Protective element

Abstract

The invention provides a protection element capable of avoiding environmental load, preventing the influence of reflow mounting on the rapid fusing property of a fuse element, and realizing low cost. A protective element (1) is provided with: an insulating substrate (2); a first electrode (4) and a second electrode (5) provided on the insulating substrate (2); a fuse element (7) that is disposed on the surfaces of the first electrode (4) and the second electrode (5) and electrically connects the first electrode (4) and the second electrode (5); and a connection conductor (8) that connects the first electrode (4), the second electrode (5), and the fuse element (7), the fuse element (7) comprising a lead-free conductor and having a liquid phase point higher than the reflux heating temperature, and the connection conductor (8) having a liquid phase point lower than the liquid phase point of the fuse element (7) and having a solid phase point lower than the reflux heating temperature.

Description

Technical Field

[0001] The present technology relates to a protection element installed on a current path and disconnecting the current path by blowing a fuse element in an abnormal situation. This application claims priority based on Japanese patent application No. 2022-115341 filed in Japan on July 20, 2022, which is incorporated herein by reference. Background Art

[0002] Lithium-ion secondary batteries (LiB) are high-output, high-energy-density batteries that are used in a variety of applications as their performance improves. However, LiBs are batteries that have the risk of emitting smoke and catching fire when the ICs and FETs that control charging and discharging fail due to some influence, and as a secondary protection measure, protection elements with built-in heating elements are used. As the applications for LiBs expand, the number of LiBs produced is also increasing, and the demand for protection elements to protect LiBs is also increasing.

[0003] Many components including the above-mentioned IC and FET used for LiB control correspond to the surface mounting process, so the protection element is also required to correspond to surface mounting. In addition, in order to safely complete the fusing action of the fuse element using the built-in heating element, it is desired that the melting point of the fuse element is as low as possible, and ideally a melting point (around 280℃ to 300℃) that can barely withstand the reflow temperature (260℃).

[0004] In order to meet this demand, from the viewpoint of cost, fuse elements generally use alloys containing a large amount of lead. On the other hand, as the demand for reducing environmental load increases, fuse elements with new structures that do not use lead have also been proposed.

[0005] Fig.10 1 and 2 are diagrams showing a structural example of a protection element, wherein (A) is a top view showing the protection element with a cover member omitted, (B) is a cross-sectional view, and (C) is a bottom view. Fig.10 The protection element 100 shown comprises: an insulating substrate 101; a first and a second electrode 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; a heating element lead-out electrode 106 stacked on the insulating layer 105 and connected to the heating element 104; and a fusible conductor, i.e., a fuse element 107, which is mounted on the first electrode 102, the heating element lead-out electrode 106 and the second electrode 103 via a connecting material 110.

[0006] As the connection material 110 , the same material as that of the fuse element 107 can be used, for example, various tin-based solder pastes such as Pb—Sn, Au—Sn, and Sn—Cu—Ag can be used.

[0007] The first and second electrodes 102 and 103 are terminal portions connected to the current path of the external circuit connected to the protection element 100, and are respectively connected to the first and second external connection electrodes 102a and 103a formed on the back side of the insulating substrate 101 via the castellated structure. The first and second external connection electrodes 102a and 103a of the protection element 100 are connected to the connection electrodes provided on the external circuit substrate on which the protection element 100 is mounted, whereby the fuse element 107 is assembled to a part of the current path formed on the external circuit substrate.

[0008] The heating element 104 is a conductive component having a relatively high resistance value and generating heat when energized, and is composed of, for example, nickel-chromium alloy, W, Mo, Ru, etc. or materials containing them. In addition, the heating element 104 is connected to a heating element electrode 108 formed on the surface of the insulating substrate 101. The heating element electrode 108 is connected to a third external connection electrode 108a formed on the back side of the insulating substrate 101 via a castellated structure. The third external connection electrode 108a of the protection element 100 is connected to a connection electrode provided on an external circuit substrate on which the protection element 100 is mounted, thereby connecting the heating element 104 to an external power supply provided in an external circuit. Moreover, the heating element 104 is always controlled to be energized by a switching element not shown in the figure.

[0009] The heating element 104 is covered by an insulating layer 105 composed of a glass layer or the like, and a heating element lead-out electrode 106 is formed on the insulating layer 105, thereby overlapping the heating element lead-out 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 heating element lead-out electrode 106 via a connecting material 110.

[0010] Thus, in the protection element 100 , the heating element 104 and the fuse element 107 are thermally connected by overlapping each other, and when the heating element 104 generates heat due to energization, the fuse element 107 can be melted.

[0011] The fuse element 107 is connected from the first electrode 102 to the second electrode 103 through the heating element lead-out electrode 106, thereby constituting a part of the current path of the external circuit equipped with the protection element 100. Moreover, the fuse element 107 is cut off between the first and second electrodes 102 and 103 by self-heating (Joule heat) when a current exceeding the rated value flows through it, or by heating and melting of the heating element 104.

[0012] Prior art literature

[0013] Patent Literature

[0014] Patent Document 1: Japanese Patent No. 2790433

[0015] Patent Document 2: Japanese Patent Application Publication No. 2015-035281 Summary of the invention

[0016] Problems to be solved by the invention

[0017] The fuse element 107 can be formed of a high melting point solder such as Pb-Sn with a lead content of 85 wt% or more. However, as described above, with the increasing demand for reducing environmental load, the use of lead-containing solder is only restrictedly permitted in the RoHS directive, etc., and it is expected that the demand for Pb-free will increase in the future.

[0018] When lead-free solder is used as the fuse element 107, the melting point is higher than that of lead-containing solder, and it is difficult to quickly melt the fuse element 107 by the heat generated by the heating element 104. In addition, when a high melting point solder such as Au-Sn with a gold content of 80 wt% or more is used as the fuse element 107, there is an advantage of not containing environmentally hazardous substances, but on the other hand, it leads to high costs.

[0019] When a structure is used as the fuse element 107 in which a tin-based low melting point (melting point: around 220°C) metal 107a such as Sn-Ag-Cu is covered with a high melting point (melting point: above 600°C) metal 107b such as Ag, the environmental load and cost issues can be taken into consideration. Fig.11 As shown in FIG. 1 , when the cross-sectional shape of the fuse element 107 changes due to the low melting point metal 107a melted at the heating temperature (near 260°C) in the surface mounting process flowing unevenly, the rapid fusing property may be impaired due to the uneven resistance value. Although the unevenness of the low melting point metal 107a can be suppressed by making the high melting point metal 107b covering the low melting point metal 107a thicker, there is a risk that the fusing time will be extended due to the heat of the heating element 104 and the heating element 104 will be damaged before the fuse element 107 is blown. As a countermeasure for the deformation of the fuse element 107, a scheme of forming a pillar of the high melting point metal 107b in the fuse element 107 has also been proposed, but this will lead to an increase in manufacturing costs.

[0020] Therefore, an object of the present technology is to provide a protection element that can avoid environmental load, prevent the influence of reflow mounting on the quick-blowing property of a fuse element, and can also achieve cost reduction.

[0021] Solutions to Solve Problems

[0022] In order to solve the above-mentioned problems, the protection element of the present technology comprises: an insulating substrate; a first electrode and a second electrode, which are arranged on the above-mentioned insulating substrate; a fuse element, which is arranged on the surface of the above-mentioned first electrode and the above-mentioned second electrode and electrically connects the above-mentioned first electrode and the above-mentioned second electrode; and a connecting conductor, which connects the above-mentioned first electrode and the above-mentioned second electrode and the above-mentioned fuse element, the above-mentioned fuse element is composed of a lead-free conductor, and the liquidus point is higher than the reflow heating temperature, the liquidus point of the above-mentioned connecting conductor is lower than the liquidus point of the above-mentioned fuse element, and has a solidus point lower than the reflow heating temperature.

[0023] Effects of the Invention

[0024] According to the present technology, environmental load can be avoided, variation in electrical characteristics can be prevented even by reflow mounting, and cost reduction can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The figures show a protection element to which the present technology is applied, wherein (A) is a top view showing the device with a cover member omitted, (B) is a cross-sectional view, and (C) is a bottom view.

[0026] Figure 2 It is a top view showing a state where the fuse element has been blown.

[0027] Figure 3 This is a plan view showing a protection element in which fuse elements are mounted respectively between the first electrode and the heat generating body lead-out electrode and between the heat generating body lead-out electrode and the second electrode, with the cover member omitted.

[0028] Figure 4 This is a circuit diagram showing a configuration example of a battery pack equipped with a protection element to which the present technology is applied.

[0029] Figure 5 This is a circuit diagram of a protection element to which this technology is applied.

[0030] Figure 6 The figures show a protective element according to a modified example to which the present technology is applied, wherein (A) is a top view showing the protective element with a cover member omitted, (B) is a cross-sectional view, and (C) is a bottom view.

[0031] Figure 7 The figures show a protective element according to a modified example to which the present technology is applied, wherein (A) is a top view showing the protective element with a cover member omitted, (B) is a cross-sectional view, and (C) is a bottom view.

[0032] Figure 8 is a circuit diagram of a protection element according to a modified example.

[0033] Fig. 9The figures show a protective element according to a modified example to which the present technology is applied, wherein (A) is a top view showing the protective element with a cover member omitted, (B) is a cross-sectional view, and (C) is a bottom view.

[0034] Fig.10 1 and 2 are diagrams showing a structural example of a protection element, wherein (A) is a top view showing the protection element with a cover member omitted, (B) is a cross-sectional view, and (C) is a bottom view.

[0035] Fig.11 This is a cross-sectional view showing a state in which the cross-sectional shape of the fuse element changes due to the low-melting-point metal melted at the heating temperature (near 260° C.) in the surface mounting process flowing unevenly. DETAILED DESCRIPTION

[0036] Hereinafter, the protection element to which the present technology is applied is described in detail with reference to the accompanying drawings. In addition, the present technology is not limited to the following embodiments, and various changes can be made without departing from the main purpose of the present technology. In addition, the accompanying drawings are schematic diagrams, and the ratios of various dimensions are sometimes different from reality. Specific dimensions should be determined by referring to the following description. In addition, the drawings also include parts with different dimensional relationships and ratios.

[0037] like Figure 1 As shown, the protection element 1 to which the present technology is applied comprises: an insulating substrate 2; a first electrode 4 and a second electrode 5 arranged on the insulating substrate 2; a fusible conductor, namely a fuse element 7, which is arranged on the surface of the first electrode 4 and the second electrode 5 and electrically connects the first electrode 4 and the second electrode 5; and a connecting conductor 8 connecting the first electrode 4 and the second electrode 5 and the fuse element 7.

[0038] The fuse element 7 is formed of an alloy composed of a material that does not contain lead and has a liquidus point higher than the reflow heating temperature. That is, the fuse element 7 does not melt at the reflow heating temperature. Therefore, the fuse element 7 does not melt during the reflow process and can be reflow mounted on the first and second electrodes 4 and 5. In addition, the fuse element 7 does not melt during the reflow process, so the protection element 1 can be mounted on the external circuit substrate by reflow.

[0039] In addition, the liquidus point of the connection conductor 8 is lower than the liquidus point of the fuse element 7, and has a solidus point lower than the reflow heating temperature. That is, the melting point of the connection conductor 8 is lower than the melting point of the fuse element 7. Therefore, the connection conductor 8 is used for connecting the fuse element 7 and the first and second electrodes 4 and 5 in a state of being melted to a certain extent at the reflow heating temperature. In addition, since the connection conductor 8 melts earlier than the fuse element 7, it can wet and spread on the first and second electrodes 4 and 5, and fill between the fuse element 7 and the first and second electrodes 4 and 5, and connect the two electrically and mechanically.

[0040] The liquidus point of the connection conductor 8 may be higher than the reflow heating temperature, but is preferably lower than the reflow heating temperature because it is preferably used for connecting the fuse element 7 to the first and second electrodes 4 and 5 in a completely molten state in order to achieve good electrical and mechanical connection.

[0041] In this way, the protection element 1 can achieve a reduction in environmental load while also achieving excellent rapid blowout performance by using an alloy composed of a material that does not use lead and has a liquidus point higher than the reflow heating temperature as the fuse element 7. In addition, it is possible to achieve both a reduction in environmental load and maintenance of rapid blowout performance without using expensive metals such as gold as the fuse element 7, and also to achieve cost reduction.

[0042] Such a protection element 1 is installed in an external circuit so that the fuse element 7 constitutes a part of the current path of the external circuit and cuts off the current path by melting under a predetermined condition (see Figure 2 ). Hereinafter, each structure of the protection element 1 will be described in detail.

[0043] Figure 1 The protection element 1 shown has a heating element 3, and a fuse element 7 is blown by the heat of the heating element 3 or an overcurrent exceeding the rated value. That is, the protection element 1 has: an insulating substrate 2; a heating element 3, which is arranged on the insulating substrate 2; a first electrode 4 and a second electrode 5, which are arranged on the insulating substrate 2; a heating element lead-out electrode 6, which is arranged between the first electrode 4 and the second electrode 5 and is electrically connected to one end of the heating element 3; and a fuse element 7, which is arranged on the surfaces of the first electrode 4, the second electrode 5 and the heating element lead-out electrode 6, and electrically connects the first electrode 4 and the heating element lead-out electrode 6, and the second electrode 5 and the heating element lead-out electrode 6.

[0044] [Insulating substrate]

[0045] The insulating substrate 2 is formed of, for example, an insulating member such as alumina, glass ceramic, mullite, or zirconium oxide. In addition, the insulating substrate 2 may also use materials used for printed wiring substrates such as glass epoxy substrates and phenol substrates. In addition, the insulating substrate 2 may also be provided with glass or solder resist at a predetermined position for the purpose of insulating or controlling the position of the connection conductor 8 and the fuse element 7. In addition, in this specification, the surface of the insulating substrate 2 on which the fuse element 7 is mounted is referred to as the front surface 2a, and the surface on the side opposite to the surface on which the fuse element 7 is mounted is referred to as the back surface 2b.

[0046] [First electrode, second electrode]

[0047] A first electrode 4 and a second electrode 5 are formed at opposite ends of the surface 2a of the insulating substrate 2. The first electrode 4 and the second electrode 5 are respectively formed of a conductive pattern of Ag, Cu, or an alloy thereof. The first electrode 4 and the second electrode 5 can be formed, for example, by printing Ag paste in a predetermined pattern by screen printing and then firing at a predetermined temperature.

[0048] The first electrode 4 is connected to the first external connection electrode 11 formed on the back side 2b via the castellated structure from the surface 2a of the insulating substrate 2. In addition, the second electrode 5 is connected to the second external connection electrode 12 formed on the back side 2b via the castellated structure from the surface 2a of the insulating substrate 2. When the protection element 1 is mounted on an external circuit substrate, the first and second external connection electrodes 11 and 12 are connected to the connection electrodes provided on the external circuit substrate, whereby the fuse element 7 is installed in a part of the current path formed on the external circuit substrate.

[0049] The first and second electrodes 4 and 5 are electrically connected via the fuse element 7 by carrying the fuse element 7 via the connection conductor 8. Figure 2 As shown, the heating element 3 generates heat when energized and causes the fuse element 7 to melt, or a large current exceeding the rated value flows through the protection element 1 and causes the fuse element 7 to melt due to self-heating (Joule heat), thereby disconnecting the first and second electrodes 4 and 5.

[0050] [Heat-generating element lead-out electrode]

[0051] The heat generating body lead-out electrode 6 is provided in a region between the first electrode 4 and the second electrode 5, and one end thereof is connected to the intermediate electrode 14 described later. The heat generating body lead-out electrode 6 is stacked on the insulating protective layer 9 described later, and overlaps the heat generating body 3 via the insulating protective layer 9.

[0052] The heat source lead electrode 6 can be formed by printing and firing a conductive paste such as Ag or Cu, similarly to the first and second electrodes 4 and 5. The heat source lead electrode 6 is connected to the fuse element 7 via the connection conductor 8 between the first and second electrodes 4 and 5.

[0053] [Connecting conductor]

[0054] The connecting conductor 8 connects the first and second electrodes 4, 5 and the heating element lead-out electrode 6 and the fuse element 7, and is formed by a paste-like solder alloy or the like. Specifically, the connecting conductor 8 is a metal bonding material having a liquidus point lower than the liquidus point of the fuse element 7 and a solidus point lower than the reflow heating temperature (260°C), such as tin-based alloys and indium-based alloys. Among them, it is preferred to use Sn-Ag3-Cu0.5 (solidus point: 217°C / liquidus point: 220°C), Sn-Ag3.5 (solidus point: 221°C / liquidus point: 223°C), Sn-Cu solder or Sn-Sb-Ag-Cu solder. In particular, by containing Sb, it is easy to adjust the liquidus point and solidus point to the desired range.

[0055] The connection conductor 8 is supplied to the position of the first and second electrodes 4 and 5 and the heating element lead-out electrode 6 where the fuse element 7 is mounted by a known method such as screen printing, and after the fuse element 7 is mounted, a reflow process is performed. The connection conductor 8 is a material having a liquidus point lower than the liquidus point of the fuse element 7 and a solidus point lower than the reflow heating temperature, and is therefore used for connecting the fuse element 7 with the first and second electrodes 4 and 5 in a state of at least some degree of melting, preferably in a state of complete melting, at the reflow heating temperature. As a result, the connection conductor 8 wets and spreads on the first and second electrodes 4 and 5, and fills between the fuse element 7 and the first and second electrodes 4 and 5, so that the two can be electrically and mechanically connected.

[0056] In addition, it is preferred that a coating of Ni / Au, Ni / Pd, Ni / Pd / Au or the like is applied on the surface of the first and second electrodes 4, 5 and the heating element lead-out electrode 6 by a known method such as plating treatment. Thus, the protection element 1 can prevent oxidation of the first and second electrodes 4, 5 and the heating element lead-out electrode 6, and prevent the change in the rated value caused by the increase in the on-resistance. In addition, when the protection element 1 is reflow mounted, the first and second electrodes 4, 5 and the heating element lead-out electrode 6 can be prevented from being eroded (solder erosion) due to melting of the connection conductor 8 connecting the fuse element 7.

[0057] In addition, the first and second electrodes 4 and 5 may also be provided with a limiting wall, which prevents the connection solder provided on the electrodes of the external circuit substrate connected to the first and second external connection electrodes 11 and 12 from melting during reflow mounting and climbing up through the castellated structure and wetting and spreading to the first and second electrodes 4 and 5. The limiting wall can be formed using an insulating material that does not have wettability to solder, such as glass, solder resist, and insulating adhesive, and can be formed on the first and second electrodes 4 and 5 by printing or the like. By providing the limiting wall, it is possible to prevent the molten connection solder from wetting and spreading to the first and second electrodes 4 and 5, and maintain the connectivity between the protection element 1 and the external circuit substrate.

[0058] [Heat generating element]

[0059] like Figure 1 As shown, a heating element 3 is formed on the surface 2a of the insulating substrate 2. The heating element 3 is a conductive component having a relatively high resistance value and generating heat when electricity is applied, and is composed of, for example, nickel-chromium alloy, W, Mo, Ru, etc. or a material containing them. The heating element 3 can be formed by mixing powders of these alloys or compositions or compounds with a resin adhesive, etc., forming a pattern of the formed paste on the insulating substrate 2 using a screen printing technique, and firing the paste. As an example, a mixed paste of ruthenium oxide paste, silver and glass paste can be adjusted according to a predetermined voltage, and a film is formed at a predetermined position and with a predetermined area on the surface 2a of the insulating substrate 2, and then fired under appropriate conditions, thereby forming the heating element 3. In addition, the shape of the heating element 3 can be appropriately designed, but as Figure 1 As shown in (A), in order to maximize the heat generation area, it is preferable to set it to a substantially rectangular shape according to the shape of the insulating substrate 2.

[0060] In addition, one end 3a of the heating element 3 is connected to the heating element electrode 17, and the other end 3b is connected to the intermediate electrode 14. The heating element electrode 17 and the intermediate electrode 14 are formed on the side edges of the insulating substrate 2 that are different from the side edges where the first and second electrodes 4 and 5 are provided. The heating element electrode 17 is a power supply electrode for supplying power to the heating element 3, is connected to one end 3a of the heating element 3, and is continuous with the third external connection electrode 13 formed on the back surface 2b of the insulating substrate 2 via a castellated structure.

[0061] The intermediate electrode 14 is an electrode provided between the heat generating element 3 and the heat generating element lead-out electrode 6 stacked on the insulating protective layer 9 , and is connected to the other end 3 b of the heat generating element 3 and to the heat generating element lead-out electrode 6 .

[0062] The heating element electrode 17 and the intermediate electrode 14 can be formed by printing and firing a conductive paste of Ag, Cu or an alloy thereof, as can the first and second electrodes 4 and 5. In addition, by making each of these electrodes formed on the surface 2a of the insulating substrate 2 from the same material, they can be formed by a single printing and firing process.

[0063] [Insulation protective layer]

[0064] In addition, the heating element 3 is covered by an insulating protective layer 9. The insulating protective layer 9 protects and insulates the heating element 3, is provided to efficiently transfer the heat of the heating element 3 to the heating element lead-out electrode 6 and the fuse element 7, and is composed of an insulating material such as glass having heat resistance to the heating temperature of the heating element 3. As glass raw materials constituting the insulating protective layer 9, there are, for example, glass paste for protective coating of silica-based glass and glass paste for insulation.

[0065] The insulating protective layer 9 can be formed by applying the glass paste by screen printing or the like and then firing it. Figure 1 In the protection element 1 shown, the insulating protection layer 9 is formed so as to cover the heat generating element 3 formed on the surface 2 a of the insulating substrate 2 .

[0066] The thickness of the insulating protection layer 9 is appropriately set according to the coating properties of the material such as the glass paste and the required disconnection time of the fuse element 7 , and is, for example, 10 μm to 40 μm, preferably 20 μm to 40 μm.

[0067] [Fuse element]

[0068] Next, the fuse element 7 is described. The fuse element 7 is installed across the first and second electrodes 4 and 5, and is melted by heat caused by the energization of the heating element 3, or melted by self-heating (Joule heat) due to the flow of current exceeding the rated value, thereby cutting off the current path between the first electrode 4 and the second electrode 5. The fuse element 7 is connected to the first and second electrodes 4 and 5 and the heating element lead-out electrode 6 via a connecting conductor 8.

[0069] The fuse element 7 is formed of a conductive material that melts due to the heat or overcurrent state caused by the energization of the heating element 3. In addition, as described above, the fuse element 7 is formed of an alloy composed of a material that does not contain lead and has a liquidus point higher than the reflow heating temperature (260°C). That is, the fuse element 7 does not melt at the reflow heating temperature. Therefore, the fuse element 7 will not be blown during the reflow process, and the first and second electrodes 4, 5 and the heating element lead-out electrode 6 can be efficiently connected to the fuse element 7 and the protection element 1 can be installed on the external circuit substrate through reflow.

[0070] In addition, the fuse element 7 is formed of an alloy composed of a material having a liquidus point higher than the reflow heating temperature (260°C). Unlike a structure in which a low-melting-point metal having a liquidus point lower than the reflow temperature is covered with a high-melting-point metal, the low-melting-point metal covered by the high-melting-point metal layer will not flow and deform during the reflow process, nor will the deformation affect the quick-blow characteristics.

[0071] As the material of the fuse element 7, for example, tin-based alloys such as Sn-Cu solder and Sn-Sb-Ag-Cu solder can be cited. Specifically, Sn-Sb10 (solid phase point: 246°C / liquid phase point: 272°C), Sn-Cu7.0 (solid phase point: 227°C / liquid phase point: about 400°C), and Sn-Sb35-Cu5-Ag5 (solid phase point: 300°C / liquid phase point: about 350°C) can be suitably used. In particular, by containing Sb, it is easy to adjust the liquid phase point and the solid phase point to a desired range.

[0072] The liquidus temperature of the fuse element 7 is preferably 400° C. or lower. If the liquidus temperature exceeds 400° C., the time required until the fuse element 7 is melted is prolonged, and there is a risk that the heating element 3 may be damaged before the fuse element 7 is melted.

[0073] The fuse element 7 can be in any shape, but is preferably in the shape of Figure 1 In addition, the protection element 1 can be equipped with a fuse element 7 from the first electrode 4 to the second electrode 5, or it can be formed into a rectangular plate shape as shown. Figure 3 As shown, fuse elements 7 are respectively mounted between the first electrode 4 and the heating element lead-out electrode 6 and between the heating element lead-out electrode 6 and the second electrode 5. Furthermore, a plurality of fuse elements 7 may be mounted in parallel from the first electrode 4 to the second electrode 5, or a plurality of fuse elements 7 may be respectively mounted in parallel between the first electrode 4 and the heating element lead-out electrode 6 and between the heating element lead-out electrode 6 and the second electrode 5.

[0074] The fuse element 7 will not be blown due to self-heating during the period of the predetermined rated current flowing. Moreover, when a current higher than the rated value flows, the fuse element 7 is blown due to self-heating, and the current path between the first and second electrodes 4 and 5 is cut off. In addition, the fuse element 7 is melted due to the heating element 3 being energized and heated, and is gathered on the first and second electrodes 4 and 5 and the heating element lead-out electrode 6 along with the introduction of the molten conductor, thereby being blown between the electrodes, thereby cutting off the current path between the first and second electrodes 4 and 5.

[0075] In addition, the fuse element 7 may be coated with flux to prevent oxidation and improve wettability during melting. In addition, the protection element 1 protects the inside of the insulating substrate 2 by covering it with a housing 30. The housing 30 can be formed using insulating components such as various engineering plastics, thermoplastics, ceramics, and glass epoxy substrates. In addition, the housing 30 has a sufficiently large internal space on the surface 2a of the insulating substrate 2 so that the fuse element 7 expands into a spherical shape when melted and the molten conductor 7a gathers on the heating element lead-out electrode 6, the first and second electrodes 4, 5.

[0076] [Circuit Configuration Example]

[0077] Next, a circuit structure example of a lithium-ion secondary battery to which the protection element 1 is applied is described. In addition, the present technology is not limited to the following structure. The protection element 1 is used by being incorporated into a circuit in a battery pack 20 of a lithium-ion secondary battery. The battery pack 20 has a battery stack 25, and the battery stack 25 is composed of a plurality of, for example, Figure 4 As shown, a total of four lithium ion secondary battery cells 21a to 21d are provided.

[0078] The battery pack 20 includes: a battery stack 25; a charge and discharge control circuit 26 for controlling the charge and discharge of the battery stack 25; a protection element 1 applying the present invention for cutting off the charge and discharge path when an abnormality occurs in the battery stack 25; a detection circuit 27 for detecting the voltage of each single battery 21a~21d; and a current control element 28 that serves as a switching element for controlling the operation of the protection element 1 based on the detection result of the detection circuit 27.

[0079] The battery stack 25 is a stack of single cells 21a to 21d connected in series, which need to be controlled to protect against overcharge and overdischarge, and is detachably connected to the charging device 22 via the positive terminal 20a and the negative terminal 20b of the battery pack 20, and is applied with a charging voltage from the charging device 22. The battery pack 20 charged by the charging device 22 can be operated by connecting the positive terminal 20a and the negative terminal 20b to an electronic device that uses the battery to operate.

[0080] The charge and discharge control circuit 26 includes two current control elements 23a and 23b connected in series to 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 gate voltage is controlled by the control unit 24 to control the conduction and disconnection of the current path of the battery stack 25 in the charging direction and / or the discharging direction. The control unit 24 operates by receiving power supply from the charging device 22, and controls the operation of the current control elements 23a and 23b based on the detection result of the detection circuit 27 to disconnect the current path when the battery stack 25 is over-discharged or over-charged.

[0081] The protection element 1 is connected to the charge and discharge current path between the battery stack 25 and the charge and discharge control circuit 26 , for example, and its operation is controlled by the current control element 28 .

[0082] The detection circuit 27 is connected to each of the cells 21a to 21d, detects the voltage value of each of the cells 21a to 21d, and supplies each voltage value to the control unit 24 of the charge and discharge control circuit 26. In addition, the detection circuit 27 outputs a control signal for controlling the current control element 28 when any of the cells 21a to 21d reaches an overcharge voltage or an overdischarge voltage.

[0083] The current control element 28 is composed of, for example, a FET, and is controlled by a detection signal output from the detection circuit 27 so that when the voltage value of the single battery 21a~21d becomes a voltage exceeding a predetermined over-discharge or over-charge state, the protection element 1 is activated to cut off the charge and discharge current path of the battery stack 25 regardless of the switching operation of the current control elements 23a and 23b.

[0084] The protection element 1 to which the present invention is applied and used in the battery pack 20 having the above-mentioned structure has Figure 5 The circuit structure is as shown. That is, the first external connection electrode 11 of the protection element 1 is connected to the battery stack 25 side, and the second external connection electrode 12 is connected to the positive terminal 20a side, so that the fuse element 7 is connected in series to the charge and discharge path of the battery stack 25. In addition, the heating element 3 of the protection element 1 is connected to the current control element 28 via the heating element electrode 17 and the third external connection electrode 13, and the heating element 3 is connected to the battery stack 25. In this way, one end of the heating element 3 is connected to the fuse element 7 and one end of the battery stack 25 via the heating element lead-out electrode 6, and the other end is connected to the current control element 28 and the other end of the battery stack 25 via the heating element electrode 17 and the third external connection electrode 13. Thus, a power supply path to the heating element 3 is formed, in which power supply can be controlled by the current control element 28.

[0085] [Operation of protection element]

[0086] When the detection circuit 27 detects an abnormal voltage of any of the cells 21a to 21d, it outputs a cutoff signal to the current control element 28. Then, the current control element 28 controls the current to energize the heating element 3. In the protection element 1, the current flows from the battery stack 25 to the heating element 3, and the heating element 3 starts to generate heat. The protection element 1 melts the fuse element 7 by the heat generated by the heating element 3, and cuts off the charge and discharge path of the battery stack 25.

[0087] The molten conductor 7a of the fuse element 7 is gathered at the connection conductor 8 formed by the first electrode 4, the second electrode 5 and the heating element lead-out electrode 6, and the electrodes are cut off ( Figure 2 At this time, the tension of the molten conductor 7a actively acts to gather on the first electrode 4, the second electrode 5 and the heating element lead-out electrode 6, and can quickly fuse the first electrode 4 and the heating element lead-out electrode 6, and the second electrode 5 and the heating element lead-out electrode 6.

[0088] In addition, the fuse element 7 is formed of an alloy composed of a material having a liquidus point higher than the reflow heating temperature (260°C). Therefore, unlike a structure in which a low melting point metal having a liquidus point lower than the reflow temperature is covered with a high melting point metal, there is no influence on the rapid blow characteristics caused by the deformation of the fuse element 7 even through reflow, and the fuse element 7 can be blown within a predetermined time to cut off the current path. In this way, the fuse element 7 can be blown quickly, thereby preventing the heating element 3 from being damaged before the fuse element 7 is blown, and the current path can be cut off safely and quickly.

[0089] The protection element 1 cuts off the power supply path to the heating element 3 by melting the fuse element 7 , so that the heating element 3 stops generating heat.

[0090] Furthermore, when an overcurrent exceeding the rated value flows through the battery pack 20 , the fuse element 7 in the protection element 1 also melts due to self-heating, thereby being able to cut off the charge and discharge path of the battery pack 20 .

[0091] The protection element 1 of the present invention is not limited to being used in a battery pack of a lithium-ion secondary battery, but can be applied to various uses that require interruption of a current path using an electrical signal.

[0092] [Modification 1]

[0093] A modification of the protection element to which the present technology is applied will be described. In the following description, the same reference numerals may be given to the same components as those of the protection element 1 described above, and detailed description thereof may be omitted. Figure 6 The protection element 40 shown has a heating element 3 , a heating element electrode 17 , an intermediate electrode 14 and an insulating protection layer 9 formed on the back surface 2 b of the insulating substrate 2 , and other structures are the same as those of the protection element 1 described above.

[0094] The heating element electrode 17 and the intermediate electrode 14 are formed on the side edges of the back surface 2b of the insulating substrate 2 that are opposite to the side edges on which the first and second electrodes 4 and 5 are provided. The heating element electrode 17 is a power supply electrode for supplying power to the heating element 3 and functions as an external connection electrode. The protection element 40 is installed in an external circuit and is connected to the current control element 28.

[0095] The intermediate electrode 14 is an electrode arranged between the heating element 3 and the heating element lead-out electrode 6 arranged on the surface 2a of the insulating substrate 2, is connected to the other end 3b of the heating element 3, and is connected to the heating element lead-out electrode 6 formed on the surface 2a of the insulating substrate 2 via a castellated structure.

[0096] In addition, if Figure 7 As shown, the protection element may be provided with the heating element 3 on the back surface 2b of the insulating substrate 2, and a power supply path for supplying power to the heating element 3 and a current path of the fuse element 7 may be independently formed. Figure 7 The protection element 50 shown in (A) omits the heating element lead-out electrode 6, but the heating element lead-out electrode 6 which is not connected to the intermediate electrode 14 may be formed. The protection element 50 omits the heating element lead-out electrode 6, thereby separating the current path of the fuse element 7 from the current path of the heating element 3. The heating element 3 provided on the back surface 2b of the insulating substrate 2 is connected to the heating element electrode 17 at one end and to the intermediate electrode 14 at the other end.

[0097] Figure 8: is a diagram showing the circuit structure of the protection element 50. The protection element 50 is installed in an external circuit so that the first external connection electrode 11 is connected to the battery stack 25 side, and the second external connection electrode 12 is connected to the positive terminal 20a side, thereby connecting the fuse element 7 in series to the charge and discharge path of the battery stack 25. The heating element 3 is connected to the current control element 28 via the heating element electrode 17, and is connected to the battery stack 25. In addition, the heating element 3 is connected to the ground wire (not shown) via the intermediate electrode 14. Thus, a power supply path to the heating element 3 is formed, in which power supply can be controlled by the current control element 28. When the fuse element 7 of the protection element 50 is blown, the power supply to the heating element 3 is stopped by detecting the blown detection circuit 27 and the current control element 28.

[0098] [Modification 2]

[0099] Next, another modified example of the protection element to which the present technology is applied is described. In the following description, the same reference numerals are sometimes used to denote the same components as those of the above-mentioned protection elements 1, 40, and 50, and their detailed description is omitted. Fig. 9 As shown, the protection element 60 to which the present technology is applied does not form the heat generating element 3 but cuts off the current path by utilizing the self-heating of the fuse element 7 caused by the overcurrent.

[0100] The protection element 60 is mounted on the external circuit substrate by reflow, so that the first external connection electrode 11 is connected to the battery stack 25 side and the second external connection electrode 12 is connected to the positive terminal 20 a side, thereby connecting the fuse element 7 in series to the charge and discharge path of the battery stack 25 .

[0101] In the above-mentioned protection elements 40, 50, 60, the connection conductor 8 is a material having a liquidus point lower than the liquidus point of the fuse element 7 and a solidus point lower than the reflow heating temperature, and is therefore used for connecting the fuse element 7 with the first and second electrodes 4, 5, and the heating element lead-out electrode 6 in a state of at least some degree of melting, preferably in a state of complete melting, at the reflow heating temperature. As a result, the connection conductor 8 wets and spreads on the first and second electrodes 4, 5, and the heating element lead-out electrode 6, and fills between the fuse element 7 and the first and second electrodes 4, 5, and the heating element lead-out electrode 6, enabling electrical and mechanical connection.

[0102] In addition, in the protection elements 40, 50, and 60, an alloy composed of a material that does not use lead and has a liquidus point higher than the reflow heating temperature is used as the fuse element 7, thereby achieving a reduction in environmental load while also achieving excellent rapid blowability. In addition, expensive metals such as gold are not used as the fuse element 7, and both the reduction in environmental load and the maintenance of rapid blowability can be achieved, and cost reduction can also be achieved.

[0103] Explanation of symbols

[0104] 1—protection element, 2—insulating substrate, 3—heating element, 4—first electrode, 5—second electrode, 6—heating element lead-out electrode, 7—fuse element, 8—connecting conductor, 9—insulating protective layer, 11—first external connection electrode, 12—second external connection electrode, 13—third external connection electrode, 14—intermediate electrode, 17—heating element electrode, 20—battery pack, 21—single battery, 22—charging device, 23—current control element, 24—control unit, 25—battery stack, 26—charge and discharge control circuit, 27—detection circuit, 28—current control element, 30—housing, 40—protection element, 50—protection element, 60—protection element.

Claims

1. A protection element, characterized in that: have: Insulating substrate; A first electrode and a second electrode, which are disposed on the insulating substrate; a fuse element disposed on surfaces of the first electrode and the second electrode and electrically connecting the first electrode to the second electrode; and a connecting conductor connecting the first electrode and the second electrode to the fuse element, The fuse element is made of a lead-free conductor and has a liquidus point higher than the reflow heating temperature. The connecting conductor has a liquidus point lower than the liquidus point of the fuse element and a solidus point lower than a reflow heating temperature.

2. The protection element according to claim 1, characterized in that: The liquidus temperature of the fuse element is 400° C. or lower.

3. The protection element according to claim 2, characterized in that: The fuse element is an alloy of Sn-Cu or Sn-Sb-Ag-Cu.

4. The protection element according to any one of claims 1 to 3, characterized in that: The connection conductor is a Sn-Cu-Ag, Sn-Cu or Sn-Sb-Ag-Cu solder alloy.

5. The protection element according to any one of claims 1 to 3, characterized in that: have: A heating element, which is arranged on the insulating substrate; A heating element electrode connected to one end of the heating element; An intermediate electrode connected to the other end of the heating element; an insulating protective layer, which at least covers the heating element; and The heating element lead-out electrode is disposed between the first electrode and the second electrode and connected to the intermediate electrode.

6. The protection element according to any one of claims 1 to 3, characterized in that: The device has external connection electrodes connected to terminals provided on an external circuit substrate and can be surface mounted on the external circuit substrate.

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