating element 106, and a relay electrode 109 which relays between the intermediate electrode 104 and the heating element 106 are formed. One end of the heating element 106 is connected to the heating element electrode 108, and the other end is connected to the relay electrode 109. As a result, the heating element 106 is connected to the fusible conductor 105 via the relay electrode 109 and the intermediate electrode 104. The heating element electrode 108 is connected to an external connection terminal (not shown) formed on the back surface of the insulating substrate 103.

[0006] The fusible conductor 105 is connected to the first and second electrodes 101 and 102 and the intermediate electrode 104, which are connected to an external circuit, by a bonding material such as solder.

[0007] When an abnormality such as overcharging of the lithium-ion battery is detected, an external power source energizes the heating element 106 via the heating element electrode 108, causing it to heat up. The fusible conductor 105 is melted by the heat from the heating element 106, and the molten conductor condenses on the intermediate electrode 104 and the first and second electrodes 101 and 102, thereby blocking conductivity between the first and second electrodes 101 and 102.

[0008] Japanese Patent Publication No. 7-153367 Japanese Patent Publication No. 2011-172399

[0009] Japanese Patent Publication No. 2011-172399 describes a protection circuit comprising a low-melting-point metal body connected in series on the charge / discharge current path between a battery and a charge / discharge control circuit, which melts when heated, and a heating element comprising a plurality of resistors connected in series, which generate heat to melt the low-melting-point metal body when energized. The protection circuit selects which resistors to energize and heat up by selecting the terminal portion of each resistor according to the voltage fluctuation range of the battery. This allows the protection circuit to expand the operating voltage.

[0010] Figure 13 shows a structure 60 that realizes the protective circuit described in Japanese Patent Publication No. 2011-172399. The surface 62a of the insulating member 62 is provided with a conductor 63a, a resistor 64a connected to the conductor 63a, a conductor 63b connected to the resistor 64a, a resistor 64b connected to the conductor 63b, and a conductor 63c connected to the resistor 64b. Conductor 63b is connected to a connecting member 613 that functions as a terminal. Conductor 63c is connected to a connecting member 614 that functions as a terminal. Figure 14 is a diagram showing the circuit configuration of this structure. As shown in Figure 14, a conductor 63b is interposed between adjacent resistors 64a and 64b, and the current supply path of resistors 64a and 64b can be switched by switching between the connecting member 613 connected to the conductor 63b and the connecting member 614 connected to the conductor 63c, which serve as current supply terminals.

[0011] The mounting surface on which the resistors 64a and 64b are mounted is covered with an insulating material such as glass (not shown). Furthermore, a fusible conductor 67 made of a low-melting-point metal is mounted on the surface covered with this insulating material via a conductor 66. That is, the fusible conductor 67 is superimposed on the resistors 64a and 64b via the insulating material and the conductor 66.

[0012] However, in this structure, the heat generated by the resistor 64b or resistors 64a and 64b escapes through the conductor 63b and the connecting member 613 to the circuit board connected to the connecting member 613. As a result, the adjacent regions of resistors 64a and 64b, i.e., the approximately middle portion of the fusible conductor 67, are not heated, and it is possible that rapid melting is not achieved, or that the fusible conductor 67 is not sufficiently melted.

[0013] Furthermore, as shown in Figure 15, a configuration in which multiple heating elements (resistors) are provided is also conceivable, in which multiple heating elements are stacked on the mounting surface of the fusible conductor (low melting point metal body) of the insulating substrate. The protective element 110 shown in Figure 15 comprises an insulating substrate 103, a first electrode 101 and a second electrode 102 formed on the surface of the insulating substrate 103, an intermediate electrode 104 provided between the first electrode 101 and the second electrode 102, and a fusible conductor 105 arranged from the first electrode 101 to the second electrode 102, electrically connecting the first electrode 101 and the intermediate electrode 104 and the second electrode 102 and the intermediate electrode 104. The first electrode 101 is connected to a first external connection electrode 113 formed on the back surface of the insulating substrate 103. Similarly, the second electrode 102 is connected to a second external connection electrode 116 formed on the back surface of the insulating substrate 103.

[0014] An insulating layer 107a is formed on the surface of the insulating substrate 103, and a first heating element 111 is formed on the insulating layer 107a. A second heating element 112 is formed on the first heating element 111 via an insulating layer 107b. The second heating element 112 is covered with an insulating layer 107c, and an intermediate electrode 104 is formed on the insulating layer 107c.

[0015] Figure 16 shows the circuit configuration of the protection element 110. The first heating element 111 has one end connected to the intermediate electrode 104 via the first lead electrode 114a and a relay electrode (not shown). The other end of the first heating element 111 is connected to the surface-side first heating element electrode (not shown) via the first lead electrode 114b. The surface-side first heating element electrode is formed on the back surface of the insulating substrate 103 and is connected to the back-side first heating element electrode 118, which serves as a connection terminal to the external circuit board. The second heating element 112 has one end connected to the first heating element 111 via the second lead electrode 115a and the surface-side first heating element electrode. The other end of the second heating element 112 is connected to the surface-side heating element electrode (not shown) via the second lead electrode 115b. The second surface-side heating element electrode is formed on the back surface of the insulating substrate 103 and is connected to the back-side second heating element electrode 119, which serves as a connection terminal to the external circuit board. As a result, the first heating element 111 and the second heating element 112 are connected to the fusible conductor 105 via the relay electrode and the intermediate electrode 104.

[0016] In the protective element 110 shown in Figure 15, the overall thickness of the first and second heating elements 111 and 112 and the insulating layers 107a to 107c becomes thick, making it difficult to secure space inside the protective element. This raises concerns that the heat required to heat and cut the fusible conductor 105 will be dissipated towards the cap member 117 when the molten conductor of the fusible conductor 105 comes into contact with the cap member 117, potentially leading to an extended cutting time or insufficient cutting. Furthermore, attempting to secure sufficient space between the fusible conductor 105 and the top surface of the cap member 117 would result in the protective element 110 becoming larger, among other drawbacks.

[0017] Furthermore, if the thickness of the insulating layer is kept thin, dielectric breakdown may occur when a high voltage is applied, and the heating elements themselves may be destroyed before the first and second heating elements 111 and 112 have sufficiently heated up. Also, the thicker the insulating layers 107a to 107c are, the lower the heat conduction efficiency to the fusible conductor 105 becomes, and if the thickness of the fusible conductor 105 is increased to realize a protective element 110 that can handle large currents, it may not be possible to quickly melt and cut it.

[0018] One aspect of the present invention aims to provide a protective element and a battery pack that prevent rapid melting and dielectric breakdown of fusible conductors, and that contribute to the thinning of the element.

[0019] Furthermore, the description of this problem does not preclude the existence of other problems. Moreover, one aspect of the present invention does not need to solve all of these problems. It is possible to extract other problems from the description in the specification, drawings, and claims.

[0020] To solve one of the above-mentioned problems, a protective element according to one aspect of the present invention comprises an insulating substrate, a first heating element formed on the surface of the insulating substrate, a first heating element electrode connected to the first heating element and serving as a current-carrying terminal for the first heating element, a second heating element formed on the back surface of the insulating substrate, a second heating element electrode connected to the second heating element and serving as a current-carrying terminal for the second heating element, and a fusible conductor provided on the surface of the insulating substrate that is melted by heating, wherein the first heating element electrode or the second heating element electrode can be selected as the current-carrying electrode from an external power source.

[0021] Furthermore, in order to solve one of the above-mentioned problems, a battery pack according to one aspect of the present invention 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 and comprises a first switch connected to the first heating element electrode, a second switch connected to the second heating element electrode, and a control unit that controls the operation of the first switch and the second switch.

[0022] According to one aspect of the present invention, dielectric breakdown between the first and second heating elements and between them and electrodes formed on other insulating substrates can be suppressed, and damage to the first and second heating elements, other electrodes, or insulating substrates can be prevented. Therefore, according to one aspect of the present invention, the first heating element or the first and second heating elements can generate sufficient heat to quickly and reliably melt and cut the fusible conductor.

[0023] Furthermore, according to one aspect of the present invention, since the first heating element and the second heating element are not stacked, the first and second heating elements and the insulating layer do not occupy a large portion of the internal space of the protective element. This ensures sufficient space for the molten fusible conductor to aggregate on the electrode, while also suppressing the enlargement of the element and enabling miniaturization and thinning.

[0024] Figure 1 is a cross-sectional view showing a protective element to which the present invention is applied. Figure 2 is a plan view showing the surface of the insulating substrate of the protective element to which the present invention is applied. Figure 3 is a bottom view showing the back surface of the insulating substrate of the protective element to which the present invention is applied. Figure 4 is a plan view showing the state in which the fusible conductor has melted and the conductivity between the first and second electrodes has been interrupted, with the cap member omitted. Figure 5 is an external perspective view showing an example of the configuration of a fusible conductor, where (A) shows a fusible conductor with a coating structure consisting of an inner layer and an outer layer, and (B) shows a fusible conductor with a laminated structure in which the lower layer is a low melting point metal layer and the upper layer is a high melting point metal layer. Figure 6 is a diagram showing an example of the circuit configuration of a battery pack. Figure 7 is a diagram showing an example of the circuit configuration of a protective element to which the present invention is applied. Figure 8 is a cross-sectional view showing a protective element in which a third heating element is formed inside the insulating substrate. Figure 9 is a diagram showing the circuit configuration of the protective element shown in Figure 8. Figure 10 is a cross-sectional view showing a protective element in which a second heating element is formed inside the insulating substrate. Figure 11 is a cross-sectional view showing a protective element in which a first heating element is formed inside an insulating substrate. Figure 12 is a diagram showing an example configuration of a protective element in which one heating element is provided on the surface of an insulating substrate, where (A) is a plan view showing the cap member and flux omitted, and (B) is a circuit diagram. Figure 13 is a diagram showing a protective element in which two resistors are provided adjacent to each other on the surface of an insulating substrate, where (A) is a plan view showing a configuration in which two resistors are provided adjacent to each other on the surface of an insulating member via a conductor, and (B) is a plan view showing a configuration in which a fusible conductor is mounted on the two resistors via an insulating layer and a conductor. Figure 14 is a diagram showing the circuit configuration of the protective element shown in Figure 13. Figure 15 is a cross-sectional view showing a protective element in which two heating elements are laminated on the surface of an insulating substrate. Figure 16 is a diagram showing the circuit configuration of the protective element shown in Figure 15.

[0025] The protective element and battery pack to which the present invention is applied will be described in detail below with reference to the drawings. It should be noted that the present invention is not limited to the following embodiments, and various modifications are possible without departing from the spirit of the invention. 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 description. It should also be noted that there are parts where the relationships and proportions of dimensions differ between drawings.

[0026] Figure 1 is a cross-sectional view showing a protective element to which the present invention is applied. Figure 2 is a plan view showing the surface of the insulating substrate of the protective element to which the present invention is applied. Figure 3 is a bottom view showing the back surface of the insulating substrate of the protective element to which the present invention is applied. As shown in Figures 1 to 3, the protective element 1 to which the present invention is applied comprises an insulating substrate 2, a first heating element 5 formed on the surface 2a of the insulating substrate 2, a first heating element electrode 6 connected to the first heating element 5 and serving as a current-carrying terminal for the first heating element 5, a second heating element 7 formed on the back surface 2b of the insulating substrate 2, a second heating element electrode 8 connected to the second heating element 7 and serving as a current-carrying terminal for the second heating element 7, and a fusible conductor 9 provided on the surface 2a of the insulating substrate 2 that melts when heated. The protective element 1 is configured to allow selection of a heating element to perform heating operation by selecting either the first heating element electrode 6 or the second heating element electrode 8 as the current-carrying electrode from an external power source.

[0027] In this invention, the surface of the insulating substrate 2 on which the fusible conductor 9 is mounted is referred to as the front surface 2a, and the surface opposite to the front surface 2a is referred to as the back surface 2b.

[0028] The fusible conductor 9 forms part of the current path of the external circuit when the protective element 1 is incorporated into the external circuit. The fusible conductor 9 is heated and melted when the first heating element 5 or the first and second heating elements 5 and 7 are energized and heated, thereby interrupting the current path of the external circuit.

[0029] In this configuration, the protective element 1 has a first heating element 5 formed on the surface 2a of the insulating substrate 2 and a second heating element 7 formed on the back surface 2b of the insulating substrate 2. This suppresses dielectric breakdown between the first and second heating elements 5 and 7 and between them and electrodes formed on the insulating substrate 2, thereby preventing damage to the first and second heating elements 5 and 7, other electrodes, or the insulating substrate 2. Therefore, with the protective element 1, the first heating element 5 or the first and second heating elements 5 and 7 can generate sufficient heat to quickly and reliably melt the fusible conductor 9.

[0030] Furthermore, since the protective element 1 does not stack the first heating element 5 and the second heating element 7, the internal space of the protective element 1 is not largely occupied by the first and second heating elements 5 and 7 or the insulating layer. This ensures sufficient space for the molten fusible conductor 9 to aggregate on the electrode, while also suppressing the enlargement of the element and enabling miniaturization and thinning.

[0031] The following describes in detail an example of the configuration of a protective element 1 to which the present invention is applied. The protective element 1 shown in Figures 1 to 3 comprises an insulating substrate 2, a first electrode 3 and a second electrode 4 provided on the insulating substrate 2, a first heating element 5 provided on the surface 2a of the insulating substrate 2, a second heating element 7 provided on the back surface 2b of the insulating substrate 2, a surface insulating layer 23 covering the first heating element 5, a back insulating layer 26 covering the second heating element 5, an intermediate electrode 15 provided between the first electrode 3 and the second electrode 4 on the surface 2a of the insulating substrate 2 and electrically connected to the first heating element 5 and the second heating element 7, a fusible conductor 9 mounted on the surfaces of the first electrode 3, the second electrode 4 and the intermediate electrode 15 and electrically connecting the first electrode 3 and the second electrode 4, and a cap member 16 covering the surface 2a side of the insulating substrate 2.

[0032] The protection element 1 is incorporated into an external circuit, such as a protection circuit for a lithium-ion secondary battery, so that the fusible conductor 9 forms part of the current path of the external circuit and interrupts the current path by melting due to the heat generated by the first heating element 5 or the first and second heating elements 5 and 7 (see Figure 4). In addition, the protection element 1 has a maximum current and rated voltage set according to the electronic device used, and when power exceeding the set value is applied, the fusible conductor 9 generates heat (Joule heating) due to the current flow and melts, thereby interrupting the conduction between the first and second electrodes 3 and 4.

[0033] Figure 4 is a plan view showing the protective element 1 in which the fusible conductor 9 melts due to the heat generated by the first heating element 5 or the first and second heating elements 5 and 7, thereby interrupting electrical conductivity between the first and second electrodes 3 and 4, with the cap member 16 omitted.

[0034] [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.

[0035] [First and Second Electrodes] A first electrode 3 and a second electrode 4 are formed on opposite ends of the surface 2a of the insulating substrate 2. The first electrode 3 and the second electrode 4 are each formed by a conductive pattern of Ag, Cu, or an alloy thereof. The first electrode 3 and the second electrode 4 can be formed, for example, by screen printing an Ag paste in a predetermined pattern and then firing it at a predetermined temperature.

[0036] The first electrode 3 is connected from the surface 2a of the insulating substrate 2 to a first external connection electrode 17 formed on the back surface 2b via castellation and / or conductive through-holes. The second electrode 4 is connected from the surface 2a of the insulating substrate 2 to a second external connection electrode 18 formed on the back surface 2b via castellation and / or conductive through-holes. In the surface mount type protective element 1, when the protective element 1 is mounted on an external circuit board, the first and second external connection electrodes 17 and 18 are connected to connection electrodes provided on the external circuit board, thereby incorporating the fusible conductor 9 into a part of the current path formed on the external circuit board.

[0037] The first and second electrodes 3 and 4 are electrically connected via a fusible conductor 9 mounted on them using various tin-based solder pastes and other conductive connecting materials. Furthermore, as shown in Figure 4, the connection between the first and second electrodes 3 and 4 is interrupted when the first heating element 5 or the first and second heating elements 5 and 7 generate heat when current is applied, causing the fusible conductor 9 to melt, or when a large current exceeding the rating flows through the protective element 1, causing the fusible conductor 9 to melt due to self-heating (Joule heating).

[0038] [First Heating Element] The first heating element 5 is a conductive material with relatively high resistance that generates heat when current is passed through it, and is made of, for example, nichrome, W, Mo, Ru, or a material containing these. The first heating element 5 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 surface 2a of the insulating substrate 2 or on the lower insulating layer 23a formed on the surface 2a using screen printing technology, and then firing it. As an example, the first heating element 5 can be formed by adjusting a mixed paste of ruthenium oxide paste, silver, and glass paste according to a predetermined voltage, forming a film on the surface 2a of the insulating substrate 2 at a predetermined location and area, and then firing it under appropriate conditions. The shape of the first heating element 5 can be designed as appropriate, such as rectangular or zigzag, but as shown in Figure 2, it is preferable to make it substantially rectangular according to the shape of the insulating substrate 2 in order to maximize the heating area.

[0039] Furthermore, the first heating element 5 has one end 5a and the other end 5b connected to the first lead electrode 21. The first lead electrode 21a connected to the one end 5a is led out from the surface-side first heating element electrode 6a formed on one side edge of the surface 2a of the insulating substrate 2. The first lead electrode 21b connected to the other end 5b is led out from the intermediate electrode 22 formed on the other side edge of the surface 2a of the insulating substrate 2. The first lead electrode 21a is led out from the surface-side first heating element electrode 6a along one end 5a of the first heating element 5, and in the protective element 1 shown in Figure 2, it extends along one side edge of the first heating element 5 which is formed in a substantially rectangular shape, and overlaps with that side edge of the first heating element 5. Similarly, the first lead electrode 21b is led out from the relay electrode 22 along the other end 5b of the first heating element 5, and in the protective element 1 shown in Figure 2, it extends along the other side edge of the substantially rectangular first heating element 5 and overlaps with the other side edge of the first heating element 5. In this specification, when there is no need to distinguish between these first lead electrodes 21a and 21b, they are simply referred to as the first lead electrode 21.

[0040] [Surface Insulating Layer] The first heating element 5 and the first lead electrodes 21a and 21b are covered with a surface insulating layer 23. The surface insulating layer 23 has a lower surface insulating layer 23a provided on the surface 2a of the insulating substrate 2, and an upper surface insulating layer 23b formed on the lower surface insulating layer 23a and covering the first heating element 5 and the first lead electrodes 21a and 21b. An intermediate electrode 15 is also formed on the upper surface insulating layer 23b. In this specification, when there is no need to distinguish between the lower surface insulating layer 23a and the upper surface insulating layer 23b, they are simply referred to as the surface insulating layer 23.

[0041] The surface insulating layer 23 is intended to protect and insulate the first heating element 5. The surface insulating layer 23 is formed with a thin thickness, for example, 10 to 40 μm on the upper and lower sides, in order to efficiently transfer heat from the first heating element 5 and the second heating element 7 to the intermediate electrode 15 and the fusible conductor 9. The surface insulating layer 23 can be formed, for example, by applying and firing a glass-based paste.

[0042] Note that the protection element 1 may be formed with only the upper surface insulating layer 23b without forming the lower surface insulating layer 23a. In this case, the first heating element 5 and the first lead electrodes 21a and 21b are formed directly on the surface 2a of the insulating substrate 2.

[0043] The first heating element electrode 6 and the relay electrode 22 are formed on opposite side edges different from the side edges where the first and second electrodes 3 and 4 of the insulating substrate 2 are provided. The first heating element electrode 6 is an electrode that serves as a power supply terminal to the first heating element 5, and includes a surface-side first heating element electrode 6a connected to one end 5a of the first heating element 5 via the first lead electrode 21a, and a back-side first heating element electrode 6b formed on the back surface 2b of the insulating substrate 2 and serving as an external connection terminal. The surface-side first heating element electrode 6a and the back-side first heating element electrode 6b are electrically connected via a castellation or a conductive through-hole. In this specification, when there is no need to distinguish between the surface-side first heating element electrode 6a and the back-side first heating element electrode 6b, it is simply referred to as the first heating element electrode 6.

[0044] The relay electrode 22 is an electrode for relaying the first lead electrode 21b and the intermediate electrode 15. The relay electrode 22 is connected to the other end 5b of the first heating element 5 via the first lead electrode 21b and is also connected to one end of the intermediate electrode 15. The relay electrode 22 may be formed inward from the side edge of the insulating substrate 2 as shown in FIG. 2, or may be formed on the side edge of the insulating substrate 2.

[0045] The first heating element electrode 6, the first lead electrode 21, and the relay electrode 22 can be formed by printing and firing a conductive paste such as Ag or Cu, similar to the first and second electrodes 3 and 4. Also, by configuring the surface-side first heating element electrode 6a, the first lead electrode 21, and the relay electrode 22 formed on the surface 2a of the insulating substrate 2 with the same material, they can be formed in one or a plurality of printing processes and firing processes.

[0046] Note that the first heating element electrode 6a on the front surface side is provided with a restriction wall (not shown) that prevents the solder for connection provided on the electrode of the external circuit board connected to the first external connection electrode 6b on the back surface side from melting during reflow mounting or the like, climbing up to the first heating element electrode 6a on the front surface side via the castellations, and wetting and spreading on the first heating element electrode 6a on the front surface side. Similarly, the first and second electrodes 3 and 4 may also be provided with restriction walls. The restriction wall can be formed using an insulating material that does not have wettability to solder, such as glass, solder resist, or insulating adhesive, and can be formed on the first heating element electrode 6a on the front surface side or on the first and second electrodes 3 and 4 by printing or the like. By providing the restriction wall, it is possible to prevent the melted connection solder from wetting and spreading to the first heating element electrode 6a on the front surface side or the first and second electrodes 3 and 4, and maintain the connectivity between the protection element 1 and the external circuit board.

[0047] [Intermediate Electrode] The intermediate electrode 15 is an electrode provided between the first and second electrodes 3 and 4 to which the soluble conductor 9 is connected. The intermediate electrode 15 is formed by a conductive pattern of Ag, Cu, or the like. One end side of the intermediate electrode 15 is connected to the other end portion 5b of the first heating element 5 via the relay electrode 22 and the first lead-out electrode 21b. Further, in the protection element 1 shown in FIG. 2, the other end side of the intermediate electrode 15 extends on the upper insulating layer 23b in the region between the first electrode 3 and the second electrode 4 and is superimposed on the first heating element 5 via the upper insulating layer 23b. Then, the soluble conductor 9 is connected to the intermediate electrode 15 by a conductive bonding material such as connection solder.

[0048] The soluble conductor 9 is mounted across the first and second electrodes 3 and 4 and is melted by self-heating (Joule heat) due to the heat generated by the energization of the first heating element 5 or the first and second heating elements 5 and 7, or the energization of a current exceeding the rated value, thereby interrupting the current path between the first electrode 3 and the second electrode 4. The flux 19 is applied to the soluble conductor 9 for the purpose of preventing oxidation, improving wettability, and achieving quick fusing. The configuration of the soluble conductor 9 will be described in detail later.

[0049] Furthermore, the surfaces of the first and second electrodes 3 and 4 and the intermediate electrode 15 may be coated with a film such as Ni / Au plating, Ni / Pd plating, or Ni / Pd / Au plating by known methods such as plating. This prevents oxidation of the first and second electrodes 3 and 4 and the intermediate electrode 15, and prevents fluctuations in the rating due to an increase in conductivity resistance. In addition, when the protective element 1 is reflow mounted, it is possible to prevent the first and second electrodes 3 and 4 and the intermediate electrode 15 from melting (solder erosion) due to the melting of the conductive connecting material connecting the fusible conductor 9.

[0050] [Second Heating Element] The second heating element 7, like the first heating element 5, is a conductive material with a relatively high resistance that generates heat when current is passed through it, and is made of, for example, nichrome, W, Mo, Ru, or a material containing these. The second heating element 7 can be formed by mixing powdered alloys, compositions, or compounds of these materials with a resin binder to make a paste, forming a pattern on the back surface 2b of the insulating substrate 2 or on the lower back insulating layer 26a formed on the back surface 2b using screen printing technology, and then firing it. As an example, the second heating element 7 can be formed by adjusting a mixed paste of ruthenium oxide paste, silver, and glass paste according to a predetermined voltage, forming a film in a predetermined area at a predetermined position on the back surface 2b of the insulating substrate 2, and then firing it under appropriate conditions. The shape of the second heating element 7 can be designed as appropriate, such as rectangular or zigzag, but as shown in Figure 3, it is preferable to make it substantially rectangular according to the shape of the insulating substrate 2 in order to maximize the heating area.

[0051] Furthermore, the second heating element 7 has one end 7a and the other end 7b connected to the second lead electrode 25. The second lead electrode 25a connected to the one end 7a is led out from the first heating element electrode 6b on the back side, which is formed on one side edge of the back surface 2b of the insulating substrate 2. The second lead electrode 25b connected to the other end 7b is led out from the second heating element electrode 8, which is formed on the other side edge of the back surface 2b of the insulating substrate 2. The second lead electrode 25a is led out from the first heating element electrode 6b on the back side along one end 7a of the second heating element 7, and in the protective element 1 shown in Figure 3, it extends along one side edge of the second heating element 7, which is formed in a substantially rectangular shape, and overlaps with that side edge of the second heating element 7. Similarly, the second lead electrode 25b is led out from the second heating element electrode 8 along the other end 7b of the second heating element 7, and in the protective element 1 shown in Figure 3, it extends along the other side edge of the second heating element 7, which is formed in a substantially rectangular shape, and overlaps with the other side edge of the second heating element 7. In this specification, when there is no need to distinguish between these second lead electrodes 25a and 25b, they are simply referred to as the second lead electrode 25.

[0052] The resistance values ​​of the first heating element 5 and the second heating element 7 may be the same, the resistance value of the first heating element 5 may be higher than the resistance value of the second heating element 7, and the resistance value of the second heating element 7 may be higher than the resistance value of the first heating element 5.

[0053] [Back surface insulating layer] The second heating element 7 and the second lead electrodes 25a and 25b are covered by the back surface insulating layer 26. The back surface insulating layer 26 has a lower back surface insulating layer 26a provided on the back surface 2b of the insulating substrate 2, and an upper back surface insulating layer 26b formed on the lower back surface insulating layer 26a and covering the second heating element 7 and the second lead electrodes 25a and 25b. In this specification, when it is not necessary to distinguish between the lower back surface insulating layer 26a and the upper back surface insulating layer 26b, they are simply referred to as the back surface insulating layer 26.

[0054] The back insulating layer 26 is intended to protect and insulate the second heating element 7. The back insulating layer 26 is formed with a thin thickness, for example, 10 to 40 μm on the upper and lower sides, in order to efficiently transfer the heat from the second heating element 7 to the intermediate electrode 15 and fusible conductor 9 via the insulating substrate 2. The back insulating layer 26 can be formed, for example, by applying and firing a glass-based paste.

[0055] In addition, the protective element 1 may have only an upper back insulating layer 26b, without a lower back insulating layer 26a. In this case, the second heating element 5 and the second lead electrodes 25a and 25b are formed directly on the back surface 2b of the insulating substrate 2.

[0056] The first heating element electrode 6b and the second heating element electrode 8 on the back side are formed on opposite side edges of the insulating substrate 2, different from the side edges on which the first and second external connection electrodes 17 and 18 are provided. The first heating element electrode 6b on the back side is an electrode that serves as a power supply terminal to the first heating element 5. When the protective element 1 is mounted on an external circuit board, it is connected to a connection electrode provided on the external circuit board, thereby connecting the first heating element 5 to the power supply of the external circuit. Furthermore, the first heating element electrode 6b on the back side is connected to one end 7a of the second heating element 7 via the second lead electrode 25a. Therefore, the second heating element 7 and the first heating element 5 are electrically connected via the second lead electrode 25a, the first heating element electrode 6b on the back side, the first heating element electrode 6a on the front side, and the first lead electrode 21a.

[0057] The second heating element electrode 8 is an electrode that serves as a power supply terminal to the second heating element 7. When the protective element 1 is mounted on an external circuit board, it is connected to a connecting electrode provided on the external circuit board, thereby connecting the second heating element 7 to the power supply of the external circuit. The second heating element electrode 8 is connected to the other end 7b of the second heating element 7 via a second lead electrode 25b, and is also connected to the first heating element electrode 6.

[0058] The first and second external connection electrodes 17 and 18, the first heating element electrode 6b on the back side, the second lead electrode 25, and the second heating element electrode 8 can be formed by printing and firing a conductive paste such as Ag or Cu. Alternatively, the first and second external connection electrodes 17 and 18, the first heating element electrode 6b on the back side, the second lead electrode 25, and the second heating element electrode 8 formed on the back surface 2b of the insulating substrate 2 can be formed in one or more printing and firing steps by using the same material.

[0059] [Cap Member] The surface 2a of the insulating substrate 2 on which the fusible conductor 9 is mounted is covered by a cap member 16. The cap member 16 protects the inside of the protective element 1 and prevents the scattering of molten material generated when the fusible conductor 9 is cut.

[0060] The cap member 16 is provided on the surface 2a of the insulating substrate 2 and is joined by an adhesive. The shape of the cap member 16 is formed according to the shape of the insulating substrate 2, and in the protective element 1 shown in Figure 1, it is formed in a rectangular shape in plan view. As the material for the cap member 16, a resin composition can be used that has heat resistance by appropriately containing insulating inorganic fillers in an insulating resin material such as LCP (liquid crystal polymer) or PPS (polyphenylene sulfite), which is an insulating resin material.

[0061] [Fusable Conductor] Next, the detailed configuration of the fusible conductor 9 will be described. The fusible conductor 9 is mounted between the first and second electrodes 3 and 4, and melts due to heat generated by the energization of the first heating element 5 or the first and second heating elements 5 and 7, 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 3 and the second electrode 4.

[0062] The fusible conductor 9 can be any conductive material that melts due to the heat generated by the energization of the first heating element 5 or the first and second heating elements 5 and 7, 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.

[0063] Furthermore, the fusible conductor 9 may be a structure containing a high-melting-point metal and a low-melting-point metal. For example, as shown in Figure 5(A), the fusible conductor 9 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 fusible conductor 9 is connected to the first and second electrodes 3 and 4 and the intermediate electrode 15 via a conductive connecting material such as connecting solder.

[0064] 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 3 and 4 and the intermediate electrode 15 and the fusible conductor 9 or the mounting of the protective element 1 onto the external circuit board is performed by reflow.

[0065] Such a fusible conductor 9 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 fusible conductor 9 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 fusible conductor 9 may also have a coating 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 5(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 by various configurations, such as a multilayer structure of 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.

[0066] The fusible conductor 9 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 fusible conductor 9 can maintain its shape and will not melt. Therefore, the connection between the first and second electrodes 3 and 4 and the intermediate electrode 15 and the fusible conductor 9, and the mounting of the protective element 1 onto the external circuit board can be efficiently performed by reflow. Furthermore, even with reflow, fluctuations in melting characteristics, such as localized increases or decreases in resistance due to deformation of the fusible conductor 9, can be prevented, such as failing to melt at a predetermined temperature or melting below a predetermined temperature.

[0067] Furthermore, the fusible conductor 9 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 3 and 4.

[0068] Furthermore, the fusible conductor 9 melts when the first heating element 5 or the first and second heating elements 5 and 7 are energized and generate heat, thereby interrupting the current path between the first and second electrodes 3 and 4.

[0069] Furthermore, in the fusible conductor 9, the molten low-melting-point metal layer 13 dissolves 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 fusible conductor 9 can be melted and cut in a short time by utilizing the dissolving action of the low-melting-point metal layer 13 on the high-melting-point metal layer 14. In addition, since the molten conductor 9a of the fusible conductor 9 is separated by the physical pulling action of the intermediate electrode 15 and the first and second electrodes 3 and 4, the current path between the first and second electrodes 3 and 4 can be quickly and reliably interrupted (Figure 4).

[0070] Furthermore, the fusible conductor 9 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 fusible conductor 9 is heated by self-heating due to overcurrent or by the heat generated by the first heating element 5 or the first and second heating elements 5 and 7, causing the low-melting-point metal to melt and dissolve the high-melting-point metal, thereby enabling rapid melting and cutting. Therefore, by forming the fusible conductor 9 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 3 and 4 can be quickly blocked.

[0071] Furthermore, in a fusible conductor 9 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 fusible conductor 9 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 has excellent rapid melting properties.

[0072] Furthermore, the fusible conductor 9 can improve resistance to surges (pulse resistance) when an abnormally high voltage is instantaneously applied to the electrical system into which the protective element 1 is incorporated. In other words, the fusible conductor 9 must not melt even when a current of, for example, 100A flows for several milliseconds. In this regard, since large currents that flow for a very short time flow through the surface layer of the conductor (skin effect), the fusible conductor 9 has a high melting point metal layer 14 such as Ag plating with low resistance as an outer layer, so that it can easily conduct the current applied by the surge and prevent melting due to self-heating. Therefore, the fusible conductor 9 can significantly improve resistance to surges compared to conventional fuses made of solder alloy.

[0073] [Manufacturing Process of Protective Element] Next, the manufacturing process of the protective element 1 will be described. The manufacturing process of the protective element 1 consists of the steps of forming a first heating element 5, a first electrode 3, a second electrode 4, a first heating element electrode 6a on the surface 2a of the insulating substrate 2, a relay electrode 22, a first lead electrode 21, a surface insulating layer 23, and an intermediate electrode 15 on the surface 2a of the insulating substrate 2, and forming a second heating element 7, a first heating element electrode 6b on the back surface 2b of the insulating substrate 2, a second heating element electrode 8, a second lead electrode 25, first and second external connection electrodes 17, 18, and a back surface insulating layer 26 on the back surface 2b of the insulating substrate 2, and the first electrode The process includes the steps of electrically connecting electrode 3 to the first external connection electrode 17, electrode 4 to the second external connection electrode 18, and the first heating element electrode 6a on the front side to the first heating element electrode 6b on the back side; connecting a fusible conductor 9 between the first electrode 3, the intermediate electrode 15, and the second electrode 4; printing flux 19 onto the fusible conductor 9 and connecting a cap member 16 to the surface 2a of the insulating substrate 2 on which the fuse element 3 is mounted to cover the substrate surface.

[0074] As described above, the first and second electrodes 3 and 4, the first heating element electrode 6, the second heating element electrode 8, the first and second external connection electrodes 17 and 18, the first and second lead electrodes 21 and 25, and the intermediate electrode 22 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.

[0075] Furthermore, the first and second heating elements 5 and 7 are made of nichrome, W, Mo, Ru, etc., or materials containing these. These can be formed by mixing powdered alloys, compositions, or compounds of these materials with a resin binder, etc., to form a paste, which is then patterned on the insulating substrate 2 using screen printing technology, etc., and fired. The surface insulating layer 23 and the back insulating layer 26 can be formed by applying a glass-based paste, etc., using screen printing technology, etc., and firing.

[0076] The first and second electrodes 3 and 4, and the intermediate electrode 15 are printed with a conductive connecting material such as connecting solder, and after the fusible conductor 9 is mounted, they are subjected to a reflow process. This connects the fusible conductor 9 to the intermediate electrode 15 and the first and second electrodes 3 and 4. In the case of a fusible conductor 9 with a laminated structure in which the lower layer is a low-melting-point metal layer 13 and the upper layer is a high-melting-point metal layer 14, the fusible conductor 9 can be connected to the first and second electrodes 3 and 4 and the intermediate electrode 15 by melting the low-melting-point metal layer 13 at the reflow temperature, so it is not always necessary to print a conductive connecting material.

[0077] Next, flux 19 is applied to the fusible conductor 9 by screen printing or the like, and then a cap member 16 is connected to the surface 2a of the insulating substrate 2 on which the fusible conductor 9 is mounted to cover the substrate surface and obtain the protective element 1.

[0078] [Circuit Configuration Example] Such a protective element 1 is used, for example, by being incorporated into the circuit of a lithium-ion secondary battery pack 30. As shown in Figure 6, the battery pack 30 has, for example, a battery stack 35 consisting of multiple lithium-ion secondary battery cells 31a, 31b, 31c...

[0079] The battery pack 30 includes a battery stack 35, a charge / discharge control circuit 36 ​​that controls the charging and discharging of the battery stack 35, 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 35, a detection circuit 37 that detects the voltage of each battery cell 31a, 31b, 31c..., and a first current control element 38 and a second current control element 39 that act as switch elements that control the operation of the protection element 1 according to the detection result of the detection circuit 37.

[0080] The battery stack 35 consists of battery cells 31a, 31b, 31c, etc., connected in series, which require control to protect against overcharging and over-discharging. The battery stack 35 is detachably connected to the charging device 32 via the positive terminal 30a and negative terminal 30b of the battery pack 30, and a charging voltage is applied from the charging device 32. The battery pack 30, once charged by the charging device 32, can power electronic devices by connecting the positive terminal 30a and negative terminal 30b to these battery-powered electronic devices.

[0081] The charge / discharge control circuit 36 ​​comprises two current control elements 33a and 33b connected in series in the current path between the battery stack 35 and the charging device 32, and a control unit 34 that controls the operation of these current control elements 33a and 33b. The current control elements 33a and 33b are composed of, for example, field-effect transistors (hereinafter referred to as FETs), and the control unit 34 controls the conduction and interruption of the current path of the battery stack 35 in the charging direction and / or the discharge direction by controlling the gate voltage. The control unit 34 is responsible for the primary protection function in the battery circuit shown in Figure 6, and operates by receiving power from the charging device 32. In accordance with the detection result by the detection circuit 37, it controls the operation of the current control elements 33a and 33b to interrupt the current path when the battery stack 35 is over-discharged or overcharged.

[0082] The protection element 1 is responsible for a secondary protection function in the battery circuit shown in Figure 6. For example, it is connected to the charge / discharge current path between the battery stack 35 and the charge / discharge control circuit 36, and its operation is controlled by the first current control element 38 or the second current control element 39.

[0083] The detection circuit 37 is connected to each battery cell 31a, 31b, 31c, etc., and detects the voltage value of each battery cell 31a, 31b, 31c, etc., and supplies each voltage value to the control unit 34 of the charge / discharge control circuit 36. The detection circuit 37 also outputs a control signal to control the first current control element 38 or the second current control element 39 when at least one of the battery cells 31a, 31b, 31c, etc. reaches an overcharge voltage or over-discharge voltage.

[0084] The first current control element 38 and the second current control element 39 are configured, for example, as FETs, and when the voltage value of the battery cells 31a, 31b, 31c... exceeds a predetermined over-discharge or overcharge state based on the detection signal output from the detection circuit 37, the protection element 1 is activated to control the charging and discharging current path of the battery stack 35 to be interrupted without the switching operation of the current control elements 33a and 33b.

[0085] The first current control element 38 is a first switch element connected to the first heating element electrode 6, and can energize and heat the first heating element 5. The second current control element 39 is a second switch element connected to the second heating element electrode 8, and can energize and heat the first and second heating element electrodes 5 and 7.

[0086] Here, the first heating element 5 provided on the surface 2a of the insulating substrate 2 covers the low resistance and low voltage side, while the second heating element 7 provided on the back surface 2b of the insulating substrate 2, together with the first heating element 5, covers the high resistance and high voltage side. For example, if over-discharge is detected by the detection circuit 37, the detection circuit 37 switches the first current control element 38 to an energized state, and the first heating element 5 becomes energized and generates heat. Also, for example, if overcharge is detected by the detection circuit 37, the detection circuit 37 switches the second current control element 39 to an energized state, and the first heating element 5 and the second heating element 7 become energized and generate heat.

[0087] Thus, the protection element 1 can switch the heating element that generates heat according to the operating voltage, and has a wide operating voltage range. Therefore, the range of rated voltages of battery circuits in which the protection element 1 can be used is widened. While a protection element with one heating element can be used with battery cells or battery stacks with an operating voltage range of, for example, 4 to 10V, the protection element 1 can be used with battery cells or battery stacks with an operating voltage range of 4 to 20V. In addition, when the voltage value of the battery cell or battery stack fluctuates, for example, between overcharging and over-discharging, the protection element 1 can select the heating element that generates heat according to the fluctuation range of the battery's voltage value.

[0088] Furthermore, by forming the first heating element 5 on the surface 2a of the insulating substrate 2 and the second heating element 7 on the back surface 2b of the insulating substrate 2, the insulation short-circuit resistance can be improved. That is, even when a high voltage is applied to the first and second heating elements 5 and 7, dielectric breakdown between the first and second heating elements 5 and 7, and between them and electrodes formed on the insulating substrate 2 such as the intermediate electrode 15, and damage to the first and second heating elements 5 and 7, other electrodes, or the insulating substrate 2 can be prevented. Moreover, while keeping the thickness of the element down, sufficient space can be secured for the molten conductor 9a to aggregate on the intermediate electrode 15 and the first and second electrodes 3 and 4 when the fusible conductor 9 melts, without compromising the reduction in the thickness of the element.

[0089] The protective element 1 to which the present invention is applied, used in the battery pack 30 having the above configuration, has a circuit configuration as shown in Figure 7. That is, the first external connection electrode 17 is connected to the battery stack 35 side, and the second external connection electrode 18 is connected to the positive electrode terminal 30a side, thereby connecting the fusible conductor 9 in series on the charge / discharge path of the battery stack 35. The first heating element 5 is connected to the first current control element 38 via the first heating element electrode 6b on the back side, and is also connected to the battery stack 35. The second heating element 7 is connected to the second current control element 39 via the second heating element electrode 8, and is also connected to the battery stack 35. Thus, the protective element 1 has a four-terminal structure consisting of the first and second external connection electrodes 17 and 18, the first heating element electrode 6b on the back side, and the second heating element electrode 8.

[0090] The first heating element 5 is connected at one end to the fusible conductor 9 and one end of the battery stack 35 via the intermediate electrode 15, and at the other end to the first current control element 38 and the other end of the battery stack 35 via the first heating element electrode 6. This creates a power supply path to the first heating element 5, whose energization can be controlled by the first current control element 38.

[0091] Furthermore, the second heating element 7 is connected at one end to the fusible conductor 9 and one end of the battery stack 35 via the first heating element electrode 6, the first heating element 5, and the intermediate electrode 15, and at the other end to the second current control element 39 and the other end of the battery stack 35 via the second heating element electrode 8. This creates a power supply path to the first and second heating elements 5 and 7, whose energization can be controlled by the second current control element 39.

[0092] [Operation of the protective elements] The first heating element 5 is connected to a first current control element 38 etc. formed in the external circuit via a first heating element electrode 6b on the back side when the protective element 1 is mounted on the external circuit board, and under normal conditions, current flow and heat generation are restricted. The second heating element 7 is connected to a second current control element 39 etc. formed in the external circuit via a second heating element electrode 8 when the protective element 1 is mounted on the external circuit board, and under normal conditions, current flow and heat generation are restricted.

[0093] Then, when the detection circuit 37 detects overcharging or over-discharging of at least one of the battery cells 31a, 31b, 31c..., it outputs a cutoff signal to the first current control element 38 or the second current control element 39. The first current control element 38 or the second current control element 39 then controls the current to energize the first heating element 5 or the first and second heating elements 5 and 7. The first heating element 5 or the first and second heating elements 5 and 7 begin to generate heat as current flows through them.

[0094] The heat from the first heating element 5 is transferred to the fusible conductor 9 via the first heating element lead electrode 21b, the relay electrode 22, and the intermediate electrode 15, and also from the upper surface insulating layer 23b to the fusible conductor 9 via the intermediate electrode 15, melting the fusible conductor 9. The heat from the second heating element 7 is transferred to the fusible conductor 9 via the second lead electrode 25a, the first heating element electrode 6, the first heating element 5, the first lead electrode 21, the relay electrode 22, and the intermediate electrode 15, and also from the lower back insulating layer 26a, the insulating substrate 2, the first and second electrodes 3 and 4, and also from the first heating element 5, the surface insulating layer 23, and the intermediate electrode 15, melting the fusible conductor 9.

[0095] The fusible conductor 9 is formed when the molten conductor 9a aggregates on the intermediate electrode 15 and the first and second electrodes 3 and 4, and is melted and cut between the first electrode 3 and the second electrode 4 (Figure 4). This allows the charge and discharge paths of the battery pack 30 to be blocked.

[0096] When the fusible conductor 9 melts, the charge-discharge path of the battery stack 35 is interrupted between the first electrode 3 and the second electrode 4. In addition, when the fusible conductor 9 melts, the first heating element 5 or the first and second heating elements 5 and 7 also stop generating heat because their power supply paths are interrupted.

[0097] Furthermore, if an overcurrent exceeding the rated current is passed through the fusible conductor 9, the protective element 1 will cause the fusible conductor 9 to melt due to self-heating, resulting in a break between the first electrode 3 and the second electrode 4. This will interrupt the charging and discharging path of the battery pack 30.

[0098] Furthermore, the protective element 1 is formed by incorporating a high-melting-point metal and a low-melting-point metal into the fusible conductor 9. This allows the low-melting-point metal to melt before the high-melting-point metal, and the fusible conductor 9 to be cut in a short time by utilizing the dissolving action of the molten low-melting-point metal on the high-melting-point metal.

[0099] 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.

[0100] Next, an embodiment of this technology will be described. In this embodiment, samples of protective elements were prepared by changing the number or configuration of heating elements. For each sample, the operating voltage range and the melting behavior when the heating element is energized were evaluated as the operating performance of the heating element (○: good, ×: poor).

[0101] [Example 1] Example 1 is a protective element to which the present invention is applied. Specifically, as shown in Figures 1 to 3, the protective element according to Example 1 has a first heating element 5 formed on the surface 2a of the insulating substrate 2 and a second heating element 7 formed on the back surface 2b of the insulating substrate 2. Current was applied to the protective element according to Example 1 from the second heating element electrode 8 to heat the first heating element 5 and the second heating element 7, thereby heating the fusible conductor 9.

[0102] [Comparative Example 1] Comparative Example 1 is a protective element 100 in which a single heating element is provided on the surface of an insulating substrate. That is, in the protective element according to Comparative Example 1, a heating element 106 is formed on the surface of an insulating substrate 103, as shown in Figure 12. Current was passed through the heating element electrode 108 to the protective element according to Comparative Example 1, causing the heating element 106 to heat up and the fusible conductor 105 to heat.

[0103] [Comparative Example 2] Comparative Example 2 is a protective element (structure 60) in which two heating elements are provided adjacent to each other on the surface of an insulating substrate. That is, in the protective element according to Comparative Example 2, as shown in Figure 13, resistors 64a and 64b are provided adjacent to each other on the surface 62a of the insulating member 62 via a conductor 63b. Current was applied to the protective element according to Comparative Example 2 from the connecting member 614, causing resistors 64a and 64b to heat up and the fusible conductor 67 to heat up.

[0104] [Comparative Example 3] Comparative Example 3 is a protective element in which two heating elements are laminated on the surface of an insulating substrate. That is, as shown in Figure 15, in the protective element according to Comparative Example 3, a first heating element 111 and a second heating element 112 are laminated on the surface of an insulating substrate 103 via an insulating layer 107b. Current was applied to the protective element 110 according to Comparative Example 3 from the second external connection electrode 116, causing the first heating element 111 and the second heating element 112 to heat up, and the fusible conductor 105 to heat up.

[0105]

[0106] In Example 1, the fusible conductor 9 melted and was able to isolate the first and second electrodes 3 and 4. Furthermore, no dielectric breakdown was observed between the first and second heating elements 5 and 7 or between them and the intermediate electrode 15, etc. In addition, Example 1 is equipped with two heating elements, and by selecting the energizing terminal, the movable voltage range is wide, from 4.0 to 19.1V.

[0107] On the other hand, in Comparative Example 1, although the fusible conductor 105 melted and the connection between the first and second electrodes 101 and 102 was interrupted, the operating voltage range was narrow, at 4.0 to 9.6 V.

[0108] Comparative Example 2 is equipped with two heating elements and allows selection of the energizing terminals, thereby providing an operating voltage range equivalent to that of Example 1. However, because a conductor 63b is provided between adjacent resistors 64a and 64b, the heat generated by resistors 64a and 64b escapes through the conductor 63b and the connecting member 613 to the circuit board connected to the connecting member 613. As a result, the adjacent regions of resistors 64a and 64b, i.e., the approximately middle portion of the fusible conductor 67, are not heated, and the melting of the fusible conductor 67 is insufficient.

[0109] Comparative Example 3 is equipped with two heating elements and allows selection of the energizing terminals, thereby providing an operating voltage range equivalent to that of Example 1. However, when a high voltage was applied to heat the first and second heating elements 111 and 112, dielectric breakdown occurred. Therefore, it can be seen that the protective element 110 in Comparative Example 3 carries the risk of damage to the first and second heating elements 111 and 112 and the intermediate electrode 104, and the resulting melting failure.

[0110] [Modification 1] Next, a modification of the present invention will be described. In the following description, the same reference numerals are used for the same components and components as those in the protective element 1 described above, and details are omitted. As shown in Figure 8, the protective element 40 to which the present invention is applied may have a third heating element 41 formed inside the insulating substrate 2.

[0111] Figure 9 shows the circuit configuration of the protective element 40. The third heating element 41 can be made of the same material as the first and second heating elements 5 and 7 described above. One end of the third heating element 41 is connected to the surface-side first heating element electrode 6a formed on the surface 2a of the insulating substrate 2 via a third lead electrode 42a and a conductive through-hole (not shown). The other end of the third heating element 41 is connected to a third heating element electrode 43 (not shown) formed on the back surface 2b of the insulating substrate 2 via a third lead electrode 42b and a conductive through-hole (not shown). The third heating element electrode 43 serves as the power supply terminal for the third heating element 41. One end of the second heating element 7 is connected to the third heating element electrode 43, and the other end is connected to the second heating element electrode 8.

[0112] The first heating element electrode 6b, the second heating element electrode 8, and the third heating element electrode 43 on the back side are each connected to a current control element whose energization is controlled, thereby controlling the energization and heating. As a result, the protection element 40 can select the heating element to be heated by selecting the first heating element electrode 6b, the second heating element electrode 8, and the third heating element electrode 43 on the back side as the energizing terminals.

[0113] The first heating element 5 covers the low resistance and low voltage side, the third heating element 41 covers the medium resistance and medium voltage side together with the first heating element 5, and the second heating element 7 covers the high resistance and high voltage side together with the first and third heating elements 5 and 41. The protection element 40 can, for example, when overcharging or over-discharging is detected by the detection circuit 37, select a heating element to energize and heat up according to the applied voltage from a power source such as a battery cell or battery stack.

[0114] The protective element 40, by forming a third heating element 41 inside the insulating substrate 2, suppresses dielectric breakdown between the first heating element 5 and the third heating element 41 and between the heating element and electrodes formed on the insulating substrate 2, similar to the protective element 1, thereby preventing damage to the first heating element 5 to the third heating element 41, other electrodes, or the insulating substrate 2. Therefore, with the protective element 40, the first heating element 5, the first and third heating elements 5 and 41, and the first to third heating elements 5, 7 and 41 generate sufficient heat to quickly and reliably melt the fusible conductor 9.

[0115] Furthermore, since the protective element 40 does not stack the first heating elements 5 to the third heating elements 41, the space inside the protective element 1 is not largely occupied by the first heating elements 5 to the third heating elements 41 or the insulating layer. This ensures sufficient space for the molten fusible conductor 9 to aggregate on the intermediate electrode 15 and the first and second electrodes 3 and 4, while also suppressing the enlargement of the element and enabling miniaturization and thinning.

[0116] [Modification 2] In addition, the protective element to which the present invention is applied may have a first heating element 5 or a second heating element 7 formed inside the insulating substrate 2. Figure 10 is a cross-sectional view showing a protective element 50 in which a second heating element 7 is formed inside the insulating substrate 2. In the protective element 50, one end of the second heating element 7 is connected to a first heating element electrode 6b on the back surface 2b of the insulating substrate 2 via a second lead electrode 25a and a conductive through-hole (not shown). The other end of the second heating element 7 is connected to a second heating element electrode 8 formed on the back surface 2b of the insulating substrate 2 via a second lead electrode 25b and a conductive through-hole (not shown).

[0117] Figure 11 is a cross-sectional view showing a protective element 51 in which a first heating element 5 is formed inside an insulating substrate 2. In the protective element 51, one end of the first heating element 5 is connected to a first heating element electrode 6b on the back surface 2b of the insulating substrate 2 or a first heating element electrode 6a on the front surface 2a of the insulating substrate 2 via a first lead electrode 21a and a conductive through-hole (not shown). The other end of the first heating element 5 is connected to a relay electrode 22 formed on the front surface 2a of the insulating substrate 2 via a first lead electrode 21b and a conductive through-hole (not shown).

[0118] 1 Protective element, 2 Insulating substrate, 3 First electrode, 4 Second electrode, 5 First heating element, 5a One end, 5b Other end, 6 First heating element electrode, 6a Front side first heating element electrode, 6b Back side first heating element electrode, 7 Second heating element, 7a One end, 7b Other end, 8 Second heating element electrode, 9 Fusible conductor, 9a Molten conductor, 13 Low melting point metal layer, 14 High melting point metal layer, 15 Intermediate electrode, 16 Cap member, 17 First external connection electrode, 18 Second external connection electrode, 19 Flux, 21 First lead electrode, 22 Intermediate electrode, 23 Surface insulating layer, 23a Lower surface insulating layer, 23b Upper surface insulating layer, 25 Second lead electrode, 26 Back insulating layer, 26a Lower back insulating layer, 26b Upper back insulating layer, 30 Battery pack, 30a positive terminal, 30b negative terminal, 31 battery cell, 32 charging device, 33 current control element, 34 control unit, 35 battery stack, 36 charge / discharge control circuit, 37 detection circuit, 38 first current control element, 39 second current control element, 40 protection element, 41 third heating element, 42 third lead electrode, 43 third heating element electrode

Claims

1. A protective element comprising: an insulating substrate; a first heating element formed on the surface of the insulating substrate; a first heating element electrode connected to the first heating element and serving as a current-carrying terminal for the first heating element; a second heating element formed on the back surface of the insulating substrate; a second heating element electrode connected to the second heating element and serving as a current-carrying terminal for the second heating element; and a fusible conductor provided on the surface of the insulating substrate that is melted by heating, wherein the first heating element electrode or the second heating element electrode can be selected as the current-carrying electrode from an external power source.

2. The protective element according to claim 1, wherein the first heating element and the second heating element are connected, and the first heating element electrode is formed between the first heating element and the second heating element.

3. The protective element according to claim 1 or 2, comprising an intermediate electrode connected to the end of the first heating element opposite to the end connected to the second heating element, wherein the fusible conductor is connected to the intermediate electrode.

4. The protective element according to claim 1 or 2, comprising a third heating element formed inside the insulating substrate, and a third heating element electrode connected to the third heating element and serving as an energizing terminal for the third heating element, wherein the first heating element electrode, the first and third heating element electrodes, or the first, second and third heating element electrodes can be selected as energizing electrodes from an external power source.

5. A protective element comprising: an insulating substrate; a first heating element formed on the surface of the insulating substrate; a first heating element electrode connected to the first heating element and serving as a current-carrying terminal for the first heating element; a second heating element formed inside the insulating substrate; a second heating element electrode connected to the second heating element and serving as a current-carrying terminal for the second heating element; and a fusible conductor provided on the surface of the insulating substrate that is melted by heating, wherein the first heating element electrode or the first and second heating element electrodes can be selected as the current-carrying electrode from an external power source.

6. A protective element comprising: an insulating substrate; a first heating element formed inside the insulating substrate; a first heating element electrode connected to the first heating element and serving as a current-carrying terminal for the first heating element; a second heating element formed on the back surface of the insulating substrate; a second heating element electrode connected to the second heating element and serving as a current-carrying terminal for the second heating element; and a fusible conductor provided on the surface of the insulating substrate that is melted by heating, wherein the first heating element electrode or the first and second heating element electrodes can be selected as the current-carrying electrode from an external power source.

7. A battery pack comprising one or more battery cells, 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 claim 1 or 2, a first switch connected to the first heating element electrode, a second switch connected to the second heating element electrode, and a control unit that controls the operation of the first switch and the second switch.

8. The battery pack according to claim 7, comprising a circuit for controlling the operation of the first switch and the second switch, wherein the first switch is activated in the event of over-discharge and the second switch is activated in the event of over-charging.

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