Protection element and battery pack

Abstract

To provide a protection element in which a fusible conductor is not fused even through a reflow process, and the fusible conductor can be fused quickly when abnormal.SOLUTION: A protection element 1 includes an insulating substrate 2, a heating element 5, a first electrode 3 and a second electrode 4 laminated on the insulating substrate 2, a heating element extraction electrode 6 provided on a current path between the first and second electrodes 3 and 4 and electrically connected to the heating element 5, and a fusible conductor 7 mounted on the first electrode 3, the second electrode 4, and the heating element extraction electrode 6 and fused by a self-heating caused by heating or overcurrent of the heating element 5 to block the current path. The fusible conductor 7 is formed of a laminated body 13 including at least a low melting point metal layer 11 having a liquidus temperature of less than 260°C and a high melting point metal layer 10 having a liquidus temperature of more than 400°C, and the laminated body 13 has a material configuration in which a liquidus temperature of an alloy composition when melted as a single alloy is 300°C or more and 400°C or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present technology relates to a protection element that is connected to a current path of an electronic device to be protected and that stops current flow to the electronic device by interrupting the current path, and a battery pack using the protection element. [Background technology]

[0002] Most rechargeable secondary batteries are manufactured into battery packs and provided to users. To ensure the safety of users and electronic devices, lithium-ion secondary batteries, which have particularly high weight energy density, generally incorporate several protection circuits, such as overcharge protection and overdischarge protection, into the battery pack, and have the function of shutting down the output of the battery pack under specified conditions.

[0003] In many electronic devices using lithium-ion secondary batteries, a built-in FET switch in the battery pack is used to turn the output on and off to protect the battery pack from overcharge or overdischarge. However, the battery pack and electronic devices must be protected from accidents such as fire if the FET switch is short-circuited for some reason, if a lightning surge or other event causes a momentary large current to flow, or if the output voltage of the battery cell drops abnormally due to its lifespan or, conversely, if an excessively large voltage is output. Therefore, to safely shut off the battery cell output in any of these possible abnormal conditions, a protective element consisting of a fuse element that can interrupt the current path in response to an external signal is used.

[0004] A protective element of a protective circuit for such a lithium-ion secondary battery or the like has a structure in which a heating element is provided inside the protective element, and a fusible conductor on the current path is melted by heat generated by the heating element. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-003665 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-185960 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-003878 Summary of the Invention [Problem to be solved by the invention]

[0006] The protective element can be efficiently manufactured by mounting a fusible conductor on the element or mounting the protective element on the protection circuit by a reflow process. Therefore, the fusible conductor is made of a high-melting-point material that does not melt due to the heat of reflow.

[0007] In addition, fusible conductors are required to melt quickly when it becomes necessary to cut off the current path, for example, when an overcurrent exceeding the rated current flows through the protection circuit or when an overvoltage is detected in a battery cell.

[0008] As described above, in the protective element, it is required to appropriately select the configuration and material of the fusible conductor so that the fusible conductor does not melt even after the reflow process and quickly melts in the event of an abnormality.

[0009] Generally, high-melting-point solder containing Pb, which has a melting point of 300°C or higher, is used as a high-melting-point fusible conductive material. However, the RoHS Directive and other regulations only permit the use of Pb-containing solder in limited circumstances, and it is expected that demand for Pb-free solder will grow stronger in the future.

[0010] Therefore, the present technology aims to provide a protective element that prevents a fusible conductor from melting even after a reflow process and that can quickly melt the fusible conductor in the event of an abnormality, and a battery pack using the same. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, the protective element of the present technology comprises an insulating substrate, a heating element, a first electrode and a second electrode stacked on the insulating substrate, a heating element lead electrode provided on a current path between the first and second electrodes and electrically connected to the heating element, and a fusible conductor electrically connected to the first electrode, the second electrode, and the heating element lead electrode, which melts due to self-heating caused by heating of the heating element or overcurrent, thereby interrupting the current path between the first electrode and the second electrode, wherein the fusible conductor is made of a laminate including at least a low-melting-point metal layer having a liquidus temperature of less than 260°C and a high-melting-point metal layer having a liquidus temperature of more than 400°C, and the laminate is made of materials such that the liquidus temperature of the alloy composition when melted together as a single alloy is 300°C or higher and 400°C or lower.

[0012] In addition, a protective element according to the present technology includes an insulating substrate, a heating element, first and second electrodes stacked on the insulating substrate, a heating element lead electrode provided on a current path between the first and second electrodes and electrically connected to the heating element, and a fusible conductor electrically connected to the first electrode, the second electrode, and the heating element lead electrode, which melts due to self-heating caused by heating of the heating element or overcurrent, thereby interrupting the current path between the first electrode and the second electrode, the fusible conductor being connected to the first electrode, the second electrode, and the heating element lead electrode via a conductive connecting medium, and the fusible conductor comprising a laminate including at least a low-melting-point metal layer having a liquidus temperature of less than 260°C and a high-melting-point metal layer having a liquidus temperature of more than 400°C, and the laminate and the conductive connecting medium are made of materials such that when fused together as a single alloy, the liquidus temperature of the alloy composition is 300°C or higher and 400°C or lower.

[0013] In addition, a battery pack according to the present technology includes one or more battery cells, a protection element connected to a charge / discharge path of the battery cell and blocking the charge / discharge path, a detection circuit that detects a voltage value of the battery cell, and a current control element that controls current flow to the protection element, and the protection element is the protection element described above. [Effects of the Invention]

[0014] According to this technology, the material composition of the fusible conductor can be appropriately selected, reflow mounting is possible, and efficient fuse blowout due to heating of the heating element or self-heating due to overcurrent can be achieved.

[0015] Furthermore, Pb-free materials can be used for the fusible conductor, making it possible to realize Pb-free protective elements. [Brief explanation of the drawings]

[0016] [Figure 1] Figure 1 shows a protective element 1 to which the present technology is applied, where (A) is a plan view with the cover member 19 removed, (B) is a cross-sectional view in the direction of current flow through the fusible conductor, and (C) is a bottom view. [Figure 2] FIG. 2 is a plan view showing a state in which the fusible conductor is fused. [Figure 3] FIG. 3 is a perspective view showing an example of the configuration of a fusible conductor, (A) shows a fusible conductor having a laminated structure, and (B) and (C) show fusible conductors having a coated structure. [Figure 4] Figure 4 is a cross-sectional view showing the state changes of the laminate during the reflow process, where (A) shows the state before reflow heating, (B) shows the state at the beginning of reflow heating, (C) shows the state at the end of reflow heating, and (D) and (E) show the state after reflow has been completed and cooling has been performed. [Figure 5] FIG. 5 is a cross-sectional view showing a state in which the soluble conductor is connected onto the first and second electrodes and the heating element lead electrode via the second low-melting point metal layer. [Figure 6] FIG. 6 is a cross-sectional view showing an example of the configuration of a fusible conductor (laminate) having a covering structure. [Figure 7] FIG. 7 is a binary alloy phase diagram of silver (Ag) and tin (Sn). [Figure 8] FIG. 8 is a ternary alloy phase diagram of tin (Sn), silver (Ag), and copper (Cu). [Figure 9] FIG. 9 is a circuit diagram showing an example of the configuration of a battery pack. [Figure 10] FIG. 10 is a circuit diagram of the protection element. [Figure 11]FIG. 11 is a diagram showing a manufacturing process of a protection element, where (A) is a cross-sectional view showing the heating, melting and connecting process of a fusible conductor, and (B) is a cross-sectional view showing the mounting process on a circuit board. [Figure 12] Figure 12 shows a protective element in which a heating element is formed on the back surface of an insulating substrate, where (A) is a plan view, (B) is a cross-sectional view in the direction of current flow of the fusible conductor, and (C) is a bottom view. [Figure 13] FIG. 13 is a cross-sectional view showing a protection element in which a heating element is formed inside an insulating substrate. [Figure 14] Figure 14 is a cross-sectional view showing a configuration of a protective element in which a heating element is provided on the surface of an insulating substrate via a surface insulating layer and a soluble conductor having a covering structure is connected, in which a surface insulating layer is formed between the heating element extraction electrode and the first electrode, and between the heating element extraction electrode and the second electrode. [Figure 15] Figure 15 is a cross-sectional view showing a configuration of a protective element in which a heating element is provided on the surface of an insulating substrate via a surface insulating layer and a soluble conductor having a laminated structure is connected, in which a surface insulating layer is formed between the heating element extraction electrode and the first electrode, and between the heating element extraction electrode and the second electrode. [Figure 16] Figure 16 is a cross-sectional view showing a configuration in which a protective element has a heating element provided on the back surface of an insulating substrate and a soluble conductor having a covering structure connected thereto, and a surface insulating layer is formed to connect between the heating element extraction electrode and the first electrode, and between the heating element extraction electrode and the second electrode. [Figure 17] Figure 17 is a cross-sectional view showing a configuration in which a surface insulating layer is formed to connect between the heating element extraction electrode and the first electrode, and between the heating element extraction electrode and the second electrode, in a protective element in which a heating element is provided on the back surface of an insulating substrate and a soluble conductor having a laminated structure is connected. DETAILED DESCRIPTION OF THE INVENTION

[0017] A protection element and a battery pack to which the present technology is applied will be described in detail below with reference to the drawings. It should be noted that the present technology is not limited to the following embodiments, and various modifications are possible within the scope of the present technology. The drawings are schematic, and the ratios of the dimensions may differ from the actual dimensions. Specific dimensions should be determined with reference to the following description. It should be noted that the drawings may also include portions in which the dimensional relationships and ratios differ.

[0018] 1 is a diagram showing a protective element 1 to which the present technology is applied, where (A) is a plan view showing the cover member 19 removed, (B) is a cross-sectional view in the direction of current flow of the fusible conductor, and (C) is a bottom view. As shown in FIG. 1, the protective element 1 to which the present technology is applied includes an insulating substrate 2 having a heating element 5, a first electrode 3 and a second electrode 4 laminated on the insulating substrate 2, a heating element lead electrode 6 provided on the current path between the first and second electrodes 3 and 4 and electrically connected to the heating element 5, and a fusible conductor 7 electrically connected to the first electrode 3, the second electrode 4, and the heating element lead electrode 6, which melts due to self-heating caused by heating of the heating element 5 or overcurrent, and interrupts the current path between the first electrode 3 and the second electrode 4.

[0019] The soluble conductor 7 has a laminated structure of at least a high-melting-point metal layer 10 and a second low-melting-point metal layer 12. This soluble conductor 7 is formed by mounting a laminate 13 including a first low-melting-point metal layer 11 having a liquidus temperature of less than 260 ° C and a high-melting-point metal layer 10 having a liquidus temperature of more than 400 ° C by reflow on the first electrode 3, the second electrode 4, and the heating element lead electrode 6. The laminate 13 is made of a material whose liquidus temperature of the alloy composition when melted together as a single alloy is 300 ° C or higher and 400 ° C or lower.

[0020] With such a protective element 1, the laminate 13 does not melt during the process of reflow mounting the laminate 13 on the first electrode 3, the second electrode 4, and the heating element extraction electrode 6, and the soluble conductor 7 does not melt during the process of reflow mounting the protective element 1 on the circuit board 34 to be protected, and the soluble conductor 7 can be melted quickly and reliably by heating of the heating element 5 or self-heating due to overcurrent.

[0021] That is, the laminate 13 to which the present technology is applied has at least a first low-melting-point metal layer 11 having a liquidus temperature of less than 260°C and a high-melting-point metal layer 10 having a liquidus temperature of more than 400°C. Generally, the reflow temperature is 260°C or less, and the first low-melting-point metal layer 11 melts during the reflow mounting process. The laminate 13 and the fusible conductor 7 are made of materials whose liquidus temperature of the alloy composition when melted together as a single alloy is 300°C or more and 400°C or less. Therefore, even if the first low-melting-point metal layer 11 or the second low-melting-point metal layer 12 melts at the reflow temperature and interdiffusion and / or melting occurs between the first low-melting-point metal layer 11 and the second low-melting-point metal layer 12 and the high-melting-point metal layer 10, the laminate structure is maintained by the high-melting-point metal layer 10, and no melting occurs.

[0022] The material composition of the high-melting-point metal layer 10 and the first low-melting-point metal layer 11 constituting the laminate 13 can be appropriately selected by referring to a phase diagram of the alloys constituting the high-melting-point metal layer 10 and the first low-melting-point metal layer 11, and determining the alloy composition showing the desired liquidus temperature and the volume ratio from the density of the metals constituting the alloy. That is, according to the present technology, the material composition of the fusible conductor 7 can be appropriately selected, reflow mounting is possible, and efficient fuse blowout due to heating of the heating element 5 or self-heating due to overcurrent can be achieved.

[0023] Here, the high-melting point metal layer 10 preferably bridges the gap between the heating element extraction electrode 6 and the first electrode 3, and between the heating element extraction electrode 6 and the second electrode 4, and is mounted so as not to be in direct contact with the insulating substrate 2 at least either between the heating element extraction electrode 6 and the first electrode 3 or between the heating element extraction electrode 6 and the second electrode 4.

[0024] Furthermore, when an insulating protective layer 8 is present at least partially between the heating element extraction electrode 6 and the first electrode 3 and / or between the heating element extraction electrode 6 and the second electrode 4, the high-melting point metal layer 10 preferably bridges the gap between the heating element extraction electrode 6 and the first electrode 3 and between the heating element extraction electrode 6 and the second electrode 4, and is preferably mounted so as not to be in direct contact with the insulating protective layer 8 and / or the insulating substrate 2 at least between the heating element extraction electrode 6 and the first electrode 3 or between the heating element extraction electrode 6 and the second electrode 4.

[0025] If the high-melting point metal layer 10 of the soluble conductor 7 is in direct contact with the insulating substrate 2 and / or the insulating protective layer 8 and the first electrode 3 between the heating element extraction electrode 6 and the first electrode 3, and between the heating element extraction electrode 6 and the second electrode 4, and is connected to the second electrode 4 via the heating element extraction electrode 6, there will be residual molten high-melting point metal layer 10 during the fusing process, and there is a risk that the appropriate insulation resistance (e.g., 100 KΩ) will not be maintained after fusing.

[0026] In other words, if there is even a partial discontinuous gap at the interface between the insulating substrate 2 and / or insulating protective layer 8, which are continuously and uninterruptedly connected from the first electrode 3 to the second electrode 4 via the heating element extraction electrode 6, and the high-melting point metal layer 10, the risk of a decrease in insulation resistance is reduced.

[0027] The specific dimensions of the gap are preferably "approximately 0.1 to 0.2 mm in the lengthwise direction" as described in

[0058] of Patent No. 5656466.

[0028] Each component of the protection element 1 will be described in detail below.

[0029] [Insulating substrate] The insulating substrate 2 is formed of an insulating material such as alumina, glass ceramics, mullite, zirconia, etc. Alternatively, the insulating substrate 2 may be made of a material used for printed wiring boards, such as a glass epoxy board or a phenol board.

[0030] [First and second electrodes] First and second electrodes 3 and 4 are formed on opposing ends of the insulating substrate 2. The first and second electrodes 3 and 4 are each formed of a conductive pattern made of Ag, Cu, or an alloy thereof. The surfaces of the first and second electrodes 3 and 4 may be coated with a film such as Ni / Au plating, Ni / Pd plating, or Ni / Pd / Au plating by a known method such as plating. This prevents oxidation of the first and second electrodes 3 and 4 and prevents fluctuations in the rated current associated with an increase in conduction resistance. Furthermore, when the protective element 1 is reflow-mounted on an external circuit board or the like, the first and second electrodes 3 and 4 can be prevented from being melted (solder erosion) by melting the conductive connection medium 35, such as solder paste, that connects the fusible conductor 7 or the second low-melting-point metal layer 12 that contacts the first and second electrodes 3 and 4.

[0031] The first electrode 3 is electrically connected to a first external connection electrode 14 formed on the back surface 2b of the insulating substrate 2 via a castellation from the front surface 2a. The second electrode 4 is electrically connected to a second external connection electrode 15 formed on the back surface 2b of the insulating substrate 2 via a castellation from the front surface 2a. When the protection element 1 is mounted on the external circuit board 34, the first and second external connection electrodes 14, 15 are connected to a connection electrode 34a provided on the external circuit board 34, and the fusible conductor 7 is incorporated into a part of the current path formed on the external circuit board 34.

[0032] Furthermore, conductive through-holes (not shown) penetrating the insulating substrate 2 may be used to connect the first electrode 3 to the first external connection electrode 14 and the second electrode 4 to the second external connection electrode 15, and castellation and conductive through-holes may be used together to reduce the connection resistance between the front and back surfaces.

[0033] The first and second electrodes 3, 4 are electrically connected to each other via the fusible conductor 7. As shown in Fig. 2, the first and second electrodes 3, 4 are disconnected when a large current exceeding the rated current flows through the protective element 1, causing the fusible conductor 7 to melt due to self-heating (Joule heat) (Fig. 2(B)), or when the heating element 5 generates heat as current flows and the fusible conductor 7 melts (Fig. 2(A)).

[0034] [Heater] The heating element 5 is a conductive material with a relatively high resistance that generates heat when current is applied, and is made of, for example, nichrome, W, Mo, Ru, or a material containing these. The heating element 5 can be formed by mixing a powder of these alloys, compositions, or compounds with a resin binder or the like to form a paste, forming a pattern on the insulating substrate 2 using a screen printing technique, and firing the paste. For example, the 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 of a predetermined area at a predetermined position on the surface 2a of the insulating substrate 2, and then firing the film under appropriate conditions. The shape of the heating element 5 can be designed as desired, but a roughly rectangular shape corresponding to the shape of the insulating substrate 2, as shown in FIG. 1(A), is preferred to maximize the heating area.

[0035] In addition, one end 5a of the heating element 5 is connected to the first heating element electrode 16, and the other end 5b is connected to the second heating element electrode 17. The first heating element electrode 16 and the second heating element electrode 17 are formed on opposing side edges different from the side edges on which the first electrode 3 and the second electrode 4 are formed. The first heating element electrode 16 is a power supply electrode to the heating element 5, and is connected to a third external connection electrode 18 formed on the back surface 2b of the insulating substrate 2 via a castellation. The second heating element electrode 17 is connected to the heating element lead electrode 6 described later. The heating element 5 is electrically and thermally connected to the soluble conductor 7 via the second heating element electrode 17 and the heating element lead electrode 6.

[0036] The first and second heating element electrodes 16, 17 can be formed by printing and firing a conductive paste of Ag, Cu, an alloy thereof, or the like, similar to the first and second electrodes 3, 4. Furthermore, by making each of these electrodes formed on the surface 2a of the insulating substrate 2 out of the same material, they can be formed in a single printing and firing process.

[0037] Furthermore, a restricting wall may be provided on the first and second electrodes 3 and 4 to prevent the connection solder provided on the connection electrodes 34a of the circuit board 34 connected to the first and second external connection electrodes 14 and 15 from melting during reflow mounting or the like, creeping up onto the first and second electrodes 3 and 4 via castellations, and spreading over the first and second electrodes 3 and 4. Similarly, a restricting wall may be provided on the first heating element electrode 16. The restricting wall may be formed using an insulating material that is not wettable by solder, such as glass, solder resist, or an insulating adhesive, and may be formed on the first and second electrodes 3 and 4 by printing or the like. The provision of the restricting wall prevents the molten connection solder from spreading over the first and second electrodes 3 and 4 or the first heating element electrode 16, thereby maintaining the connectivity between the protection element 1 and the circuit board 34.

[0038] [Insulating protective layer] 1(A) and 1(B), the entire heating element 5 and parts of the first heating element electrode 16 and second heating element electrode 17 are covered with an insulating protective layer 8. The insulating protective layer 8 is provided to protect and insulate the heating element 5, and is made of an insulating material such as glass that has heat resistance to the heat generation temperature of the heating element 5. Examples of glass raw materials that make up the insulating material include silica-based glass overcoat glass paste and insulating glass paste.

[0039] The insulating protective layer 8 can be formed by applying, for example, a glass-based paste by screen printing or the like, followed by baking. The thickness of the insulating protective layer 8 is set in consideration of the applicability of the glass paste or the like, and is, for example, greater than 10 μm and equal to or less than 40 μm, and preferably equal to or greater than 20 μm and equal to or less than 40 μm.

[0040] [Heater element extraction electrode] A heating element extraction electrode 6 is formed on the insulating protective layer 8. One end of the heating element extraction electrode 6 is connected to the second heating element electrode 17, and is also connected to the soluble conductor 7 between the first and second electrodes 3, 4 via a second low-melting point metal layer 12 or a conductive connection medium 35 such as solder paste. In addition, the heating element extraction electrode 6 overlaps with the heating element 5 via the insulating protective layer 8.

[0041] The heater lead electrode 6 can be formed by printing and firing a high-melting-point metal paste such as Ag, Cu, or an alloy thereof, similar to the first and second electrodes 3 and 4. The surface of the heater lead electrode 6 may be coated with a film such as Ni / Au plating, Ni / Pd plating, or Ni / Pd / Au plating by a known method such as plating.

[0042] [Fusible conductor] Next, we will explain the fusible conductor 7. The fusible conductor 7 is mounted between the first and second electrodes 3 and 4, and melts due to heat generated by the passage of current through the heating element 5 or due to self-heating (Joule heat) caused by the passage of a current exceeding the rated current, thereby interrupting the current path between the first electrode 3 and the second electrode 4. Figure 3 is a perspective view showing an example of the configuration of the fusible conductor 7, where (A) shows a fusible conductor 7A having a laminated structure, and (B) and (C) show fusible conductors 7B having a coated structure (see Figure 1).

[0043] As shown in FIG. 3A, the soluble conductor 7A is a laminated structure consisting of an upper layer and a lower layer, with a high-melting-point metal layer 10 as the upper layer and a second low-melting-point metal layer 12 as the lower layer. In the protective element 1, for example, it has a rectangular plate shape in a plan view. The soluble conductor 7A can be formed from a laminate 13A. The laminate 13A is formed by laminating a high-melting-point metal layer 10 and a first low-melting-point metal layer 11. The high-melting-point metal layer 10 and the first low-melting-point metal layer 11 of the laminate 13A can be laminated by known lamination methods such as rolling, crimping, and plating coating. The soluble conductor 7A is formed by reflow heating the laminate 13A during the process of connecting it to the first and second electrodes 3 and 4 and the heating element lead electrode 6 of the insulating substrate 2.

[0044] The soluble conductor 7B has a coating structure in which both surfaces and both side surfaces of the second low-melting-point metal layer 12 are coated with a high-melting-point metal layer 10 having a melting point higher than that of the second low-melting-point metal layer 12, as shown in FIG. 3(B), for example. In the protective element 1, for example, it may be a rectangular plate in plan view, or as shown in FIG. 3(C), it may be a round wire. The soluble conductor 7B can be formed from a laminate 13B. The laminate 13B has a coating structure in which both surfaces and both side surfaces of the first low-melting-point metal layer 11 constituting the inner layer are coated with a high-melting-point metal layer 10 having a melting point higher than that of the first low-melting-point metal layer 11 constituting the outer layer. The laminate 13B can be formed, for example, by plating a high-melting-point metal on a low-melting-point metal foil. In addition, the laminate 13B may be formed by plating a long low-melting-point metal foil with a high-melting-point metal and then cutting it to a predetermined length, so that the cut surfaces are exposed at both ends and the periphery is covered with the high-melting-point metal layer 10. In addition to plating, well-known lamination techniques and film formation techniques may be used to form the high-melting-point metal layer. In the process of connecting the soluble conductor 7B to the first and second electrodes 3 and 4 of the insulating substrate 2 and the heating element lead electrode 6, the laminate 13B is reflow-heated, and a second low-melting-point metal layer 12 is formed by a liquefaction reaction between the first low-melting-point metal layer 11 and a part of the high-melting-point metal layer 10.

[0045] In this specification, when there is no need to distinguish between the soluble conductor 7A of the laminated structure and the soluble conductor 7B of the coated structure, they are simply referred to as "soluble conductor 7." Also, when there is no need to distinguish between the laminated body 13A of the laminated structure and the laminated body 13B of the coated structure, they are simply referred to as "laminate 13."

[0046] The high-melting-point metal layer 10, the first low-melting-point metal layer 11, and the second low-melting-point metal layer 12 are metals that have different melting points and can melt, with the metal layer with a relatively low melting point being the "low-melting-point metal layer" and the metal layer with a relatively high melting point that dissolves into the molten low-melting-point metal being the "high-melting-point metal layer." The high-melting-point metal layer 10, the first low-melting-point metal layer 11, and the second low-melting-point metal layer 12 may be metal layers made of a single metal or alloy layers made of two or more metals. While unintended metals may be contained as impurities in addition to the metals that make up each metal layer, these impurities are not considered to be constituent metals.

[0047] The high-melting point metal constituting the high-melting point metal layer 10 is, for example, Ag or Cu, or a metal containing Ag and / or Cu. The high-melting point metal layer 10 has a liquidus temperature exceeding 400°C, and has such a high melting point that it does not melt and become a complete liquid even when the first and second electrodes 3 and 4 and the heating element lead electrode 6 are connected to the soluble conductor 7 or when the protective element 1 is mounted on the circuit board 34 by reflow.

[0048] The high-melting point metal constituting the high-melting point metal layer 10 may be an alloy containing Sn as the main component but also containing Ag and / or Cu, and having a liquidus temperature exceeding 400°C.

[0049] The low-melting-point metal constituting the first low-melting-point metal layer 11 of the laminate 13 is, for example, a solder or a metal containing Sn as a main component, a material generally called "Pb-free solder." The liquidus temperature of the first low-melting-point metal layer 11 does not necessarily have to be higher than the reflow temperature, and may be, for example, less than 260°C, and may melt at about 200°C.

[0050] The low-melting point metal constituting the second low-melting point metal layer 12 of the soluble conductor 7 is composed of an alloy of the low-melting point metal constituting the first low-melting point metal layer 11 and the high-melting point metal constituting the high-melting point metal layer 10. By undergoing the reflow mounting process of the laminate 13, the second low-melting point metal layer 12 becomes an alloy of the low-melting point metal constituting the first low-melting point metal layer 11 and the high-melting point metal constituting the high-melting point metal layer 10 by melting a part of the high-melting point metal constituting the high-melting point metal layer 10 into the melted first low-melting point metal layer 11. The liquidus temperature of the second low-melting point metal layer 12 does not necessarily have to be higher than the reflow temperature, and may be, for example, less than 260 ° C., and may melt at about 200 ° C.

[0051] In the laminated fusible conductor 7A, the second low-melting-point metal layer 12 is formed by interdiffusion and / or dissolution of a portion of the high-melting-point metal layer 10 and the first low-melting-point metal layer 11 in a laminate 13A, which has a high-melting-point metal layer 10 as an upper layer and a first low-melting-point metal layer 11 as a lower layer, due to heating such as reflow mounting. Figure 4 is a cross-sectional view schematically showing the state changes of the laminate 13A during the reflow process, where (A) shows the state before reflow heating, (B) shows the early stage of reflow heating, (C) shows the late stage of reflow heating, and (D) and (E) show the state after reflow has been completed and cooled. As shown in Figures 4(B) and (C), a liquid phase 13L of the metal constituting each metal layer is formed at the interface between the high-melting-point metal layer 10 and the first low-melting-point metal layer 11 due to reflow heating, and the liquid phase 13L dissolves a portion of the high-melting-point metal layer 10 and the first low-melting-point metal layer 11. After the reflow is completed and the material is cooled, a second low-melting-point metal layer 12 is formed, consisting of a part of the high-melting-point metal layer 10 and the constituent metal of the first low-melting-point metal layer 11 (FIG. 4(D)). As the second low-melting-point metal layer 12 cools, a soluble conductor 7A consisting of a laminate of the high-melting-point metal layer 10 and the second low-melting-point metal layer 12 is formed, and the soluble conductor 7A is connected to the first and second electrodes 3, 4 and the heating element lead electrode 6 via a conductive connection medium 35 such as solder paste or the second low-melting-point metal layer 12. FIG. 5 is a cross-sectional view showing the state in which the soluble conductor 7A is connected to the first and second electrodes 3, 4 and the heating element lead electrode 6 via the second low-melting-point metal layer 12.

[0052] 4(E), the second low-melting point metal layer 12 may form a laminated structure with the first low-melting point metal layer 11 because the first low-melting point metal layer 11 of the laminate 13A is not completely melted and remains. The soluble conductor 7A may be formed using a conductive connection medium such as solder paste, or the first low-melting point metal layer 11 of the laminate 13A may be mounted facing the first electrode 3, the heating element lead electrode 6, and the second electrode 4, and connected to the first electrode 3, the heating element lead electrode 6, and the second electrode 4 by the first or second low-melting point metal layer 11, 12.

[0053] The melting point of the first low-melting-point metal layer 11 may be higher than the reflow temperature for mounting the fusible conductor 7. In the laminate 13A, at the lamination interface between the high-melting-point metal layer 10 and the first low-melting-point metal layer 11, the metal atoms constituting each metal layer interdiffuse to form the second low-melting-point metal layer 12. This process is also known as eutectic melting (a phenomenon in which dissimilar materials come into contact and begin to melt at a temperature lower than the melting point of the original material). The melting point of the second low-melting-point metal layer 12 decreases as the diffusion progresses, approaching the eutectic temperature. Therefore, even if the melting point of the first low-melting-point metal layer 11 is higher than the reflow temperature, if the eutectic line of the second low-melting-point metal layer 12 is lower than the reflow temperature, the second low-melting-point metal layer 12 will be in a liquid phase, or at least in a state in which both solid and liquid phases coexist.

[0054] In addition, the second low-melting point metal layer 12 is formed by interdiffusion and / or dissolution of a portion of the high-melting point metal layer 10 and the first low-melting point metal layer 11. However, if the thickness of the first low-melting point metal layer 11 is less than 1 / 10 of the thickness of the high-melting point metal layer 10 (this ratio varies depending on the material) or if the reflow mounting temperature is higher than the liquidus temperature of the first low-melting point metal layer 11, at any time during the process from mounting the fusible conductor 7 on each electrode to mounting the protective element 1 on the circuit board 34, the temperature rise due to reflow mounting causes interdiffusion and / or dissolution of a portion of the high-melting point metal layer 10 and the entire first low-melting point metal layer 11, and the high-melting point metal layer 10 and the first low-melting point metal layer 11 become an alloy.

[0055] In the coated soluble conductor 7B, when the laminate 13B, which has a high-melting-point metal layer 10 as the outer layer and a first low-melting-point metal layer 11 made of a low-melting-point metal as the inner layer, is connected across the first electrode 3, the heating element lead electrode 6, and the second electrode 4 by heating such as reflow mounting, a second low-melting-point metal layer 12 is formed by interdiffusion and / or dissolution of part of the high-melting-point metal layer 10 and the metals in the first low-melting-point metal layer 11. The soluble conductor 7B is connected to the first electrode 3, the heating element lead electrode 6, and the second electrode 4 by a conductive connection medium 35 such as solder paste applied to the first electrode 3, the heating element lead electrode 6, and the second electrode 4 (see FIG. 1).

[0056] In addition, by using a metal with low resistance such as Ag as the high-melting point metal layer 10 of the soluble conductor 7, it is possible to suppress an increase in internal resistance and improve the rated current while suppressing an increase in the size of the protective element 1.

[0057] The fusible conductor 7 can improve resistance to surges (pulse resistance) in which an abnormally high voltage is instantaneously applied to an electrical system incorporating the protective element 1. In other words, the fusible conductor 7 must not melt even when a current of, for example, 100 A flows for several milliseconds. Since large currents that flow in an extremely short time flow through the surface layer of the conductor (skin effect), the fusible conductor 7 has a low-resistance, high-melting-point metal layer 10, such as Ag, as its upper layer. This allows the current applied by a surge to flow easily, preventing melting due to self-heating. Therefore, the fusible conductor 7 can significantly improve surge resistance compared to fuses made of conventional solder alloys.

[0058] The fusible conductor 7 is coated with a coating flux 36 to prevent oxidation and improve wettability during fusing. The inside of the protective element 1 is protected by covering the insulating substrate 2 with a cover member 19. The cover member 19 can be formed using insulating materials such as various engineering plastics, thermoplastic plastics, ceramics, and glass epoxy boards. The cover member 19 also has an internal space on the surface 2a of the insulating substrate 2 that is sufficient to allow the fusible conductor 7 to expand spherically when melted, and for the molten conductor 7a to aggregate on the heating element lead electrode 6 and the first and second electrodes 3 and 4.

[0059] [Liquid phase temperature of a single alloy composition] The laminate 13 to which this technology is applied is made of materials whose liquidus temperature of the alloy composition when melted together as a single alloy is 300°C or higher and 400°C or lower. As described above, the laminate 13 is connected to the first electrode 3, the heating element lead electrode 6, and the second electrode 4 by melting a conductive connecting medium such as solder paste by reflow, or by melting the first low-melting point metal layer 11 in the case of the laminate 13A. The reflow temperature is often set to about 190°C to 260°C or lower, which is several tens of degrees higher than the melting point of the solder paste material, which is generally about 140°C to 220°C.

[0060] Therefore, by setting the metal and thickness of each layer constituting the laminate 13 so that the liquidus temperature of the alloy composition when melted together as a single alloy is 300°C or higher and 400°C or lower, the first low-melting point metal layer 11 melts at the reflow temperature, and even if interdiffusion and / or dissolution of the high-melting point metal and the low-melting point metal occurs between the high-melting point metal layer 10 and the first low-melting point metal layer 11, the high-melting point metal layer 10 maintains the laminated or coated structure and does not melt. Also, the fusible conductor 7 can be reliably melted.

[0061] Furthermore, the metal and thickness of each layer constituting laminate 13 may be such that the liquidus temperature of the alloy composition when melted together as a single alloy is 325° C. or higher and 400° C. or lower. This can further improve resistance to melting of laminate 13 caused by a conductive connecting medium such as solder paste, and more reliably prevent deformation during reflow mounting on first and second electrodes 3 and 4 and heating element lead electrode 6, and during reflow mounting of protection element 1 on circuit board 34.

[0062] [Example of fusible conductor configuration] 6 is a cross-sectional view showing an example of the configuration of a soluble conductor 7B with a coating structure. The soluble conductor 7B shown in FIG. 6 is formed by reflow-mounting a laminate 13B, in which a first low-melting-point metal layer 11 (Sn-3.0Ag-0.5Cu alloy) serving as an inner layer is coated with a high-melting-point metal layer 10 (Ag) serving as an outer layer, onto the first electrode 3, the heating element lead electrode 6, and the second electrode 4 (reflow conditions: 240°C oven, 2 minutes). When the thickness T1 of the first low-melting-point metal layer 11 of the laminate 13B is 100 μm, the thickness T2 of one side of the high-melting-point metal layer 10 is preferably greater than 3 μm, more preferably greater than 4 μm. As a result, even if the first low-melting point metal layer 11 melts at the reflow temperature and mutual diffusion and / or dissolution of the high-melting point metal and the low-melting point metal occurs between the first low-melting point metal layer 11 and the high-melting point metal layer 10, the stacked structure is maintained by the high-melting point metal layer 10 and does not melt.

[0063] In addition, when the thickness T1 of the first low melting point metal layer 11 of the laminate 13B is 100 μm, it is preferable that the thickness T2 of one side of the high melting point metal layer 10 is 10.5 μm or less. This makes it possible to reliably fuse the fusible conductor 7 because the liquidus temperature of the alloy composition when melted together as a single alloy is 400 ° C or less.

[0064] Even under the same reflow conditions, if the metals constituting the high-melting-point metal layer 10 are different, the range of thickness T2 within which the liquidus temperature of the alloy composition when melted together as a single alloy falls within a predetermined temperature range will also differ. That is, the range of thickness T2 within which the liquidus temperature of the alloy composition when melted together as a single alloy falls within a predetermined range differs between the case where silver (Ag) is used as the high-melting-point metal layer 10 and the case where, for example, copper (Cu) is used.

[0065] [Single alloy composition] The liquidus temperature of the alloy composition when the fusible conductor 7 consisting of a laminate of a high melting point metal layer 10 and a second low melting point metal layer 12 melts together as a single alloy can be determined from the weight ratio of the constituent metals of the single alloy, which is the sum of the constituent metals of the high melting point metal layer 10 and the first low melting point metal layer 11 that make up the laminate 13, and the phase diagram (phase diagram) of the constituent metals of the single alloy.

[0066] When the single alloy is a binary alloy of Sn--Ag, the liquidus temperature is determined by referring to the phase diagram of FIG. 7, and when the single alloy is a ternary alloy of Sn--Ag--Cu, the liquidus temperature is determined by referring to the phase diagram of FIG.

[0067] The composition of the fusible conductor 7 can be determined, for example, by determining the fusing conditions (fusing temperature, fusing time) and taking into account the reflow conditions (profiles such as peak temperature and reflow heating time) and, from the phase diagram of the constituent metals of the fusible conductor 7, by determining the volume ratio or weight ratio at which the liquidus temperature of the alloy composition when melted together as a single alloy is 300°C or higher and 400°C or lower.

[0068] [Fusible conductor mounting and melting test 1] Next, the mounting and fusing test 1 of the soluble conductor 7B will be described. In this mounting and fusing test 1, a soluble conductor having a thickness of 100 μm and a volume of 0.23 mm was used as the first low-melting point metal layer of the laminate 13B. 3 A plurality of laminates 13B were prepared using the Sn-3.0Ag-0.5Cu alloy, with the high melting point metal layer (Ag) having different thicknesses. The high melting point metal layer (Ag) was formed by plating on the surface of the first low melting point metal layer (Sn-3.0Ag-0.5Cu alloy).

[0069] Each laminate 13B was reflow-mounted on the first electrode 3, the second electrode 4, and the heating element lead electrode 6, and the presence or absence of melting of the soluble conductor 7B was evaluated. Next, the protective element on which the soluble conductor 7B was mounted was reflow-mounted on an evaluation circuit board, and the presence or absence of melting of the soluble conductor 7B was evaluated. Furthermore, the heating element of the protective element was energized to generate heat, and the time required for melting of the soluble conductor 7B was measured.

[0070] The protective element used had a surface heater structure in which a heating element was formed on the surface of an insulating substrate (see Figure 1). The reflow conditions for mounting the laminate 13B and the protective element were both 2 minutes at 240°C in an oven. The applied power to the heating element of the protective element was 35W.

[0071] [Example 1] In Example 1, the plating thickness of the high-melting-point metal layer was 4.06 μm on one side. The thickness of the high-melting-point metal layer was twice the plating thickness on one side. The metal composition of the alloy when melted together as the above-mentioned single alloy was 13.04% Ag, 86.5% Sn, and 0.45% Cu. The liquidus temperature of this alloy composition was 325°C, and the solidus temperature was 221°C.

[0072] [Example 2] In Example 2, the plating thickness of the high-melting-point metal layer was 5.02 μm on each side. The thickness of the high-melting-point metal layer was twice the plating thickness on each side. The metal composition of the alloy when melted together as the above-mentioned single alloy was 15.12% Ag, 84.4% Sn, and 0.44% Cu. The liquidus temperature of this alloy composition was 345°C, and the solidus temperature was 221°C.

[0073] [Example 3] In Example 3, the plating thickness of the high-melting-point metal layer was 6.29 μm on one side. The thickness of the high-melting-point metal layer was twice the plating thickness on one side. The metal composition of the alloy when melted together as the above-mentioned single alloy was 17.72% Ag, 81.9% Sn, and 0.42% Cu. The liquidus temperature of this alloy composition was 360°C, and the solidus temperature was 221°C.

[0074] [Example 4] In Example 4, the plating thickness of the high-melting-point metal layer was 8.16 μm on one side. The thickness of the high-melting-point metal layer was twice the plating thickness on one side. The metal composition of the alloy when melted together as the above-mentioned single alloy was Ag: 21.27%, Sn: 78.3%, and Cu: 0.41%. The liquidus temperature of this alloy composition was 380°C, and the solidus temperature was 221°C.

[0075] [Example 5] In Example 5, the plating thickness of the high-melting-point metal layer was 9.36 μm on one side. The thickness of the high-melting-point metal layer was twice the plating thickness on one side. The metal composition of the alloy when melted together as the above-mentioned single alloy was Ag: 23.39%, Sn: 76.2%, and Cu: 0.39%. The liquidus temperature of this alloy composition was 385°C, and the solidus temperature was 221°C.

[0076] [Example 6] In Example 6, the plating thickness of the high-melting-point metal layer was 10.45 μm on each side. The thickness of the high-melting-point metal layer was twice the plating thickness on each side. The metal composition of the alloy when melted together as the above-mentioned single alloy was Ag: 25.22%, Sn: 74.4%, and Cu: 0.39%. The liquidus temperature of this alloy composition was 395°C, and the solidus temperature was 221°C.

[0077] [Comparative Example 1] In Comparative Example 1, the plating thickness of the high-melting-point metal layer was 1.61 μm on each side. The thickness of the high-melting-point metal layer was twice the plating thickness on each side. The metal composition of the alloy when melted together as the above-mentioned single alloy was Ag: 7.25%, Sn: 92.3%, and Cu: 0.48%. The liquidus temperature of this alloy composition was 275°C, and the solidus temperature was 221°C.

[0078] Comparative Example 2 In Comparative Example 2, the plating thickness of the high-melting-point metal layer was 2.23 μm on each side. The thickness of the high-melting-point metal layer was twice the plating thickness on each side. The metal composition of the alloy when melted together as the above-mentioned single alloy was Ag: 8.78%, Sn: 90.7%, and Cu: 0.47%. The liquidus temperature of this alloy composition was 290°C, and the solidus temperature was 221°C.

[0079] [Table 1]

[0080] As shown in Table 1, the laminates 13B according to Examples 1 to 6 were mounted by reflow mounting on the first electrode 3, the second electrode 4, and the heating element lead electrode 6 in a state where they maintained their shape without fusing. Also, the soluble conductors 7B according to Examples 1 to 6 were mounted by reflow mounting on the evaluation board of the protective element in a state where they maintained their shape without fusing. Furthermore, the protective element on which the soluble conductors 7B according to Examples 1 to 6 were mounted fused within 0.75 seconds after the start of current flow to the heating element 5.

[0081] On the other hand, the laminate 13B according to Comparative Examples 1 and 2 was blown out when mounted on the first electrode 3, the second electrode 4, and the heater lead electrode 6 by reflow soldering.

[0082] However, in Comparative Examples 1 and 2, the reflow conditions were 240°C oven for 2 minutes, but by using a low-melting-point solder paste with a melting point of around 140°C, reflow at around 190°C, which is lower than the liquidus temperature of the first low-melting-point metal layer 11, 220°C, is possible, and it can be said that the fusible conductor mounting evaluation and evaluation board mounting evaluation are met.

[0083] Also, in the heating element heating test, it is clear that the tendency of the meltdown times of Examples 1 to 6 indicates that Comparative Examples 1 and 2 melt down faster than Examples 1 to 6.

[0084] In other words, Comparative Examples 1 and 2 are also within the practical range.

[0085] [Fusible conductor mounting and melting test 2] Next, the mounting and fusing test 2 of the soluble conductor 7B will be described. In this mounting and fusing test 2, a 100 μm thick, 0.23 mm volume fusible conductor was used as the first low melting point metal layer of the laminate 13B. 3A plurality of laminates 13B were prepared using the Sn-3.0Ag-0.5Cu alloy, with the high melting point metal layer (Cu) having different thicknesses. The high melting point metal layer (Cu) was formed by plating onto the surface of the first low melting point metal layer (Sn-3.0Ag-0.5Cu alloy).

[0086] The evaluation items and methods, the configuration of the protection element, and the reflow conditions are the same as those for the mounting and fusing test.

[0087] [Example 7] In Example 7, the plating thickness of the high-melting-point metal layer was 1.5 μm on each side. The thickness of the high-melting-point metal layer was twice the plating thickness on each side. The metal composition of the alloy when melted together as the above-mentioned single alloy was Ag: 2.90%, Sn: 93.14%, and Cu: 3.96%. The liquidus temperature of this alloy composition was 360°C.

[0088] Comparative Example 3 In Comparative Example 3, the plating thickness of the high-melting-point metal layer was 2.5 μm on each side. The thickness of the high-melting-point metal layer was twice the plating thickness on each side. The metal composition of the alloy when melted together as the above-mentioned single alloy was Ag: 2.83%, Sn: 91.03%, and Cu: 6.14%. The liquidus temperature of this alloy composition was 440°C.

[0089] [Table 2]

[0090] As shown in Table 2, the laminate 13B according to Example 7 was mounted on the first electrode 3, the second electrode 4, and the heating element lead electrode 6 by reflow mounting in a state where it maintained its shape without fusing. In addition, the soluble conductor 7B according to Example 7 was mounted on the evaluation board of the protective element by reflow mounting in a state where it maintained its shape without fusing. Furthermore, the protective element on which the soluble conductor 7B according to Example 7 was mounted fused within 0.5 seconds after the start of current flow to the heating element 5.

[0091] On the other hand, the laminate 13B according to Comparative Example 3 did not melt when reflow-mounted onto the first electrode 3, the second electrode 4, and the heating element lead electrode 6, and the soluble conductor 7B also did not melt when reflow-mounted onto the evaluation board of the protective element, but did not melt within a predetermined time after energizing the heating element 5. This is because the liquidus temperature of a single alloy composition is as high as 440 ° C.

[0092] [Circuit configuration example] Such a protection device 1 is used by being incorporated into a circuit in a battery pack 20 of, for example, a lithium ion secondary battery. As shown in Fig. 9, the battery pack 20 has a battery stack 25 made up of, for example, a total of four battery cells 21a to 21d of lithium ion secondary batteries.

[0093] The battery pack 20 includes a battery stack 25, a charge / discharge control circuit 26 that controls the charging and discharging of the battery stack 25, a protection element 1 to which the present invention is applied that cuts off the charge / discharge path when an abnormality occurs in the battery stack 25, a detection circuit 27 that detects the voltage of each battery cell 21a to 21d, and a current control element 28 that serves as a switch element that controls the operation of the protection element 1 in accordance with the detection result of the detection circuit 27.

[0094] The battery stack 25 is a series connection of battery cells 21a to 21d that require control to protect against overcharge and overdischarge, and is detachably connected to a charging device 22 via the positive terminal 20a and negative terminal 20b of the battery pack 20, and a charging voltage is applied from the charging device 22. The battery pack 20 charged by the charging device 22 can be used to operate an electronic device that runs on a battery by connecting the positive terminal 20a and negative terminal 20b to the electronic device.

[0095] The charge / discharge control circuit 26 includes two current control elements 23a, 23b connected in series to a 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, 23b. The current control elements 23a, 23b are configured, for example, by field-effect transistors (hereinafter referred to as FETs), and the control unit 24 controls the gate voltage to control conduction and interruption of the current path of the battery stack 25 in the charging and / or discharging directions. Depending on the detection result by the detection circuit 27, when the battery stack 25 is over-discharged or over-charged, the control unit 24 controls the operation of the current control elements 23a, 23b to interrupt the current path.

[0096] The protection element 1 is connected, for example, on a charge / discharge current path between the battery stack 25 and the charge / discharge control circuit 26, and its operation is controlled by the current control element .

[0097] The detection circuit 27 is connected to each of the battery cells 21a to 21d, detects the voltage value of each of the battery cells 21a to 21d, and supplies each voltage value to the control unit 24 of the charge / discharge control circuit 26. The detection circuit 27 also outputs a control signal for controlling the current control element 28 when any one of the battery cells 21a to 21d reaches an overcharge voltage or an overdischarge voltage.

[0098] The current control element 28 is configured, for example, by a FET, and when the detection signal output from the detection circuit 27 indicates that the voltage value of the battery cells 21a to 21d exceeds a predetermined over-discharge or over-charge state, it activates the protection element 1 and controls the charge / discharge current path of the battery stack 25 to be cut off regardless of the switch operation of the current control elements 23a and 23b.

[0099] The protective element 1 to which the present invention is applied and used in the battery pack 20 configured as described above has a circuit configuration as shown in FIG. 10. That is, the protective element 1 has the first external connection electrode 14 connected to the battery stack 25 and the second external connection electrode 15 connected to the positive terminal 20a, thereby connecting the soluble conductor 7 in series to the charge / discharge path of the battery stack 25. The protective element 1 also has the heating element 5 connected to the current control element 28 via the third external connection electrode 18, and the heating element 5 is connected to one end of the battery stack 25. Thus, one end of the heating element 5 is connected to the soluble conductor 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 third external connection electrode 18. This forms a power supply path to the heating element 5, the current supply of which can be controlled by the current control element 28.

[0100] [Protection element operation] When the detection circuit 27 detects an abnormal voltage in any of the battery cells 21a to 21d, it outputs a cutoff signal to the current control element 28. Then, the current control element 28 controls the current so that electricity is supplied to the heating element 5. The protection element 1 causes current to flow from the battery stack 25 to the heating element 5, causing the heating element 5 to start generating heat. In the protection element 1, heat from the heating element 5 is transferred to the fusible conductor 7 via the second heating element electrode 17 and the heating element lead electrode 6, which have excellent thermal conductivity, and also via the insulating protective layer 8 and the heating element lead electrode 6, causing the fusible conductor 7 to melt and cut off the charge / discharge path of the battery stack 25. In addition, since the protective element 1 is formed by stacking the fusible conductor 7 on a high-melting point metal layer 10 and a second low-melting point metal layer 12, the second low-melting point metal layer 12 melts before the high-melting point metal layer 10 melts, and the melting action of the molten second low-melting point metal layer 12 on the high-melting point metal layer 10 can be used to melt the fusible conductor 7 in a short time.

[0101] When the fusible conductor 7 melts, the protection element 1 also cuts off the power supply path to the heating element 5, and the heating element 5 stops generating heat.

[0102] In addition, even when an overcurrent exceeding the rated current flows through the battery pack 20, the protective element 1 can cut off the charge / discharge path of the battery pack 20 by melting the fusible conductor 7 due to self-heating.

[0103] Thus, in the protective element 1, the fusible conductor 7 melts due to heat generated by energization of the heating element 5 or self-heating of the fusible conductor 7 due to overcurrent. As described above, even when the protective element 1 is reflow-mounted to the circuit board 34 at 260°C or when the circuit board 34 on which the protective element 1 is mounted is further exposed to a high-temperature environment such as reflow heating, the laminate 13 and the fusible conductor 7 are made of materials whose liquidus temperature of the alloy composition when melted together as a single alloy is 300°C or higher and 400°C or lower. Therefore, even if the first low-melting-point metal layer 11 or the second low-melting-point metal layer 12 melts at the reflow temperature and interdiffusion and / or dissolution of the high-melting-point metal and the low-melting-point metal occurs between the first low-melting-point metal layer 11 and the second low-melting-point metal layer 12 and the high-melting-point metal layer 10, the high-melting-point metal layer 10 maintains the laminated and coated structure, and the protective element 1 does not melt. Furthermore, the protective element 1 can be quickly melted by a predetermined overcurrent or heat generated by the heating element 5.

[0104] The protective element 1 according to the present invention is not limited to use in a battery pack for lithium ion secondary batteries, but can also be used in various applications that require the interruption of a current path due to an overcurrent or an electrical signal.

[0105] [Protection element 1 manufacturing process] Next, the manufacturing process of the protection element 1 will be described. As shown in Fig. 11, the manufacturing process of the protection element 1 includes a mounting process of a laminate 13 (not shown), a heating process of heating the laminate 13 (not shown), a melting process of melting the first low melting point metal layer 11 (not shown), and a connecting process of forming a soluble conductor and connecting it to an electrode. Below, an example will be described in which a laminate 13B with a coated structure and a soluble conductor 7B with a coated structure are used.

[0106] [Mounting process] Prior to the mounting step, a first electrode 3, a second electrode 4, a heating element 5, an insulating protective layer 8, a heating element lead electrode 6, a first heating element electrode 16, and a second heating element electrode 17 are formed on the front surface 2a of the insulating substrate 2, and a first external connection electrode 14, a second external connection electrode 15, and a third external connection electrode 18 are formed on the back surface 2b of the insulating substrate 2 to form an element main body. A conductive connection medium 35 such as solder paste is applied to the first electrode 3, the second electrode 4, and the heating element lead electrode 6 in advance. Next, the laminate 13B is mounted over the first electrode 3, the heating element lead electrode 6, and the second electrode 4 formed on the insulating substrate 2.

[0107] [Heating, melting, and connection process] FIG. 11(A) is a cross-sectional view showing the heating, melting, and connection process of the soluble conductor 7. The soluble conductor 7 can be efficiently connected to each electrode by reflow mounting. In the melting process, a second low-melting-point metal layer 12 is formed by interdiffusion and / or melting of a part of the high-melting-point metal layer 10 and the first low-melting-point metal layer 11. In the connection process, the molten conductive connection medium 35 cools, thereby connecting the soluble conductor 7B to the first electrode 3, the heating element lead electrode 6, and the second electrode 4 via the conductive connection medium 35.

[0108] [Mounting on circuit board] The protective element 1 connected to the fusible conductor 7B is protected from the inside by applying a coating flux 36 to the fusible conductor 7B and then providing a cover member 19 on the surface 2a of the insulating substrate 2. Next, as shown in Fig. 11(B), the protective element 1 is mounted on a circuit board 34, and the fusible conductor 7B is incorporated into at least a part of the current path of the circuit board 34, and the current in the circuit board 34 is cut off when an abnormality occurs in the circuit board 34.

[0109] The method for mounting the protection element 1 on the circuit board 34 is not particularly limited, but can be efficiently performed by reflow soldering. A conductive connection medium 35 such as solder paste is applied to the multiple connection electrodes 34a provided on the circuit board 34, and the first external connection electrode 14, second external connection electrode 15, and third external connection electrode 18 provided on the back surface 2b of the insulating substrate 2 are mounted thereon, followed by reflow heating. The conductive connection medium 35 used to connect the protection element 1 to the circuit board 34 may be made of the same material as the conductive connection medium 35 used to connect the first electrode 3, second electrode 4, and heating element lead electrode 6 to the laminate 13B, or may be made of a different material. As a result, the soluble conductor 7B is connected in series to the current path formed on the circuit board 34, and the heating element 5 is connected to the current control element 28 via the third external connection electrode 18, and the heating element 5 is connected to one end of the battery stack 25 via the current control element 28.

[0110] Here, the metals and thicknesses constituting the high-melting-point metal layer 10 and the first low-melting-point metal layer 11 of the laminate 13B are set so that the liquidus temperature of the alloy composition when melted together as a single alloy is 300° C. or higher and 400° C. or lower. As a result, even if the first low-melting-point metal layer 11 or the second low-melting-point metal layer 12 melts at the reflow temperature when the laminate 13B is mounted or when the protection element 1 is mounted on the circuit board 34, and interdiffusion and / or dissolution of the high-melting-point metal and the low-melting-point metal occurs between the first low-melting-point metal layer 11 and the second low-melting-point metal layer 12, the coating structure is maintained by the high-melting-point metal layer 10, and no melting occurs.

[0111] [Backside heater structure] The heating element 5 may be formed on the rear surface 2b of the insulating substrate 2. FIG. 12 shows a protection element 30 to which the present technology is applied, where (A) is a plan view, (B) is a cross-sectional view in the direction of current flow through the soluble conductor, and (C) is a bottom view. In the protection element 30 shown in FIG. 12, the heating element 5 is formed on the rear surface 2b of the insulating substrate 2. Accordingly, an insulating protective layer 8 is also formed on the rear surface 2b of the insulating substrate 2, and the third external connection electrode 18 functions as a first heating element electrode. Unlike the protection element 1, the second heating element electrode 17 is formed on the rear surface 2b of the insulating substrate 2 and has a second heating element electrode 17B connected to the heating element 5, and a second heating element electrode 17A formed on the front surface 2a of the insulating substrate 2 and connected to the heating element lead electrode 6, and these second heating element electrodes 17A and 17B are connected via castellations. The second heating electrode 17A and the second heating electrode 17B may be connected via a conductive through-hole that penetrates the insulating substrate 2 instead of the castellation.

[0112] The third external connection electrode 18 and the second heating element electrode 17B are provided on one and the other of a pair of side edges perpendicular to the pair of side edges on which the first external connection electrode 14 and the second external connection electrode 15 are provided. The protection element 30 may also have a resistance measurement electrode 38 provided on the front surface 2a of the insulating substrate 2 and electrically connected to the third external connection electrode 18 formed on the back surface 2b via a castellation. As shown in FIGS. 9 and 10 , the protection element 30 has the heating element 5 connected to the current control element 28 via the third external connection electrode 18, and the heating element 5 connected to one end of the battery stack 25 via a fusible conductor 7.

[0113] The heating element lead electrode 6 is formed on the surface 2a of the insulating substrate 2, and one end is connected to the second heating element electrode 17A. As a result, the heating element lead electrode 6 is overlapped with the heating element 5 via the insulating substrate 2. In the protective element 30, the heating element 5 and the soluble conductor 7 are thermally connected by being overlapped via the insulating substrate 2 and the heating element lead electrode 6, and the heat of the heating element 5 is conducted to the soluble conductor 7 also via the insulating substrate 2 and the heating element lead electrode 6.

[0114] [Internal heater structure] The heating element 5 may also be provided inside the insulating substrate 2. In the protective element 40 shown in Fig. 13, the insulating substrate 2 has a two-layer structure consisting of an upper layer and a lower layer, and the heating element 5 and a first extraction electrode and a second extraction electrode (not shown) are formed between the upper and lower layers.

[0115] The first extraction electrode is connected to one end of the heating element 5 and is connected to a second heating element electrode 17 provided on the surface 2a of the insulating substrate 2 via a castellation or a conductive through-hole. The heating element 5 is electrically and thermally connected to the fusible conductor 7 via the second heating element electrode 17 and the heating element extraction electrode 6.

[0116] The second extraction electrode is connected to the other end of the heating element 5, and is also connected via a castellation or a conductive through-hole to a third external connection electrode 18 provided on the rear surface 2b of the insulating substrate 2. The heating element 5 is connected to a current control element 28 via the third external connection electrode 18.

[0117] Here, the high-melting point metal layer 10 preferably bridges the gap between the heating element extraction electrode 6 and the first electrode 3, and between the heating element extraction electrode 6 and the second electrode 4, and is mounted so as not to be in direct contact with the insulating substrate 2 at least either between the heating element extraction electrode 6 and the first electrode 3 or between the heating element extraction electrode 6 and the second electrode 4.

[0118] Furthermore, when an insulating protective layer 8 or a surface insulating layer 9 is formed in a portion of the space between the heater extraction electrode 6 and the first electrode 3 and / or between the heater extraction electrode 6 and the second electrode 4 in the protective element 1 as shown in Figures 14 and 15, or when a surface insulating layer 9 is provided in the protective element 30 connecting the heater extraction electrode 6 and the first electrode 3 and / or between the heater extraction electrode 6 and the second electrode 4 as shown in Figures 16 and 17, it is preferable that the high-melting point metal layer 10 bridges the space between the heater extraction electrode 6 and the first electrode 3 and the space between the heater extraction electrode 6 and the second electrode 4, and is mounted so as not to be in direct contact with the insulating protective layer 8, the surface insulating layer 9 and / or the insulating substrate 2 at least between the heater extraction electrode 6 and the first electrode 3 or between the heater extraction electrode 6 and the second electrode 4.

[0119] The surface insulating layer 9 can be formed using the same material and method as the insulating protective layer 8.

[0120] If the high-melting point metal layer 10 of the soluble conductor 7 is in direct contact with the insulating protective layer 8, the surface insulating layer 9, and / or the insulating substrate 2 and the first electrode 3 between the heating element extraction electrode 6 and the first electrode 3, and between the heating element extraction electrode 6 and the second electrode 4, and is connected to the second electrode 4 via the heating element extraction electrode 6, there will be residual molten high-melting point metal layer 10 during the fusing process, and there is a risk that the appropriate insulation resistance (e.g., 100 KΩ) will not be maintained after fusing.

[0121] In other words, if there is even a partial discontinuous gap (i.e., no adhesion) at the interface between the insulating protective layer 8 and the surface insulating layer 9, which are continuously and seamlessly connected from the first electrode 3 to the second electrode 4 via the heating element extraction electrode 6, and / or the insulating substrate 2 and the high-melting point metal layer 10, the risk of a decrease in insulation resistance is reduced.

[0122] The specific dimensions of the gap are preferably "approximately 0.1 to 0.2 mm in the lengthwise direction" as described in

[0058] of Patent No. 5656466.

[0123] [Variations] In the above-described protective elements 1, 30, and 40, the laminate 13 is made of materials whose liquidus temperature of the alloy composition when melted together as a single alloy is 300° C. or higher and 400° C. or lower.

[0124] In the protective elements 1, 30, and 40 to which this technology is applied, even when the soluble conductor 7 is mounted on the first electrode 3, the second electrode 4, and the heating element extraction electrode 6 via the conductive connecting medium 35, the conductive connecting medium 35 is applied only to the first electrode 3, the second electrode 4, and the heating element extraction electrode 6, and fillets (not shown) of the conductive connecting medium 35 are formed by surface tension around the parts of the soluble conductor 7 that intersect with each electrode end, but the amount of conductive connecting medium 35 in the parts that have the fuse fusing function, "between the heating element extraction electrode 6 and the first electrode 3" and "between the heating element extraction electrode 6 and the second electrode 4," is small compared to the conductive connecting medium 35 on each electrode, and the configuration of the parts that essentially have the fuse function is the same as when the soluble conductor 7 is mounted directly on the first electrode 3, the second electrode 4, and the heating element extraction electrode 6.

[0125] When the fusible conductor 7 is mounted on the first electrode 3, the second electrode 4, and the heating element lead electrode 6 via the conductive connecting medium 35, the melting point due to heating of the heating element is between the heating element lead electrode 6 and the first electrode 3 and between the heating element lead electrode 6 and the second electrode 4, just as when the fusible conductor 7 is mounted directly on the first electrode 3, the second electrode 4, and the heating element lead electrode 6. The single alloy formed by the fusible conductor 7 on the heating element lead electrode 6 when heated by the heating element 5 does not flow into the melting point but generates a force (surface tension) that pulls the fusible conductor 7 in the melting point toward the heating element lead electrode 6. Since the distance between the first electrode 3 and the second electrode 4 and the heating element 5 is longer than the distance between the heating element lead electrode 6 and the heating element 5, the fusible conductor 7 on the first electrode 3 and the second electrode 4 does not melt completely to form a single alloy (see Figure 2(A)). That is, the main factor that determines whether the soluble conductor 7 will melt is the laminate 13 of the low-melting-point metal layer 11 and the high-melting-point metal layer 10 that make up the soluble conductor 7. However, when the conductive connection medium 35 melts due to the heat of the heating element, the surface tension of each soluble conductor 7 that is not a single alloy on the first electrode 3 and the second electrode 4 is drawn in the direction from the heating element lead electrode 6 toward the first electrode 3 and the second electrode 4 to which each soluble conductor is connected, which can also be a factor that promotes the melting of the soluble conductor 7.

[0126] Furthermore, when the fusible conductor 7 is mounted on the first electrode 3, the second electrode 4, and the heating element lead electrode 6 via the conductive connecting medium 35, the melting point due to self-heating caused by an overcurrent is between the heating element lead electrode 6 and the first electrode 3 and / or between the heating element lead electrode 6 and the second electrode 4, just as when the fusible conductor 7 is mounted directly on the first electrode 3, the second electrode 4, and the heating element lead electrode 6. In particular, when the melting point due to self-heating caused by an overcurrent occurs, the heat-generating portion of the fusible conductor 7 is between the heating element lead electrode 6 and the first electrode 3 and / or between the heating element lead electrode 6 and the second electrode 4, which are not connected to the respective electrodes and therefore have high conductor resistance and poor heat dissipation. Therefore, most of the fusible conductor 7 on the first electrode 3, the second electrode 4, and the heating element lead electrode 6 does not melt and form a single alloy (see Figure 2(B)). In actual melting, in most cases only one of the gaps between the heating element extraction electrode 6 and the first electrode 3 and the gap between the heating element extraction electrode 6 and the second electrode 4 melts, and in rare cases both gaps melt.

[0127] In other words, even when the soluble conductor 7 is mounted on the first electrode 3, the second electrode 4, and the heating element extraction electrode 6 via the conductive connecting medium 35, by using a material configuration in which the liquid phase temperature of the alloy composition when the laminate 13 melts together as a single alloy is 300°C or higher and 400°C or lower, the same effect can be achieved as when the soluble conductor 7 is mounted directly on the first electrode 3, the second electrode 4, and the heating element extraction electrode 6 without the conductive connecting medium 35. [Explanation of symbols]

[0128] REFERENCE SIGNS LIST 1 protection element, 2 insulating substrate, 2a surface, 2b back surface, 3 first electrode, 4 second electrode, 5 heating element, 6 heating element lead electrode, 7 fusible conductor, 7A laminated structure, 7B coating structure, 8 insulating protection layer, 9 surface insulating layer, 10 high melting point metal layer, 11 first low melting point metal layer, 12 second low melting point metal layer, 13 laminate, 13A laminated structure, 13B coating structure, 14 first external connection electrode, 15 second external connection electrode, 16 first heating element electrode, 17 second heating element electrode, 18 third external connection electrode, 19 cover member, 20 battery pack, 20a positive electrode terminal, 20b negative electrode terminal, 21a to 21d battery cell, 22 charging device, 23a, 23b current control element, 24 control unit, 25 battery stack, 26 Charge / discharge control circuit, 27 detection circuit, 28 current control element, 30 protection element, 34 circuit board, 34a connection electrode, 35 conductive connection medium, 36 coating flux, 40 protection element

Claims

1. an insulating substrate; A heating element; a first electrode and a second electrode laminated on the insulating substrate; a heating element extraction electrode provided on a current path between the first and second electrodes and electrically connected to the heating element; The first electrode, the second electrode, and the heating element extraction electrode are electrically connected to each other, and the heating element is heated or self-heated due to overcurrent. A soluble conductor is provided to cut off the current path between the first electrode and the second electrode. The soluble conductor is composed of a laminate including at least a low-melting point metal layer having a liquidus temperature of less than 260 ° C. and a high-melting point metal layer having a liquidus temperature of more than 400 ° C., The laminate is made of materials whose liquidus temperature of the alloy composition when melted together as a single alloy is 300°C or higher and 400°C or lower. Protection element.

2. 2. The protection element according to claim 1, wherein the laminate is made of materials having a liquidus temperature of 325° C. or higher and 400° C. or lower when melted together as a single alloy.

3. 3. The protection element according to claim 1, wherein the high-melting point metal layer bridges the gap between the heating element extraction electrode and the first electrode, and between the heating element extraction electrode and the second electrode, and is mounted so as not to be in direct contact with the insulating substrate at least between the heating element extraction electrode and the first electrode or between the heating element extraction electrode and the second electrode.

4. a surface insulating layer formed at least partially between the heating element lead electrode and the first electrode and / or between the heating element lead electrode and the second electrode; 3. The protection element according to claim 1, wherein the high-melting point metal layer bridges the gap between the heating element extraction electrode and the first electrode, and between the heating element extraction electrode and the second electrode, and is mounted so as not to be in direct contact with the surface insulating layer and / or the insulating substrate at least between the heating element extraction electrode and the first electrode and between the heating element extraction electrode and the second electrode.

5. 3. The protection element according to claim 1, wherein the low-melting-point metal layer is made of Sn or a metal containing Sn as a main component, and the high-melting-point metal layer is made of Ag, Cu, or a metal containing Ag and / or Cu.

6. The protection element according to claim 1 or 2, wherein the soluble conductor is mounted on the first electrode, the second electrode, and the heating element lead electrode via the low melting point metal layer.

7. The protection element according to claim 1 or 2, wherein the soluble conductor is connected to the first electrode, the second electrode, and the heating element lead electrode via a conductive connection medium.

8. an insulating substrate; A heating element; a first electrode and a second electrode laminated on the insulating substrate; a heating element extraction electrode provided on a current path between the first and second electrodes and electrically connected to the heating element; The first electrode, the second electrode, and the heating element extraction electrode are electrically connected to each other, and the heating element is heated or self-heated due to overcurrent. A soluble conductor is provided to cut off the current path between the first electrode and the second electrode. The soluble conductor is connected to the first electrode, the second electrode, and the heating element lead electrode via a conductive connecting medium, The soluble conductor is composed of a laminate including at least a low-melting point metal layer having a liquidus temperature of less than 260 ° C. and a high-melting point metal layer having a liquidus temperature of more than 400 ° C., The laminate and the conductive connecting medium are made of materials whose liquidus temperature of the alloy composition when melted together as a single alloy is 300°C or higher and 400°C or lower. Protection element.

9. The heating element is formed on the surface of the insulating substrate on which the soluble conductor is mounted or on the surface thereof via the surface insulating layer, and an insulating protective layer is formed between the heating element and the heating element extraction electrode. The protective element described in claim 1 or 8.

10. The protection element according to claim 1 or 8, wherein the heating element is formed on a back surface opposite to a surface on which the fusible conductor is mounted of the insulating substrate.

11. The protection element according to claim 1 or 8, wherein the heating element is formed inside the insulating substrate.

12. one or more battery cells; a protection element connected to a charge / discharge path of the battery cell and blocking the charge / discharge path; a detection circuit for detecting a voltage value of the battery cell; a current control element for controlling current flow to the protection element; The protective element is the protective element according to claim 1. Battery pack.

13. one or more battery cells; a protection element connected to a charge / discharge path of the battery cell and blocking the charge / discharge path; a detection circuit for detecting a voltage value of the battery cell; a current control element for controlling current flow to the protection element; The protective element is a protective element according to claim 8. Battery pack.

Images